Management of Wastes from Uranium Mining and

752
Management of Wastes PROCEEDINGS OF A SYMPOSIUM ALBUQUERQUE 1 0 - 1 4 MAY 1982 JOINTLY ORGANIZED BY IAEA AND NEA(OECD) from Uranium Mining and \ffij INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1982

Transcript of Management of Wastes from Uranium Mining and

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Management of Wastes

PROCEEDINGS OF A SYMPOSIUM ALBUQUERQUE 10-14 MAY 1982 JOINTLY ORGANIZED BY IAEA AND NEA(OECD)

from Uranium Mining and

\ffij INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1982

file:///ffij
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The cover picture shows the Open-cut Uranium Mine Mary-Kathleen, Queensland, Australia. (Provided by courtesy of the Australian Information Service).

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MANAGEMENT OF WASTES

FROM URANIUM MINING AND MILLING

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PROCEEDINGS SERIES

MANAGEMENT OF WASTES FROM

URANIUM MINING AND MILLING

PROCEEDINGS OF AN INTERNATIONAL SYMPOSIUM ON MANAGEMENT OF WASTES FROM URANIUM MINING AND MILLING

JOINTLY ORGANIZED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY

AND THE OECD NUCLEAR ENERGY AGENCY

AND HELD IN ALBUQUERQUE, 10-14 M A Y 1982

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1982

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MANAGEMENT OF WASTES FROM URANIUM MINING AND MILLING IAEA, VIENNA, 1982

STI/PUB/622 ISBN 92 -0 -020282-9

© IAEA, 1982

Permission to reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Wagramerstrasse 5, P.O. Box 100, A-1400 Vienna, Austria.

Printed by the IAEA in Austria November 1982

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FOREWORD

For improvement in the prospects for nuclear power, proper management of the radioactive wastes produced from the nuclear fuel cycle is of paramount importance. Studies have shown that the wastes from the mining and milling of uranium ores have long-term radiological impacts, highlighting the importance of improved means of managing such wastes, existing and future.

The uranium mining and milling industry was the first industry to be involved in the development of the nuclear power industry, its involvement dating back to the 1940s. The wastes produced from such operations were managed in differing ways, depending on various local philosophies, though certain overall general safety requirements were similar. In consequence, wastes have accumulated, and in the light of modern knowledge, many require remedial action from technical, health and safety points of view. With the present tech­nological development, and with the improved understanding of the hazards involved, better practices are being incorporated for waste management.

Both the International Atomic Energy Agency and the Nuclear Energy Agency of the OECD have been active in this field for many years. There have been a number of technical meetings and various technical publications have been issued. However,the International Symposium on the Management of Wastes from Uranium Mining and Milling was the first devoted exclusively to the management of waste from the uranium mining and milling industry.

The Symposium, jointly organized by the IAEA and the NEA, was held in Albuquerque, USA, in May 1982, and was attended by 191 participants from 16 Member States and 2 international organizations. The 45 papers published in these Proceedings were presented in seven sessions covering the following subjects: review of national programmes; objectives and criteria for long-term management and disposal; concept evaluation for management and disposal; characterization of wastes; waste water treatment and tailings conditioning; decommissioning and rehabilitation technology development; radiological impact assessment; environmental surveillance and monitoring; radiation measurements; and national research and development programmes. In addition, there is a summary of the panel discussion on the objectives, problems and solutions for waste management in the uranium mining and milling industry.

The Proceedings provide an authoritative account of the status of manage­ment of waste from the uranium mining and milling industry throughout the world at the beginning of the 1980s, the experience that has been gained and the investigations that have been performed to study various alternative possibili­ties for the safe disposal of such radioactive wastes, including those which have

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already accumulated. Particular attention has been given to the long-term aspect

of managing these wastes from the radiological, health and safety points of view

while the areas in which further work requires to be done are highlighted.

The IAEA and the NEA gratefully acknowledge the assistance and co­

operation of the United States Department of Energy, and Sandia National

Laboratories in the preparation and holding of the Symposium in Albuquerque.

EDITORIAL NOTE

The papers and discussions have been edited by the editorial staff of the International Atomic Energy Agency to the extent considered necessary for the reader's assistance. The views expressed and the general style adopted remain, however, the responsibility of the named authors or participants. In addition, the views are not necessarily those of the governments of the nominating Member States or of the nominating organizations.

Where papers have been incorporated into these Proceedings without resetting by the Agency, this has been done with the knowledge of the authors and their government authorities, and their cooperation is gratefully acknowledged. The Proceedings have been printed by composition typing and photo-offset lithography. Within the limitations imposed by this method, every effort has been made to maintain a high editorial standard, in particular to achieve, wherever practicable, consistency of units and symbols and conformity to the standards recommended by competent international bodies.

The use in these Proceedings of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries.

The mention of specific companies or of their products or brand names does not imply any endorsement or recommendation on the part of the IAEA.

Authors are themselves responsible for obtaining the necessary permission to reproduce copyright material from other sources.

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CONTENTS

KEYNOTE ADDRESS

The management of radioactive waste from uranium mining and milling (Keynote Address) 3 F.E. Coffman

REVIEW OF N A T I O N A L PROGRAMMES

The management of uranium mill tailings in the United States of America (Invited Review Paper) (IAEA-SM-262/60) 9 D.H. Groelsema

A summary of the Canadian uranium mill tailings situation

(Invited Review Paper) (IAEA-SM-262/61) 21 P. Hamel, J. Howieson

Regulation of the management of waste from uranium mining and milling in Australia (Invited Review Paper) (IAEA-SM-262/62) 41 R.M. Fry, I.W. Morison

La gestion des d£chets solides de l'extraction et du traitement des minerals d'uranium en France (Rapport general) (IAEA-SM-262/64) 55 /. Pradel

OBJECTIVES AND CRITERIA FOR LONG-TERM MANAGEMENT AND DISPOSAL

Criteria for the long-term management of uranium mill tailings (IAEA-SM-262/40) 71 R.M. Fry

Recent developments in the regulation and management of Canadian uranium tailings (IAEA-SM-262/1) 85 K. Bragg, C. Potter, A. James

Uranium mill licensing requirements in the United States of America (IAEA-SM-262/53) 103 K. Hamill

Geomorphic hazards and uranium-tailings disposal (IAEA-SM-262/50) I l l S.A. Schumm, J.E. Costa, T.J. Toy, J.C. Knox, R.F. Warner

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CONCEPT EVALUATION FOR MANAGEMENT AND DISPOSAL

Modelling of the underwater disposal of uranium mine tailings in Elliot Lake (IAEA-SM-262/4) 127 B.E. Halbert, J.M. Scharer, J.L. Chakravatti, E. Barnes

Hydrogeological investigations and evaluation of the Stanleigh mine tailings impoundment site (IAEA-SM-262/5) 141

J.M. Boyd, T.G. Carter, R.A. Knapp, K.B. Culver

Close-out concepts for the Elliot Lake uranium mining operations (IAEA-SM-262/7) 157 K.B. Culver, J.L Chakravatti, DM. Gorber, R.A. Knapp, J.B. Davis

Evaluation de differents scenarios de gestion d'un stockage de residus de traitement de minerai d'uranium (IAEA-SM-262/18) 169 N. Fourcade, P. Zettwoog

Uranium mill tailings containment systems performance and cost (IAEA-SM-262/43) 197 V.C. Rogers, K.K Nielson, D.C Rich, M.W. Grant, M.L. Mauch, G.M. Sandquist, G.B. Merrell

CHARACTERIZATION OF WASTES

Hydrogeochemical evolution of an inactive pyritic uranium tailings basin and retardation of contaminant migration in a surrounding aquifer (IAEA-SM-262/14) N.K Dave, T.P. Lim, A.J. Vivyurka, N. Dubrovsky, K.A. Morin, D.J.A. Smyth, R. W. Gillham, J.A. Cherry

Geochemical processes in uranium mill tailings and their relationship to contamination (IAEA-SM-262/23) G. Markos, K.J. Bush

Radionuclides in process and waste streams at an operating uranium mill (IAEA-SM-262/26) R.J. Ring, D.M. Levins, F.J. Gee

Review of the non-radiological contaminants in the long-term management of uranium mine and mill wastes (IAEA-SM-262/58) R. T. Pidgeon

Implications of alternative geochemical controls on the temporal behaviour of Elliot Lake tailings (IAEA-SM-262/54) W.J. Snodgrass, D.L. Lush, J. Capobianco

WASTE WATER TREATMENT AND TAILINGS CONDITIONING

Uranium mill tailings conditioning technology (IAEA-SM-262/56) 311 D.R. Dreesen, E.J. Cokal, L.E. Wangen, J.M. Williams, P.D. O'Brien, E.F. Thode

215

231

247

263

285

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A study on the development of a process for treating uranium mill effluents (IAEA-SM-262/29) 325 J.L. Kharbanda, P.K. Panicker, K. Balu

Concentrations and observed behaviour of 2 2 6 Ra and 2 1 0 P o around uranium mill tailings (IAEA-SM-262/32) 339 S.A. Ibrahim, S.L. Flot, F.W. Whicker

Development of a precipitation and filtration process for radium-226 removal (IAEA-SM-262/10) 353 D.W. Averill, J.W. Schmidt, D. Moffett, R.T. Webber, E. Barnes

DECOMMISSIONING AND REHABILITATION TECHNOLOGY DEVELOPMENT

Tailings technology. Decommissioning and rehabilitation remedial action technology development (IAEA-SM-262/65) 367 R. W. Ramsey, Jr.

Water quality and hydrologic impacts of disposal of uranium mill tailings by backfilling (IAEA-SM-262/51) 373 B.M. Thomson, R.J. Heggen

An ecological approach to the assessment of vegetation cover on inactive uranium mill tailings sites (IAEA-SM-262/2) 385 M. Kalin, C. Caza

The technology development effort of the uranium mill tailings remedial actions project (IAEA-SM-262/42) 403 M.L. Matthews

Thickened tailings experiment for close-out of uranium mill tailings at Denison Mines Limited (IAEA-SM-2 62/3) 417 J.L. Chakravatti, E. LaRocque, D.W. Reades, E.I. Robinsky

Uranium mill tailings remedial action project (UMTRAP) — Cover and liner technology development project (IAEA-SM-262/39) 429 J.N. Hartley, G.W. Gee, H.D. Freeman, J.F. Cline, P.A. Beedlow, J.L. Buelt, J.R. Relyea, T. Tamura

Uranium mill tailings stabilization with additives (IAEA-SM-262/49) 449 D. Marcus, D.A. Sangrey

RADIOLOGICAL IMPACT ASSESSMENT

Optimizing radiation protection in the management of uranium mill tailings (IAEA-SM-262/30) 471 R. V. Osborne

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Aquatic pathway variables affecting the estimation of dose commitment from uranium mill tailings (IAEA-SM-262/9) 483 D.L. Lush, W.J. Snodgrass, P. McKee

Comparative assessment of radiological impact from uranium and thorium milling (IAEA-SM-262/17) 505 Y.C Yuan, C.J. Roberts

ENVIRONMENTAL SURVEILLANCE AND MONITORING

L'apport des mesures hydrobiologiques dans l'6tude radioecologique d'un site francais d'extraction et de traitement d'uranium (IAEA-SM-262/20) 523 B. Descamps, L. Foulquier, Y. Cartier, Y. Baudin-Jaulent

Evaluation du cycle du radium dans l'environnement a partir d'observations in situ de son impact radiologique (IAEA-SM-262/21) .... 535 /. Hugon, J. Delmas, J. C. Caries

Environmental surveillance around the uranium complex at Jaduguda (IAEA-SM-262/27) 541 P.M. Markose, S. Venkataraman, K.P. Eapen, G.K. Srivastava, M. Raghavayya

Pre-operational environmental survey for two uranium mine sites in northern Italy (IAEA-SM-262/41) 553 G.F. Clemente, R. Gragnani, G.G. Mastino, F. Scacco, G. Sciocchetti, M. Dall'Aglio, G.P. Santaroni

Finding and evaluating potential radiological problems in the vicinity of uranium milling sites (IAEA-SM-262/67) 573 W.A. Goldsmith, W.G. Yates

RADIATION MEASUREMENTS

Monitoring radon around uranium mine and mill sites with passive integrating detectors (IAEA-SM-262/25) 589 J.E. Gingrich, R.A. Oswald, H.W. Alter

Statistical decision procedures for uranium mill tailings remedial action (IAEA-SM-262/16) 609 L.P. Sanathanan, R.R. MacDonald, C.J. Roberts, W.E. Kisieleski

An in situ gross alpha monitoring technique for delineating fugitive mill tailings (IAEA-SM-262/35) 621 W.J. Smith, F. W. Whicker

A counting system and resultant data from field determinations of 2 2 6 Ra at twelve uranium mill tailings sites (IAEA-SM-262/45) 633

H.L. Rarrick, D.M. Minnema, L.W. Brewer

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NAT IONAL RESEARCH AND DEVELOPMENT PROGRAMMES

Research on uranium tailings disposal technology at CANMET, Ottawa (IAEA-SM-262/12) 645 J.M. Skeaff, G.M. Ritcey, A. Jongejan, M. Silver

The Canadian research programme into the long-term management of uranium mine tailings (IAEA-SM-262/13) 663 V.A. Haw

Uranium mill tailings management - A Swedish approach (IAEA-SM-262/22) 679 /. Eurenius, A. Osihn, E. Strandell

Colorado's prospectus on uranium milling (IAEA-SM-262/44) 693 A.J. Hazle, G.A. Franz, R. Gamewell

PANEL DISCUSSION AND CLOSING REMARKS

Panel discussion on waste management in the uranium mining and milling industry — Objectives, problems and solutions 703

Closing remarks 707 R.A. Scarano

Chairmen of Sessions and Secretariat of the Symposium 711 List of Participants 713 Author Index 733 Index of Papers by Number 735

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KEYNOTE ADDRESS

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Keynote Address

THE MANAGEMENT OF RADIOACTIVE WASTE

FROM URANIUM MINING AND MILLING

F.E. COFFMAN Nuclear Waste Management

and Fuel Cycle Programs, United States Department of Energy, Washington, DC, United States of America

Presented by R.W. Ramsey, Jr.

Ladies and gentlemen,

I am pleased to take part in this International Symposium on the Management of Wastes from Uranium Mining and Milling. On behalf of the Secretary of Energy, I am honoured to welcome the distinguished speakers and participants from the nations of the sponsoring organizations, the IAEA and the OECD/Nuclear Energy Agency. A symposium such as this is beneficial to all of us for it facilitates an exchange of ideas on the actions and developments that are taking place in our respective countries. I am happy to share with you some thoughts on the programmes to manage uranium mill tailings wastes and I look forward to the discussion of your related plans and programmes to address this common aspect of nuclear energy utilization.

There is high interest in both the executive and legislative branches of our Government in what we have termed the closure of the nuclear fuel cycle. For the past several months we have been deeply involved with post reactor fuel cycle operations and waste processing and disposal activities which provide this closure. It is therefore an honour to come here today and initiate your dicussion of the equally important programmes that derive from the front end of the fuel cycle, namely the management of the tailings from extraction of uranium from natural sources. What I propose to do at this time is to review briefly the historical bases for our approach to the long-term management of uranium mill tailings, to out­line the programmes underway, and to identify what we consider to be the key issues still to be resolved.

To place our uranium mill tailing programmes in perspective, we might recall that the technology to handle such radioactive materials developed with the challenge to produce large quantities of very pure uranium on a very short schedule during World War II. The potential radiological hazards associated with the naturally occurring ores of uranium and thorium were not well understood.

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This was especially true for the low concentrations found in most ores, where large quantities of material were handled in bulk forms and radiological assay and monitoring techniques were still evolving.

Following World War II, our Government offered incentives to the mining industry to provide a larger domestic supply of uranium to meet the requirements of defence programmes and the development of a commercial nuclear energy industry. Many new uranium mills were built to extract uranium and thorium from the mined ores. During these years, neither the milling activities nor the disposal of uranium tailings were regulated by the Federal Government. These were considered sources of natural radiation and were generally regarded as exempt from radiological controls. Later, as radiological studies and investigations of the effects of low-level radiation were performed, criteria and guidelines were established that applied to the levels of exposure obtainable from natural sources. These criteria became more restrictive as additional research on the effects of low-level radiation was completed.

Much of the uranium ore mined within the United States of America from the early 1940s through 1970 was processed for the Federal Government by private companies on sites conveniently located near mines in the West. When processing operations for the Government stopped and many of those mills shut down, millions of tons of uranium mill tailings remained. Stabilization of these tailings piles was not attempted because the effects of the low-level radioactivity from tailings on the population were thought to be minimal.

Initial legislation for the Remedial Action Program grew out of concern for the potential health impact on the citizens of Grand Junction, Colorado, the site of a large, commercially operated uranium mill. Between 1952 and 1966, several hundred thousand tons of the uranium mill tailings were removed by local citizens and builders for use as construction-related material. Because there were no controls on its removal, the sand-like material was used extensively as fill under and around the foundations of building and under streets, sidewalks, walls and sewer mains and for the grading of open land.

In 1966, the Colorado Department of Health and the United States Public Health Service determined that the tailings being used for construction posed a potential radiological health problem to occupants of these structures, and the removal of tailings was stopped. The Environmental Protection Agency (EPA) and the State of Colorado health authorities did surveys and found that the contamination was extensive in the community.

Early in 1970, the United States Surgeon General provided guidelines for determining the levels of radiation from radon and radon daughters in structures that would require remedial action. A comprehensive radiological measurements programme was conducted, and many locations throughout the area were found where radiation exposure was above the Surgeon General's guidelines.

In 1972, Congress authorized money to assist the State of Colorado in conducting a 'Remedial Action Program'. The objective of the Grand Junction

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Remedial Action Program, which was our first established remedial action programme, is to remove tailings or to use other techniques to minimize exposure to people living or working in structures which exceed the Surgeon General's guidelines for radon daughter concentration and gamma radiation. Out of more than 20 000 properties which have been surveyed, it is estimated that approximately 740 properties will be found eligible for cleanup under this programme. Work has been completed on approximately 400 of these properties. The programme is scheduled for completion in 1987, with a total estimated cost of US $23 million, or approximately US $32 000 per property.

In 1974, the Atomic Energy Commission (USAEC) began an investigation of other inactive uranium milling sites. The USAEC reports showed that in an unstabilized condition the tailings were a potential environmental and health problem and that remedial action in the form of long-term stabilization and control should be performed to preclude any future 'Grand Junctions'.

In 1978, Congress passed the Uranium Mill Tailings Radiation Control Act. This act authorized the Department of Energy (AEC's successor) to designate sites needing remedial action, to establish priorities, and to enter into cooperative agreements with the affected States to implement remedial action at the sites. The act requires that the programme be performed in accordance with standards established by the EPA and in close collaboration with the Nuclear Regulatory Commission (NRC) , other Federal Agencies and the States.

Under the Uranium Mill Tailings Remedial Action (UMTRA ) Program, 24 sites located in 10 States have been designated for remedial action. To date these sites have been characterized, alternative approaches for remedial action have been identified, assessment of potential environmental impacts is underway, and a technology development programme, directed to improved, long lasting and economic stabilization techniques is being pursued. Remedial action at the two highest priority sites is scheduled to begin in 1984.

For the future, the management of uranium mill tailings must be conducted in such a way that extensive programmes of remedial action will be unnecessary. To provide a foundation for such long-term management in the United States, the Uranium Mill Tailings Radiation Control Act directs the Environmental Protection Agency to develop and promulgate standards under which the United States Nuclear Regulatory Commission and the States are to regulate the active uranium mills.

Because of the importance of these standards to those concerned with public safety and the protection of the environment and also to those engaged in uranium processing, who are responsible for financing and implementing tailings stabilization approaches and practices, this has been an area of controversy. The standards which were proposed by the EPA for the UMTRA Program are currently being revised in response to comments provided by the Department of Energy, the industry, and the public. In like manner, the Regulations for Uranium Milling,

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which were issued by the NRC in October 1980, have been challenged in the courts and have been rendered ineffective until at least October 1982 by the United States Congress. A number of basic questions in the debate which has taken place are:

What are the potential health effects resulting from unstabilized uranium mill tailings?

To what degree is reduction of such potential health effects justified when weighed against associated costs?

For what period of time should stabilized tailings remain stabilized?

For what period of time should institutional surveillance and control be relied upon?

Such questions must ultimately be answered independently by each of the nations involved in uranium milling, taking into account available data and site-specific considerations, and applying their own value judgments. I trust, however, that the information presented and discussed in this meeting and the studies being carried out under the NEA Coordinating Committee for the Long-Term Manage­ment of Uranium Mill Tailings will be useful to all of us in arriving at a sound basic approach in this area.

SUMMARY

I wish to close by reminding those involved in managing uranium mill tailing waste activities that we must recognize and reaffirm the burden of technical responsibility that we carry as active participants. But that alone is not enough. We must also recognize that success in our programmes will require a delicate blending of new knowledge in the physical and engineering sciences with the development of new forms of societal accommodation and collaboration. Such an inescapable linkage calls for programme leadership and strong initiatives on both counts if we are to meet the challenge.

Thank you.

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REVIEW OF NATIONAL PROGRAMMES

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Chairman

R.W. RAMSEY, Jr. United States of America

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Invited Review Paper

THE MANAGEMENT OF URANIUM MILL

TAILINGS IN THE UNITED STATES OF AMERICA

D.H. GROELSEMA United States Department

of Energy, Washington, DC, United States of America

Abstract

THE MANAGEMENT OF URANIUM MILL TAILINGS IN THE UNITED STATES OF AMERICA.

This paper provides an overview of the status and plans for uranium mill tailings manage­ment in the United States of America. The discussion includes organizational structures and responsibilities, progress in the development and adoption of standards and regulations, the status of tailings management activities at the active and inactive processing sites and plans for the future.

Introduction

The management of uranium mi l l t a i l i ng s in the USA consists of two main l ines of a c t i v i t y : the management of the t a i l i n g s at act ive uranium processing s i t e s and the cleanup and s t a b i l i z a t i o n of t a i l i ng s and res idual contaminated material at a number of inact ive uranium processing s i t e s . While these a c t i v i t i e s have much in common from the standpoint of s t a b i l i z a t i on technology, I sha l l discuss them separately because of the di f ferences in bas ic author i t i es , r e s p o n s i b i l i ­t i e s , and organizational s t ructures . The respons ib i l i ty for the management of the t a i l i ngs at the act ive s i tes rests with the private sector , that i s , the mi l l owners and operators, under l icenses issued by the U.S. Nuclear Regulatory Commission or the States. The respons ib i l i ty for the management of the t a i l i n g s at most of the inactive s i tes has been assumed by the Federal Government, and the U.S. Department of Energy has been authorized to conduct a program of remedial action at these s i t e s , in cooperation with the affected states and Indian t r i b a l nations. I t i s this program for which I have responsi ­b i l i t y in the Department of Energy and I w i l l describe i t f i r s t .

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STATE PROCESSING SITE PRIORITY TAILINGS (10 tons)

Arizona

Colorado

Idaho

New Mexico

North Dakota

Oregon

Pennsylvania

Texas

Utah

Wyoming

*Monument Valley Low *Tuba City Medium

Durango High Grand Junction High Gunnison High Maybell Low Naturita Medium New R i f l e High Old R i f l e High Sl ick Rock (NC) Low Sl ick Rock (UC) Low

Lowman Low

Ambrosia Lake Medium *Shiprock High

Be l f i e l d Low Bowman Low

Lakeview Medium

Canonsburg High

Fa l l s City Medium

Green River Low *Mexican Hat Medium Salt Lake City High

Converse County Low Riverton High

1.100 0.800

1.555 1.900 0.540 2.600

2. 700 0.350 0.037 0.350

0.090

2.600 1.650

0.130

0.414

2.500

0.123 2.200 1.880

0.187 0.900

24.606 (Tota l )

*Processing s i t e on Navajo t r i b a l lands

TABLE 1

DESIGNATED UMTRA PROJECT SITES

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The Uranium M i l l Ta i l ings Radiation Control Act of 1978 (Publ ic Law 95-604) authorizes the Department of Energy to perform remedial action at 24 inact ive uranium mil l ing s i t e s which processed uranium exclus ive ly for the U.S. Government in the period before 1970. These s i tes contain approximately 25 mi l l ion tons of t a i l i n g s . Twenty-three of these s i tes are located in nine western s tates ; one s i te is in the eastern United States , at Canonsburg, Pennsylvania. Most of the western s i tes are in semi-arid regions. Many of them are in mountainous t e r r a in .

In designating the s i t e s , the Department of Energy, in consultation with the EPA, assigned p r i o r i t i e s of high, medium, and low, depending on the proximity of the t a i l i ng s to centers of population, s i ze of the t a i l i ngs p i l e , degree of s t a b i l i z a ­t ion , e t c . Nine of the s i tes were assigned a p r i o r i t y of high, and from this group the s i t e s at Canonsburg, Pennsylvania; Sa l t Lake City , Utah; Durango, Colorado and Shiprock, New Mexico have been selected for top p r i o r i t y treatment. The names and locations of the s i t e s , the i r p r i o r i t i e s and the quantit ies of t a i l i n g s present are shown in Table 1.

The remedial action to be performed consists of the s t ab i l i z a t i on of the mi l l t a i l i n g s , e ither in s i tu or at new disposal s i t e s , and of the cleanup of v i c i n i t y propert ies which have been contaminated by the spread of the t a i l i ng s from the disposal s i t e s . The Act a lso provides that an opportunity be given for reprocessing of the t a i l i ng s by commercial interests to remove any commercially a t t rac t ive residues of uranium, or other minerals, before f ina l d i sposa l .

The program w i l l be carried out in close cooperation with the affected states and Indian Tr iba l nations. Costs w i l l be shared on a 90/10 bas i s with the s ta tes . The Federal Govern­ment w i l l pay the ent i re cost for s i t e s on Indian lands. A l l remedial action plans must have the concurrence of the U.S. Nuclear Regulatory Commission (NRC).

A l l remedial actions under Public Law 95-604 are LO be conducted in accordance with standards to be promulgated for this purpose by the Environmental Protection Agency (EPA). The standards which have been proposed by the EPA for public review and comment are in two par t s :

o Proposed Cleanup Standards for Inactive Uranium Processing S i tes , dated Apr i l 22, 1980 (40 GFR Part 192)

The Uranium M i l l Ta i l ings Remedial Action (UMTRA) Program

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2/82

CANONSBURG SALT LAKE CITY DURANGO SHIPROCK GRAND JUNCTION RIFLE (OLD & NEW) RIVERTON GUNNISON MEXICAN HAT GREEN RIVER SLICK ROCK (TWO) LOWMAN LAKEVIEW MAYBELL SPOOK AMBROSIA LAKE NATURITA TUBA CITY MONUMENT VALLEY FALLS CITY BELFIELD BOWMAN

WSS///S//. J PLANNING AND DESIGN NEPA PROCESS I

FIG. 1. UMTRA Master Site Schedule.

REMEDIAL ACTION

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o Proposed Disposal Standards for Inact ive Uranium Processing S i t e s , dated January 9, 1981 (40 CFR Part 192)

Opportunity for more deta i led consideration of these and other standards w i l l occur l a te r in the symposium. At this time I w i l l simply point out that the comment on the standards was extensive and strongly to the e f fect that the proposed standards were unduly s t r ingent , would be technical ly d i f f i c u l t and expensive to implement, and would not be cost e f f ec t ive considering the postulated bene f i t s . Of par t i cu la r concern were the proposed l imi ts for radon daughter concentrations in structures (0.015 WL), radium 226 concentration in s o i l (5 picocuries/grara) and radon 222 re lease from a f i n a l , s t ab i l i z ed disposal s i t e (2 p C i - m • s"^").

Since the close of the comment period, in July 1981, the EPA s ta f f has prepared revised dra f ts of the standards, and, as of th is wr i t ing , the dra f ts are under review by the EPA manage­ment. We ant ic ipate that the draft revised standards, which we understand to be l e ss stringent in several pa r t i cu l a r s , w i l l be made ava i l ab l e to the affected government agencies for review in the near future , in preparation for f ina l promulgation l a t e r this year .

Since the work to be performed under the UMTRA Project f a l l s within the category of "major federal actions potent ia l ly a f fect ing the environment," the program must a lso be conducted within the framework of the National Environmental Pol icy Act (NEPA), and an environmental impact statement or environmental assessment w i l l be prepared for each of the s i t e s .

F ina l ly , under the terms of the Act, the program i s to be completed within the 7-year period fol lowing promulgation of the EPA standards. Our current schedule for carrying out the project on this bas i s i s shown on the UMTRA Master Site Schedule (see Fig. l ) • This schedule assumes that the EPA standards for the program w i l l be issued in January 1983, and that the progress of the work w i l l not be constrained by funding, which must be appropriated year -by-year by the Federal Government and the s ta tes . The work i s divided into three phases: NEPA a c t i v i t i e s , planning and design, and remedial act ion. I t may be noted that we are currently in the NEPA phase, with work underway on e i ther environmental assessments or environmental impact statements for most of the s i t e s . We are also nearing the completion of the assay of the 12 t a i l i n g s p i l e s which show the most potentia l for economic reprocessing. I t may a lso be noted that completion of the program in a period of 7 years requires that work be underway at substant ia l ly a l l

Page 28: Management of Wastes from Uranium Mining and

the s i tes in p a r a l l e l for a 2-3 year period at the peak of the project a c t i v i t y .

The current total estimated cost of the project is $540 mi l l ion in 1981 d o l l a r s , including a contingency of 20 percent, or $84 mi l l i on . This estimate also includes approximately $100 mi l l ion for the cleanup of 5000-6000 contaminated properties in the v i c in i t y of the processing s i t e s , leaving a balance, without contingency, of $356 mi l l ion for planning, engineering and remedial action at the processing s i t e s themselves. This estimate i s based on assumed standards somewhat less stringent than the proposed standards. More s p e c i f i c a l l y , i t i s assumed that i t w i l l be necessary to re locate the t a i l i ng s at only one s i t e (Durango, Colorado) , and that the cover w i l l consist of two meters of l o c a l l y ava i l ab l e s o i l . The importance of cover thickness in the cost estimate is shown by a sens i t i v i ty ana lys i s , which indicates that the do l l a r value of a one-meter change in thickness over the estimated area of the disposal s i tes i s $37 mi l l i on .

The design approach to be employed in the s t ab i l i z a t i on of the s i tes w i l l be decided on a case-by-case ba s i s , taking advantage of ex ist ing favorable s i t e characte r i s t i cs , p ro ­viding engineering features to overcome potentia l problems, and re locating to new disposal s i tes only when the exist ing s i t e i s unsuitable , for either engineering or socio-economic reasons. However, i t appears at this time that the basic approach w i l l consist of configuring the t a i l i ng s p i l e to a stab le configuration, covering i t with a layer of so i l and a layer of rock to provide s t a b i l i t y , radon contro l , and erosion protection, and providing a l i ne r beneath the p i l e when necessary to prevent the contamination of ground water.

In preparation for actual s t ab i l i z a t i on design, the project is sponsoring a research and development program which addresses a wide range of subjects of interest to design economy and du r ab i l i t y . This program w i l l be discussed in a number of papers l a t e r in the symposium. At this time I wish only to note that the program emphasizes the development and testing of cover and l iner technology, and includes a ser ies of l a r ge - sca l e tests of various cover designs on the t a i l i ngs p i l e at Grand Junction, Colorado. Data from these tests i s s t i l l being co l lected , but resu l t s to date indicate that the attainment of radon f lux suppression to the 2 pCi*m~^'s""^ required by the proposed EPA standards is not eas i l y achieved and would require either complex design coupled with exacting construction procedures, or very heavy earthen covers.

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Responsibi l i ty for carrying out the program of remedial action has been assigned to the UMTRA Project Of f ice , located within the DOE's Albuquerque Operations O f f i ce . The Project Of f ice w i l l be ass isted by three main contractors . The Technical Assistance Contractor, or TAC, w i l l a s s i s t in the se lect ion of the remedial action concept to be employed at each s i t e and in the ove ra l l management of the pro ject . The Jacobs Engineering Group, ass isted by the Roy Weston Corporation, has recently been selected as the TAC. The Remedial Action Contractor, or RAC, w i l l perform the detai led engineering design and manage (and in some cases may perform) the on-s i te construction work. The process for the se lect ion of the RAC i s underway, and i s scheduled for completion by August 1982. The Sandia National Laboratory i s phasing out of the interim technical support ro le i t has provided in the past , but w i l l continue to manage the NEPA e f f o r t .

Before leaving the program for the inactive s i t e s , I should discuss b r i e f l y the planned program for the cleanup of contaminated v i c i n i t y proper t ies . Preliminary surveys have indicated that some 5000-6000 propert ies w i l l require work. A l l but approximately 1000 of these propert ies are located in Grand Junction, Colorado, where a Federal -State cooperative program for the cleanup of occupied structures has been underway since 1972. Under this program about 400 of an estimated tota l of 740 structures have been completed. This has involved the removal of some 63,000 tons of t a i l i n g s and contaminated so i l from underneath and around these bu i ld ings , an average of about 150 tons per bu i l d ing . Most of the Grand Junction properties to be cleaned up under the UMTRA Project w i l l consist of open lands. Most of the other v i c i n i t y propert ies under the UMTRA Project are located in Salt Lake C i ty , Utah; Canonsburg, Pennsylvania; Durango and R i f l e , Colorado, and Shiprock, New Mexico. The work on this program began l a s t summer with the cleanup of Salt Lake County Fire Station #1, where a tota l of 7000 cubic yards of t a i l i n g s and contaminated s o i l , which had been used as f i l l , were removed. We expect to proceed with addit ional propert ies at Salt Lake City and at Canonsburg during this construction season.

Ta i l ings Management at Active M i l l s

Tai l ings at the act ive processing s i t e s are managed by the mi l l owners and operators under l icenses issued by the NRC or by the states that have acquired authority through a formal l i cense agreement with the NRC.

Table 2 l i s t s 30 mi l l s which are in the " a c t i v e " or " l i c ensed " category. These s i tes house more than 170 mi l l ion

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GROELSEMA

TABLE 2

ACTIVE" URANIUM MILLS I N THE USA

Tailings Inventory

Mill 1981 Status License

Location Millions of Tons Agency Date

Exxon Highland Converse Co., WY 8 Operating NRC 1977 Federal Am Partners Gas Hills, WY 6 On Hold NRC 1980 Lucky Mc Pathfinder Gas Hills,WY 9.5 Operating NRC 1979 Petrotomics Shirley Basin, WY 5.5 Operating NRC 1977 S. B. Pathfinder Shirley Basin, WY 5 Operating NRC 1977 Union Carbide Gas Hills, WY 8 Operating NRC 1979 Western Nuclear Jeffry City, WY 7.7 On Hold NRC 1980 Bear Creek Converse Co., WY 4 Operating NRC 1977 Minerals Exploration Sweetwater Co., WY 0.3 Operating NRC 1979 United Nuclear Converse Co., WY - Planned NRC 1979 Atlas Minerals Moab, UT 10.2 Operating NRC 1980 Rio Algom La Sal, UT 2 Operating NRC 1980 White Mesa Blanding, UT 0.5 Operating NRC 1980 Plateau Resources Shootering Can., UT (new) Operating NRC 1980 Anaconda Grants, NM 23.6 On Hold N.M. 1976* Homestake Grants, NM 21.2 Operating N.M. 1976* Kerr McGee Grants, NM 30.4 Operating N.M. 1976* Sohio Ceboyta, NM 4 On Hold N.M. 1975 Bokum Marquez, NM - Planned N.M. 1980 Gulf Mt. Taylor Mt. Taylor, NM - Planned N.M. 1980 Pioneer Slick Rock, NM - Planned N.M. 1981 Homestake Saguache Co., CO - Planned Co. 1980 Cyprus Hansen Freemont Co., CO - Planned Co. 1981 Cotter Canon City, CO 1.9 Operating Co. 1979 Union Carbide Uravan, CO 9.9 Operating

(part time) Co. 1968*

Dawn Ford, WA 3 Operating Wa. 1981 West. Nucl. Sherwood Ford, WA 1.5 Operating Wa. 1978 Conquista Falls City, TX 7.8 On Hold TX 1971* Chevron Panna Maria, TX 3.2 Operating TX 1977* Anaconda Rhode Ranch McMullin Co., TX - Planned TX 1982

Total 173.2

*License renewal pending

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tons of ta i l ings—more than six times the amount involved in the UMTRA Program. This quantity i s expected to grow to we l l in excess of 200 mi l l ion tons by the year 2000. I t may be noted that a l l the act ive s i tes are in the western United States. Twenty-one of the s i tes are in the states of Wyoming, Colorado and New Mexico. The three largest s i tes (Anaconda, Homestake, and Kerr McGee) are in the area of Grants, New Mexico and contain almost 75 mi l l ion tons of t a i l i n g s . The Grants mineral be l t l i e s about 75 miles to the west of Albuquerque and w i l l be v i s i t ed on the tour which has been arranged for Wednesday afternoon. F ina l ly , i t may be noted from Table 2 that as a resu l t of the current depressed market for uranium, several ex ist ing mi l l s have been placed in a standby or hold s tatus , and several mi l l s for which there were firm plans a few years ago are not being constructed.

There has been considerable progress in the management of the t a i l i ng s at the active s i t e s since the l a s t IAEA Symposium on M i l l Ta i l ings was held here in Albuquerque In 1978. However, the progress has been uneven and the s i tuat ion i s somewhat confused, l a rge ly because agreement has not yet been reached on the standards and the regulations which are to govern these a c t i v i t i e s .

The subject of l icensing requirements in the United States w i l l be covered f u l l y by Ms. Kathleen Hamill of the U.S. Nuclear Regulatory Commission in the fol lowing sess ion; hence, I w i l l present only a b r i e f sketch.

In l a te 1976, fol lowing the f i r s t U.S. Department of Energy studies of the inactive mi l l t a i l i ng s s i tes and the increased publ ic awareness and concern about exposure to this source of low leve l rad iat ion , the NRC f i r s t addressed d i rec t ly the issue of mi l l t a i l i n g s management. A set of Interim Guidelines was issued in May 1977. The guidel ines were b r i e f , covering the periods of s i t ing and design, operation and post reclamation, and were intended to al low industry f l e x i b i l i t y in developing management a l t e rna t i ves . In November 1978 the Uranium Mi l l Ta i l ings Radiation Control Act (the same Act which authorized the UMTRA Program) directed the U.S. Environmental Protection Agency to issue standards of general appl icat ion for the management of mi l l t a i l i ng s at the inactive and the active s i t e s ; the former were to be issued by November 1979 and the l a t t e r by May 1980. The standards for the active s i tes are to provide a framework, within Xvrtiich the NRC and the states would l icense and regulate the industry. As we have seen ea r l i e r in this paper, the promulgation of these standards has been delayed•

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However, by October 1980, the NRC had completed i t s Generic Environmental Impact Statement on Uranium Mi l l ing and promulgated i t s regulations at that time. Numerous industry organizations claim that NRC's regulations are overly str ingent and challenged the regulat ions on this bas i s as wel l as on the issue of whether NRC had the authority to issue such requ i re ­ments in advance of EPA's issuance of standards. In March of th is year the Tenth Circuit Court of Appeals decided that NRC did have the authority to issue the subject regulat ions , had followed proper procedures, and had provided an adequate bas is for the requirements. Notwithstanding th i s , an amendment to NRC's FY 1982 authorization act prohibits NRC implementation or enforcement of the mi l l t a i l i ngs regulations unt i l October 1982. Further, there is an amendment to NRC's FY 1983 authorization b i l l , pending in the U.S. Congress, which would extend the embargo on the use of the Commission's mi l l t a i l i n g s regu la ­tions unt i l EPA issues f ina l standards, seeks to expedite the promulgation of the required EPA standards, and authorizes the NRC to regulate the industry in the interim, on the bas is of the 1977 guide l ines . The amendment a lso addresses the degree of f l e x i b i l i t y which should be accorded the agreement states in regulating the industry within their states under their agreements with the NRC.

Despite the above uncertainties much has been achieved. A glance at Table 2 w i l l indicate that most of the active s i t e s have obtained l icense renewals in the period since 1977 and that several new s i t e s have been l icensed.

The most d i rect and straightforward appl icat ion of the NRC guidel ines and regulations has been in the l icensing of new m i l l s . In support of a l icense appl icat ion the applicant is required to submit an evaluation of f eas ib le t a i l i ng s manage­ment a l ternat ives for the new s i t e . In the case of new mi l l s a l l options for s i t ing and t a i l i ngs disposal are open for consideration, and th is has lead to the proposal of a number of innovative schemes designed to meet the object ives of the NRC guide l ines . Many of these approaches involve below grade t a i l i ng s d i sposa l , into either l a r ge , mined-out p i t s or into ind iv idua l ly constructed c e l l s , excavated to a depth of 12-15 meters below the exist ing grade. Generally the p it or c e l l i s l ined with clay or a synthetic l ine r material before the t a i l i n g s are emplaced. When f i l l e d , the p i t or c e l l i s covered with s o i l , or a combination of clay and s o i l l ayers , which is in turn protected from long-term erosion by a rock or vegeta ­t ive cover.

The approach for ex i s t ing , operating mi l l s under NRC j u r i sd i c t i on has been to c a l l for the operator to propose a

Page 33: Management of Wastes from Uranium Mining and

program for meeting the NRC guidel ines r e l a t i v e to the periods of operation and reclamation. The proposals which have been received and approved are of three basic types: ( a ) continued use of the ex ist ing t a i l i ng s area , ( b ) discontinued use of the ex ist ing t a i l i n g s area with newly generated t a i l i ng s impounded in mined out p i t s , and ( c ) the emplacement of both newly generated and ex is t ing t a i l i ng s in mined out p i t s . In each case a firm reclamation plan, with surety arrangements s u f f i ­cient for carrying out the plan has been adopted. Such reclamation plans have been approved for a l l of the exist ing mi l l s under l icense by the NRC.

Commingled Ta i l ings

Thirteen of the processing s i t e s l i s t ed in Table 2 contain substantia l quantit ies of t a i l i n g s , which, l ike the t a i l i ngs at the inactive s i t e s were generated during the period before 1970, in producing uranium for sa le exclus ive ly to the U.S. Government. There i s a tota l of approximately 50 mi l l ion tons of such t a i l i n g s at these s i t e s . However, these mi l l s have continued in operation, producing uranium for commercial s a l e s , and the resu l t ing t a i l i ng s are now commingled with those generated in the e a r l i e r per iod.

Public Law 95-540 d i rects the Department of Energy to develop a plan for a cooperative program to provide assistance in the s t ab i l i z a t i on and management of defense-re lated uranium mi l l t a i l i ng s commingled with other t a i l i n g s . In response to this d i r ec t i ve the Assistant Secretary for Defense Programs, through the Department's Grand Junction Area Of f i ce , has undertaken a study to determine the amount and condition of the t a i l i ng s generated under Federal contracts, and to examine methodologies for determining the amount and kind of Federal assistance that might be appropriate to aid in the f ina l d i s ­posal of these t a i l i n g s . The f ina l report of this study i s to be submitted to the Congress by June 30, 1982.

Uranium Mining Wastes

The Uranium M i l l Ta i l ings Radiation Control Act, in addit ion to i t s provisions concerning uranium mi l l t a i l i n g s , requires the Environmental Protection Agency, in consultation with the Nuclear Regulatory Commission, to provide a report to the Congress which i den t i f i e s the location and potentia l health, safety and environmental hazards of uranium mine wastes, together with recommendations, i f any, for a program to eliminate these hazards. This report has been prepared and i s under review by the EPA management pr ior to i t s re lease for publ icat ion and transmittal to the Congress.

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Summary

Considerable progress has been made in estab l ishing r e spons ib i l i t y , requirements, technology and implementing pract ices for the long term management of uranium mil l t a i l i ng s in the United States . The IMTRA Program i s ready to proceed with the cleanup of v i c in i t y propert ies , has establ ished i t s plans and organization for the s t ab i l i z a t i on of the inactive processing s i t e s , and has almost completed the draft environ­mental impact statements for the f i r s t high p r i o r i t y s i t e s . Long-term t a i l i n g s management plans have been adopted for most of the active and proposed processing s i t e s . The promulgation of standards which embody adequate protection of the public and the environment on a cost e f fect ive bas i s i s urgently needed to set the framework for further progress in this a rea .

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Invited Review Paper

A SUMMARY OF THE CANADIAN URANIUM MILL

TAILINGS SITUATION

P. HAMEL Atomic Energy Control Board, Ottawa, Ontario

J. HOWIESON Energy, Mines and Resources

Canada, Ottawa, Ontario, Canada

Abstract

A SUMMARY OF THE CANADIAN URANIUM MILL TAILINGS SITUATION. As a leading uranium producer, Canada has a strong interest in developing strategies for

the long-term management of uranium tailings. In this presentation a number of factors are briefly described such as geology, climate, population, regulation and politics which combine to give the management of uranium tailings in Canada their own unique characteristics. The major thrusts of the Canadian research programme are to determine the extent of any long-term problems that may arise and to develop optimum close-out methods. The Canadian contributions to this conference provide a comprehensive review of the developments to date and the plans for future work.

A. Canada's Mining Industry

In the p roduc t i on o f many m i n e r a l s , non-minera ls and f u e l s Canada now ranks amongst the premier mining na t i ons o f the w o r l d .

There a r e c u r r e n t l y about 60 d i f f e r e n t m ine ra l s e x t r a c t e d from Canadian rock and s o i l by some 270 ope ra t i ng mines . M ine ra l s a re shipped t o a lmost 100 d i f f e r e n t c o u n t r i e s and account f o r 21% o f Canada's merchandise e x p o r t s .

As shown in Tab l e 1, o ve r t en per c en t o f Canada's GNP i s now d e r i v e d from mining, r e f i n i n g and a s s o c i a t e d i n d u s t r i e s .

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FIG. I. Location of hard rock mines in Canada.

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TABLE 1 1980 CANADIAN MINING STATISTICS

V A L U E OF 1 9 8 0 P R O D U C T I O N OF $ M

C O P P E R 1 8 6 0 I R O N O R E 1701 N I C K E L 1 4 9 7 G O L D 1 1 6 5 Z I N C 8 5 8 SILVER 8 2 9 U R A N I U M 7 0 2 M O L Y B D E N U M 2 9 9 LEAD 2 7 4 OTHER METALS 511 P E T R O L E U M 9 0 3 8 N A T U R A L G A S 6 149 N A T U R A L G A S B Y P R O D U C T S 1 8 2 5 C O A L 9 3 2 N O N M E T A L L I C M I N E R A L S 2 5 3 2 S T R U C T U R A L M A T E R I A L S 1 6 6 9

T O T A L 31 8 4 1

C A N A D I A N G N P - 1 9 8 0

V A L U E OF M I N I N G P R O D U C T I O N A S % C A N A D I A N G N P

E M P L O Y M E N T IN C A N A D I A N M I N I N G I N D U S T R Y

M I N I N G E M P L O Y M E N T A S % T O T A L C A N A D I A N

T O T A L OF H A R D ROCK M I N E TAIL INGS IN 1980

E S T I M A T E D U R A N I U M T A I L I N G S P R O D U C E D IN 1980

= $ 2 8 5 8 9 0 M

= 11.1%

= 2 2 0 0 0 0

= 1.9%

= 154 x 1 0 6 T O N N E S

= 7 x 1 0 6 T O N N E S

Mining o p e r a t i o n s a r e w i d e l y d i s t r i b u t e d i n Canada as shown i n F i gu re 1. A l l the p r o v i n c e s and t e r r i t o r i e s have t r a d i t i o n a l l y regarded the mining o f t h e i r na tu ra l r e sources as a b e n e f i c i a l i n d u s t r i a l deve lopment . The l e g a l , r e g u l a t o r y and t e c h n i c a l i n f r a s t u c t u r e s a t a l l l e v e l s o f government were des igned t o encourage such deve lopment .

M ine ra l r e sources i n the Canadian j u r i s d i c t i o n a l system a r e c o n t r o l l e d by the p r o v i n c i a l governments w i t h r e s p e c t t o r a t e o f deve lopment , s a f e t y , t a x a t i o n and r e g u l a t i o n so long as these r esources and any e f f e c t s from them remain w i t h i n the p r o v i n c e o f o r i g i n . The

Page 38: Management of Wastes from Uranium Mining and

FIG.2. Areas in Canada favourable for the occurrence of uranium deposits.

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f e d e r a l government has f u l l j u r i s d i c t i o n o ve r the "Canada" l ands ( the j t e r r i t o r i e s o u t s i d e p r o v i n c i a l boundar ies ) and a few d e c l a r e d r esources w i t h i n p r o v i n c i a l boundar ies such as uranium. The Canadian f e d e r a l government has a l s o p rov ided such s e r v i c e s t o the indus t r y , as g e o l o g i c a l in f o rmat i on and p rocess development r e s ea r ch .

Mining p r a c t i c e has o b v i o u s l y e v o l v e d over the y e a r s . Many improvements have been made i n mine s a f e t y , i n reduc ing the l o c a l env i ronmenta l d eg rada t i on due t o mine w a s t e s , and i n a v o i d i n g the c r e a t i o n o f new " g h o s t " towns. Problems i n these a r eas have been t a c k l e d w i t h many d i f f e r e n t approaches and t h i s broad expe r i ence w i th mining has been drawn on e x t e n s i v e l y i n the uranium mining indus t r y .

B . Canada's Uranium Indust ry

Uranium m i n e r a l i z a t i o n i s widespread i n Canada as shown i n F i gu re 2. The mining o f uranium s t a r t e d i n the North West T e r r i t o r i e s , but i s concen t ra t ed now i n two r e g i o n s - Nor thern Saskatchewan and E l l i o t Lake i n O n t a r i o . Both o f these r e g i o n s a r e l o c a t e d on the Canadian pre-Cambrian S h i e l d . These a reas have v e r y l i t t l e s o i l c o ve r as they were sub j ec t ed i n v e r y r e c en t g e o l o g i c a l t ime t o the scour ing a c t i o n o f g l a c i a t i o n .

The indus t ry expanded r a p i d l y in the l a t e 1950 's i n response t o U.S. and U.K. demands f o r de f ence purposes ( F i g . 3 ) . I n 1959, 23 mines and 19 o r e p rocess ing m i l l s were o p e r a t i n g . However, the de f ence market cou ld not sus ta in snch a p roduc t i on r a t e . The m id -60 1 s saw a r ap id d e c l i n e in p roduc t i on and the Canadian government had t o i n s t i t u t e s t o c k p i l i n g programs t o mainta in a c o r e o f p roduc t i on c a p a b i l i t y t o supply the coming c i v i l i a n market .

Canada has produced ove r 20 per c en t o f the t o t a l , wor ld p roduc t i on o f uranium t o d a t e . 85% o f Canadian produc t i on i s e xpo r t ed and t h i s p r o p o r t i o n should c on t i nue . The remaining p roduc t i on i s be ing used i n Canadian CANDU power s t a t i o n s . Canadian p o l i c y , announced i n 1974, r e q u i r e s t h a t a 30-year supply o f f u e l r e sources be mainta ined f o r a l l domest ic nuc lear power r e a c t o r s t h a t a r e , o r w i l l b e , o p e r a t i n g i n the immediate t en - y ea r forward p e r i o d .

Canada's p o l i c y t h a t e x p o r t s o f uranium be used o n l y f o r p e a c e f u l purposes has been r e i t e r a t e d i n many s tatements s ince 1965, and has r equ i r ed s t r i n g e n t sa feguards agreements w i t h i t s uranium t r ad ing p a r t n e r s . These sa feguards

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1950 1960 1970 1980 Y E A R

FIG.3. Canadian uranium production history.

requirements have been s t a b i l i z e d s i n c e 1976. A l l new s a l e s o f Canadian uranium s i n c e the e a r l y 1960 's have gone t o p u r e l y c i v i l i a n power p roduc t i on programs. In 1981, $770M worth o f uranium was shipped from Canadian mines .

Expansion i n p roduc t i on c a p a c i t y i s s t i l l underway in the E l l i o t Lake and Northern Saskatchewan r e g i o n s . A p r o j e c t i o n o f p roduc t i on c a p a b i l i t y f o r Canada i s shown in F i gure 4. To mainta in a s teady growth - o r a s teady p roduc t i on r a t e beyond 1990 - new mines w i l l have t o be opened as the e x i s t i n g ones a r e mined o u t . Further expansion o f a c t u a l p roduc t i on i s o f course dependent upon the maintenance and growth o f the market f o r nuc lear power.

The j u r i s d i c t i o n o f uranium mining i s unique i n t h a t the f e d e r a l government pre-empted p r o v i n c i a l c o n t r o l , f o r n a t i o n a l s e c u r i t y r easons , by enac t ing the Atomic Energy

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J _ ( , 1 1 1 1 1 1 1 1 1

1981 1983 1985 1987 1989 1991

FIG.4. Canadian uranium, production capability versus estimated domestic requirements.

Con t r o l A c t o f 1946. During the r a the r h e c t i c growth o f the uranium mining indus t ry i n the l a t e 1950 ' s , the f e d e r a l r e g u l a t o r y body, the Atomic Energy Con t r o l Board (AECB) was p r i m a r i l y i n v o l v e d i n the s e c u r i t y a spec t s and r e l i e d on agreements w i t h the p r o v i n c e s t o l ook a f t e r the s a f e t y a p e c t s . The p r o v i n c i a l a u t h o r i t i e s t h e r e f o r e c o n t r o l l e d the r a d i a t i o n exposure o f the miners and the p u b l i c , the t r a i n i n g o f mining company and p r o v i n c i a l r a d i a t i o n i n s p e c t o r s , and checked compl iance w i t h a p p l i c a b l e p r o v i n c i a l s a f e t y l aw .

In 1975, the On ta r i o government commissioned a study o f the s a f e t y o f the mining o p e r a t i o n s in the p r o v in c e by Dr . James Ham. Among the many sub j e c t s examined by t h i s study was the exposure o f uranium miners t o radon-daughters . As one r e s u l t o f t h i s commission, the AECB a s s e r t e d i t s f u l l s t a t u t o r y a u t h o r i t y ove r p u b l i c and o ccupa t i ona l r a d i a t i o n h e a l t h and s a f e t y i n uranium mining by i n s t i t u t i n g i t s own i n s p e c t i o n and enforcement measures. P r o v i n c i a l requirements i n o the r a r eas were a l s o en fo r ced by i n c l u s i o n as c o n d i t i o n s i n the mines o p e r a t i n g l i c e n c e s .

The AECB i s p r e s e n t l y in t roduc ing a new s e t o f r e g u l a t i o n s which a r e intended t o have uni form a p p l i c a t i o n t o uranium mining a c r o s s Canada.

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TABLE 2

SOME CHARACTERISTICS OF TAILINGS

PROPERTY RANGE

PARTICLE SIZE DISTRIBUTION % SAND 1 97

% SILT 0 96 % CLAY 0 - 40

AVAILABLE WATER STORAGE CAPACITY % 0 - 35

BULK DENSITY g/crn^ 0.2 - 3.1

PARTICLE DENSITY g/crr)3 0.01 - 4.29

pH OF GROUND WATER 1.8 9.4

CATION EXCHANGE CAPACITY meq/100 g 0.19 46.5

ORGANIC MATTER % 0.02 25

ELECTRICAL CONDUCTIVITY mmhos/cm 0.1 22.4

AVAILABLE ELEMENTS P ppm 0.1 400 K ppm 1 564

Ca ppm 40 52 480

TOTAL ANALYSIS N % 0.001 0.166 S % 0.01 38.87

Fe % 0.4 56.81 Al % 0.1 8.1 As % 0 0.2 Ca % 0.01 10.95 Mg % 0.04 5.0 Na % 0 01 2.9

K % 0.04 3.32 Mn % 0.01 4.0

Si % 4 37 Cd ppm 2 280 Cr ppm 20 7 000 Co ppm 1 • 10 000 Hg ppm 0.005 1.2 Mo ppm 10 800

Ni ppm 10 546 Pb ppm 0.3 2 810 Sb ppm 10 2 000 Ti ppm 200 10 000

Zn ppm 1 5 000 Cu ppm 1 15 000

Ra226 pCi/gm 0.5 400

SOURCE: CANMET PIT SLOPE MANUAL SUPPLEMENT 10-1. EMR REPORT 77-31

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C. Mine T a i l i n g s i n Canada

The t a i l i n g s from hard-rock mine/mi l l ing o p e r a t i o n s i n Canada have been produced from a wide range o f o r e s and m i l l i n g p r o c e s s e s . Every t a i l i n g s p i l e i s unique in r e s p e c t t o i t s s i t e , i t s chemica l makeup, i t s hydro logy and i t s p o t e n t i a l hazards . Tab le I I l i s t s the ranges o f some o f the chemica l c o n s t i t u e n t s found i n Canadian t a i l i n g s . C l e a r l y , many o f these c o n s t i t u e n t s cou ld r e s u l t i n env i ronmenta l and h e a l t h damage i f the t a i l i n g s were not t r e a t e d w i th r e s p e c t .

Perhaps the most obv ious env i ronmenta l damage observed t o d a t e i s tha t due t o a c i d p roduc t i on i n t a i l i n g s w i th h igh su lph ide c o n t e n t s . Seepages i n t o wate rcourses a t a pH o f 3 o r l e s s from a c i d g ene ra t i ng t a i l i n g s a r e not uncommon and r e s u l t i n the d e s t r u c t i o n o f aqua t i c s p e c i e s downstream. Su lphur i c -ac id fo rmat ion in the t a i l i n g s a l s o tends t o d i s s o l v e and then d i s t r i b u t e o ther m e t a l l i c contaminants i n t o the environment.

I n a d d i t i o n t o p o s s i b l e chemica l hazards , t h e r e a r e ques t i ons on the s t a b i l i t y o f the p h y s i c a l s t r u c t u r e o f the t a i l i n g s p i l e s . Most Canadian t a i l i n g s have been d i scharged from the m i l l as a s l u r r y w i th w a t e r . The s o l i d s were i n i t i a l l y d e p o s i t e d in na tura l o r a r t i f i c i a l (dammed) d ep r e s s i ons and, w i th cont inued p roduc t i on , these dams have o f t e n been b u i l t up i n h e i g h t . A l though the f i n a l t a i l i n g s conta ined have a c ons i s t ency s i m i l a r t o na tu ra l sand o r quicksand d e p o s i t s , the c o n f i g u r a t i o n does not n e c e s s a r i l y r e s t a t the na tu ra l ang l e o f r epose . Thus, the r e i s the p o s s i b i l i t y o f p h y s i c a l r e c o n f i g u r a t i o n ove r t i m e , as e i t h e r a g radua l or an instantaneous p r o c e s s .

I n Canada t h e r e a r e now some 3 400 m i l l i o n tons o f t a i l i n g s from hard rock mining d i s t r i b u t e d i n hundreds o f s i t e s t o t a l l i n g some 230 square k i l o m e t r e s . These t a i l i n g s a r e l o c a t e d i n a l l a r eas ac ross the country where mining has been p r a c t i s e d and F i gu re 5 g i v e s an i n d i c a t i o n o f t h e i r d i s t r i b u t i o n .

Wh i l e most o f these t a i l i n g s a r e i n a r eas o f low popu la t i on d e n s i t y , some a r e ad jacen t t o popu la t i on c e n t r e s .

The r e l e a s e from t a i l i n g s o f env i ronmenta l p o l l u t a n t s which might a f f e c t l o c a l popu la t i ons i s p r i m a r i l y governed by the compos i t i on o f the t a i l i n g s , p r e c i p i t a t i o n , temperature and wind speeds . F i gu r e s 6 and 7 show annual p r e c i p i t a t i o n and ave rage annual temperatures ac ross Canada. Cons ide rab l e v a r i a t i o n s a r e n o t i c e a b l e a c r o s s the country

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FIG.5. Total accumulated tails across Canada.

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FIG. 6. Mean annual precipitation in centimetres for the period 1931-1960.

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FIG. 7. Mean daily temperature in °C for the period 1931-1960.

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al though the t e r r a i n i s g e n e r a l l y wet o r f r o z e n . The major d i s t r i b u t i n g medium i n Canada i s water f l o w ra the r than wind. The weather v a r i a t i o n s g i v e r i s e t o d i f f e r e n t magnitudes o f seepage and e r o s i o n and t o d i f f e r e n t b i o t a i n d i f f e r e n t r e g i o n s so tha t the r e can be no s i n g l e "Canadian" answer t o the ques t i ons which a r i s e on the fu ture o f t a i l i n g s .

The bulk o f r e h a b i l i t a t i o n work on Canadian t a i l i n g s t o da t e has been concent ra ted i n two a r e a s :

- R e v e g e t a t i o n , which reduces seepage through the d e p o s i t , h e l p s t o s t a b i l i z e the p i l e p h y s i c a l l y and improves the a e s t h e t i c appearance, and

- Concent ra t ion o f hazardous chemica ls f o r separa te g e o l o g i c a l d i s p o s a l , which d e l a y s and reduces the r a t e o f the r e l e a s e t o the environment.

Methods f o r r e v e g e t a t i o n have been deve loped and app l i ed t o many d i f f e r e n t t a i l i n g s ac ross Canada. The methods used a re g e n e r a l l y expens i ve as p l a n t n u t r i e n t s must be supp l i ed a r t i f i c i a l l y f o r some y e a r s u n t i l a s u f f i c i e n t depth o f s o i l has b u i l t up f o r unaided s u r v i v a l . The a e s t h e t i c e f f e c t s a r e immediate; but the e f f e c t s on r educ t i on o f seepage and p h y s i c a l s t a b i l i z a t i o n a r e s t i l l under i n v e s t i g a t i o n .

In some o ther c o u n t r i e s , t a i l i n g s have been managed in s i m i l a r ways f o r much l onger p e r i o d s than i n Canada. P h y s i c a l i n s t a b i l i t i e s , a c id d ra inage and some mercury and l e a d p o l l u t i o n have been observed from o l d mine was t e s . Other contaminants r e l e a s e d from the t a i l i n g s a t o l d mines should be measurable a t chem i ca l - ana l y s i s l e v e l s i n the environment a f t e r hundreds o f y e a r s bu t , i n most c a s e s , have not been looked f o r .

D. Uranium T a i l i n g s in Canada

The d i s t r i b u t i o n o f uranium t a i l i n g s i s i n d i c a t e d on F i gure 5. These t o t a l some 130 m i l l i o n tons and cove r some 10 square k i l o m e t r e s .

The r a d i o a c t i v e contaminants a s s o c i a t e d w i th uranium t a i l i n g s have in t roduced an a n a l y t i c a l c a p a b i l i t y s e v e r a l o rd e r s o f magnitude h igher than i s a v a i l a b l e from the chemica l a n a l y s i s o f t a i l i n g s contaminants in the environment . Normal a n a l y t i c a l t echniques f o r most heavy

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meta l s can determine p a r t s per m i l l i o n and o c c a s i o n a l l y p a r t s per b i l l i o n . Radium, Lead 210, e t c . , a r e measurable i n p a r t s per 10^2 because o f t h e i r r a d i o a c t i v i t y . Th i s p r o p e r t y , t h e r e f o r e , a l l o w s e a r l i e r d e t e c t i o n o f any movement from the p o i n t o f d e p o s i t i o n .

From the uranium boom o f the l a t e 1950 ' s , Canada has been l e f t w i th a dozen abandoned uranium t a i l i n g s a reas which have been l a r g e l y untouched f o r t h i r t y y e a r s . The game f i s h popu la t i on o f the Serpent R i v e r system was s e v e r e l y a f f e c t e d by the a c i d d ra inage from E l l i o t Lake t a i l i n g s i n the 1960s. Cont inuing remed ia l a c t i o n i n v o l v i n g t reatment o f a l l a c i d seepage has brought tha t s i t u a t i o n under c o n t r o l . No o ther major env i ronmenta l o r p u b l i c h ea l th e f f e c t s from o ther o l d uranium t a i l i n g s have been obse rved .

R a d i o a c t i v e a n a l y s i s techniques should a l l o w the development o f a s u f f i c i e n t understanding o f the movement o f the r a d i o a c t i v e components t o be ab l e t o make a reasonab le e s t ima t e o f the p o t e n t i a l env i ronmenta l and p u b l i c h ea l th problems in the long term. I f s i g n i f i c a n t problems are p r e d i c t e d , then s t eps w i l l have t o be taken now t o reduce the f o r e c a s t damage t o a c c ep tab l e l e v e l s .

Th i s task i s compl i ca ted by the p u b l i c concerns about r a d i o a c t i v i t y . Th is f e a r i s p a r t i c u l a r l y e v i d e n t in many p r e s e n t a t i o n s t o the i n q u i r i e s i n t o uranium mining which have taken p l a c e under p r o v i n c i a l ausp i c es . I n Saskatchewan and O n t a r i o , these i n q u i r i e s r e s u l t e d i n approva l s t o proceed w i th an expansion o f uranium mining. I n B r i t i s h Columbia, a p o l i t i c a l moratorium o f seven y e a r s on uranium e x p l o r a t i o n and development was announced b e f o r e the commission r e p o r t e d . I n Newfoundland, the development permi t f o r a proposed uranium mine was not g ranted on the b a s i s t h a t a s a t i s f a c t o r y d i s p o s a l method f o r the t a i l i n g s was not proposed .

Th i s widespread p u b l i c f e a r o f uranium mining appears t o be based on p e r c e p t i o n s o f the immediate- and l ong - t e rm e f f e c t s o f the r a d i o a c t i v i t y r e l e a s e d . Th i s p e r c e p t i o n does i n f l u ence the c l i m a t e i n which miners , p o l i t i c i a n s , r e s ea r che r s and r e g u l a t o r s have t o work. And, a t t h i s t i m e , t h e r e i s not enough in fo rmat ion i n Canada w i th which ques t i ons about long term hea l th and env i ronmenta l e f f e c t s can be answered w i t h s c i e n t i f i c r i g o u r . Many s t u d i e s have been i n i t i a t e d i n r e c en t y e a r s a t both the i n t e r n a t i o n a l and n a t i o n a l l e v e l s t h a t w i l l h e l p t o p r o v i d e the s c i e n t i f i c answers r e q u i r e d .

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Th i s symposium p r o v i d e s an e x c e l l e n t oppo r tun i t y f o r Canada t o p repare a comprehensive s e r i e s o f papers r e v i ew ing the p r e s e n t s t a t e o f knowledge, the s t a tus o f r e g u l a t i o n and the p lanning f o r the fu ture by the many o r g a n i z a t i o n s i n t e r e s t e d i n the management o f uranium t a i l i n g s .

The Canadian c o n t r i b u t i o n s a r e be ing g i v e n by authors r ep r e s en t ing t h r e e mining companies, two u n i v e r s i t i e s , f i v e c o n s u l t i n g f i r m s , four f e d e r a l departments o r a g enc i e s and two p r o v i n c i a l m i n i s t r i e s .

In Canada, the e x i s t i n g uranium t a i l i n g s do not p r e s e n t unacceptab le env i ronmenta l and h e a l t h r i s k s , as long as they a r e mainta ined and superv ised t o c o n t r o l hazardous e f f l u e n t s and t o p r e v en t human i n t e r v e n t i o n . From t h i s s i t u a t i o n the two main o b j e c t i v e s o f the Canadian e f f o r t s on t a i l i n g s can be s t a t e d as f o l l o w s .

The f i r s t o b j e c t i v e i s t o ensure t h a t the e x i s t i n g or improved l e v e l s o f supe r v i s i on and c o n t r o l a re maintained f o r as l ong as i s r e q u i r e d .

The second o b j e c t i v e i s t o determine what w i l l happen i n the long term a f t e r these i n s t i t u t i o n a l c o n t r o l s are no l onger e f f e c t i v e . By app ly ing p r e d i c t i v e techniques t o a l t e r n a t i v e d i s p o s a l methods, the optimum d i s p o s a l method which can be shown t o produce accep tab l e l e v e l s o f long term env i ronmenta l and hea l th damage a t each t a i l i n g s s i t e w i l l be determined and a p p l i e d .

Because o f our c l i m a t e and geography, i t i s a n t i c i p a t e d t h a t the waterborne e f f l u e n t s w i l l be o f major importance f o r Canada.

The Canadian papers a t t h i s con f e r ence proceed from those which a r e main ly d e s c r i p t i v e through p r e s e n t a t i o n s o f completed and ongoing r esearch work, the work done t o da t e on a l t e r n a t i v e d i s p o s a l t e c h n o l o g i e s and the p r e l i m i n a r y models used f o r long term s imu la t i on t o the i n i t i a l a t t empts t o de termine l o g i c a l l y the optimum d i s p o s a l t echno logy a t one p a r t i c u l a r s i t e .

A f u l l d e s c r i p t i o n o f the Canadian r e g u l a t o r y system _ and i t s r e c en t development i s g i v e n i n the paper by Bragg e t a l .

E. S tud i e s o f Uranium T a i l i n g s in Canada

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Summaries o f the q e n e r i c research and development work a s soc i a t ed w i th uranium t a i l i n g s which has been underway a t the d i f f e r e n t i n s t i t u t i o n s in Canada f o r a number o f y ea r s a re g i v e n in the papers by K a l i n e t a l , Boyd e t a l , Skea f f e t a l , Dave' e t a l , and Aver i l l e t a l . These cove r the i n v e s t i g a t i o n s t o da t e i n t o the b i o l o g i c a l , h y d r o q e o l o g i c a l and hydrogeochemical f e a t u r e s o f e x i s t i n g t a i l i n g s s i t e s and the work on v e g e t a t i o n and improvements t o e x i s t i n g m i l l p r o c e s s e s .

Three papers from the E l l i o t Lake mining companies by Chakravat t i e t a l , Ha lbe r t e t a l and Culver e t a l , r epo r t on the exper imenta l and a n a l y t i c a l work underway on the e v a l u a t i o n o f a l t e r n a t i v e d i s p o s a l t e c h n o l o g i e s .

The f i r s t a t tempts a t e v a l u a t i o n o f a l t e r n a t i v e d i s p o s a l t e c h n o l o g i e s by means o f mathematical mode l l ing and pathways a n a l y s i s a re r epor t ed in papers by Lush e t a l and Snodgrass e t a l . A p p l i c a t i o n o f o p t i m i s a t i o n techniques as suggested by the ICRP in the ALARA p r i n c i p l e i s attempted by Osborne.

Th i s in fo rmat ion p r o v i d e s a good b a s i s o f knowledge and he lps t o d e f i n e the route which i s be ing f o l l o w e d . The paper by Haw d e s c r i b e s the f e d e r a l p roposa l f o r expansion o f the research work which should r e s u l t i n a s i g n i f i c a n t expansion o f bas i c knowledge and improvements in long term s imula t i on c a p a b i l i t y .

Th i s body o f work i n d i c a t e s tha t the e xpe r i ence and knowledge a v a i l a b l e on the management o f t a i l i n g s from o ther hard rock mines has a l r eady been incorpora ted i n t o Canadian uranium mining p r a c t i c e . The uranium indust ry i s now tak ing the l ead in d e v e l o p i n g , understanding and app ly ing new assessment t echno logy and p o s s i b l y new p h y s i c a l s o l u t i o n s .

There are s e v e r a l o b s e r v a t i o n s we would l i k e t o make b e f o r e conc lud ing t h i s paper .

1. There may be a l i m i t t o the t ime tha t p a s s i v e d i s p o s a l methods must l a s t i n Canada tha t i s d e f i n ed by the v e r y high p r o b a b i l i t y o f renewed g l a c i a t i o n w i t h i n the next 15 000 y e a r s . G l a c i a t i o n w i l l r e s u l t i n the d e s t r u c t i o n o f the p r esen t environment, the removal o f popu la t i on and the p h y s i c a l r e d i s t r i b u t i o n and d i l u t i o n o f t a i l i n g s remaining on the s u r f a c e .

2. For a success fu l d i s p o s a l method which i s r equ i r ed t o con ta in p o l l u t a n t s f o r up t o 15 000 y e a r s i t i s necessary

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t o l ea rn methods which w i l l c oope ra t e w i th the na tura l f o r c e s o f b i o l o g y , weather and geomorphology. Some d e s i g n s , such as tha t f o r deep l ake d i s p o s a l , w i l l o ve r t ime inc r ease the i s o l a t i o n o f the t a i l i n g s from the b iosphere n a t u r a l l y .

3. I t i s known tha t human misuse o f t a i l i n g s can l ead t o h e a l t h problems from radon r e l e a s e in b u i l d i n g s . There i s r e a l d i f f i c u l t y in de termin ing the e x t e n t o f measures tha t should be taken t o p r e ven t fu ture g e n e r a t i o n s from harming themse lves by such p o t e n t i a l human i n t e r v e n t i o n s .

4. A s i g n i f i c a n t p a r t o f reaching agreement on d i s p o s a l methods l i e s in convey ing in fo rmat ion t o the p u b l i c t o counter the p r e sen t p e r c e p t i o n o f f e a r . P r o v i s i o n o f w ider p e r s p e c t i v e s o f i n d i v i d u a l r i s k s from h i s t o r i c a l and economic v i e w p o i n t s w i l l h e l p in reaching r a t i o n a l c o n c l u s i o n s .

5. Regu la to ry bod i es a re be ing f o r c ed by c i rcumstances beyond t h e i r c o n t r o l (such as mine c l o s u r e s ) t o make d e c i s i o n s when on l y p a r t i a l answers a r e a v a i l a b l e on the long term e f f i c i e n c y o f d i s p o s a l a l t e r n a t i v e s . In the absence o f proven t e chn iques , two approaches a re p o s s i b l e . The be s t o f the a v a i l a b l e t echno logy can be r equ i r ed in the e x p e c t a t i o n tha t i t w i l l e v e n t u a l l y p rove t o be a c c e p t a b l e , or the e x i s t i n g c o n t r o l s can be maintained w i th f i n a n c i a l p r o v i s i o n made f o r the adopt ion o f an a c c ep tab l e method when one becomes a v a i l a b l e .

6. To t h i s i n t e r n a t i o n a l s c i e n t i f i c aud ience , we would suqgest tha t you have a c r i t i c a l r o l e i n d e v e l op ing and aq ree ing on the use o f s c i e n t i f i c a l l y based p r o j e c t i o n methods. The i n t e r n a t i o n a l s c i e n t i f i c community can be o f g r e a t use in p r o v i d i n g the en l a r ged h i s t o r i c a l , s o c i a l and economic p e r s p e c t i v e s required- f o r the development o f a b road l y based and accep tab l e approach t o the i s sues r e l a t e d t o the management o f uranium m i l l t a i l i n g s .

B i b l i o g r aphy

AVE RILL , D.W., MOFFETT, D . , WEBBER, R . T . , SCHMIDT, J .W . , BARNES, E . , Development o f a P r e c i p i t a t i o n and F i l t r a t i o n P r o c e s s f o r Radium-226 Removal , IAEA-SM-262-10

BAYDA, J u s t i c e E . D . , C l u f f Lake Board o f I n q u i r y , r epo r t ed 1978 - Saskatchewan

BOYD, J . M . , CARTER, T . G . , KNAPP, R .A . , CULVER, K . B . , H y d r o g e o l o g i c a l I n v e s t i g a t i o n s and E v a l u a t i o n o f the S t a n l e i g h Mine T a i l i n g s Inipoundment Site, IAEA-SM-262-5

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BRAGG, K., POTTER, C , JAMES, A., Recent Developments in the Regulation and Management of Canadian Uranium Tailings, IAEA-SM-262-1

CHAKRAV7ATTT, J . L . ,LAROCQUE, E . , READES, D.W., and ROBINSKY, E . I . , Thickened T a i l i n g s Experiment f o r C lose Out o f Uranium M i l l T a i l i n g s a t Denison Mines L t d . IAEA-SM-262-3

Commission o f Inqu i r y i n t o Hea l th and Environmental P r o t e c t i o n - Uranium Mining , r epo r t ed 1980, B r i t i s h Columbia

CULVER, K.B:, CHAKRAVATT I , J.L., GORBER, D.M., KNAPP, R.A., DAVIS, J.B., Close-Out Concepts for the Elliot Lake Uranium

.Mining Ope ra t i ons , IAEA-SM-262-7

DAVE, N.K., LIM, T.P., MURRAY , D.R., V IVYURKA , A.J., MORIN, K., DUBROVSKY, N., SMYTH, D.J.A., GILLHAM, R.W., CHERRY, J.A., Hydrogeochemical Evolution of an Inactive Pyritic Uranium T a i l i n g s Basin and Re ta rda t i on o f Contaminant M i g r a t i o n i n a Surrounding A q u i f e r , IAEA-SM-262-14 EMR Map No. 900A 30th E d i t i o n 1980

Environmental Inqu i ry i n t o K i t t s - M i c h e l i n Uranium Mine - r epo r t ed 1980 - Newfoundland Expansion o f the Uranium Mines in the E l l i o t Lake Area - On ta r i o Environmental Assessment Board r epo r t ed 1979

HALBERT, B . E . , SCHARER, J . M . , CHAKRAVATTI, J . L . and BARNES, E . , Mode l l i ng o f Underwater D i sposa l o f Uranium Mine T a i l i n g s i n E l l i o t Lake , IAEA-SM-262-4

HAM, J . , Repor t on the Royal Commission on the Hea l th and Sa f e t y o f Workers in Mines , Toronto 1976

HAW, V . , A Canadian Research Program i n t o the Long Term Management o f Uranium Mine T a i l i n g s , IAEA-SM-262-13

KALIN, M. , CAZA, C . , An E c o l o g i c a l Approach t o the Assessment o f V e g e t a t i o n Cover on I n a c t i v e Uranium M i l l T a i l i n g s S i t e s , IAEA-SM-262-2

LUSH, D .L . , SNODGRASS, W. , McKEE, P. f Aquatic Pathway Variables Affecting the Estimation of Dose Commitment from Uranium Mill Tailings, IAEA-SM-262-9

OSBORNE, R .V . , Opt imis ing Rad ia t i on P r o t e c t i o n i n the Management o f Uranium M i l l T a i l i n g s , IAEA-SM-262-30

P i t S lope Manual Supplement 10-1 V o l s 1 and 2 CANMET Energy, Mines and Resources Canada

SKEAFF, J .M. ,RITCET, G.M., JONGEJAN, A . , SILVER, M . , Research on Uranium T a i l i n g s D i s p o s a l Techno l ogy a t CANMET, Ottawa, IAEA-SM-262-12

SNODGRASS, W . J . , LUSH, D .L . , and CAPOBIANCO, J . , I m p l i c a t i o n s o f A l t e r n a t i v e Geochemical C o n t r o l s on the Temporal Behaviour o f E l l i o t Lake Ta i l ings , IAEA-SM-262-54

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S t a t s Canada p u b l i c a t i o n s Cata logue 26-202 1981 Monthly s t a t i s t i c s Feb 1982 The Chemical C h a r a c t e r i s t i c s o f M ine ra l T a i l i n g s i n the P r o v ince o f O n t a r i o , On ta r i o M i n i s t r y o f Environment 1979

The Eco logy and Rec lamat ion o f Lands d i s tu rbed by Mining - B i b l i o g r a p h y o f Canadian r e f e r e n c e s Environment Canada Working Paper #1 A p r i l 1980

Uranium i n Canada EMR Repor t No. EP-81-3

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Invited Review Paper

REGULATION OF THE MANAGEMENT OF WASTE

FROM URANIUM MINING AND MILLING IN AUSTRALIA

R.M. FRY Office of the Supervising Scientist, Sydney

I.W. MORISON Department of National

Development and Energy, Canberra, Australia

Abstract

REGULATION OF THE MANAGEMENT OF WASTE FROM URANIUM MINING AND MILLING IN AUSTRALIA.

Development of new uranium deposits in Australia is being undertaken following extensive inquiry into the issues involved. Under the Australian Federal system in which States are primarily responsible for mining activities, public health and environmental protection, national controls are being achieved mainly through development of national codes of practice. A special situation exists in the Northern Territory where the Commonwealth Government maintains a role complementary to that of the State authorities. The paper outlines Common­wealth/State arrangements and current waste management regimes applying to uranium mining operations in the various States, with particular reference to the effectiveness of the two-level system in meeting operational and public safety requirements.

1. BACKGROUND

Ye l lowcake was first produced in Australia in 1954 from a small treatment plant - 180 t U^Og per annum - located at Rum Jungle about 90 km south of Darwin in the Northern Terr i tory. A number of other deposits were developed in the 1950s leading, over the next 20 years, to the production of about 8 000 t of uranium. This production is sum­marised in Table 1 [1 ] , Most of the mining was carried out by open cut methods and the ore treated by sulphuric acid leaching in plants located (with the exception of Radium Hill ) in the vicinity of the mines. A t Radium Hill the ore was physically concentrated (by a factor of about six) and railed to Port P ir ie (also in South Australia, some 400 km away) for t reatment . Some upgrading of run-of-mine ore, by radiometric sorting, was also carried out at Mary Kathleen.

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TABLE I Australian Uranium Production 1954-1971

Location Production Period

Ore Treated t

Average Grade % U

Production t U

Rum Jungle (Northern Territory)

1954-71 863 000 0.24 - 0.34 3 000

El Sherana (Northern Territory)

1959-64 128 000 0.30 - 0.58 440

Rockhole (Northern Territory)

1959-62 13-500 0.95 117

Mary Kathleen (Queensland)

1958-63 2 947 000 0.20* 3 460

Radium Hill (South Australia)

1954-62 970 000 0.59 - 0.76* 720

* Average grade of ore concentrates at the mill after some physical upgrading of run-of-mine ore.

These mines were all located in remote areas and the environ­mental protect ive measures that were taken could not be considered adequate by today's standards. The sites were usually abandoned after l i t t le more was done than to dismantle buildings and salvage equipment and the tailings were left unstabilised and uncovered.

In the absence of comprehensive clean up and rehabilitation measures, some abandoned mine and mill sites have lately given rise to concern over potential radiation exposure of members of the public and the continuing damaging e f fec ts of heavy metal leaching on the environ­ment. Much of the environmental concern at Rum Jungle arises from this latter source as the ore bodies in that area contained significant quantities of copper and base metals. Copper concentrates containing 13 200 tonnes of copper were produced during the period of operation of the mill.

Recent ly , commitments have been made by various Governments to rehabil itate some of these abandoned sites. The Commonwealth Government, for example, announced in 1980 a $12 million program for rehabilitation of the Rum Jungle site. The costing was based on a notional plan to cover the tailings, vege ta te waste rock dumps and treat highly contaminated water remaining in the open cut pits. Copper bearing material was to be buried. The aim was to reduce significantly

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the release of pollutants; it was not considered practical to el iminate i t . A detai led, costed program is currently being developed by the Northern Terr i tory Government.

The South Australian Government has carried out a rehabilitation program at Radium Hill, a remote , arid, semi-desert site, where some weathering of the tailings dam had occurred. Bund walls were built along the four sides of the dam and the top covered with a metre of compacted clay; this program was completed in Apri l 1981. Considerat­ion is also being given to rehabilitation of the tailings storage area at the mill site at Port P ir ie .

The Commonwealth Government's decision to al low development of uranium deposits discovered during the 1970s was made following an extensive environmental inquiry - the Ranger Uranium Environmental Inquiry [2 ] - into issues, both generic and site speci f ic, associated with the mining and milling of uranium in Australia. A summary of the most significant of these new resources is contained in Table II. Commonwealth policy, announced in 1977, involved a commitment to the acceptance of the highest international standards for the protection of persons and the environment, and an undertaking to develop uniform Australian codes of pract ice for the regulation of uranium mining and milling developments. Within this background this paper outlines Australian act iv i ty , at national and State level , to properly manage the wastes that wil l arise in the development of these resources.

2 . COMMONWEALTH-STATE ARRANGEMENTS

Under Australia's Federal system, the States - now including the Northern Terr i tory which was granted self government in 1978 - are responsible for those functions of Government not explicit ly al located to the Commonwealth. The State Governments are therefore able to adjust the services they provide to correspond to local needs, while maintaining a strong vo ice in national af fairs. They are primarily responsible for administering most aspects of mining act iv i t ies , public health and environment protect ion.

Although the States have responsibility for the management of wastes from uranium mining and milling, the export of uranium is controlled by the Commonwealth. This enables the Commonwealth to attach conditions ("Environmental Requirements") to the development of uranium deposits in addition to the specif ic controls imposed by the States through the issue, under State law, of licences and authorisations to the mining companies. Commonwealth control is exercised through the requirement (under Commonwealth law) upon the companies seeking export l icences to prepare statements analysing in detail the

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TABLE II Major Australian Uranium Resources

Orebody Location Average Ore Grade

% U

Contained Uranium

t U

Proposed Mining

Technique

Ore Treatment Process

Quantity of

Tailings t x 10"

Quantity of Waste

Rock t x 1 0 3

Koongarra No. 1 Alligator Rivers Region Northern Territory

0.78 12 500 Open-cut Acid-leach; amine solvent extraction

5 000 10 000

Nabarlek * ii 2.00 10,200 Open-cut ti 600 4 000

Jabiluka No. 2 ii 0.33 171 600 Underground n 52 000 10 000

Ranger No. 1 * II 0.33 44 800 Open-cut ii 17.000 140 000

Ranger No. 3 II 0.20 60 900 Open-cut & Underground

II 23 000 not known

Yeelirrie Western Australia 0.12 40 100 Open-cut Carbonate-leach

27 000 30 000

Mary Kathleen * Queensland 0.10 5 300 Open-cut (near exhausted)

Acid leach; amine solvent extraction

6 000 18 000

Beverley South Australia 0.22 13 000 In situ leaching 5.000 -Honeymoon II 0.18 2.000 II - -

* Operating at May 1982

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environmental impact of the development. Developmental approval may be made conditional upon specified Commonwealth Environmental Requirements being met by the companies.

2.1 The Supervising Scientist for the Alligator Rivers Region

In the Northern Terr i tory the situation dif fers because the Commonwealth owns the uranium and has its own responsibilities towards environmental protection of Aboriginal land and national parkland. By agreement between the two Governments, uranium mining act iv i t ies are being regulated under Northern Terr i tory law, the Commonwealth's Environmental Requirements being met by conditions incorporated into Authorisations issued by the Northern Terr i tory Supervising Authorit ies.

Essential interests of the Commonwealth in the Al l igator Rivers Region of the Northern Terr i tory are provided for under the Environment Protect ion (Al l igator Rivers Region) A c t 1978, which establishes a Statutory Of f i cer , the Supervising Scientist, who co ­ordinates and supervises environmental regulatory act iv i t ies . A Co ­ordinating Commit tee , also established under this Ac t , and which comprises representatives of relevant Commonwealth and Northern Terr i tory government authorities, the mining companies, the Aboriginals and national park interests, has proved to be a valuable forum in which the sometimes competing views of these parties are aired. The outcome has been the forging of an e f f e c t i v e regulatory reg ime in which all participants have growing confidence.

A Research Institute has also been established within the O f f i ce of the Supervising Scientist to carry out research into the environmental impact (which includes radiological impacts on people) of the uranium mining developments in the Region.

3. CODE OF PRACTICE ON THE MANAGEMENT OF RADIOACTIVE WASTES FROM THE MINING A N D MILLING OF RADIOACTIVE ORES

The Commonwealth Environment Protect ion (Nuclear Codes) A c t 1978 provides a formal mechanism for the Commonwealth to consult with the States in the development of uniform codes of pract ice applicable to the nuclear energy industry. Under the A c t consultation takes place at a technical and policy level in the process of developing approved national codes and provision is made for the calling of public comment. Once codes are formulated and approved, it is the responsibility of the States, and the Northern Terr i tory, to implement the provisions of the codes through their own legislat ive and regulatory machinery.

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Under this legislation three Codes of Pract ice have been developed dealing with:

. Radiation Protect ion in Mining and Milling of Radioact ive Ores (1980);

. Safe Transport of Radioact ive Substances (1982);

. Management of Radioact ive Wastes from Mining and Milling of Radioact ive Ores (1982).

3.1 Basic waste management criteria

The waste management Code sets out basic cr i ter ia to be applied in the management of radioactive wastes; it does not deal with non­radioactive wastes but points out that requirements under other laws relating to these wastes must also be implemented. The Code requires that radiological protection standards, as set out in the radiation protection Code, be met at all t imes but does not otherwise specify technical standards, since the definition of such standards is seen to be the responsibility of the appropriate State authorities, having regard to site-specif ic factors.

Two basic criteria for radioactive waste management set down in the Code are:

. Releases of radioact ive materials from the mine site during and after the l i fe of the mining operation are to be "minimised".

. The final disposition of radioactive wastes, and rehabilitation of sites shall be such that the need for subsequent inspection, monitoring and maintenance is "minimised", or preferably rendered unnecessary.

3.1.1 Minimisation of releases

Although not using the specif ic formulation of the International Commission on Radiological Protect ion (e .g . as in ICRP Publication No. 26) the radiation protection Code invokes the principle of keeping radiation exposures as far below prescribed .dose limits as is pract ic­able - now widely referred to as the A L A R A principle, an acronym formed from the initial letters of "as low as reasonably achievable". Waste management procedures under the waste management Code must also therefore ensure that the exposure to radiation of employees and members of the public is kept below prescribed dose limits and as low as reasonably achievable, and this would be interpreted in the sense of the system of dose l imitation of the International Commission on Radio­logical Protect ion. Where radioact ive eff luents are released from a site in a controlled manner, discharge limits must be set so as to minimise

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releases in this sense. Releases of radioactive material which cannot be controlled in this way (e .g . seepage from tailings dams) must be minimised by the use of Best Pract icable Technology (BPT ) .

BPT as defined in the Code is closely related to the A L A R A concept and is that technology, from t ime to t ime relevant to a speci f ic project, which enables radioactive wastes to be managed so as to minimise radiological risks and detriment to people and the environment having regard to a number of specif ied factors such as available technology, cost re lat ive to the protection achieved, the adequacy of protection already being achieved, local site conditions and the potential hazard of the wastes over the " long term" . The duration of the "long te rm" is not defined but to be compatible with the definition of BPT, structures associated with the management of the wastes would need to be designed and constructed to minimise releases for as long as can be achieved by the use of BPT.

3.1.2 The "walk-away" goal

The second basic criterion sets as a goal for long term radioact ive waste management the construction of systems which do not require ac t i ve maintenance to preserve their e f f i cacy , i .e. the aim is the achievement of a "walk-away" situation. Recognising that a true walk­away system may not be achievable in pract ice, the Code requires that dependence on surveillance and maintenance be minimised. This limits the class of technology which could be considered acceptable for the long term management of radioactive wastes to that which does not depend on act ive maintenance to ensure that it continues to perform according to design specif ication throughout its design l i fe [ 3 ] . The Code makes provision for the possible implementation of inspections, monitoring and maintenance, if considered necessary, a f ter the termination of the licensee's responsibility. Clear ly this would have to be carried out by the State .

3.2 Approvals

Before any uranium mining or milling operation commences, waste management programs covering the full l i fe of the operation must be developed and approved and these programs must be periodically rev iewed and updated. A final waste management plan detailing the decommissioning, stabilisation and rehabilitation program must be developed and approved before the permanent cessation of an operation. Approved monitoring programs - pre-operational, operational and post-operational - must be implemented, as appropriate, throughout the l i fe of an operation to demonstrate compliance with regulatory requirements.

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3.3 Guidelines

A necessary adjunct to the Code is the development of guidelines to assist licensees and the State authorities in interpreting and implementing the requirements of the Code and in developing standards. The following guidelines, for uranium mining operations, are in preparation or contemplated:

. Mining by in-situ leaching

. Tailings impoundment

. Derivation of discharge limits and development of associated monitoring programs

. Development of waste management programs

. Water management

. Rehabil itation and decommissioning

. Monitoring techniques

. Management of heap leach piles

. Management of waste rock heaps and ore stockpiles

. Airborne emissions

As with the Code, the guidelines are being developed against both a practical and theoret ical background. The experience gained in the Northern Terr i tory, for example, is being directly applied in the development of the guidelines.

A guide to a theoretical approach to the assessment of BPT will be provided by the OECD-NEA study on the long term management of uran­ium mill tailings [ 3 ] . This study seeks to examine the application of the ICRP system of dose limitation to the evaluation of alternative options for managing uranium tailings so as to achieve optimum radiological protection in the long term; and to formulate performance objectives and criteria for tailings retention systems. Australia has contributed to this study because it believes it will lead to a valuable expression of international consensus on best practicable technology for the manage­ment of uranium tailings under a variety of c l imatic and geomorphic conditions.

The legislation provides for the revision of the Australian Code and guidelines and it is possible to improve them progressively in the light of experience and international thinking. A number of uranium deposits in Australia, including Pancontinental's Jabiluka, which would be one of the biggest uranium mines in the world, are on the threshhold of develop­ment. The Code of Pract ice wil l be kept under rev iew in the light of both national and world experience as these projects begin to generate radioactive wastes.

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4. CURRENT WASTE MANAGEMENT REGIMES

Considerable variation exists in the machinery of each State for implementing provisions developed under the Environment Protect ion (Nuclear Codes) A c t . These variations are illustrated by the situation in States which are currently act ive in uranium development; Northern Terr i tory, Western Australia, South Australia and Queensland.

4.1 Northern Territory

Uranium mining act iv i ty in Australia is at present mainly centred on the Al l igator Rivers Region in the Northern Terr i tory . This is an area of special significance for Aboriginal people, and with great environ­mental attract ion. A major part of the Region is either Aboriginal reserve or national park - the Kakadu National Park - which has recently been placed on the World Heritage List by the World Heri tage Commi t t ee . This List is a compilation of places forming part of the world's cultural and national heritage which are considered to have outstanding universal value.

4.1.1 Waste management in the Alligator Rivers Region

Of the four major ore bodies in the Region listed in Table II the small very rich deposit at Nabarlek has been mined, by open cut, and the stock-piled ore is being milled over the next eight years. The Ranger mine is also an open cut and production of yel low cake from its No. 1 ore body has begun; operations there are expected to last for at least 25 years. Final approval has not yet been given for the development of the major underground mine at Jabiluka or the deposit at Koongarra, which will also be mined by open cut methods.

The Al l igator Rivers Region is in the tropics and has a typical wet and dry season with temperatures ranging between 18°C and 38°C, the diurnal range being greater than annual variations. Rainfall is about 1300-1500 mm per year received almost entirely within the f ive wet months November to March through high intensity, sometimes very local, convectional downpours and monsoonal and cyclonic storms. Evaporation of about 2200 mm exceeds rainfall in most years. Because of the environmental sensitivity of the Region, the Commonwealth Government has imposed on the uranium developments a more general­ised concept of Best Pract icable Technology 1 applicable to all phases

This concept of BPT is more general than that defined in the waste management Code discussed in section 3.1.1. which is l imited to consideration of radioactive wastes. BPT, in the more general sense, is that technology from t ime to t ime relevant to a uranium development project which produces the minimum envir­onmental pollution and degradation than can reasonably be achieved having regard to a number of expl ic i t ly listed economic and social factors.

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and all aspects of the mining operations. As a consequence of this each development must operate a water management system which allows no planned releases of contaminants to the environment. Al l contaminated water, such as seepage through dam walls, waste rock and ore piles, pit water and runoff from disturbed areas of the mine site, is retained in storage and evaporation ponds, the volumes and areas of which are designed to ensure retention of all waters under a highly improbable sequence of disadvantageous high rainfall wet and low evaporation dry seasons.

The waste management programs at the four sites have however some significant dif ferences in the methods proposed for the ultimate disposal of the tailings.

. A t Nabarlek, mining having been completed, the tailings are being disposed of directly into the mined-out pit. On completion of the milling, the tailings will be dewatered and covered by a zoned clay, gravel and rock cap which wil l be revegetated.

. Ranger's tailings, during operation, are stored in a large (110 ha) zoned earth and rockfil l ring dyke dam located in a geomorphological ly stable area. The walls of this dam will be built up as required and will eventually reach a height of 30 m or so. Present requirements are that at the completion of the mining of the No. 1 ore body the tailings are to be returned to the pit. It is not clear that this is, environmentally, the most desirable way to manage the tailings in this case - they would for example be completely below ground water and unsealed from it - and a study of the long term stabilisation and rehabilitation of the tailings in the surface dam is being planned. Present thinking is that the tailings would be dewatered and capped with a multilayered cover with the dam walls graded down and protected in some way against long term erosion. It may be necessary to set up experimental slopes to establish denudation rates of slopes treated in dif ferent ways.

. The Koongarra project currently is proposing below-grade disposal of the tailings into two specially dug pits, each of about 14 ha, though mining will be carried out rapidly (over two years) as at Nabarlek and the mine pit could be used if desired. The tailings pits are to be sunk 9-10 m in weathered shists with their floors 10-15 m above the local aquifer. Experience gained in decommissioning and stabilising the first pit can be applied to the rehabilitation of the second. The final combination of materials to be used in the design of the capping and the manner of contouring and stabilising the final surface have yet to be determined.

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. A t Jabiluka, tailings management will be di f ferent again. Being an underground mine, some of the tail ings, the coarse sandy fraction, can be mixed with concrete and used as back­fi l l ing. The slimes will be stored, together with waste rock, in a surface impoundment. Stabilisation and capping of this dam will be required but the manner of achieving this will have to take account of the predominantly slimy nature of the tailings.

No tailings stabilisation and rehabilitation plan has yet been approved for an operation in the Region. No limit on radon emanation rate after rehabilitation has been proposed and current thinking is directed more towards the design of containment structures for long l i fe rather than for radon control, if indeed these two are incompatible. To do this, more geomorphological and cl imatological information about the Region is required than is available at present. It will be a major program of the Research Institute of the Supervising Scientist to acquire this information.

4.1.2 Role of the Supervising Scientist

The role of the Supervising Scientist in the Al l igator Rivers Region was mentioned in Section 2.1 above. His functions require him to promote the development of standards and measures for the protection and rehabilitation of the environment and to assist the Northern Terr i tory to establish an e f f e c t i v e regulatory reg ime for uranium mining.

The Co-ordinating Commit tee , which he chairs, in addition to examining technical aspects of the mining developments, also considers administrative and institutional arrangements. Agreement has been reached on several key issues resulting in, for example, a delineation of the respect ive responsibilities of the companies, the Supervising Authorit ies and the Supervising Scientist in demonstrating and verifying compliance with regulatory requirements; and in the definition of monitoring programs and the establishment of guidelines for reporting monitoring results.

These arrangements established in the Northern Terr i tory are elaborate but they are achieving the high standard of environmental protection for the Region promised by the Commonwealth Government. Continuing surveillance and monitoring, and research and development is still needed to ensure the successful decommissioning of the sites and the long term stabilisation of the final repositories for the tailings.

The experience gained in the Al l igator Rivers Region and the research program of the Supervising Scientist on the environmental impact of uranium mining operations, and on the long term management of tailings in particular, though oriented towards mining in a tropical environment, should yield results applicable to uranium development (and other mining operations) elsewhere in Australia.

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4.2 Western Australia

Although no uranium mining operations are currently in progress in Western Australia, proposals for the development of a number of deposits are being formulated. An agreement, rati f ied by an Ac t of Parl iament, has been concluded between the West Australian Govern­ment and one company in relation to Yee l i r r i e , the most advanced of these projects.

This agreement is wide ranging, covering all aspects of the proposed project including environment protection. It covers the preparation of an environmental management program, for Ministerial approval; the undertaking of a continuous program of investigation and research, including monitoring and study of sample areas to ascertain ef fect iveness of environment protection and management measures; the preparation of yearly and three-yearly reports for the Minister on the results of environmental investigations and research; and the observation of national and international codes of pract ice relating to uranium mining and milling. The Yee l i r r ie project will also be subject to regulatory regimes which apply to non-uranium operations.

4.3 South Australia

In South Australia the Radioact ive Substances and Irradiating Apparatus regulations under the Health A c t require that the Health Commission g ive written approval for the disposal of any radioactive wastes including mining and milling wastes. A new Radiation Protect ion and Control A c t has very recently been passed by the Parl iament. Under this A c t new regulations to control management and disposal of mining and milling wastes will be written; these will incorporate the requirement of the national Code of Pract ice , when this is finalised. The regulations will be drafted by an expert commit tee including health, mining and environmental interests, and the draft wil l be circulated to the industry for comment, before presentation to Parl iament.

4.4 Queensland

The only operational uranium mine in Queensland, Mary Kathleen, is about to be decommissioned. No legislation exists which is specif ical ly directed at uranium mining; the operations of the company have been controlled by means of an agreement existing between it and Queensland Government.

The scope of rehabilitation for this mine, which is also controlled through formal agreement with the Government, has yet to be announced.

Other uranium prospects in Queensland are being developed under regulatory regimes in health, water quality, e tc . , which apply to mining operations generally in that State.

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5. CONCLUSIONS

In 1977 the Commonwealth Government allowed uranium mining to proceed, but only under strict environmental controls to be imposed through an e f f e c t i v e regulatory system. A particularly high standard of environmental protection was promised in the Al l igator Rivers Region, the site of the first of the new wave of uranium developments, because of its magnificent scenery and deep significance to the Aboriginal people. Much of the Region is, in fact , national park and Aboriginal land.

Since then, the Commonwealth, States and the Northern Terr i tory have been working together to fashion a consistent regulatory reg ime, backed by nuclear codes of pract ice, to g ive e f f e c t to the Government's decision. Under the Australian Federal system, the most appropriate and practical means of maintaining consistency in the development of codes of pract ice at the national level is through a consultation process involving the Commonwealth and the States. National codes must necessarily concentrate on principles, rather than specif ic standards, because of the dif ferent individual legislative requirements of the States, and the need to maintain f lexibi l i ty in the general applicability of the codes in a wide range of physical environments.

The new mines in the Northern Terr i tory have been developed at a t ime of heightened public environmental awareness and this is re f lected in the Codes, guidelines and regulations to which these developments are subject. The standards and regulations to achieve national goals, and their technical basis, are derived from the best advice available nationally and internationally plus the results of local research and operational experience. Two of these goals in the management of radioact ive wastes from uranium mining operations are agreed to be:

. the minimisation of environmental and public health detriment during the l i fe t ime of the operation and in the long term;

. the achievement of the long term minimisation of detriment without the need for surveillance and act ive maintenance.

Ways of attaining these goals will be kept under rev iew and amended as new information becomes available and thinking on waste management philosophy and basic criteria develops. The work of the IAEA and of the OECD Nuclear Energy Agency, and the pooling of experience at inter­national Symposia such as this are all contributing to the achievement of these high standards of waste management.

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REFERENCES

[1 ] W A R N E R , R.K., The Australian Uranium industry, A tomic Energy in Australia_19 2 (1976) 19.

[2 ] Ranger Uranium Environmental Inquiry. First Report 1976. Second Report 1977. Australian Government Publishing Service, Canberra.

[3 ] F R Y , R.M., Criter ia for the long term management of uranium mill tailings, (This Symposium), IAEA-SM-262/40.

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Rapport general

LA GESTION DES DECHETS SOLIDES DE L'EXTRACTION ET DU TRAITEMENT DES MINERAIS D'URANIUM EN FRANCE

J. PRADEL

Departement de protection,

CEA, Institut de protection et de surete nucleaire,

Centre d'etudes nucleaires de Fontenay-aux-Roses,

Fontenay-aux-Roses,

France

Abstract-Resume'

MANAGEMENT OF SOLID WASTES FROM URANIUM MINING AND MILLING IN FRANCE. The paper gives a list of storage locations for different types of solid waste which have

appeared in France since the start of mining and milling activities in 1950 and presents the experimental results obtained at various French sites for the transport of radioactivity in the atmosphere, surface waters and the food chain. The purpose of compiling these results is to take stock of the problems posed in the particular conditions of French deposits and their geographic and climatic environment. With regard to the management goals for both old wastes and those currently being created, conclusions are drawn which can reasonably be proposed to mining companies, taking into account local conditions and the well-known ICRP recommendations.

LA GESTION DES DECHETS SOLIDES DE L'EXTRACTION ET DU TRAITEMENT DES MINERAIS D'URANIUM EN FRANCE.

Ce memoire presente un inventaire des stockages de dechets solides de differentes natures qui sont apparus en France depuis le debut des operations d'extraction et de traitement (1950) ainsi que les resultats experimentaux obtenus en differents sites francais sur les transferts de radioactivite dans l'atmosphere, dans les eaux de surface et dans la chaine alimentaire. La synthese de ces resultats a pour objectif de situer le niveau des problemes poses dans les conditions particulieres des gisements francais et de leur environnement geographique et climatique. On en deduit quels sont les objectifs de gestion des dechets anciens ou en cours de constitution qu'il est raisonnable de proposer aux companies minieres, de facon a tenir compte des conditions locales et desrecommandationsbien comprises de la CIPR.

Les minerals d'uranium sont exploites en France depuis plus de trente ans.

Jusqu'en 1980, on a essentiellement rencontre des gisements subverticaux de type

filonien dont Pexploitation a entraine" la creation de nombreuses mines, de

dimensions variables, mais en general assez reduites, situees au gre des caprices

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de la mineralisation des regions uraniferes. II n'est done pas possible de decrire ici comment a ete resolu, dans tous les cas, le probleme des dechets miniers. Nous nous limiterons done a presenter quelques exemples principaux en ne traitant que les sites miniers de la Companie generate des matieres nucleaires (Cogema) ou se trouve egalement implantee une usine de traitement et ou se pose done le probleme essentiel des residus de traitement. Apres une rapide presentation de quatre sites ainsi retenus, nous examinerons les resultats des mesures effectuees dans l'environnement et nous en tirerons les conclusions quant a l'orientation a donner aux reglementations nationales ou internationales.

1. SITE DES BOIS NOIRS

1.1. Description (fig. 1)

Sur ce site, dont l'activite a cesse en 1981, on a realise les operations suivantes: 1) Des travaux miniers comprenant:

— des travaux souterrains jusqu'a la cote —400 metres partiellement remblayes (notamment les ouvrages verticaux) avec un million de tonnes de residus de traitement cyclones provenant de Tusine et contenant 9- 10 1 2 Bq (250 Ci) de radium 226; — une mine a ciel ouvert en cours de remblaiement dans le cadre de la restauration du site.

2) Une usine de traitement de minerai, qui a traite 2,41 • 10 6 tonnes de minerai et produit 7500 t d'uranium (teneur moyenne: 0,3% en U) et qui comprend un bassin de rejet cree artificiellement par un barrage situe dans la vallee d'une petite riviere, la Besbre, dont le lit a ete detourne. Dans ce bassin ont ete rejetes, avec les effluents liquides de la mine et de l'usine, 700 000 t de rSsidus cyclones contenant environ 2-10 1 3 Bq (600 Ci) de radium et 600 000 t de fines contenant 6-10 1 3 Bq (1600 Ci).

Les concentrations en radium sont done respectivement de l'ordre de 4-10 7 B q - t - 1 e t 9 -10 " 7 Bq-t " 1 (2,5 mCi-1" 1 ) , soit en moyenne 6-10 7 Bq-.t"1

(1,7 mCi • t~ 1 ) pour les 1,3 • 10 6 t de residus sees. Les effluents liquides etaient traites au chlorure de baryum, puis rejetes dans la riviere apres decantation dans un petit bassin annexe.

Actuellement l'usine est demantelee, la mine est inondee et une station de traitement des eaux a 6t6 placee en aval du barrage. Elle recoit les eaux de surface et de debordement du bassin en periode humide et les eaux qui s'ecoulent des anciens travaux miniers. Des solutions sont a Petude quant au devenir du bassin.

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1.2. Surveillance de l'environnement

1.2.1. Eaux

En 1981, on a effectue sur le site 1024 prelevements avec 579 analyses de radium soluble, 481 d'uranium soluble et 43 de radium insoluble. Les preleve­ments sont effectues en continu, chaque decade, dans la riviere en amont, en aval a 2 et 6 km et sur les rejets avant et apres traitement. Divers prelevements instantanes sont effectues chaque decade ou chaque mois. Les resultats essentiels, donnant les concentrations moyennes annuelles, sont indiques dans le tableau I.

Le rejet global dans la Besbre, dont le debit moyen est de 1000 m 3 • h - 1 , est de 2-10 8 Bq (5,6 mCi) par an de radium soluble.

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TABLEAU I. CONCENTRATIONS MOYENNES ANNUELLES POUR LE SITE DES BOIS NOIRS

Radium soluble Bq -L - 1 ( pC i -L - 1 )

Uranium soluble mg-L - 1

Besbre amont 0,02 (0,5) <0,01

Besbre aval (2 km) 0,10 (2,7) 0,02

Besbre aval (6 km) 0,09 (2,5) <0,01

Bassin avant traitement 2 (54)

Concentration eau de la mine durant noyage 5 (135)

Rejet bassin apres traitement 0,37 (10)

Rejet eau mine apres traitement 0,12 (3,2)

Sources en aval du site <0,04 K O

1.2.2. Atmosphere

Depuis 1980, deux dosimetres a de site [1 ] permettant de prelever l'air en continu et de mesurer chaque mois l'energie potentielle a des descendants du radon sont implantes sur le site, l'un A, pres du bassin, et l'autre, B, a 2 km en aval dans l'axe des vents dominants et pres d'un village. Les resultats, presentes ci-dessous et exprimes en millijoules par an pour une inhalation continue de 0,8 m 3 • h" 1 sont a comparer a la nouvelle recommandation de la CIPR pour les travailleurs, soit 20 mJ-a - 1 :

Dosimetre A B

1981 0,37 0,45 1980 0,48 0,55

1.2.3. Chaine alimentaire

De nombreuses mesures effectuees dans la chaine alimentaire sont exposees dans d'autres memoires. Seul le cas des poissons vivant dans le bassin ou Ton rencontre les activites les plus elevens est presente ici car il constitue une enveloppe maximale du risque.

La quantite de radium present dans la chair des poissons est: - pour la perche: 465 Bq-kg" 1 (12 555 pCi -kg" 1 ) , - pour la tanche: 690 Bq-kg- 1 (18 600 pC i -kg - 1 ) ,

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ce qui correspond aux quantities suivantes pour ingerer la limite annuelle ( L A I ) = 7-10 3 Bq (189 000pCi) :

— perche: 15 kg — tanche: 10 kg

2. SITE DU BRUGEAUD

2.1. Description (fig.2)

Sur ce site en activite on trouve egalement de vieux travaux miniers souterrains, une mine a ciel ouvert, des tas de minerals a teneur trop faible pour etre traites, dits <steriles>, et une usine de traitement de minerai de 1800 t d'uranium par an de capacite.

Actuellement, 8,6 • 10 6 t de residus de traitement sont stockes sur le site, dont 6 • 10 6 t dans un bassin d'une superficie de 0,25 km 2 realise a flanc de coteau a partir d'une digue construite avec les sables les plus gros. La hauteur de boue est voisine de 30 metres et l'activite en radium est evaluee a 1,2 • 10 1 4 Bq (3400 Ci). Les 2,6 • 10 6 t complementaires et la production journaliere sont stockees dans la mine a ciel ouvert.

Les minerals lixivies en surface representent 2 • 10 6 t pour une activite presente en radium de 6 -10 1 2 Bq (170 Ci), les steriles eux representent 14-10 6 t e t 7 , 4 -10 1 2 Bq (200 Ci).

Actuellement les effluents liquides de l'usine sont envoyes avec les residus solides dans la mine a ciel ouvert. lis sont ensuite repris par pompe, envoyes dans une station de traitement au chlorure de baryum, puis ils decantent dans l'ancien bassin avant rejet a la riviere, la Gartempe.

2.2. Surveillance de l'environnement

2.2.1. Eaux

Les prelevements sont effectues comme pour le site precedent. Les resultats essentiels sont les suivants (concentration en radium soluble,

moyenne annuelle en B q - L - 1 ( p C i - L - 1 ) ) : - Gartempe amont: 0,02 (0,5) - Gartempe aval: 0,026 (0,7) - Avant traitement: 7,4 (200) - Rejets apr&s traitement: 0,26 (7)

Le rejet global dans la Gartempe, dont le debit moyen est de 30 000 m 3 • h - 1 , est evalue a 9 • 10 8 Bq (25 mCi) de radium par an.

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FIG.2. Site du Brugeaud.

2.2.2. Atmosphere

Deux stations situees autour du site dans l'axe des vents dominants et munies des memes detecteurs a de site fonctionnent depuis decembre 1981. La moyenne des resultats obtenus pour les 3 premiers mois en 1982 est de 0,1 et 0,02 mJ- a - 1 .

Un troisieme detecteur, place directement sur la digue du bassin, indique une moyenne de 0,17 mJ, ce qui correspond, etant donne l'implantation, aux valeurs maximales possibles.

3. SITE DE L'ECARPIERE

3.1. Description (fig.3)

Ce site, tres semblable a celui du Brugeaud, comprend une mine souterraine en exploitation, une mine a ciel ouvert dont l'exploitation est terminee, une usine traitant 470 000 t de mineral par an pour une production de 700 t d'uranium, une

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STATION TRAITEMENT DES EAUX

FIG.3. Site de I'Ecarpiere.

aire de lixiviation, une station de traitement des eaux et un bassin artificiel de stockage des residus de. l'usine.

Actuellement le bassin contient 5,5 • 10 6 t de residus contenant 10 1 4 Bq (2700 Ci) de radium pour une superficie de 0,25 km 2 . Ce bassin recoit toutes les eaux du site, a l'exception d'une partie des eaux souterraines dont le traite­ment n'est pas encore operationnel et qui sont ensuite envoyees a une station de traitement puis rejetees apres decantation dans un bassin de 10 000 m 2 dans la riviere, la Moine; 300 000 t de sables contenant environ 3,7 • 10 1 2 Bq (100 Ci) de radium ont ete utilises pour remblayer une partie des travaux souterrains; 500 000 t de minerai lixivie sont egalement sur le site et contiennent 2 -10 1 2 Bq (60 Ci) de radium.

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3.2. Surveillance de 1'environnement

3.2.1. Eaux

Les resultats essentiels des controles sont les suivants pour les concentrations moyennes annuelles exprimees en Bq- L" 1 ( pC i - L - 1 ) :

Le rejet global dans la riviere, dont le debit moyen est de 2000 m 3 • h - 1 , est evalue a 9 -10 8 Bq (25 mCi) de radium par an dont 1'essentiel provient des eaux souterraines qu'il est prevu de traiter cette annee.

3.2.2. Atmosphere:

Deux stations equipees de dosimetres a de site fonctionnent depuis 1982, les premiers resultats donnant des valeurs comprises entre 0,17 et 1,4 mJ par an.

4. LE SITE DE L 'HERAULT

4.1. Description (fig.4)

Ce nouveau site cree en 1978 se differencie des precedents du fait qu'il s'agit d'un gisement sedimentaire. On y trouve des travaux miniers souterrains et de surface et une usine qui peut traiter 400 000 t de minerai par an pour une production de 850 t d'uranium et qui a commence a fonctionner en juin 1981.

Les effluents liquides du procSde alcalin sont concentres par evaporation et les distillats sont soit recycles soit rejetes dans une petite riviere, la Lergue. Les residus solides de traitement ne contiennent que 30% d'eau; ils sont envoyes par bande transporteuse dans les excavations des mines a ciel ouvert ou il est prevu de les recouvrir de plusieurs metres de materiaux steriles.

Les eaux de la mine et les eaux de surface, ainsi que quelques rejets de l'usine, sont envoyes dans une station de traitement au chlorure de baryum. Une partie de ces eaux est recyclee dans l'usine.

4.2. Surveillance de l'environnement

— Moine amont site: — Moine aval site: — Rejets avant traitement: — Rejets apres traitement: — Eaux de la mine non traitees:

<0,02 (<0,5 ) 0,05 (1,5) 8,5 (230) 0,09 (2,4) 3,5 (95)

Cette surveillance a ete mise en place avant le demarrage des installations. On possede done les donnees concernant l'etat initial pour ce nouveau site.

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FIG.4. Site de I'Herault.

4.2.1. Eaux

Les resultats essentiels sont donnes dans le tableau II pour les concentrations moyennes exprimees en Bq - L" 1 ( p C i - L - 1 ) pour le radium et en mg-L" 1 pour l'uranium

Le rejet global est evalue a 7 • 10 7 Bq (2 mCi) de radium par an dans la Lergue dont le debit moyen est de 20 000 m 3 • IT 1 .

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TABLEAU II. CONCENTRATIONS MOYENNES ANNUELLES POUR LE SITE DE L 'HERAULT

Ra soluble Ra insoluble U soluble Bq -L _ l (pCi -L - 1 ) Bq -L - 1 (pCi -L - 1 ) mg-L - 1

Lergue amont <0,02 « 0 , S ) — —

Lergue aval <0,02 « 0 , 5 ) <0,02 « 0 , 5 ) 0,01

Rejets de l'usine 0,074 (2) 0,2 (5) 2,5

Rejets station de traitement 0,05 (1,4) 0,3 (8,4) 0,7

4.2.2. Atmosphere

Sept stations de controle sont equipees de dosimetres a de site qui fonctionnent depuis 3 ans. En moyenne, pour les 7 stations, l'exposition est la suivante:

1979 1980 1981

0,26 0,37 0,30

avec, en 1981, un maximum de 0,38 mJ pour l'une des stations. II n'est pas possible d'evaluer, au stade actuel, la contribution de l'exploitation a ces niveaux.

Dans les 7 stations, on mesure egalement tous les 2 jours l'activite a a vie longue des poussieres prelevees en continu, toutes les 2 semaines la masse de poussieres deposees et chaque trimestre les doses dues aux irradiations externes.

Les resultats essentiels ont ete les suivants en 1981:

- activite a a vie longue moyenne: 1,8-10"4 B q - m - 3 (5 • 10" 1 5 C i - m - 3 ) avec un maximum pour 2 jours de 27 • 10" 4 (74 • 10 1 5 ) ;

— dose moyenne anuelle y: 130 a 220 mrad, ce qui correspond a l'irradiation naturelle qui peut atteindre 400 mrad dans certaines habitations.

5. RESULTATS D'ENSEMBLE

L'examen de l'ensemble des resultats obtenus nous permet d'effectuer la synthese suivante.

5.1. Radioactivite des eaux dans l'environnement

Les concentrations en radium 226 dans les rivieres en aval des 4 sites sont toutes tres faibles:

0,1 - 0 , 3 - 0 , 5 - < 0 , 2 B q - L - 1 (ou 2,7 - 0,7 - 1,5 - < 0 , 5 pCi- L _ 1 ) .

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Ces valeurs sont comparables a celles que Ton trouve pour de nombreuses eaux de consommation; elles ne peuvent en trainer qu'une ingestion ne representant qu'environ le centieme des limites recommandees par la CIPR pour une consommation permanente.

Les concentrations que Ton peut rencontrer localement dans des eaux au contact des residus peuvent atteindre 100 fois les valeurs precedentes. On voit done que, dans ces cas extremes, on pourrait atteindre les limites d'exposition recommandees par la CIPR. Mais des procedes de traitement existent, sont efficaces et permettent de reduire considerablement les rejets pendant la periode d'exploitation. Quant au stockage definitif, il suffit de prendre des dispositions limitant les circulations d'eau au travers des residus pour qu'une dilution in situ par les eaux du bassin hydrographique concerne rende totalement negligeable l'impact reel au niveau des populations critiques.

5.2. Energie potentielle o; des descendants du radon dans l'air

Toutes les mesures maintenant disponibles sur nos sites correspondent a des expositions pour les personnes du public nettement inferieures au dixieme de la nouvelle recommandation de la CIPR applicable aux travailleurs. On a done une situation extremement satisfaisante quand on sait que cette limite est extremement basse, et qu'il semble bien que les valeurs mesurees proviennent en grande partie du site naturel et non pas de l'exploitation. Le cas de Lodeve, ou Ton dispose de mesures faites avant exploitation, est particulierement significatif. En effet, on a obtenu les resultats suivants:

— a l'exterieur des habitations avant exploitation: 0,08 a 0,3 mJ-a - 1

— a l'exterieur actuellement: 0,2 a 0,3 mJ - a - 1

— a l'interieur des habitations avant exploitation: 0,8 a 10 mJ-a - 1

6. DISPOSITIONS ENVISAGEES

II apparait done que la situation est actuellement satisfaisante dans les quatre principaux sites en France. II est possible qu'a la fermeture certains problemes apparaissent, mais on dispose de moyens simples, efficaces et suffisants qui peuvent etre mis en ceuvre. Fort de ces resultats, on peut se demander ce qu'il convient de faire a l'avenir en tenant compte des points de vue des differents organismes concernes: specialistes de la radioprotection, compagnies minieres et autorites reglementaires.

Du point de vue de la radioprotection, aucun individu de la population n'etant soumis a des expositions excessives, les efforts doivent tendre a reduire les doses collectives de fagon raisonnable autant que faire se peut. C'est done en tenant compte des contraintes economiques et avec un souci d'optimisation que

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les dispositions doivent etre envisagees. II en resulte aussi que la situation ne presente aucun caractere d'urgence et que Ton doit acquerir le maximum de donnees avant de prendre des decisions souvent tres onereuses.

Les compagnies minieres peuvent souhaiter connaitre le plus rapidement possible les dispositions qui leur seront imposees. Elles peuvent aussi vouloir effectuer les travaux necessaires des la fin de l'exploitation pour eviter d'avoir a se reimplanter ulterieurement. En fait, cette derniere exigence ne concerne pas le cas des anciens stockages avec des installations deja arretees. Pour les exploitations en cours, la solution consiste a effectuer, des la phase d'exploitation, toutes les etudes necessaires pour evaluer l'impact reel, c'est-a-dire determiner avec precision les mecanismes de transfert (diffusion atmospherique reelle, hydro-graphie, transfert dans les sols) permettant de definir la capacite d'acceptation du site, definir ensuite l'efficacite des protections reelles envisageables (efficacite des materiaux du site pouvant servir d'ecran pour la diffusion du radon, possibilite de mise en vegetation, etc.) puis realiser progressivement ce qu'il est raisonnable-ment possible de faire si Ton veut etre pret au moment de la fermeture. Bien entendu, les compagnies souhaitent ne pas etre contraintes a effectuer des travaux peu utiles.

Quant aux autorites reglementaires et organismes internationaux, elaborant des recommandations, ils doivent trouver la solution la mieux adaptee a ces diverses exigences.

Ils doivent considerer que l'impact resultant d'un site de stockage est tres lie aux differentes caracteristiques de ce site (climat, geologie, vegetation, hydro-graphie, etc.) et que les dispositions a prendre doivent etre adaptees a chaque cas. Par exemple:

— en zone desertique, les effluents liquides peuvent etre evaporeset les problemes de rejet d'existent pas;

— en zone tres humide, pour limiter le flux de radon, les terrains de recouvrement maintenus humides et convenablement choisis peuvent voir leur epaisseur reduite pour une meme efficacite.

Pour eviter la lixiviation par les eaux pluviales, un drainage et des revete-ments argileux peuvent s'averer utiles si le site alimente un petit ruisseau; ils peuvent etre inutiles si la riviere a un fort debit ou si Ton est en zone desertique.

En periode d'exploitation, il semble logique de tolerer dans certains cas des rejets a 7,5 B q - L - 1 (200 p C i - L - 1 ) de radium (soit approximativement la nouvelle limite derivee pour l'eau de consommation courante d'apres la CIPR). Par contre, si ces rejets ne sont pas acceptes et si Ton decide d'effectuer un traite­ment au chlorure de baryum, on doit s'astreindre a limiter les rejets en dessous de 0,37 B q - L - 1 (10 pC i -L " 1 ) , ce qui est raisonnablement possible techniquement.

II serait aussi insense d'interdire la consommation d'eau contenant quelques picocuries par litre de radium pour des populations assoiffees et il est sans doute injustifiable d'exiger des recouvrements de 3 m de materiaux de couverture pour limiter le flux de radon en zone desertique.

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Pour repondre au souci legitime des compagnies qui desirent connaitre l'enveloppe maximale des exigences des autorites, il peut etre envisage d'exiger certaines dispositions maximales, correspondant a un site theorique, comme la couverture de residus par trois metres de materiaux et la limitation des rejets d'effluents liquides a une concentration ne depassant pas 0,37 B q - L - 1 (10 p C i - L - 1 ) .

Mais il nous paraft alors indispensable que soit instauree une procedure permettant d'accorder des derogations, sur presentation d'un dossier d'impact justificatif, qui soient adaptees au site reel et non pas a un site theorique presentant l'ensemble des risques de tous les sites du monde.

Certaines restrictions, comme l'interdiction de construire, pourront rester attachees a un site. II faut prevoir le transfert de la responsabilite du respect de ces restrictions a une institution stable. II peut etre souhaitable de confier a un organisme d'Etat la propriete ou la responsabilite des sites. Par exemple, il est probable qu'en France, on confiera a l'Agence nationale pour la gestion des dechets radioactifs la gestion de certains sites de stockage de residus de traitement.

Quant a la surveillance, elle doit rester a la charge des compagnies pendant une periode probatoire de 5 a 10 ans suivant les cas. Puis, ayant pour objectif de verifier a long terme le bien-fonde des dispositions prises a la fermeture et de deceler toute anomalie non previsible, elle doit alors etre prise en charge par les autorites dont la mission est de veiller, de fagon generate, a la sante des populations. II est tres important de noter que ce controle de la qualite de Penvironnement s'impose a toute societe evoluee, et que la radioactivite ne constitue qu'une nuisance parmi d'autres comme les nuisances bacteriologiques ou chimiques; il ne s'impose pas du fait du developpement de Tenergie nucleaire, mais il decoule de l'accroissement de nos connaissances scientifiques dans le domaine de l'effet des rayonnements. La seule radioactivite naturelle suffit a le justifier pour les generations futures. On ne peut imaginer que la societe evoluee ne se preoccupe plus de la radioactivite naturelle presente dans les materiaux de construction, certains aliments ou les eaux de boisson. Nos connaissances se sont accrues avec l'ere nucleaire et il en resulte un progres dans l'amelioration des conditions de vie de l'homme sur la terre qui aboutit a lui eviter de s'exposer inutilement aux rayonnements naturels dans quelques cas extremes. Un tel controle de la radio­activite dans l'environnement est a maintenir au meme titre qu'un controle des autres nuisances.

7. CONCLUSIONS

Les dechets provenant de l'extraction et du traitement des minerals d'uranium sont actuellement l'objet d'une grande attention en France comme dans tous les pays qui possedent des mines d'uranium et dans les organismes internationaux. La production de ces dechets en quantite importante a commence tout au debut de l'ere nucleaire. Leur gestion a ete traitee avec soin, mais en fonction des moyens

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et connaissances de l'epoque, et a partir des techniques minieres habituelles. On a vu que si les dispositions de gestion prises jusqu'a maintenant ne sont peut-etre pas toujours optimales, la surete correspondante est cependant parfaitement convenable et les consequences sur l'environnement de faible importance.

II faut se rappeler qu'a ce stade de l'energie nucleaire, on ne produit pas d'elements radioactifs nouveaux. On ne fait que deplacer les elements naturels et modifier la forme physique et chimique de leur support. Le potentiel de nuisance naturelle reste le meme; on peut meme dire que, par suite de l'extraction de l'uranium, il est un peu diminue, mais de facon trop peu significative pour qu'on puisse en tirer argument. On a toujours affaire a des matieres de faible activite massique, mais qui ont ete rendues plus dispersables qu'elles ne l'etaient a l'origine.

Actuellement, l'objectif essentiel est la reduction des doses collectives. Pour ce faire, il faut prendre en compte les differentes voies de transfert dans l'environne-ment avec les comportements a long terme, d'ou la complexity de l'oeuvre entre-prise. L'experience deja acquise en matiere de gestion permet de conclure que la presence des dechets miniers n'entrainera qu'une exposition des individus ou de l'ensemble de la population a des risques hypothetiques tout a fait acceptables au sens de la CIPR, c'est-a-dire tres inferieurs aux risques habituels provenant de la collectivite auxquels l'individu est soumis en dehors de sa volonte. II ne faut done ni surestimer le probleme pose par les dechets miniers au niveau des risques individuels du fait de leur faible activite massique, ni le sous-estimer dans l'optique de la reduction des doses collectives.

Nous devons avoir confiance dans l'avenir de nos institutions et dans le maintien des controles sanitaires permettant de deceler les situations anormales de longue duree. Le retour a l'etat primitif de nos societes n'est peut-etre pas impossible, mais e'est une hypothese qui ne doit pas etre prise en compte pour le probleme qui nous preoccupe car celui-ci restera de toute facon mineur par rapport aux nombreux problemes de survie.

Les niveaux naturels couramment rencontres et qui sont l'oeuvre du createur doivent nous guider dans la recherche des solutions optimales. Exiger que Ton se place en dessous de ces niveaux peut paraitre intuitivement relever plutot d'un comportement demoniaque que d'un comportement de responsable.

REFERENCE

[1 ] DUPORT, P., CHAPUIS, A.M., PRADEL, J., «Appareil individuel pourla dosimetric du radoro, Advances in Radiation Protection Monitoring (C.R. Coll., Stockholm, 1978), AIEA,Vienne (1979) 435.

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OBJECTIVES AND CRITERIA FOR LONG-TERM MANAGEMENT AND DISPOSAL

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Chairman

R.V. OSBORNE Canada

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CRITERIA FOR THE LONG-TERM MANAGEMENT OF URANIUM MILL TAILINGS

R.M. F R Y

Office of the Supervising Scientist,

Sydney,

Australia

Abstract

CRITERIA FOR THE LONG-TERM MANAGEMENT OF URANIUM MILL TAILINGS. Uranium tailings contain non-radioactive pollutants which can be damaging to the

environment but which, with some notable exceptions, are unlikely to be a hazard to man; and virtually all the radioactive daughter products of the original uranium which, while of little direct environmental consequence, pose a potential radiological public health risk. Proper management of these tailings will aim to minimize environmental and radiological detriment due to both these components. Sources of radioactive contaminants will persist long into the future giving rise to radiological impacts which are remote both geographically and in time. The basic goal of tailings management, from a radiological point of view, must be to reduce these impacts to acceptable levels for the indefinite future. In radiological protection philosophy, as recommended by the ICRP, what is 'acceptable' is assessed by application of the ALARA principle. If approached quantitatively, this would entail examining the cost of a number of alternative ways of achieving increasingly effective manage­ment of the tailings and the cost of the residual radiation detriment associated with each alternative: an acceptable (or optimum) management scheme would be one for which the sum of these two costs is a minimum. Formal optimization analysis runs up against the difficulty of assessing realistically the residual collective dose associated with each manage­ment option, a major problem being the variation of the source terms, and environmental and demographic factors, over the long time periods of concern. The OECD/NEA is sponsoring an international study to assess the applicability of the ICRP system of dose limitation to the long-term management of tailings. The United States Nuclear Regulatory Commission has not found formal optimization analysis useful in this area. Basic criteria that are being developed for acceptable tailings management are reviewed. It is suggested that the longevity of tailings containment structures should take precedence in design over radon emanation control.

1. INTRODUCTION

The cumulative l i f e t ime uranium requirement for the roughly 1000 GW(e ) of nuclear generating capacity projected by INFCE to be in serv ice in the world by the year 2000 would be about four million tonne. The annual requirement at that t ime would be 150 000 t/a. If this were produced from 0.1% uranium ore, some k 000 million tonne of uranium mill tailings would be l e f t behind for disposal, plus large quantities of below ore grade material and other waste rock, and the

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tailings inventory would be accumulating at the rate of some 150 million tonne per year. These materials will remain at the mine and mill site and unless properly treated will constitute a continuing source of environmental pollution and radiation exposure.

The wastes are a concern and require some form of long term management because they contain non-radioactive pollutants, in particular heavy metals, which can be damaging to the environment but which, with notable exceptions, (e.g. As , Hg, Cd, Se) are unlikely to be a hazard to man; and because they contain long lived radioactive nuclides which, while of l i t t le direct environmental consequence, pose a potential radiological public health risk.

Public apprehension over uranium mining wastes appears to centre largely on the radioactive components of the tailings. However, the major environmental impact from these wastes, during both operational and post-operational phases is due to non-radioactive contaminants. Protect ion and management practices required to minimise environ­mental detriment due to non-radioactive contaminants must therefore be considered alongside the measures to be taken to isolate radioactive components from the environment, particularly in the long term. It is not obvious that the measures required to optimise protection against both components will always be compatible. For example, the optimum pH of the tailings slurry for the precipitation of heavy metals will not necessarily be best for the immobilisation of radium.

1.1. OECD/NEA study on the long term management of uranium mill tailings

The aim of this paper is to consider briefly the public health problem posed by uranium mill tailings and to rev iew the basis of criteria that have been developed to govern their disposal in the long term. The paper should also be seen as an introduction to a number of other papers that will be delivered during this Symposium and which have arisen out of, or were produced through association with, a study on the long term management of uranium mill tailings established by the OECD Nuclear Energy Agency ( N E A ) . This study seeks to examine the application of the ICRP system of dose l imitation to the evaluation of alternative options for managing uranium tailings so as to achieve optimum radiological protection in the long term; and to formulate performance objectives and criteria for tailings retention systems.

Because the emphasis of the study was on the long term, particular attention was paid to geomorphic factors which need to be taken into account in the design and siting of stable containment structures [1 ] and in the assessment of changes in the rate of release of contaminants from these structures that might arise as the result of changes over long periods in the ef fect iveness of containment. This release rate

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information was necessary to carry out assessments of the radiological impact of alternative tailings confinement options.

The study, which commenced in March 1980, is due for completion at the end of 1982; some preliminary results of the optimisation evaluation wil l be presented during this week by Dr Osborne [2 ] .

2. RADIOLOGICAL HAZARDS OF TAILINGS

Long term radiological protection problems arise in the management of uranium mill tailings because of the presence of the long l ived Th230 and its daughter Ra226 which remain in the tailings fol lowing conventional extraction processes. Though the radioact ive content of the tailings is essentially the same as the original ore body the various radionuclides (and the heavy metals), after the milling process, are more mobile and potentially more accessible to the environment and man than they were in the mineralised state, underground. However because of their low speci f ic act iv i ty, direct exposure to tailings over long periods would be required to produce significant health e f fec ts in individuals. They pose a problem - a large problem, because of the large volumes involved - in the management of low level radioactive waste; as such they constitute a major nuisance rather than a major radiological threat.

2.1 Local hazards

Radiation exposure of people living in the vicinity of unstabilised, uncovered tailings piles in the U.S.A. has been assessed by the U.S. Environmental Protect ion Agency [3 ] . These studies have indicated that the probability that harm has resulted from these exposures is small.

The mean enhanced risk of inducing lung cancer in a local populat­ion living within 10 km of an uncovered tailings pile emanating 10 000 Ci Rn222 per year is about 4 x 10 per year. (This is the average risk estimated in the existing local populations in the vicinity of f i ve such tailings piles). The estimated individual l i fe t ime risk of lung cancer associated with living continuously 0.5 miles from a tailings pile emanat­ing 10 000 Ci of radon per year is 2 000 x 1 0 - 6 , i .e. about 30 x 1 0 " 6 per year. This is about the same as the risk of living in an average U.S.A. or European house arising from enhanced levels of radon indoors. Ave rage concentrations of radon daughters in houses in U.S.A. and Europe are around 0.004 WL which leads, making appropriate assumptions about the t ime spent indoors, to an annual exposure of about 0.15 WL per year. This is a risk of 30 x 10 per year assuming a population risk factor of 200 excess cases of lung cancer per 10 persons per WLM.

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It is also estimated that the l i fe t ime risk of lung cancer associated with living continuously within 100 metres of the Salt Lake Ci ty tailings pile (100 acres, 11 500 Ci/a) is 0.03 which is about half the risk of dying of lung cancer for a normal, smoking male member of the Australian population.

The risk to those living near a pile associated with other sources of exposure, such as gamma rays and ingestion and inhalation of other radionuclides, e.g. Pb210 - Po210, is estimated to be less than 1/10 of that due to radon.

2 . 2 . R e m o t e h a z a r d s

The more remote radiological impacts of radon emanating from tailings are removed both geographically and in t ime. They arise because, although radon itself has a hal f- l i fe of only 3.8 days, it will continue to be produced in tailings as long as Th230 persists; that is, its production rate has a hal f- l i fe of about 80 000 years.

Geographically remote people may be irradiated by radon released to the atmosphere because it takes only a fortnight or so ( three to four half-l ives) for weather patterns to circumnavigate the globe. Thus radon released from tailings piles leads to a calculable, though immeasurably small, increase in naturally occurring levels of radon in the atmos­phere. A very simple estimation puts this risk into perspective. It takes about 4 500 t of uranium to fuel a 1 000 MW(e) l ightwater reactor for its full l i fe (30 years). If the tailings from the ore required to produce this amount of uranium were all stored on the surface in piles of conven­tional configuration with no covering material, the radon emanation rate to the atmosphere would be about 3 000 Ci/a. A thousand such tailings piles spread around the Northern Hemisphere, providing the uranium to fuel one thousand 1 000 MW(e) reactors, would thus contribute some [0 Ci of radon to the atmosphere of the Northern Hemisphere each year. This is to be compared with the emanation rate of 10 Ci of radon per year that occurs naturally from the surface of the earth in the Northern Hemisphere. Thus the risk associated with the 1 000 tailings piles would be 0.1% of whatever risk is associated with naturally occurring radon in the open atmosphere. Many people throughout the world are exposed to levels of radon some f i ve times that occurring in the open atmosphere for the greater part of their lives due to living in houses.

Though the increase in world levels of radon from uncovered tailings piles would be minute, it would persist and decrease only with the half- l i fe of Th230^. Every person who lives on the earth during this t ime would suffer this increased exposure and if a relation between radon exposure at these levels and risk of lung cancer induction can be assumed, a radiation detriment may be calculated. The logic of the

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ICRP system of dose l imitation requires that such temporally remote exposures be taken into account in arriving at "acceptable" long term management practices for persistent radioactive contaminants. The meaning given by the ICRP to "acceptabi l i ty" is discussed below.

3. RADIOLOGICAL ACCEPTABILITY

The basic goal of uranium tailings disposal in the long term, from a radiological point of v iew at least, must be to remove concerns associated with the radiological impacts outlined above. There are essentially only two ways of doing this; remove (or reduce below the leve l of concern) the sources of the problem, or isolate the tailings and their hazardous emissions and emanations from the environment for the hazardous l i fe-t imes of the contaminants.

Extraction processes which remove noxious components from tailings, especially Th230 and Ra226 are being assessed and wil l doubt­less be discussed during this Symposium. To be of any use almost all the radium and thorium must be removed from the tailings otherwise one would end up with two problems rather than one; the same low leve l radioactive tailings management problems only marginally reduced, and a high level radioact ive waste disposal problem of some magnitude.

Isolation of the tailings from the environment is an ill defined goal, especially for the t ime periods considered relevant. In pract ice, com­plete isolation would be an impossible goal, for absolute containment is unattainable over any period. Containment which is sufficient to reduce the escape of contaminants to the environment to an "acceptable" rate is, however, a more reasonable, though still undefined, goal.

In radiological protection philosophy as recommended by the ICRP, what is considered an "acceptable" exposure to radiation is to be determined by the application of a system of dose limitation [4 ] . In its

An apparently straightforward statement such as this obviously bears l i t t le relation to what might happen in the real world given the t ime scales involved. More than just the radioactive half- l i fe of Th230 is concerned. The amount of radon reaching the atmosphere wil l depend, doubtless amongst many other things, on geochemical processes within the pile as they might a f f ec t the leachability and mobility of thorium, where the thorium may go if it does move, (deeper into the pile, into the ground where it may become fixed, into groundwater whence it may find surface expression) mass movement of the tailings themselves, and, since Th230 is not itself the proximate source of radon, on dif ferences in the behaviour between thorium and radium in any of these processes.

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simplest terms a radiation exposure situation would be considered acceptable (provided any exposure is justifiable at all) if no individual receives more than certain recommended dose limits and if, in addition, everything reasonable has been done to reduce all exposures to their lowest levels. The latter proviso, the A L A R A principle, is formally expressed as, "al l exposures shall be kept as low as reasonably achievable, economic and social factors being taken into account". It places emphasis, in judging whether a proposed radiation protection pract ice is acceptable or not, on the reasonableness of what is proposed. In 1973 [5 ] , and with added emphasis in 1977 [4 ] , the ICRP indicated how A L A R A might be implemented in a formal manner using some form of dif ferential cost-ef fect iveness analysis. This quantitative approach to reasonableness in a radiological problem is called the optimisation of protection.

One of the major aims of the NEA study mentioned above is to examine the applicability of this quantitative methodology to the optimisation of the management of uranium mill tailings in the long term. The study has required the examination of the cost of a number of al ternative engineered options for achieving increasingly e f f e c t i v e management of tailings, and the monetised cost of the residual radiation harm associated with each alternative. The optimum management scheme would be the one for which the sum of these two costs is a minimum.

3.1. Problems in the assessment of radiation detriment in the long term

A number of conceptual problems arise in any attempt to carry out a formal optimisation analysis. These include the definition of radiation detriment, its realistic determination, and the expression of its value in dollar terms. I propose to mention here only problems arising in the environmental and dosimetric modelling that is necessary to assess the long term residual radiation detriment associated with a given method of tailings management.

The radiation detriment may be considered to be the direct health e f f ec ts arising from the radiation exposure remaining after the imple­mentation of a given level of protection. If one assumes that the probability of inducing a health e f f e c t (usually cancer) is linearly related to dose (with no threshold - the linear hypothesis) the expected number of health e f fec ts induced in an irradiated population is simply proport­ional to the " to ta l dose" received by all members of the population. The dollar value of this detriment is the number of health e f fec ts multiplied by the dollar value that society requires be al lotted to such health e f fec ts arising from such a source. The " t o ta l dose" to be determined is the " co l l ec t i ve e f f e c t i v e dose equivalent commitment" and requires, for its complete estimation, knowledge of the total population and its distribution ( local , regional, continental, global) that will ever come in

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contact with radiation the source of which had its origin in the tailings; and the e f f e c t i v e dose equivalent received by each individual taking into account where and when he l ived. Even in the simplest co l l ec t i ve dose calculations there are practical diff iculties in developing realistic environmental transport and dosimetric models. In this study however, two major parts of the modelling come up against serious conceptual as well as practical diff iculties because of the long t ime frame over which the optimisation of tailings management needs to be considered. These are the modelling of the rate of release of contaminants from the tailings impoundment and the manner in which this release rate changes with t ime; and the modelling of the dispersion of released materials and of population distributions, and the manner in which these will change with cl imatic, landform, ecological and demographic factors over the very long periods of interest.

J.I .1 R ate of release of conta minants

The determination of release rate behaviour is riddled with unknowns. As a source of contaminants a rehabilitated tailings pile can be considered in two parts, a primary source, the tailings themselves, and an outer containment which isolates them from the environment. The rate at which material escapes to the environment at a given t ime wil l be determined by the rate of release of individual contaminants from the primary source, and by the "transmissivity" of the containment. Both of these terms would be expected to change significantly over much shorter periods than the hundreds of thousands of years during which the radioactivity in the tailings remains of concern.

The primary source term will vary as the many complex chemical systems within the tailings seek new states of thermodynamic equilib­rium and the geochemical and mineralogical characteristics of the tai l ­ings change. Aspects of this behaviour wil l be discussed by Pidgeon [6 ] and Markos and Bush [7 ] during this Symposium.

A t the same t ime the containment would be subject to geomorphic processes including, very likely, the erosion and degradation of the containment structure (though at some sites - and it would be sensible to choose such sites - the opposite might occur) leading to a decrease in the ef fect iveness of the containment structure as a barrier to release. Eventually, one would postulate the complete breakdown of the contain­ment accompanied by the erosion or mass release and dispersion of the tailings themselves. No-one seems to have much idea of what the mechanical properties of tailings might be after a f ew thousand years of internal geochemical and mineralogical act iv i ty under the pressures obtaining in a heavily capped pile, so that the rate at which the tailings would be eroded would also be unknown.

Geomorphic factors relevant to long term tailings management will be discussed in the paper by Schumm et al [ 1 ] .

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3.2 Optimisation of radiological protection

These diff iculties sap credibil ity from co l lect ive dose calculations as the t ime scale over which the doses are to be integrated stretch into a future measured in thousands of years. Since, as mentioned above, co l l ec t ive dose is the essential basis of the est imate of the cost of residual detriment, there are those who are sceptical of the utility of such quantified approaches in arriving at reasonable solutions to protection problems involving long t ime periods. The U.S. Nuclear Regulatory Commission in its major generic study of the environmental impact of uranium milling has applied the approach to the tailings problem and did not find it useful. " I t would be impracticable and inappropriate to make a fully monetized, incremental, cost-benefit optimization the basis for establishing limits on radon flux, given the complex, multi-dimensional and long-term nature of the mill tailings disposal problem. While such an optimization process appears to of fer a "rational approach" to decision-making, it can be misleading, because it grossly oversimplif ies the problem. Furthermore, it can be quite arbitrary, given the highly subjective nature of some of the major factors and assumptions which must be decided upon to use it ." [8]

3.2.1. Optimisation intheOECD/NEA study

Despite this good advice the NEA considered it worthwhile to have another look at the application of the quantified approach to the tailings management problem. The study group has attempted to apply it to a wider range of tailings management systems and geographic conditions than were considered by the U.S. Nuclear Regulatory Commission (a typical Canadian and an Australian site are being examined) not, I bel ieve, with much hope that the method would provide practical answers, but rather to illustrate its application and to demonstrate its limitations in this area. It should be said that a number of groups from the U.S.A., including the Nuclear Regulatory Commission, are making a major contribution to this study.

One aspect of the methodology being examined is its usefulness in making comparative evaluations of alternative management options over l imited and more realistic periods of t ime for which the modelling assumptions one has to make are not entirely fanciful. The basic assumption in this approach is that when the containment fails, the release and dispersion of contaminants, including the tailings themselves, and the co l lec t ive dose associated with this release, wil l be the same as they would have been had the containment never existed. What has been achieved, however, is the elimination of, or at least a great reduction in, the co l lect ive dose that would have been received had no confinement of any kind ever been emplaced. It is possible that the quantitative approach may be helpful in assessing the cost-ef fect iveness of alternative options in saving co l lec t ive dose over the

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periods during which each option is able to maintain containment. Dr Osborne's paper wil l present some preliminary results of this approach [2 ] .

4. THE NON-QUANTITATIVE APPROACH TO REASONABLENESS

I have accepted it as axiomatic that a basic goal of tailings management is to contain them to the extent necessary to reduce the rate of escape of contaminants to the environment to an acceptable leve l . In radiation protection, what is acceptable is what is reasonable as defined in the A L A R A principle. Though recent ICRP thinking would appear to favour a quantitative interpretation of this principle, it is the A L A R A principle as formulated in the system of dose limitation that is overriding, and in this formulation the emphasis is on reasonableness. A quantified optimisation evaluation may be one approach to reasonableness but there are others.

4.1. The N R C s guiding principles

As mentioned above the U.S. Nuclear Regulatory Commission found that for the most part the formal application of the ICRP optimisation procedure did not lead to useful results, particularly in arriving at criteria for radon control. They have nevertheless formu­lated a number of cr i ter ia relating to the long term aspects of tailings management based on a comprehensive analysis of the potential environ­mental and radiological impacts of tailings, and the application of the principles of A L A R A and engineering judgement.

The principles that guided the Nuclear Regulatory Commission in the development of their technical cr i ter ia appear to have been

. future generations should not be committed to an "obligation to care for wastes generated to produce benefits which those generations will rece ive only indirectly, if at al l" (Re fe rence [8 ] page 15);

. the radiological hazards associated with tailings are such as to warrant that they "be isolated from people and the environ­ment in such a manner to reduce potential exposures to as low as is reasonably achievable" [9 ] ;

. " the site where tailings are stored should be returned to conditions reasonably near those of the surrounding environment" [9 ] .

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4.2. Some basic criteria for long term tailings management

There is unlikely to be disagreement with the ethical intent of the Nuclear Regulatory Commission's first principle though some may wish to phrase it di f ferently. The U.S. Environmental Protect ion Agency for example in its proposed criteria for radioactive wastes thought that " a t a minimum, the current generation should not pose larger risks to a future generation than it would be willing to accept for itself" [10] . Either way, the first and the second of the Nuclear Regulatory Commission's principles cited above taken together lead to two basic criteria for the long term management of mill tailings:

. The tailings and their associated contaminants should be contained so that they are isolated from the environment for as long as best practicable technology will al low.

. The tailings should be managed in such a manner that no act ive maintenance is required to preserve the e f f icacy of the containment.

These concepts are incorporated in the criteria being developed in a number of countries, e.g. Canada [11] and Australia [12]; and are re f lec ted in the discussion of practices for the confinement of uranium tailings in IAEA.Technical Report No. 209 [13].

4.2.1. The length of the isolation period

The length of t ime envisaged for the tailings to remain isolated appears to be reasonably consistent among the various bodies. For the IAEA the period of confinement should be " indef inite" but as long as can be achieved through use. of " the best current technical and economic abil ity" [13] . It should be " f o r thousands of years" according to the U.S. Nuclear Regulatory Commission (Criter ion 1 of Appendix A to 10CFR40 [9 ] ) ; "a reasonable expectat ion" of " a t least 1 000 years" for the U.S. Environmental Protect ion Agency [14]; "o f the order of 100's or even 1000's of years" for Canada (Criterion 3 of [11]) ; whilst the New Mexico Radiation Protect ion Regulations (1981) require that tailings shall be protected by a cover "against erosion for a period of 200 years". The Australian Code [12] requires that the release of radioactive material from the tailings be minimised by the use of best practicable technology, which, by definition, must take account of " the potential hazards from the wastes over the long term".

4.2.2. The achievement of a "walk-away" management system

The requirement that a tailings management system should not depend upon monitoring and act ive maintenance to ensure that it continues to perform according to specif ication throughout its design l i fe is incorporated in the U.S.A., Canadian and Australian proposed regulations.

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The U.S. Environmental Protect ion Agency would also support this criterion since it does not bel ieve that institutional controls such as monitoring and maintenance should be relied upon for periods longer than a century [14] .

Engineering designs for tailings impoundments have been rev iewed in IAEA Technical Report No. 209 [13] and a complementary survey of engineering design objectives for tailings management wil l be given by Burgess et al [15] . Current good engineering pract ice will aim to provide complete and secure retention of the tailings themselves, and an adequate level of containment of the mobile contaminants, for the "design l i f e " of the retention structure. Engineers do not claim to be able to guarantee the performance to design specif ication of man made structures for more than a f ew hundred years at the most. This does not mean that the structure will not last and continue to perform, albeit less e f f ec t i ve ly , for periods much longer than this. The structure l i fe of a well engineered tailings dam, during which it would continue to provide some degree of containment without maintenance, could be some thousands of years. To achieve this, however, it would be essential to take into account in both the design and the siting of the structures, geomorphic processes and c l imat ic change that would become significant over that t ime.

Though a "walk-away" situation with no act ive maintenance may be the goal of long term containment design, it is considered prudent, in some regulations, to implement some form of long-term site surveillance to confirm the continuing integrity of the containment system.

4.3 The control of radon emanation

The third Nuclear Regulatory Commission's guiding principle, that sites should be returned to conditions which are reasonably near those of the surrounding environs, is perhaps more controversial, particularly as it is applied to the formulation of an explicit numerical standard for the control of radon emanation at rehabilitated sites. In v iew of the miniscule individual risk to remote populations arising from radon emanating from a complete ly uncovered pile, and the small risk even to those living quite close to such a pile (see 2.1 and 2.2 above) the reasonableness of the 2 pCi-m -sec standard - and indeed the need to specify a radon emanation limit at all, if adequate attention is given to the stability and longevity of the capping - might be questioned.

A large e f for t in the U.S.A. is going into the development of radon attenuating covers. Some of this research and development has been described recently [16] and there appears, as yet , to be no confidence that such a standard could be reached in pract ice and at reasonable cost. Also there must be some doubt about the long term stability of these covers, the main aim in the design of which appears to be radon attentuation rather than longevity.

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A major purpose in specifying an emanation rate close to background levels would seem to be to el iminate the need for institutional controls to prevent occupation of rehabilitated tailings areas. However the success of this measure in preventing excessive exposures will last only as long as the radon attenuating cover continues to perform e f f ec t i ve ly . A relat ively small deterioration in performance would make the site unsuitable for permanent occupation and one would again be faced with the desirability of discouraging this. This situation is likely to arise a considerable t ime before the cover fails as a barrier to the release of the tailings.

Perhaps it would be reasonable, and more cost -e f f ec t i ve than trying to rely on the continuing high performance of radon barriers, to acknowledge at the outset that for the highest level of long term protection, containment would need to be supplemented in some way. Excessive exposure to radon could be discouraged from the beginning by the installation at the site of a monument which would inform people of the existence of a potential hazard and advise them not to linger there.

It should be possible to build such a monument which had a structure l i fe at least as long as the tailings confinement structure itself. With the matter of site occupation addressed in this way priority in the design of the containment could be placed on the longevity of the structure. Ach ieve­ment of a prescribed leve l of radon emanation control would not then be necessary, though it is unlikely that design for longevity would not provide a significant degree of radon attenuation as wel l .

REFERENCES

[1 ] SCHUMM, S.A., COSTA, J.E., TOY, T., K N O X , J.C., W A R N E R , R., Geomorphic hazards and uranium tailings disposal, (This Symposium), IAEA-SM-262/50.

[2 ] OSBORNE, R.V., Optimising radiation protection in the management of uranium mill tailings, (This Symposium), IAEA-SM -262/30.

[3 ] Draft Environmental Impact Statement for Remedial Act ion Standards for Inactive Uranium Processing Sites (40CFR192), U.S. Environmental Protect ion Agency, EPA520/4-80-011 (1980).

[4 ] Recommendations of the International Commission on Radiological Protect ion. ICRP Publication 26, Pergamon Press, Oxford (1977).

[5 ] Implications of Commission Recommendations that Doses be dept as Low as Reasonably Achievable . A Report of ICRP Commit tee 4, I C R P Publication 22, Pergamon Press, Oxford (1973).

[6 ] P IDGEON, R.T., Rev i ew of the non-radiological contaminants in the long-term management of uranium mine and mill wastes, (This Symposium). IAEA-SM-262/58.

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[7 ] M A R K O S , G., BUSH, K.J., Geochemical processes in uranium mill tailings and their relationship to contamination, (This Symposium), IAEA-SM-262/23.

[8 ] Final Generic Environmental Impact Statement on Uranium Milling, U.S. Nuclear Regulatory Commission. NUREG-0706 Vols I, II, III (1980).

[9 ] Cr i ter ia Relat ing to Uranium Mill Tailings and Construction of Major Plants. U.S. Nuclear Regulatory Commission, Federal Register kk_ 166 (1979) 50017.

[10] Cri ter ia for Radioact ive Wastes. U.S. Environmental Protect ion Agency, Federal Register 43 221 (1978) 53266.

[11] Long Term Aspects of Uranium Tailings Management. Proposed Regulatory Guide, Consultative Document C - l , A tomic Energy Control Board, Canada (1981).

[12] Proposed Code of Pract ice on the Management of Radioact ive Wastes from the Mining and Milling of Radioact ive Ores (1981). Department of Home Af fa irs and Environment, Commonwealth of Australia, Canberra (1981).

[13] Current Pract ices and Options for Confinement of Uranium Mill Tail ings. Technical Report Series No. 209, IAEA , Vienna (1981).

[14] Proposed Disposal Standards for Inactive Uranium Processing Sites. U.S. Environmental Protect ion Agency , Federal Register _46 6 (1981) 2560.

[15] BURGESS, P.3., P U L L E N , P.F., VOLPE, R.L., Application of engineering design objectives for the long-term stabilisation of uranium tailings, (This Symposium), not pub l i shed .

[16] Uranium Mill Tailings Management. Proceedings of the Fourth Symposium October 26-27, 1981. Colorado State University, Fort Collins, Colorado (1981).

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RECENT DEVELOPMENTS IN THE REGULATION AND MANAGEMENT OF CANADIAN URANIUM TAILINGS

K. BRAGG Atomic Energy Control Board, Ottawa, Ontario

C. POTTER Saskatchewan Department of

the Environment, Prince Albert, Saskatchewan

A. JAMES Ontario Ministry of the

Environment, Toronto, Ontario, Canada

Abstract

RECENT DEVELOPMENTS IN THE REGULATION AND MANAGEMENT OF CANADIAN URANIUM TAILINGS.

The last two to three years have produced rapid changes in the way uranium tailings are managed in Canada. This is due both to the development of new technology and changes in regulatory approach. The thrust of this paper will be to clarify the interrelationships between these two areas with a particular focus on long-term management. The interaction between federal and provincial agencies will also be reviewed to illustrate how a co-operative regulatory approach works, even in areas of complex and sometimes confusing jurisdiction.

1.0 Introduction

In order to understand the recent developments, i t is necessary to develop some perspective on the period p r io r to 1979. In this i n i t i a l period approximately one hundred mil l ion tons of t a i l i ngs were deposited in Canada. These t a i l i ng s cover an area of approximately one thousand acres and are located mainly in the E l l i o t Lake area of Ontario and to a lesser extent in northern Saskatchewan and near Bancroft in southeastern Ontario. All of these t a i l i ng s were placed into conventional surface containment

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structures with some minor b a ck - f i l l i n g operations a lso being conducted. During the 1950s and 1960s, the confinement structures used were predominantly natural topographic basins in combination with permeable embankments. During the expansion of the 1970s improved containment structures were bu i l t with an emphasis on impermeability and improved geotechnical engineering. As r e su l t , i t can general ly be concluded that there is a high degree of confidence in our a b i l i t y to physical ly contain the t a i l i ng s within the storage areas. The primary focus in t a i l i ng s management in the l a s t few years has thus shifted towards a consideration of the long-term or c lose -out aspects of t a i l i ng s management.

A second major component of t a i l i n g s management in Canada has been the need for water treatment systems, par t i cu la r ly focusing on the removal of Radium 226. Such a need was f i r s t ident i f ied in the mid-1960s as a resu l t of the elevation of radium and acidity leve ls in several of the major lakes near E l l i o t Lake. In response, the f i r s t systems were ins ta l l ed to treat ef f luents prior to the i r re lease to the environment. The treatment systems involved the addition of lime or limestone to elevate the pH and the addition of barium chloride to remove the Radium 226 in set t l ing basins or small lakes. More recent examples of se t t l ing systems for the removal of Radium 226 have been exclusively oriented to engineered lagoons usually involving l ined basins.

2.0 Technical I n i t i a t i ve s

Having b r i e f l y set out the status of uranium ta i l i ng s management systems up to approximately 1979, i t i s appropriate to take a more detai led look at recent developments. These developments can loosely be grouped into placement technologies and environmental health and safety technologies.

2.1 Placement Technology

The new placement technologies attempt to address the ultimate disposal of the t a i l i ng s as opposed to the storage of the t a i l i n g s in conventional f a c i l i t i e s . There are three new approaches to placement in Canada:

2.1.1 Dry Placement Method

The term dry placement usually re fers to methods which resu l t in t a i l i ng s which are either unsaturated a f ter they

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have been placed or to t a i l i ng s which do not segregate into a sands and slimes f ract ion . The two principal methods currently being evaluated in Canada are coning or stacking techniques and the sub-aeria l t a i l i ngs placement technique. The coning and stacking technique is currently under detai led evaluation in the E l l i o t Lake area. One benef i t to be achieved by this technique is the increase in storage capacity within an area for any given e levat ion of the external containment structures or embankments. Another benef it is the po s s i b i l i t y of developing a f inal surface contour which is much more suited to final c lose -out . A coning or stacking arrangement wi l l usually seek to develop a topographic high or a continuous slope which is suited to shedding surface water rather than al lowing i t to i n f i l t r a t e and appear as seepage. In Canada, net prec ip i tat ion exceeds evapo-transpiration by up to f i f t y per cent and thus the control of surface water i n f i l t r a t i o n is an important aspect of long-term t a i l i n g s management. While not al l of the detai led technical resu l ts have been fu l l y evaluated for these two techniques, the preliminary indications are very pos i t ive . Suf f ic ient physical or geotechnical s t ab i l i t y is being achieved with these placement techniques to provide the necessary integr i ty and confidence in this approach when applied on full sca le .

The second major dry placement technique is the subaerial method which has not been used in Canada to date. The Key Lake Uranium Mining operation in northern Saskatchewan wi l l be the f i r s t such appl ication to uranium t a i l i n g s . The principal benef i ts which are f e l t to be a t t r ibutab le to this approach are the high ultimate s t a b i l i t y of the f inal t a i l i n g s mass and the water shedding capabi l i ty of the interna l ly layered system. While a l l indications for such a system are very pos i t ive we should voice one cautionary note. In Canada, and par t icu la r ly in northern Canada, we have a very severe winter cl imate. This means that for a period of 'approximately f ive months the laminar approach is not deemed to be practical due to freezing of the system. This means that moderately thick layers must be placed in a f a i r l y conventional t a i l i n g s deposition manner during the winter period. The e f fect of this discontinuity in the system is not well documented and remains an area for further study.

2.1.2 P i t Disposal

A r e l a t i ve l y new disposal technology in Canada is the use of a mined out p i t for the placement of the t a i l i n g s .

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This technique is only now becoming a poss i b i l i t y for Gulf Minerals due to the a v a i l a b i l i t y of a mined out pit in the immediate proximity of a new ore body. I t is v isual ized that the t a i l i ng s generated from this new open pit wi l l be placed into the mined out p i t . In addition to the new t a i l i n g s , i t is currently proposed that the old t a i l i n g s which are currently in a conventional land based t a i l i ngs management f a c i l i t y wi l l a lso be placed in the p i t . Several interest ing and novel approaches to this system of p i t disposal have been suggested and are worth consideration here. The groundwater system in this region of northern Saskatchewan is normally very near to the surface which means that t a i l i n g s placed in the pit wil l be below the groundwater tab le . Thus an important consideration for environmental and health protection is the interaction between the t a i l i ng s and the groundwater system. Gulf is proposing a hydraulic barr ier which u t i l i z e s a zone of very coarse waste rock placed between the pit wall and the t a i l i ng s mass. This zone acts as a hydraulic short c i r cu i t in the system thus preventing any s ign i f i cant interactions between the groundwater and the t a i l i ng s pore water. Furthermore the t a i l ings wi l l be deposited in a dry s tate , to l imit the amount of pore water at the outset . Any seepage water wi l l need to be co l lected and treated during some transit ion period. Once f inal equil ibrium has been achieved the only interaction wi l l be through di f fusion processes across the coarse inter face . The principal advantage to this approach i s that the t a i l i ng s wi l l be placed in a truly inaccessible manner. Thus there wi l l be much less need for land use contro ls . Radon emanation and gamma f i e lds ar is ing from the material w i l l be extremely low as we l l .

2.1.3 Deep Lake Disposal

Canada as you know has many lakes in the Precambrian Shie ld . Considerable work has been undertaken during the l a s t year to evaluate Quirke Lake in the E l l i o t Lake region as a poss ib le disposal s i te for large amounts of t a i l i n g s . Quirke Lake is approximately four hundred and f i f t y feet deep and current estimates would allow f ive hundred mil l ion tons of t a i l i ng s to be deposited with one hundred feet of overlying water. The advantage of using such a system is that lakes in this setting are in a depositional environment. That i s , in the long term, the t a i l i n g s wil l be covered with lake sediments which wi l l reduce the exchange of contaminants between the t a i l i ng s mass and the overlying water. Of fsett ing this main benefit however are considerable technical uncerta int ies .

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There has never been in Canada nor in any other country a sett ing which is to ta l l y analogous to the Quirke Lake disposal s i t e . Thus i t is not c lear precisely what the degree of interaction of various contaminants wi l l be e i ther during the short or long term. This interaction may be c r i t i c a l since the flow through the lake is roughly 4 000 L/s and water qual ity for downstream users needs to be protected. A preliminary review of current information has been completed and is serving as a base for future decis ions .

2.2 Health and Environmental Aspects

A second major area involving new in i t i a t i v e s concerns the environmental and health protection aspects of uranium t a i l i n g s management. This area also can be subdivided as fol1ows:

2.2.1 Radium 226 in Eff luents

Over the l as t several years several new technologies have been developed for Ra removal within Canada. The principal d i f f i cu l t y in operating a radium removal system is to insure adequate s o l i d - l i q u i d separation. Thus by f ine tuning the process to optimize pH, f locculant addition and by the use of ba f f l e s to ensure that the ful l retention time is a va i l a b l e , s ign i f i cant improvements have been achieved.

A second major approach to the s o l i d - l i q u i d separation problem has been the use of sand or multi-media f i l t r a t i o n methods. Several examples are ava i lab le within Canada at the present time. A major laboratory and p i l o t plant operation was conducted as a j o in t government and industry project to identi fy the most su i tab le methods for applying multi media f i l t r a t i o n . The results of these studies show c lea r ly that i t is poss ib le by using a well operated multi media f i l t r a t i o n system to achieve leve ls of less than 0.3 Bq/L total radium in ef f luents from conventional uranium t a i l i n g s operations. Another somewhat larger scale f i l t e r operation has been in use for e f f luent pol ishing a f ter a conventional lagoon system and has been used primarily to eliminate peaks in radium which are a t t r ibutab le to high flows over loading the se t t l ing lagoons. This ins ta l l a t i on has a lso demonstrated sat is factory operation and has produced ef f luents of acceptable quality for d i rect discharge to the environment.

An important aside to the development of f i l t r a t i o n techniques is the question of disposal of high spec i f i c

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act iv i ty backwash solut ions. I t was necessary to evaluate the v i a b i l i t y of returning the backwash solutions d i rec t ly to the t a i l i n g s ponds since this represented the most r e a l i s t i c means of handling the mater ia l . The regulatory agencies in Canada have evaluated such methods on a general basis and, within l imits imposed by a spec i f i c operation, have decided that they are not fundamentally opposed to such pract ice . However, each applicant w i l l have to verify that no unacceptable impacts wi l l occur through such a pract ice .

During the period where these new technologies for radium removal were being developed the ICRP reevaluated the dosimetry of Radium 226 and concluded that the ALI for the material should be ra ised . This new primary standard by the ICRP leads to a drinking water standard in Canada of 1 Bq/L total Ra 226 as a maximum permissible concentration and a target level set at ten per cent of that. We thus have what appears to be a paradox in that there are treatment methodologies which can produce ef f luents from a t a i l i ng s operation which may be higher in qua l i ty , with respect of Radium 226, than required by the maximum permissible drinking standard. This in turn has led to considerable confusion over e f f luent standards and water qual ity standards.

2.2.2 Ammonia in Eff luents

Ammonia is a f a i r l y serious environmental pol lutant and is toxic to biota at very low concentrations par t icu la r ly in s ituations where the pH level is in excess of 6.5 - 7.0. In addit ion, ammonia has been used extensively as a process reagent in uranium extraction f a c i l i t i e s . In order to reduce environmental impact magnesium hydroxide or hydrogen peroxide are increasingly used as a prec ip i tat ing agent in place of ammonium hydroxide. Another approach would be to insta l l an ammonium extraction f a c i l i t y and the conversion of that ammonia to ammonium nitrate for subsequent use as a f e r t i l i z e r . I f ammonia can be eliminated at the source through changes in the process, there wi l l s t i l l be a small residue in the final e f f luent due to the b last ing agents used in mining. This small amount of ammonia is probably unavoidable and in a practical sense is untreatable . The only solution therefore , appears to be to ensure that the pH level in the discharge and the ass imi lat ive capacity within the environment are adequate to allow for this small discharge of ammonia.

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2.3 Economic Aspects

As a final component of our review of new developments up to the present date, i t is necessary to look b r i e f l y at the economic s ituation facing the industry today. Several years ago yellowcake was se l l ing for approximately f i f t y do l l a r s a pound whereas today i t is se l l ing for something s l i gh t l y less than twenty-f ive do l la rs a pound. Over the l a s t two years considerable increases in the cost of production due to in f la t ion have also occurred. Thus i t is c lear that the economic situation which the industry faces today and in par t icu la r the s ituation faced by producers of f a i r l y low grade ore deposits has changed very dramatical ly . While environmental health and safety considerations do not normally impose a major economic burden upon the industry i t would be naive for any regulatory agency to ignore this a ltered economic r ea l i t y . This may become a part icu lar issue when dealing with the long-term aspects. The technology and the possible solutions to some of the long term concerns may be more expensive than the short term operational solutions. Thus i t is necessary that a l l regulatory agencies be cognizant of the impact of their actions on industry. In Canada we attempt to keep ourselves cognizant through dialogue with industry and by consulting them as part of the regulatory process. The deta i l s of this process wi l l be discussed in the next part of the paper.

3.0 Regulatory In i t i a t i ve s

In order to understand the new regulatory developments which have occurred in Canada i t is not only necessary to understand the technical developments which have already been discussed, but i t i s a lso necessary to understand the ro le of the public and the prevai l ing regulatory environment in Canada. This involves both federal and provincial author i t i es . As far as the public is concerned t a i l i ng s management issues have assumed an extremely high p ro f i l e in the l a s t few years . In order to emphasize th i s , a b r i e f review of some of the major public hearings and enquiries is i l l u s t r a t i v e . As part of the E l l i o t Lake expansion an environmental assessment board was establ ished by Ontario which conducted hearings over a two year period. The main resu l t of that review process was to conclude that the expansion could proceed without any unacceptable environmental or health r i sks . Another major enquiry referred to as the Bayda Commission took place in

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Saskatchewan. Its mandate was to determine whether there were any reasons why s ign i f i cant new development of uranium mining could not take place in Saskatchewan. I t focussed in part on the proposed CIuff Lake mining operation but addressed many moral, social and environmental issues general to the entire industry. I ts conclusion was similar to the E l l i o t Lake review, in that, no unacceptable s ituations wi l l develop where current technology is used and recommended that the industry proceed. Another major enquiry was the Bates Commission which took place in Br i t ish Columbia. The final report of the Bates Commission again recommended that there was no part icu lar reason to stop development. However pr ior to the release of the final document the government of Br i t i sh Columbia decided to impose a seven year moratorium on exploration and development of uranium mining in the province. Again in the province of Newfoundland a publ ic review process was held and its recommendation was that development of uranium mining not proceed unti 1 some f inal resolution of the long term aspects of t a i l i ng s management be obtained. The government subsequently accepted the recommendation and there is e f f ec t ive ly a moratorium on development in that province as we l l . Returning again to Ontario, the Ontario government set up a se lect committee of the provincial government to look at Hydro a f f a i r s . Part of that committee's review focused on the front end of the fuel cycle and made a number of recommendations a f fect ing ju r i sd ic t iona l issues. The next major enquiry was the Key Lake Inquiry, again in Saskatchewan, which focused s t r i c t l y on the development of the Key Lake mining operation and again concluded that there was no reason why that development could not proceed subject to specif ic conditions. The most recent set of public meetings has taken place in the Northwest Te r r i to r i e s which as yet has no uranium development but has some potential properties which may be developed over the next decade. F ina l ly the province of Nova Scotia is estab l ishing a uranium inquiry to look at a l l aspects of uranium exploration and development and in the meantime has imposed an exploration moratorium.

I t should be very c lear from this rather extended l i s t how important public opinion has been in the formation of a number of major enquir ies . In v i r tua l l y al l of these enquir ies , t a i l i n g s management, and in part icu lar their long term aspects, have assumed a very prominent ro l e . Another aspect of public concern is the provision of complete and accurate information. In v i r tua l l y a l l instances in Canada, major i n i t i a t i ve s such as development

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of new regulat ions , po l ic ies and the detai led review of submissions by proponents is now made ava i lab le to the public who are invited to respond.

In order to understand the regulatory situation in Canada i t is a lso necessary to understand the d is t r ibut ion of powers between the federal government and the various provincial governments. Section 109 of the Br i t i sh North America Act, the Act that created Canada, states that a l l lands, mines, minerals and royal t ies derived therefrom belong to the provinces. In 1946, using its power under Section 92.10(c) of the BNA Act to declare a " local work and undertaking" to be for "the general good of Canada," the federal government passed The Atomic Energy Control Act .

Until the mid-1970's The Atomic Energy Control Act was used primari ly to control the production and management of uranium products . 1 The policy of the Federal government was that, except in matters of national security and foreign pol icy, uranium mines should be subject to the same rules as those which the provinces exercize over other mines.^ Environmental aspects of uranium mining were control led by the provinces in a s imilar manner to environmental control of a l l mines, which admittedly was not overly adequate.

In the 1970's much more emphasis was being placed on protection of the Canadian environment. Both the Atomic Energy Control Board and the provincial environment departments began exercizing much t ighter control over the environmental e f fects of the uranium industry.

Saskatchewan Requirements

I t is the policy of the Government of Saskatchewan to exercize firm control over the environmental and health aspects of resource developments. I t is also the policy of the Province to do this with a fu l ly co-operative and consultat ive approach with the Atomic Energy Control Board and other Federal agencies.

In Saskatchewan a number of companies began development of new uranium ore bodies in the 1970's. Gulf Minerals began operating the Rabbit Lake Mine in 1974. Amok Limited submitted the Environmental Impact Statement for the project near Cluf f Lake in November, 1976. As we l l , projects at Key Lake, Midwest Lake, Col l ins Bay, Dawn Lake and Candy Lake were on the horizon.

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In view of the potential for s ign i f i cant uranium development in Saskatchewan, with i ts potential for environmental and social impact, and in view of growing public opposition to the developments, the Government of Saskatchewan set up the "Cluf f Lake Board of Inquiry" under Justice E.D. Bayda in February, 1977. The terms of reference of the inquiry were very broad. The committee was asked to conduct a public inquiry into the probable environmental, health, safety, social and economic e f fects of the Cluf f Lake mine, as well as the soc ia l , economic and other implications of the expansion of the uranium industry in Saskatchewan.

On the general industry-wide issues and the ju r i sd ic t iona l questions Bayda recommended: a) the administration of regulations pertaining to pol lution control in the mining industry be transferred from the Saskatchewan Mineral Resources to Saskatchewan Environment; b) Saskatchewan Environment require an environmental assessment process pr ior to approval of any new uranium mining operation; c) the province undertake to develop regulations and standards for the release of substances from uranium operations into the environment; d) regulations and requirements for mine s ite abandonment procedures be developed in greater d e t a i l ; e) the granting of surface leases require compliance with these regulat ions ; f ) the governments in co-operation with companies carry out research and development of processes to reduce the re lease of radioactive materials from uranium mine s i t e s ; and g) the creation of an "Environmental Protection Fund" to finance monitoring and reclamation work a f ter closure of the mine s i t e s .

Al l of these recommendations were accepted by the government of Saskatchewan and have since been implemented. Recommendation a) was accomplished by the creation of a Mines Pol lut ion Control Branch within Saskatchewan Environment, and by means of two Orders - in -Council passed in January, 1980, which transferred j u r i s d i c t i o n . The transfer e f f ec t ive ly separated the promotional aspects from the control function. Until new regulations are passed, environmental control of normal operations is accomplished by negotiating and issuing approvals to construct and operate under the Water Resources Management Act and the A i r Pol lut ion Control Act. The approvals include conditions respecting operations, invest igat ions , e f f luent standards, monitoring requirements and abandonment requirements. The negotiations are conducted in close co-ordination with the Atomic Energy Control Board.

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Measure b) has been provincial policy since the Bayda Inquiry, and is now formalized with the passing of the new Environmental Assessment Act. The Act has been in the draft stage since 1976 and has been used as a guidel ine since then. The requirement of a detai led Environmental Impact Assessment ensures that the necessary environmental control features are bu i l t into a project at the conceptual design stage. The process also requires the proponent to design abandonment procedures into the project and to commence research where needed to develop environmental control technology. The assessment process has contributed s i gn i f i cant ly to the development of unique and superior t a i l i n g s disposal schemes for the Key Lake and Col l ins Bay pro jects .

New regulations have been drafted under the Department of the Environment Act. The regulations ent i t led "The Uranium Mining Environmental Control Regulations" have undergone an extensive public review and are now in the hands of the attorney general for legal rev is ions . The regulations cover the environmental control of uranium development from a detai led exploration stage, through construction, operation and through the abandonment-reclamation phase. The regulations include design and construction requirements, contingency procedures, reclamation and abandonment requirements, e f f luent qual ity standards, a i r qual ity standards, and monitoring requirements. The regulations increase the penalties for infract ions by twenty- fo ld.

Measure d) has been implemented through the formal Environmental Assessment process and the new regulat ions .

Measure e) i s being implemented for a l l new mining pro jects . Detai led surface lease agreements have been negotiated and signed for the Amok Limited and Key Lake pro jects . The surface lease for Key Lake was negotiated over a six month period result ing in an eighty (80) page lease agreement. The lease includes detai led agreements by the company to comply with al l regulat ions, to meet set standards, to design, construct and operate the project such that the environment is protected and to decommission and abandon the property according to plans approved by the province.

The land and minerals in Saskatchewan are owned by the province. The minerals are developed under a mineral lease granted to companies. The lands are leased as described above so that the development may proceed. Upon

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depletion of the ore and close-out of the mine, the lands wi l l eventually revert back to the ownership of the province. The provincial government desires to ensure that proper c lose-out procedures are implemented so that future generations in the province are not burdened with the cost of continued maintenance of the s i te without the benefits of the resource development. The surface lease agreements pa r t i a l l y f u l f i l this des i re . As we l l , a new "Environmental Protection Div i s ion" of the Heritage Fund has been in i t i a t ed . The money for the fund has been i n i t i a l l y derived from provincial roya l t ies obtained from the uranium resource development. A move is now underway, as we l l , to have the companies contribute d i rect ly , according to production.

The government of Saskatchewan bel ieves i t is the full r espons ib i l i ty of the project proponent to properly reclaim the mine s i te so that the environment is protected over the long term. The province does, however, recognize that companies dissolve and that the province wi l l eventually control the land. After a company has conducted the decommissioning procedures, a transit ion phase wi l l be entered when the company and the regulatory agencies wi l l monitor to evaluate the reclamation procedures. The company wi l l not be re l ieved of i t s responsibi l it ies until this phase is over. Inst i tut ional control of the mine s i te lands wi l l be implemented under the Provincial Lands Act. The future land use and future developments can be c losely contro l led by the Province under this Act.

Recommendation f ) has been implemented with the establishment about one year ago of the "Mines Waste Research Secretar ia t " within Saskatchewan Environment. The Secretar ia t finances and furthers investigations into the mining waste management and s t ab i l i z a t i on . In i t i a l concentration is being placed on some previously abandoned uranium mine t a i l i n g s . The t a i l i ngs s i tes are being used as ful l scale laborator ies to investigate their e f fect and to study procedures to minimize this e f f ec t .

All of the environmental regulatory functions of the province of Saskatchewan are conducted in close association with the Federal agencies. There have not been any conf l ic ts between one ju r i sd i c t i on and another. Generally speaking, one agency may wish to impose a more str ingent standard or rule than the other agency, but in such a case, the company must fol low the more stringent ru l e .

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In Saskatchewan, i t is fortunate that the more stringent rules have been implemented pr ior to the major expansion of the industry and that the operations are mining a high grade ore so that economics allow them to implement the necessary sophisticated environmental control features.

3.2 Ontario Requirements

The Ontario Ministry of the Environment is proposing to introduce Surface Water Guidelines in addition to the Drinking Water Guidelines which were developed j o in t l y with the Federal Government. The Surface Water Guidelines wi l l present objectives for the concentration of radionuclides in surface water. These objectives wi l l be numerically equivalent to the maximum acceptable concentrations of the radionuclides in drinking water. I f there is more than one radionuclide in the surface water, then the combined ef fect of the radionuclides must be no greater than the e f fect of only one radionuclide present at i t s maximum acceptable concentration.

The MOE is also developing "Guidelines for the Discharge of Radionuclides to Surface Waters" whereby l imits can be set to the concentrations of radionuclides in an e f f luent stream at i t s discharge point. These l imits wi l l be re lated to the MOE's surface water guidel ines but w i l l al low for a mixing zone between the point of discharge and the point where the surface water guidel ines must be met. The guidelines wi l l also propose a maximum permissible detriment to a drinking water supply as a resu l t of the e f f luent . These draft e f f luent guidelines wi l l soon be c i rcu lated to the affected industries and trade unions in Ontario with a request for their comments.

3.3 Federal Requirements

The Atomic Energy Control Board is the Federal agency which controls uranium mine t a i l i ng s management f a c i l i t i e s in Canada under the authority of the Atomic Energy Control Act. The main mechanisms for exercising this control are the application of regulations and the issuance of l icences for each operating f a c i l i t y which specify deta i led operating requirements. In order to develop these l icences and to ensure that al l issues are addressed, i t is the policy of the Board to act as a coordinator for various other inputs. These inputs are not only the inputs from the province but also from other federal government agencies. The Board uses as advisors departments such as the Department of the Environment to help in areas such as environmental review and the establishment of acceptable ef f luent release l imi t s .

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A major area of concern over the l a s t year has been the development of a set of close out c r i t e r i a in i t iated by the AECB in January, 1981. Since that time, meetings and public consultations have taken place and we can now summarize the substance of those comments. Industry in part icu lar f e l t that the f i r s t draft lacked suf f ic ient s i t e spec i f i c i ty and expressed concern over the choice of performance objectives for radon emanation and gamma f i e l d s or ig inat ing from the t a i l i n g s . They also expressed concern over the possible costs of meeting the objectives and that there would be insu f f ic ient benef it gained. The comments received from the public at large were very l imited and covered a f a i r spectrum of opinion from recommendations to cease future developments to general support for the i n i t i a t i v e to develop c r i t e r i a .

In response to the representations made, AECB staf f have undertaken a reevaluation and a redraft ing of the c lose out c r i t e r i a and while the deta i l s are not as yet ava i l ab le for public d i s t r i but ion , certain general statements on new directions can be made. The thrust of the second draft wi l l allow for more s i te spec i f i c i t y . In addition i t is v isual ized that fewer performance oriented numbers wi l l be included and that these wi l l be replaced with some form of dose l imitat ion. This l a t te r implies that the ro le of pathways analysis and source term modelling wi l l be increased. In e f fect a l l operators wi l l have to do a pathways analysis to determine a dose to indiv iduals and groups and to determine what e f fect various remedial actions may have on that dose. Speci f ic dose l imits wil l be ident i f ied alorrg with a de-minimis dose representing a level which can be neglected. The time frame implied in the c r i t e r i a has been adjusted to focus on a period of approximately f ive years a f ter operations cease. Thus when industry has met the c r i t e r i a at the end of the f ive year period i t may be allowed to return control over the closed out s ite to an appropriate regulatory agency. This agency would l i ke ly impose some form of longer term inst itut ional control which is impl ic i t in our approach to c lose -out . The methods we are looking at to manage the t a i l i ng s in the long term may not prevent certain exposure s ituations such as the construction of dwellings on or very close to the t a i l i ng s or the removal and mishandling of material in some other manner. The deta i l s re la t ing to the dose l imits for the c r i t e r i a should be resolved in the very near future and we are hoping that the final set of close out c r i t e r i a wi l l be ava i l ab le for review by al l interested parties by l a te spring which wi l l al low for the final document to be released some time in the fa l l of 1982.

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In addition to the technical requirements of the close out c r i t e r i a , we are also engaged in reviewing various f inancial guarantee mechanisms which wi l l a ss i s t al l government departments and agencies in carrying out the i r assigned r e s p o n s i b i l i t i e s . The close out c r i t e r i a focus on an i n i t i a l f ive year period in part to f a c i l i t a t e the de f in i t ion of f inancial guarantees. Thus i t should be poss ib le to develop f a i r l y simple and f a i r l y s t ra ight forward mechanisms whereby assurance is provided that an operator completes the i n i t i a l close out work to a standard which is compatible with the close out c r i t e r i a i r respect ive of his f inancial circumstances at the time o f c lose out. The question of f inancial guarantees beyond the f ive year period is rather more d i f f i c u l t to define and is currently subject to detai led negotiations between the federal and provincial governments as well as industry i t s e l f .

4.0 Technical-Regulatory Interaction

At this stage i t is interest ing to ask how well the regulatory process works or for that matter how i t works in some level of d e t a i l . Another form of this question is to ask whether technology leads the regulatory process or whether the regulatory process is pushing technology. As you can see from the above discussion there is a third component which is often ignored and that is public involvement and perception. Considering the unique approach to regulations which exists in Canada, that i s , the consultat ive approach, the resolution of this question is not at al l c lear cut. Technology, regulations and public perception are c lear ly l inked. The maximum separation between progress in any one of the three f i e ld s is severely l imited. I t is l imited in part because research cannot and is not done without some understanding of the objectives which that research is aiming to achieve. In the regulatory f i e l d this may be a performance oriented objective re lat ing to close out. I t may be the stated goal of a regulatory agency to separate undesirable contaminants from a large mass of e s sent i a l l y clean material or i t may represent a new technical break through in the process of uranium extraction which prevents the release of undesirable contaminants.

Furthermore i t may be re lated to a new public outcry or a new public awareness which demands a more thorough or a more rigorous approach to the entire regulatory process.

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An obvious example here is the long term aspects of t a i l i ng s management which have received impetus in the l a s t few years .

An example of how al l of these various issues have to be f i t t ed together could be given with reference to the Quirke Lake disposal study which was previously mentioned. Some sectors of the public are c lear ly in favour of this approach even though they have not yet been apprised fu l ly of the technical issues that surround the use of Quirke Lake as a disposal s i t e . This same public group is opposed to further expansion of conventional on-land uranium disposal f a c i l i t i e s which in most cases wil l involve the loss of small lakes in the same general area as Quirke Lake. From a regulatory point of view, the issues are equally complex. The use of a lake for the deposition of t a i l i ng s is not considered normal practice in Canada and in some quarters is not regarded as the most des i rab le general approach to the problem. I t is however recognized that, in part icu lar circumstances, i t may be des i rab le and preferential to u t i l i z e such an option. Thus the implication for most regulatory agencies is that the use of a deep lake may involve modifications to prevai l ing regulatory po l i c i e s . Modifications of regulations has not been a common procedure in Canada and as such car r ies with i t considerable amount of inert ia which may delay the overall approval process. Another aspect of concern to the regulatory agencies is the question of novelty. Novel technology carr ies with i t a certain element of uncertainty - - a certain element of r i sk . I t is thus impossible to say with complete assurance that a proposed new approach wi l l work as designed or as predicted. The question may ar ise i f a system should fa i l to perform in the proper way as to who is responsible for undertaking the necessary remedial action - industry or the regulatory agencies themselves or a combination of the two. H i s to r i ca l l y i t has been the position in Canada that even when a regulatory agency grants approval i t does not absolve the proponent from respons ib i l i ty for def ic iencies in the system for whatever reason. This constraint however is a very serious and very sobering one from the point of view of industry and tends to make industry cautious in its application of new and unproven technologies. Turning then to the technical aspects of disposal of t a i l i n g s into a deep lake, we immediately are confronted with a wide range of uncerta int ies . The mechanisms which wi l l control such a system a f ter operations have ceased are not well understood. The movement of contaminants across the t a i l i ngs water inter face , the mechanisms which may ex i s t

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within the ecosystem which would remove contaminants from the water column and redeposit them in the sediment are not well documented. In addit ion, the rate at which these phenomenon wi l l change with time over the next several hundreds of years is also unclear. The net e f fect of al l of this uncertainty is to make even the most dedicated advocate of such a system pause to r e f l e c t .

From the above discussion i t is c lear that for disposal into a deep lake no s ingle aspect (technology, regulations or public opinion) can be taken in i so l a t i on . Complete openness and consultation is mandatory. Fortunately this process of consultation has been ongoing as the normal mode of operation in the Canadian regulatory environment. There are c r i t i c s of such an approach who claim that i t s ef fect iveness is l imited, that i t allows the biases of various part ies too much credence, and that i t is inherently slow and cumbersome. We in Canada feel however that the benefits of such a system far outweigh any possib le l i a b i l i t i e s . We wi l l continue to pursue our approach to consultation and we wi l l also continue to set general c r i t e r i a which allow industry the freedom to implement measures in an innovative and cost e f f ec t i ve manner. We wi l l furthermore continue to refine our standards when i t is appropriate to do so given newer, better and less cost ly technology. We wi l l also continue to consider on a case-by-case basis the need to r e t r o f i t new technology into exist ing operations. It has not been our policy to universa l ly r e t r o f i t a new technology and in fact general ly speaking new technology has not been r e t ro f i t t ed to exist ing operations. In order to ju s t i f y such a r e t r o f i t one would have to be able to demonstrate a strong need to improve the current situation and also be able to show that such a r e t r o f i t represents a reasonably e f f ec t ive use of ava i l ab le resources. F ina l ly , we wi l l strongly r e s i s t the urge to allow the regulatory process to become dominated by any one approach or by any one group. We wi l l endeavour to continue to take that d i f f i c u l t middle road which seeks to balance complex and sometimes conf l ic t ing requirements in a manner which of fers the greatest co l l e c t i ve benef it to al l of the people of Canada.

References

Robinson, Ian, Queen's Univers i ty , 1981 "A Study of intergovernmental issues in the regulation of environmental and occupational health aspects of the nuclear industry. " Final Report - C luf f Lake Board of Inquiry - 1978.

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URANIUM MILL LICENSING REQUIREMENTS IN THE UNITED STATES OF AMERICA

K. HAMILL Uranium Recovering

Licensing Branch, United States Nuclear

Regulatory Commission, Washington, DC, United States of America

Abstract

URANIUM MILL LICENSING REQUIREMENTS IN THE UNITED STATES OF AMERICA. Since the last international symposium on uranium mill tailings management, the United

States Nuclear Regulatory Commission has made significant progress in developing a comprehensive regulatory programme for protecting the public health and safety and the environ­ment from hazards associated with mill tailings. The NRC issued regulations governing mill tailings licensing in October 1980. The bases for the regulations are contained in the Generic Environmental Impact Statement. The significant features of NRC's mill tailings regulations, outlined in this paper, relate to the following areas: (1) long-term isolation; (2) operational controls; (3) radon control; (4) reclamation cover; (5) institutional requirements.

INTRODUCTION

Full realization of the potential hazards of mill tailings in the United States did not begin to occur until the early 1970s. Consequently, in the early days of the milling industry, tailings were not well controlled. Awareness of the problems which have resulted from this former lack of concern, such as construction of many homes, schools, and other public buildings using tailings materials, led to the recognition that uranium mill tailings disposal was an issue of national importance. Studies conducted by the Department of Energy (DOE) and its predecessor agencies identified the need for a massive remedial action program. Thus, in 1978, the U.S. Congress authorized the cleanup of approximately two dozen abandoned uranium mill tailings disposal sites through enactment of the Uranium Mill Tailings Radiation Control Act. Faced with this need for an enormously costly remedial action program at the inactive sites, Congress also strengthened regulatory authorities relating to active mill operations and tailings disposal in order to assure that mistakes of the past would not be repeated and the public would not again be faced with a similar burden.

In the Mill Tailings Act, Congress sought to establish a uniform national regulatory program under which the solutions developed for tailings disposal problems would be permanent and would not rely upon long-term

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maintenance. Under provisions of the act, the Environmental Protection Agency, the Department of Energy, the Nuclear Regulatory Commission and a number of States regulating mill tailings under agreements with the NRC were delegated certain responsibilities. With respect to active milling operations, EPA was directed to establish general standards governing mill tailings disposal. NRC was given lead responsibility to assure, through the licensing process, that milling operations and mill tailings disposal were carried out in such a manner as to assure protection of the public health and safety and the environment. The States licensing under agreements with the NRC were to develop mill tailings regulatory programs equivalent, to the extent practicable, to the Commission's regulatory program.

Before passage of the Mill Tailings Act, the Commission became aware of the problems of tailings disposal. Even before the Department of Energy reported to Congress on the full extent of problems associated with the inactive tailings sites, NRC recognized the importance of beginning to tackle the problems in its mill licensing program -- to avoid adding to the list of abandoned, unreclaimed tailings sites.

In 1976, in response to expressions of these kinds of concerns and other public interest, the Commission announced its intention to conduct a review to determine what regulatory and legislative changes were needed with respect to the uranium mill licensing program. This review was to be carried out through the preparation of a Generic Environmental Impact Statement (referred to as the GEIS) on uranium milling. At that time, the Commission also announced its intention to continue mill licensing. Recognizing that it would take several years to complete the GEIS and associated formal rulemaking, the Commission staff developed interim tailings management performance objectives in May 1977 to guide continued licensing activities.

The performance objectives addressed fundamentally the same concerns that were ultimately addressed in the regulations. They essentially called for control of seepage and airborne emissions during mill operation. They also called for siting and design measures to assure long-term tailings isolation and control of emissions without relying upon routine maintenance to preserve the integrity of the reclaimed area.

Upgrading the type of tailings management programs approved for new facilities was established as a first priority. Because options for disposal are limited after several million tons of tailings are generated (which can occur in a relatively short period of mill operation), the Commission obtained commitments from applicants to programs of tailings management meeting the performance objectives prior to issuance of new licenses. Financial surety arrangements were also established to guarantee that these license commitments would be carried out. In addition, through the license renewal process, the staff worked with existing mill operators to develop acceptable tailings management programs. Developing such programs at existing mills proved to be more difficult because, as previously stated, options at such sites are fewer. The performance objectives could not be applied in precisely the same fashion at existing operations as they were at new mills. However, after a detailed in-house review of available alternatives at each existing mill, we have been able to arrive at acceptable tailings management programs.

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GENERIC ENVIRONMENTAL IMPACT STATEMENT AND MILL TAILINGS REGULATIONS

NRC published the draft Generic Environmental Impact Statement on Uranium Milling and the proposed regulations in mid-1979. After an extended period of public comment, the staff reviewed and responded to all of the comments, and final regulations were issued by the Commission in October 1980. It should be noted that the NRC regulations preceded the promulgation of general standards that the U.S. EPA was directed to develop by the Tailings Act. As will be discussed later, the EPA standards have yet to be issued. The NRC regulations are based upon (1) an evaluation of alternatives documented in the GEIS, (2) provisions of the Mill Tailings Act, (3) an extensive program of research on various aspects of the disposal problem (specific studies in this research program will be discussed later in the symposium), and (4) actual licensing experience.

The basic conclusion of the GEIS was that there is a range of tailings disposal alternatives which can be implemented at reasonable cost to return tailings disposal sites to conditions which are essentially the same as those of the surrounding environs, without having to rely upon routine maintenance to preserve such conditions. Recognizing that problems associated with uranium mill tailings are highly site specific, the regulations (like the interim staff guidance) were largely cast in the form of performance objectives to provide the flexibility needed by both industry and regulators to work out tailings management programs which are reasonable and appropriate. Further, the NRC regulations contain sufficient flexibility to provide for some of the objectives being satisfied to a lesser extent at existing sites than at new sites.

The mechanism employed to assure that site-specific conditions are fully evaluated and costs and benefits are appropriately taken into account is the environmental impact statement. This site-specific document, prepared independently by the staff in connection with each major licensing action, is circulated for comment to provide an opportunity for full public involvement in agency decision making.

At this point I'd like to discuss some of the significant features of the NRC mill tailings regulations.

Long-Term Isolation

Perhaps the most significant problem associated with tailings is that the material will remain hazardous for many thousands of years. Given this, the overriding objective, which is the basis for most of the criteria, is isolation and containment of the tailings and associated contaminants over the long term. The tailings siting and design measures specified in the NRC regulations are intended to provide a degree of isolation which is consistent with the reality that the tailings present long term hazards. Specific features have been identified as appropriate for consideration, given the potential failure mechanisms which can occur in the very long term. The identified features are also considered appropriate in view of the Congressional objective to eliminate, to the extent practicable, the need for long term maintenance. Several of the following papers will address in greater detail the potential failure mechanisms in the semi-arid uranium milling regions of the western United States. The mechanisms of chief concern identified by our review are those of wind and water erosion. Thus, the NRC requirements call for the siting and design of tailings disposal areas in accordance with basic

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erosion control principles. This generally would include: locating the tailings disposal area away from floodplains and where upstream precipitation drainage is minimal; disposing of the tailings below grade or in an area otherwise naturally protected from weathering forces; reducing the steepness of reclaimed impoundment slopes; and, covering the tailings with thick earthen layers protected from surface erosion by vegetation or rock covers.

Operational Controls

The primary objectives identified as being necessary to protect the public health and safety and the environment for the operational period (during which time tailings are continuing to be discharged) are: impoundment stability; groundwater protection; and reduction of airborne effluents and tailings dusting to levels which are as low as is reasonably achievable. The steps identified to achieve these objectives include:

1. Daily inspection of tailings embankments following construction in accordance with guidance issued by the staff related to dam stability;

2. Lining tailings disposal facilities or siting them above relative^ impermeable layers, dewatering tailings, and recirculating solutions;

3. Controlling airborne effluents at point sources as well as employment of strict control measures with respect to diffuse sources such as tailings in order to minimize exposures and contaminant spread away from the tailings thereby reducing the required extent of final site decontamination. Probably the most effective way to solve the problems of tailings dusting is to cover the tailings as operations progress. However, if the tailings management program does not lend itself to such a phased operation, other techniques such as wetting or spraying with chemical binders, can be employed to provide interim tailings stabilization.

Although, as I previously indicated, most of the criteria in the NRC mill tailings regulations are cast in the form of performance objectives, the requirements are specific where the Commission considered it appropriate and necessary to identify a minimum level of protection. Those criteria in which specific requirements are established pertain to residual radon control and minimum reclamation cover thickness.

Radon Control and Reclamation Cover

The NRC established the tailings'radon flux limit based upon an evaluation of a wide range of public health and cost factors, and the variability of site-specific conditions. More specifically, these factors included evaluation of alternative radon release limits in terms of: (1) impacts on maximum exposed individuals as they compare with existing radiation protection standards; (2) total population exposures as they compare with population exposures from natural and technologically enhanced radon releases, both short and long term; (3) radon fluxes that occur from natural soils; and (4) costs for applying a final tailings cover under a full range of conditions such as will occur with varying ore grades, impoundment sizes and shapes, cover material types and thicknesses.

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In consideration of these perspectives, it was determined that the most reasonable residual radon emission limit would be one that would assure that tailings disposal sites are eventually returned to conditions which are reasonably near those of the surrounding environs. The radon flux limit established (2 pCi/m2-sec.) assures that radon exhalation rates will be within the range of flux rates occurring naturally from nearby soils.

It should be noted that the NRC regulations call for placement of sufficient reclamation cover to result in a calculated reduction of radon exhalation from the tailings to 2 pCi/m2-sec~ This indicates that radon flux measurements will not be required following reclamation to determine compliance. Such a procedure was evaluated and determined to be impracticable. Recognizing the difficulties that relying upon flux measurements to determine compliance would present for both the industry and the regulatory authorities, NRC has strongly encouraged EPA to follow a similar approach, that is to develop more of a design standard as opposed to a performance standard.

After evaluating all aspects of the matter of tailings impoundment long-term cover requirements, the staff concluded that it was prudent to establish a minimum cover thickness requirement in order to provide a reasonable measure of physical isolation of the tailings. Such a minimum thickness requirement also reduces the likelihood and potentially disruptive effects of root penetration and provides protection from burrowing animals. While the overall tailings disposal program must effectively eliminate the potential for disruption by erosion or other natural phenomena, there are undeniable uncertainties about long-term cover performance. The minimum cover thickness specified (three meters) provides a desirable margin of safety in the face of these uncertainties. Deciding what the minimum cover thickness should be certainly involved the exercise of some judgement. NRC considered it prudent to specify a minimum thickness given our knowledge of the problems which have just been described. It is clearly not beyond the realm of possibility that techniques could be found to more economically resolve the concerns that led to establishment of the minimum cover thickness requirement. In fact, the NRC regulations allow for lesser amounts of non-soil materials if long term stability can be demonstrated. However, NRC was not at that time and for that matter is still not aware of any proven technology that would provide long term isolation and considered it inappropriate to ignore a known problem in hopes that it might be resolved at some future date.

Institutional Requirements

Other aspects of NRC's regulations have been termed "institutional requirements" since they call for financial and land ownership arrangements to assure that all appropriate decommissioning, reclamation, and long-term site control is facilitated. These requirements call for establishment of a financial surety arrangement to cover the costs associated with site decommissioning and reclamation; transfer of title to the land on which tailings are disposed to a government agency as an added measure of protection against disruption of the tailings; and, payment of a one-time charge to cover costs associated with long-term government surveillance and site control.

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CURRENT SITUATION

Legal and Congressional Actions

Shortly after NRC promulgation of the final mill tailings regulations in late 1980, several industry organizations filed a legal challenge in United States Federal Court claiming that the Commission did not have the authority to establish such requirements prior to EPA issuance of related standards and that, even if we did have the authority, we had not followed proper procedures in developing the regulations. Just this past March the Court issued a decision in this matter finding that the Commission did have the authority to issue the subject regulations, had followed proper procedures, had examined all of the important issues, and had provided an adequate basis for the requirements. Notwithstanding this decision, NRC has been prohibited by legislative action from implementation or enforcement of the mill tailings regulations until October of this year.

Further, there is another piece of legislation currently pending in the U.S. Congress which, if passed, would extend the embargo on the use of the Commission's mill tailings regulations until EPA issues final standards. In addition, this proposed legislation seeks to expedite promulgation of the required EPA standards and seeks to provide greater flexibility for the Agreement States to determine the practicability of Federal requirements. In view of the recent Court decision and the fact that three of the four Agreement States regulating milling activities have established regulatory programs essentially equivalent to the NRC's, the Commission has submitted comments to the Congress indicating that they do not consider the proposed legislation to be warranted. In spite of the Commission's concern related to the proposed legislative action, NRC supports the Congressional objective of expediting EPA issuance of general mill tailings standards.

Status of EPA Standards

EPA proposed disposal standards for use in the Department of Energy's remedial action program at the abandoned U.S. mill tailings sites over a year ago. These proposed disposal standards addressed the same areas of concern as do the NRC's mill tailings regulations. After having considered an extensive series of comments on the proposed standards, EPA is in the process of finalizing the standards and expects to reissue them early this summer. It is impossible to predict at this point what precise limits will be specified by. EPA in the final standards, however, it is considered likely that the general nature of the standard will remain unchanged. If this is true, the EPA standard will specify a radon exhalation limit, will restrict degradation of surface and groundwaters, and will address the issue of long-term containment by identifying a period of applicability of the standard.

EPA has yet to propose the second set of standards which they are chartered to promulgate under provisions of the Mill Tailings Act. These standards will govern mill tailings disposal at currently operating uranium mill facilities. Although one cannot automatically assume that the standards established for the abandoned sites will necessarily set a precedent for the active site standards, it certainly seems reasonable to assume that the concerns addressed will not be substantially different.

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SUMMARY

In summary, since the last international symposium on uranium mill tailings management, the United States has continued to make progress in developing what we consider to be a reasonable regulatory program for protecting the public health and safety and the environment from both the radiological and non-radiological hazards associated with mill tailings. The broad performance objectives have been further refined to provide additional guidance to the milling industry. In turn, the U.S. milling industry itself has proposed many innovative schemes for achieving the identified objectives. We look forward to the industry continuing to take the lead in developing innovative, cost-effective plans that provide an appropriate measure of protection of the environment and the public health and safety.

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GEOMORPHIC HAZARDS AND URANIUM-TAILINGS DISPOSAL

S.A. SCHUMM

Colorado State University,

Fort Collins, Colorado

J.E. COSTA, T.J. TOY

University of Denver,

Denver, Colorado

J.C. KNOX

University of Wisconsin,

Madison, Wisconsin,

United States of America

R.F. WARNER

University of Sydney,

Sydney, New South Wales,

Australia

Abstract

GEOMORPHIC HAZARDS AND URANIUM-TAILINGS DISPOSAL. In order to assess the long-term stability of a uranium-tailings disposal site the potential

for climate change, tectonic activity, baselevel change, and vegetation and landform modification by man must be considered. All of these processes affect landforms, and a change in any or all may create geomorphic hazards as a result of their influence on runoff, sediment yields, river behaviour, and slope erosion. In addition, during the passage of time landforms may be so modified by the operation of natural, erosional and depositional processes that a site may become unstable. Predictions of site stability improve as the amount of information available on landform evolution at that site increases. In addition to climatic and hydrologic data, geomorphic information on channel, hillslope and drainage-basin characteristics is needed in order to predict probable future landform changes and the extent to which the change may be deemed hazardous.

1. INTRODUCTION

A c r i t i c a l aspect of the disposal of uranium t a i l i n g s and radioact ive wastes i s the long-term geomorphic s t a b i l i t y of the disposal s i t e . Deep burial may eliminate most geomorphic hazards, but shallow burial or above surface (above grade) disposal requires an evaluation of the geomorphic s t a b i l i t y of

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the s i t e . This necessitates that geomorphic hazards be ident i f i ed and evaluated. Our object ive is to consider the geomorphic s t a b i l i t y of t a i l i ngs -d i sposa l s i t e s .

A geomorphic hazard is defined as any landform change, natural or otherwise, that adversely a f fects the geomorphic s t a b i l i t y of a disposal s i t e . This de f in i t ion is very broad, and i t includes those geomorphic changes that occur so slowly that they are a hazard only in the sense that over thousands of years the i r cumulative e f fect may threaten s i t e s t a b i l i t y .

A s i t e should, to the degree poss ib l e , be situated on a r e l a t i v e l y stab le geomorphic surface. Each s i t e has i t s own environmental sett ing (c l imatic regime, bedrock type, h is tory , and rate of change). For each s i t e , potential changes of erosion rates and nearby stream behavior must be evaluated with regard to c l imat ic , baselevel and tectonic s t a b i l i t y for very long periods of time.

2. THE FLUVIAL SYSTEM

Within a landscape there are safe and hazardous locations for long-term disposal of radioactive mater ia ls . Hazardous locations may be geomorphicly unsuitable because of landform change or hydrologicly unsuitable because of inundation by large f loods [ 1 ] ,

A uranium-tai l ings-disposal s i t e w i l l be located within the landform complex that is termed the f luv ia l system (F ig . 1). The f luv ia l system can be divided into three zones as f o l l o w s [ 2 ] :

zone 1 - the drainage bas in , a sediment and runoff production zone

zone 2 - the major streams and va l l ey s , a sediment and water transport zone

zone 3 - the piedmont or coastal p l a in , a depositional zone.

Obviously this t r i p a r t d iv is ion of a complex system is f a r too s imp l i s t i c , and in nature a c lear d is t inct ion between each zone is d i f f i c u l t . In addit ion, there can be sediment deposi ­tion and storage in zones 1 and 2 and erosion in zone 3 as these zones adjust to climate change, tectonic e f f e c t s , and baselevel change. Nevertheless, the subdivision does aid in the discussion of t a i l i n g s - s i t e locat ion, and the geomorphic

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Upstream Controls (climate, diastrophism, land-use.)

ZONE I (production)

Drainage basin

ZONE 2 (transfer)

Downstream Controls

(baselevel, diastrophism.)

ZONE 3 (deposition)

FIG.l. Sketch of fluvial system showing location of tailings disposal sites (after Schumm, 1977): (1) divide or plateau; (2) valley head or tributary; (3) large valley, flood plain, terrace; (4) alluvial plain, fan, delta, pediment.

Table I . Fluvial System Variables

1 Time

2 I n i t i a l Rel ie f ( t ecton ics )

3 Geology ( l i tho logy and structure )

4 Climate

5 Hydrology (runoff and sediment y i e l d )

6 Drainage network morphology

7 Hi 11 si ope morphology

8 Hydrology (discharge of water and sediment to zones 2 and 3)

9 Channel and va l l ey morphology (zone 2)

10 Depositional system morphology (zone 3)

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hazards that influence s i t e s t a b i l i t y . For example, the s i t e s w i l l be located d i f f e rent ly in each zone as fol lows (F ig . 1 ) :

zone 1 - drainage divide or plateau s i t e s , va l l ey head or t r ibutary s i tes

zone 2 - l a r ge - va l l ey s i t e s , terrace and f lood -p la in s i tes

zone 3 - a l l uv i a l fan, coastal p l a in , delta and pediment s i t e s .

I f a landscape i s s ta t i c then only the potential e f fect of extreme hydrologic events needs to be considered in s i t e se lect ion [ 3 ] . C lear ly , i f landform evolution i s slow or i f the time span of concern i s short then most var iab les that cause landform change can be dismissed. Unfortunately this is not the case, and in Table I the var iab les that influence the f l uv i a l system are l i s t ed in order of the i r s ign i f i cance . Time, of course, is not a true independent v a r i a b l e , but i t i s a measure of the extent of landform evolution under the influence of geomorphic agents of erosion and deposit ion. The i n i t i a l r e l i e f , geology and climate w i l l estab l i sh the process ( f l u v i a l , eo l i an , g l a c i a l ) that w i l l act on a landform and the rate at which change w i l l occur. Climate, through i t s control of vegetat ion, r e l i e f through i t s control of gravitat ional fo rces , and geology through i t s control of e r o d i b i l i t y and permeability w i l l determine the morphology of zone 1 and the runoff and sediment y i e ld per unit area of zone 1 that i s del ivered to zones 2 and 3. The quantity and type of sediment and the hydrologic character of the runoff events w i l l in the absence of other external controls (baselevel and tectonic e f f ec t s ) es tab l i sh the channel, v a l l ey , and depositional land-form morphology of zones 2 and 3.

I t should be c lear why the landform complex is referred to as a system because of the interaction between zones. Upstream hydrologic changes w i l l influence the landform morphology and s t a b i l i t y of zones 2 and 3, and a baselevel change in zone 3 can have an e f fect upon zones 1 and 2.

Of the var iab les l i s t ed on Table I the fol lowing appear to be most s i gn i f i cant for landform s t a b i l i t y :

1) time - natural landform evolution

2) r e l i e f - change of r e l i e f as a resu l t of tectonics ( u p l i f t or downwarping) and baselevel change ( r i s e or f a l l of sea level and lake l e v e l s , or an abrupt change of stream p r o f i l e )

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ar id semi ar id subhumid nonglacial uniform to to to to to

Var iables semiarid subhumid humid g l ac ia l seasonal

Discharge + + + + +

Sediment Load + - - + +

Baselevel

lake + + + + 0

ocean 0 0 0 0

Table I I I . Tectonic Effects

Variables Upstream

Up l i f t Downwarp Downstream

Up l i f t Downwarp

Discharge o o o o

Sediment Load + - o o

Baselevel o o +

Table IV. Man's Effects

Increased Dam Construction .. Channelization Variables Land Use Upstream Downstream Upstream Downstream

Discharge + - o + o

Sediment

Load + - o + o

Baselevel 0 0 + 0

Table I I . Effects of Climate Change

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Table V. Variables a f fect ing geomorphic hazards and the s i te r i sk associated with each hazard

GEOMORPHIC HAZARDS

VARIABLES ' RISK

GEOMORPHIC HAZARDS TIME DISCHARGE +

SEDIMENT LOAD

+

BASE-LEVEL up down

1000 a sub­

surface qrad(

10 000 a sub-

; surface qrade

: 100 000 a sub- deep qrade burial

1. Drainage Networks a) Erosion

1 rejuvenation 2 extension

b) Deposition 1 valley filling

c) Pattern change 1 capture X

X X

X X

X

X

X X

X

X X

X X X X

X

X X

X X X X

X

X X

X X X

X X 2. Slopes

a) Erosion 1 denudation-retreat 2 dissection 3 mass failure

X

X

X X X

X X X

X X X

X X X

X X X

X X X

3. Channels a) Erosion

1 degradation (incision) 2 nickpoint formation

and migration 3 bank erosion

b) Deposition 1 aggradation 2 back and downfilling 3 berming

X

X

X

X

X

X X

X

X

X X

X X X

X

X

X X

X X

X X

X X

X

X X X

X X

X X X

X X X

X X

X

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c) Pattern Change 1 meander growth and shift 2 island and bar formation

and shift 3 cutoffs 4 avulsion

d) Metamorphosis 1 straight to meandering 2 straight to braided 3 braided to meandering 4 braided to straight 5 meandering to straight 6 meandering to braided

Piedmont and Coastal Plains a) Erosion

1 dissection b) Deposition

1 aggradation 2 progradation

c) Pattern change

1 development of pattern 2 avulsion

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3) climate change - change of vegetation and hydrologic regimen.

The e f fect of these var iab les w i l l occur as changes of runoff ( d i scharge ) , sediment load, and base leve l . Depending on the direct ion of change, the resu l t can be benef ic ia l or detrimental to t a i l ings -d i sposa l s i t e s in a l l three zones of the f luv ia l system.

Tables I I , I I I , and IV show the e f fect of c l imate, tectonics , and man upon discharge, sediment load, and baselevel . The symbols p lus , minus, or zero , indicate an increase, decrease,, or no change respect ive ly of the s i gn i f i cant va r i ab l e s .

The e f fect of climate change on discharge is based on the re lat ions developed by Langbein et a l . [ 4 ] , which show that a decrease of temperature and/or an increase of prec ip i tat ion w i l l increase runoff and vice versa. The changes of sediment load are more complex, as sediment y i e ld [ 5 ] i s a maximum in semiarid climates [ 6 ] . I t i s a lso accepted that g l ac ia l ac t i v i ty increases sediment y i e l d , as does an increase in the seasonal ity of p rec ip i ta t ion . Baselevel w i l l be a f fected , as more or less water is del ivered to lakes and as large quantit ies of water are stored in continental g l a c i e r s , thereby, s i gn i f i cant l y lowering sea leve l .

Tectonic ac t i v i ty [ 7 ] that e i ther ra ises or lowers a portion of the landscape w i l l a f f ec t a s i t e d i f f e rent ly depending on the location of the change (Table I I I ) . I f the e f fect is downstream i t i s a baselevel change, but i f i t i s upstream i t w i l l a f fect r e l i e f and sediment y i e l d .

Table IV attempts to summarize the e f fects of three common types of man's a c t i v i t i e s .

3. GEOMORPHIC HAZARDS

A l i s t of 28 geomorphic hazards, the influence of four major var iab les on them and the r isk posed by each hazard to surface, subgrade and deep-burial s i tes i s summarized in Table V. Time is included with the va r i ab l e s , discharge, sediment load and baselevel change, because landforms are a l tered natura l ly through time.

The hazards are grouped according to the landforms affected (drainage network, s lopes , channels, p la ins ) and the resu l ts of the hazard ( e ros ion , deposit ion, pattern change, metamorphosi s ) .

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Using Tables I I , I I I and IV, i t i s poss ib le to determine i f , under a given set of circumstances, discharge, sediment load and baselevel change w i l l be a f fected. I f so , the e f f ec t of a change on the geomorphic hazards can be determined, and the hazards af fected by a change of one of the var iab les i s indicated by an X in Table V.

An X also indicates the hazards that w i l l a f fect surface, subgrade and deep-burial s i t e s , during three periods of time. There is no attempt to quantify the r e l a t i ons , but i f the extent of the change i s assumed or known then an estimate of the magnitude of the hazard can be made.

Note that for 1000 and 10 000 years surface and subgrade s i t e s are considered, whereas for 100 000 years subgrade and deep buria l s i t e s are considered. I t i s assumed that in most cases surface s i t e s w i l l be affected a f te r 10 000 years .

3.1 Drainage Network Hazards (Zone 1)

Rejuvenation ( l a l ) i s the deepening or incis ion of a drainage network. The deepening w i l l a lso cause extension ( l a2 ) or headward growth of t r i bu ta r i e s and perhaps the addition of t r i bu ta r i e s in formerly undissected areas . The depth of incis ion may be minor i f discharge i s increased s l i g h t l y or i f sediment loads are decreased, but i t can be major and deep i f a major decrease of baselevel occurs. Under the l a t t e r s i tuat ion any disposal s i t e may be in jeopardy but under the former, only s i t e s on f loodpla ins or terraces would be a f fected.

Extension, of course, causes erosion c loser to drainage d iv ides , and surface disposal s i tes could be s i gn i f i c an t l y af fected by gul ly ing and the headward growth of channels. Both of these hazards can a f fect surface and subgrade s i t e s , and a major rejuvenation w i l l a f fect deep-disposal s i t e s . Sites at locations 1 and 2 (F ig . 1) in par t icu la r w i l l be a f fected .

Val ley f i l l i n g ( l b ! ) i s the f i l l i n g of a va l l ey with sediment. This i s caused by a great inf lux of sediment or by baselevel r i s e . Subgrade s i tes w i l l be buried, and surface s i tes could be buried i f the deposition is s i gn i f i c an t . During the f i l l i n g process, surface s i tes may be inundated by f loods that might erode the t a i l i n g s before burial i s complete. Sites at locations 2 and 3 (F ig . 1) w i l l be a f fected.

Capture ( l e i ) i s the change of a stream course by the natural diversion of water into a stream at a lower e levat ion . That i s , a r i ve r flowing near the edge of a highland may be

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diverted into the adjacent lowland by the headward extension of a lowland stream. The diversion causes steepening of the stream gradient and rejuvenation and probably extension ( l a l , 2) of the captured drainage network. The process can be induced by baselevel lowering, which increases the energy of the lowland stream or by baselevel r i s e , which through deposi ­tion may cause a channel to sh i f t to a steeper s t ra ighter route.

3.2 Slope Hazards (Zone 1)

Slope erosion ( 2 a l ) , of both hi 11 si opes and escarpments, can be accelerated by increased water flow over the slope and by increased flow in adjacent streams [ 8 ] that leads to channel degradation and undercutting of slopes ( 3a l ) or to drainage network rejuvenation ( l a l ) . However, slope erosion w i l l occur inev i tab ly , during the passage of time.

Slope dissection (2a2) by channels w i l l occur i f there is network extension, as a resu l t of adjacent channel incis ion or headward growth. Both normal and increased slope erosion w i l l be a hazard to a s i t e on a h i l l or plateau top (S i te 1, Fig. 1 ) . In addit ion, slope mass f a i l u r e (2a3) may occur (slumping, debris f low) owing to increased water content of the slope material or by an increase of slope height by channel inc is ion .

3.3 Channel Hazards (Zone 2)

Channels, wherever they are located in the f luv ia l system, change morphology and behavior with time, and they pose the greatest hazard to t a i l ings -d i sposa l s i t e s . For example, as a var iab le changes in such a manner as to produce degradation or incis ion of a stream ( 3 a l ) , a l l s i tes near r ivers become vulnerable . In Zone 2 the va l l ey has an a l l uv i a l f i l l with a f loodpla in and terraces adjacent to the r i ve r . These a l l uv i a l deposits are usual ly read i ly e rod ib le .

Erosion can take place by nickpoint formation and upstream migration (3a2 ) . Above the nickpoint or point of longitudinal p ro f i l e change, the channel is unaffected, whereas i t i s incis ing and adjusting downstream. I t is important to recognize that through time a s tab le reach of r i ve r may become suddenly very unstable as a resu l t of passage of a nickpoint.

Bank erosion (3a3 ) , of course, i s a natural consequence of normal r i ve r behavior through time, but i t can be accelerated by changes of discharge, sediment load and base leve l . Both an increase or decrease of sediment load or a r i s e or f a l l of

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baselevel can cause bank erosion. Channel inc is ion increases bank height and the l ike l ihood of bank f a i l u r e . Deposition in the channel a lso concentrates erosion along the bank l i n e s .

Deposition occurs e i ther by aggradation, general f i l l i n g of the channel ( 3 b l ) , downstream migration of a sediment wave (downf i l l ing ) or by back f i l l i ng of the channel ( 3b2 ) , or berming (3b3 ) , which i s deposition of f ine sediments along the sides of the channel. Al l four processes reduce channel capacity, and this subjects an above-grade disposal s i t e to f looding and potential eros ion, as overbank f loods increase in frequency.

Channel pattern change i s for the most part expectable through time. For example, meander bends grow and sh i f t down­stream ( 3 c l ) , and is lands and bars may form and sh i f t posit ion within the channel (3c2 ) . Nevertheless, these changes cause bank (3a3) and f loodpla in eros ion, and, there fore , they pose a hazard to any disposal s i t e on a f loodpla in or terrace (S i t e 3, Fig. 1 ) .

Meander cutoffs (3c3) abruptly change the posit ion of a channel l o c a l l y , but more importantly they steepen the channel at the point of cutoff , forming a nickpoint. There w i l l be channel inc is ion and widening both at the cutoff reach and upstream with concurrent deposition downstream. Hence, d i f f e rent channel changes and hazards can be expected, depend­ing on the location of a s i t e with reference to the cutoff .

Channel avulsion (3c4) i s a r e l a t i v e l y abrupt l a te ra l change of r i ve r pos i t ion , as i t abandons an old course for a new one. The new course w i l l be shorter and perhaps at a lower e levat ion (see capture ( l e i ) above) . This channel sh i f t can s i gn i f i c an t l y a f fect areas that are assumed to be well away from an active channel. I f the channel i s f ree to sh i f t within a va l l ey i t w i l l do so during large f loods .

Channel metamorphosis ( 3d l -5 ) i s a total change of channel morphology as a resu l t of change of discharge, sediment load or baselevel change. Some of the s i gn i f i cant changes that may a f fect s i t e s t a b i l i t y are as fo l l ows :

(3d l ) Stra ight to meandering w i l l cause bank erosion (3a3) and meander growth and sh i f t ( 3 c l )

(3d2) Stra ight to braided w i l l cause bank erosion ( 3a3 ) , the metamorphosis probably is the resu l t of aggradation ( 2 b l , 2)

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(3d3) Braided to meandering w i l l cause narrowing of the channel and meander growth and sh i f t ( 3 c l )

(3d4) Braided to s t ra ight w i l l cause major channel narrowing with an e f fect s imi lar to berming (3a3)

(3d5) Meandering to s t ra ight w i l l cause s i gn i f i cant channel steepening by cutoffs (3c3) with the p o s s i b i l i t y of degradation ( 3a l )

(3d6) Meandering to braided w i l l be associated with e i ther major cutoffs (3c3) or aggradation ( 3 b l ) . Bank erosion w i l l be act ive (3a3)

3.4 Piedmont and Coastal Plain Hazards (Zone 3)

On a coastal p l a in , piedmont p l a in , a l l uv i a l fan, or de l t a , the major hazards are associated with the channel changes discussed above. For example, an increase of discharge, a decrease of sediment load, or a f a l l of baselevel w i l l cause channels to inc i se , dissect ing ( 4a l ) the a l l uv i a l or bedrock surface. Similar change may cause rejuvenation and extension of ex ist ing drainage networks ( l a l , 2) or the development of a new drainage network ( 4 c l ) .

Deposition on the surface by general aggradation ( 4b l ) w i l l eventual ly bury a surface s i t e , but before the burial i s complete, i t w i l l be subjected to increased f looding and potential erosion. Progradation (4b2) i s the growth of a delta or fan. I t i s character i s t ic of a dynamic landform that w i l l be subjected to periods of erosion as i t grows, and although below grade disposal on such a surface appears to be the best s i tuat ion , in f a c t , local incis ion can be important.

On an unconfined surface such as an a l l uv i a l p l a in , delta or a l l uv i a l fan avulsion (4c2) w i l l be common espec ia l l y i f progradation or aggradation is occurring. This channel s h i f t ­ing w i l l render any surface s i t e hazardous. The avulsion can also occur on piedmont or a l l uv i a l plains by capture ( l e i ) .

4. DATA NEEDS

The purpose of geomorphic s i t e assessment i s to locate the s i t e in a landform assemblage and on a landform that w i l l be r e l a t i v e l y s tab le for long periods. In order for the geomorphologist to be able to identi fy potential long-term and short-term geomorphic hazards the fol lowing materials are desi r ab le .

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1) Aerial photographs of s i t e and surrounding area

2) Topographic maps of s i t e and surrounding area

3) Geologic maps of s i t e and surrounding area

In addit ion, information on the fol lowing topics is necessary.

1) Climate - temperature, p rec ip i ta t ion , c l imatic v a r i a b i l i t y and extreme events

2) Hydrology - runoff, sediment y i e l d , stream discharge

and f lood frequency and magnitude

3) Vegetation - type, density, and changes

4) Geomorphology -a. Stream morphology - stream dimensions, gradient ,

pattern, sediment character, longitudinal p r o f i l e , location of bedrock contro ls .

b. H i l l s l ope and scarp morphology - slope inc l ina t ion , p r o f i l e shape, sediment character, evidence of mass movement (creep , slump, rock f a l l s , e t c . ) presence of bedrock or gravel cap rock.

c. Drainage network morphology - drainage patterns, drainage dens i ty , potential for stream capture.

Obviously much of this information may not be read i ly a v a i l a b l e , and cer ta in ly much geomorphic information w i l l have to be obtained from f i e l d invest igat ions . Although this w i l l add to the cost of s i t e development, the cost w i l l be neg l i g i b l e when compared to costs of construction, mining and t a i l i n g s d i sposa l , and much less than the cost of s i t e f a i l u r e .

5. SUMMARY

A great var iety of landform changes can occur natura l ly through time or as a resu l t of changes in runoff, sediment loads or base leve l . A geomorphic evaluation of each s i t e i s required in order to determine i f geomorphic hazards are present and i f they w i l l a f fect s i t e s t a b i l i t y through time.

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Even i f there is no geomorphic hazard, the location of a s i t e in a va l ley or on a plain renders i t susceptible to large f loods . Normally hydro!ogic records are too short to provide information on extreme flood events, and therefore , a geomorphic approach to this problem is a l so necessary [ 3 ] .

REFERENCES

[ 1 ] COSTA, J.E. and BAKER, V.R. , Sur f ic ia l geology, bui lding with the earth: John Wiley, NY (1981).

[ 2 ] SCHUMM, S .A. , The f luv ia l system, Wiley Inters icence, NY (1977).

[ 3 ] COSTA, J .E . , Holocene strat igraphy in f lood-frequency ana lys i s : Water Res. Research T4 (1978) 626.

[ 4 ] LANGBEIN, W.B. ET AL., Annual runoff in the United States : U. S. Geo!. Survey Ci rcu lar 52 (1949).

[ 5 ] LANGBEIN, W.B. and SCHUMM, S .A . , Yie ld of sediment in re lat ion to mean annual p rec ip i ta t ion , Am. Geophys. Union, Trans. 39 (1958) 1076.

[ 6 ] KNOX, J .C . , Responses of r i ve r systems to Holocene cl imates: in Late Quaternary of the United States , 2. the Holocene: (S. C. Porter and H. E. Wright, Eds. ) Univ. Minnesota Press , Minneapolis (1982).

[ 7 ] OLLIER, C D . , Tectonics and landforms: Longman, London (1981).

[ 8 ] TOY, T . J . , H i l l s l ope form and cl imate: Geo!. Soc. America, Bu l l . 88 (1977) 16.

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CONCEPT EVALUATION FOR MANAGEMENT AND DISPOSAL

Page 140: Management of Wastes from Uranium Mining and

Chairman

R.M. F R Y Australia

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MODELLING OF THE UNDERWATER DISPOSAL OF URANIUM MINE TAILINGS IN ELLIOT LAKE

B.E. HALBERT, J.M. SCHARER SENES Consultants Limited, Toronto, Ontario

J.L. CHAKRAVATT I Denison Mines Limited, Elliot Lake, Ontario

E. BARNES Rio Algom Limited, Elliot Lake, Ontario, Canada

Abstract

MODELLING OF THE UNDERWATER DISPOSAL OF URANIUM MINE TAILINGS IN ELLIOT LAKE.

Underwater disposal of uranium mine tailings from the Elliot Lake area operations offers potential advantages in controlling radon gas release, emission of airborne particulate matter, and acid production from pyrites in the tailings. In addition, the proximity of the three active properties, one owned by Denison Mines Limited and two by Rio Algom Limited, to a large deep lake has spurred interest in the concept. It has been estimated that the place­ment of approximately 150 million tonnes of tailings from future planned production would occupy less than 20% of the lake volume. To assess the applicability of the underwater tailings disposal concept, a multi-stage study was developed in conjunction with the regulatory agencies. The most important facet identified for investigation during the first-stage investi­gations was an assessment of the effects of underwater disposal on water quality in the Serpent River Basin watershed. To simulate the effects of underwater disposal, a computer simulation routine was developed and integrated with a water quality model previously developed for the Basin which predicts levels of total dissolved solids, ammonia, dissolved radium-226 and pH. The underwater disposal model component reflects the effects of direct input of tailings into the hypolimnion, the chemical/biological transformation of dissolved constituents in the water column, the reactions of pyritic tailings deposited on the bottom, and the flux of dissolved constituents from the tailings into the water column. To establish site-specific values for the underwater disposal model, field and laboratory experiments were utilized to evaluate rates of pyrite and ammonia oxidation, and pH-alkalinity relationships. The results of these studies and their use in the water quality model are discussed. In addition, the results of two model run simulations are presented.

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Introduction

Uranium mining at Elliot Lake, Ontario, is noted as being the largest such development in existence. Historically, tailings management has involved containment in natural basins and ongoing investigations have focussed primarily on further development of these land-based tailings manage­ment areas.

In recent years, interest has been expressed in the concept of underwater tailings disposal. This interest has stemmed from the consideration that underwater disposal may offer certain advan­tages with respect to the long-term management of uranium tailings. Potential advantages cited for application to the Elliot Lake operations include control of radon gas release, airborne emission of particles and acid production from the oxidation of the tailings pyrite content.

The close proximity of the active mining operations to Quirke Lake, a large deep oli-gotrophic lake in the Serpent River Basin, has also spurred consideration of the underwater dis­posal concept. Quirke Lake covers an area of 2100 ha and has a mean depth of approximately 35.5 m. The lake occupies a total volume of 745 million m 3

and contains three deep sub-basins with depths of 90 m or more. It has been estimated that the placement of approximately 150 million tonnes of tailings in Quirke Lake from future planned produc­tion at the three currently operating properties of Denison Mines Limited and Rio Algom Limited would occupy less than 20 percent of the lake volume.

To assess the applicability of the underwater tailings disposal concept, a multi-stage study was developed in conjunction with the regulatory agencies. One facet identified for investigation during the first stage was an assessment of the effects of underwater disposal on water quality in the Basin during both the operational and post-operational periods. It was agreed early in the study that a water quality model previously developed for the Serpent River Basin would be used in the assessment of downstream effects with suitable modifications added to simulate the effects in Quirke Lake of underwater tailings disposal. The basic model allows the simulation of four constituents, total dissolved solids (TDS), ammonia, dissolved radium-226, and pH, at 14 key

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locations in the Basin on a monthly basis over an extended time frame. Details concerning the basic model are given elsewhere [1].

Underwater Disposal Model Structure

To simulate the effects of underwater tailings disposal, it was necessary to develop a model component which reflects: the direct input of tailings into the hypolimnion; the chemical/bio­logical transformation of dissolved constituents in the water column (both epilimnion and hypo­limnion) ; the reactions of pyritic tailings deposi­ted on the bottom; and, the flux of dissolved matter from the tailings into the water column. Differential equations describing these water quality aspects are given as follows:

Epilimnion

dC EQ.C. (Q + Q ) Q, e 1 l o p h — — = + r - — — r + — C (1) dt V e V e V U h K 1 )

e e e Hypolimnion

dC ZQ C J A Q Q

h,t h,t h,t h,t Where:

C = constituent concentration in the epilimnion e (g/m 3)

= constituent concentration in the hypo­limnion (g/m 3)

C i = constituent concentration in the fresh­water inflow (g/m 3)

C T = constituent concentration in tailings pore-water (g/m 3)

Q i = freshwater inflow (m 3/month)

Q Q = lake outflow (m 3/month)

Q e = water exchange between epilimnion and hypo­limnion (m 3/month)

= water exchange between hypolimnion and epilimnion (m 3/month)

Q™ = flow of tailings (m 3/month)

Page 144: Management of Wastes from Uranium Mining and

J

r

V

r

e

e

h

h, t

f

volume of the epilimnion, top 10 m of water (m 3) volume of the hypolimnion, function of time (m 3) rate of constituent formation or disappea­rance in the epilimnion (g/m3- month) rate of constituent formation or disappea­rance in the hypolimnion (g/m3- month) flux of dissolved constituents from tailings (g/m2- month) area of lake bottom covered with tailings, function of time (m 2)

Solution was sought by appropriate transfor­mation of variables to yield homogeneous differen­tial equations. The equations were then integrated to give predictions on a monthly basis.

Equations (1) and (2) were applied directly to modelling ammonia (as N ) , total dissolved solids, and dissolved radium-226. To model the pH, however, it was necessary to define a net cation concentra­tion (Al in equivalents/m 3). This parameter takes into account the concentration of those water quality constituents, which possess pH-independent ioniza­tion states at expected pH values in the lake system.

Al = [(Na +) + (K +) + 2(Ca ) + 2(Mg )] - [(CI ) + (NOj) + 2 ( S C V - ) ]

Al = net cation concentration (equivalents/m 3) ( ) = concentration of a constituent (moles/m 3)

The net cation concentration expressed by equation (3) is affected by ammonia oxidation to nitrate in the water column, the flux of sulphate resulting from pyritic sulphur oxidation at the bottom of the lake, and acidic input from preci­pitation. Thus, acid generation in the lake implied a time dependent decline of the quantity, Al. The net cation concentration, Al, was modelled according to equations (1) and (2), and the pH was calculated from the following ionic equilibrium:

(H +) + (Fe (OH) X) + 2(Fe(OH) 2 +) + 3 ( F e 3 + ) + (NH.. + )

Where:

+ Al = (HC0 3 ) + (OH ) ( 4 )

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With exception of the quantity Al, each term in equation ( 4 ) can be expressed as an explicit function of pH. Since the equation is a complex function of pH, the solution required iteration utilizing the Newton-Raphson technique [2].

To establish site-specific parameter values for the model, a series of field and laboratory experiments were undertaken. In particular, the rates of pyrite and ammonia oxidation, and the pH-alkalinity relationship were studied in detail. The results of these studies and their use in the water quality model are discussed below.

Oxidation Rates in Pyritic Deposits

The oxidation of pyritic substances is known to be a function of a number of parameters including ore composition, particle size, temperature, pH, presence of chemolithotrophic bacteria, and oxygen concentration. A model for pyrite oxidation has been provided as follows [3]:

In pyritic tailings, oxygen is regarded as a limiting reactant [ 4 ] . Thus, active oxidation of pyrites in lake deposits takes place in a zone located at the tailings-water surface. The stoichiometry of the oxidative process is as follows:

2FeS 2 + 7 .5 0 2 + 7H 2 0 — 2Fe(OH) 3 (s) + 8 H + + 4 S O i t2 "

Fe(0H) 3(s) + H + ^1 Fe(OH ) t + H 2 0 Fe(OH) 3(s) + 2 H + X F e ( O H ) 2 + + 2H 20 Fe(OH) 3(s) + 3 H + X F e 3 + + 3H 20

The differential equation describing the oxy­gen concentration at some depth, z, in the tailings, neglecting infiltration rates, is given by:

2 —

~ 1 Fe (III) F e ( O H ) 3 (s)

<S(02) 6t = D, T 6z 2 1.88 R p (5)

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Since the oxidation process is expected to proceed for long time periods at slow rates, a steady state solution:

( i . e . ^ i = 0 ,

is not unreasonable. Assuming steady state, the sulphate flux (moles of sulphate produced/m 2•month) becomes:

-r = !!2L_ d(0 2) u s 1.88 dz

z = o

Where:

C = oxygen concentration at the interface (moles/m 3)

= diffusivity of 0 2 through tailings (m 2/month) 2 —

J g = sulphate flux (moles SO^ /m 2* month)

(0 2)= concentration of oxygen (moles/m 3)

z = depth into the tailings (m) 2 —

R g = sulphate production rate (moles SO^ /kg*month)

p = bulk density of tailings (kg/m 3) Values of the parameter R s were derived from

tailings oxidation experiments using Denison and Rio Algom tailings containing 2 to 4% sulphide _ 3

sulphur. Sulphate production rates of 1.11 x 10 to 3.78 x 1 0 - 3 moles SO^ 2"/(kg.:month) were obtained at a temperature of 4°C, the likely in situ tailings temperature at the bottom of Quirke Lake.

Solution of equation (6) was sought assuming an oxygen diffusivity of 6.8 x 1 0 ~ 6 c m 2 / s (1.8 x 10~ 3 m 2 / m o n t h ) , a dissolved oxygen concentration at the tailings-water interphase of 10 mg/L (3.1 x 1 0 ~ 1 m o l e s / m 3 ) , and an average tailings bulk density of 1.28 x 10 3 kg/m 3. The sulphate produc­tion flux was assessed to range from 1.4 x 10~ 2 to 2.6 x 10~ 2 moles S O 4 2 ~ / ( m 2 • month) for the range of R s values established from the laboratory tai­lings oxidation experiments.

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Since the tailings would be covered by over 30 m of hypolimnetic water in Quirke Lake, the effect of tailings oxidation on the sulphate con­tent of the lake water was assessed to be insigni­ficant. For example, a sulphate export flux of 2.6 x 10~ 2 moles SCH 2~/(m 2 -month) would result in no more than a 6.7 g/m 3 increase in the sulphate content of Quirke Lake assuming the oxidation rate is maintained indefinitely.

The limited extent of tailings oxidation under water cover as indicated by the analysis presented above, is in agreement with observations made in the field. Since 1975, a number of experimental, lined pits filled with 200 tonnes of tailings from the Quirke Mine have been monitored by Rio Algom Limited to measure the effects on tailings porewater and runoff water quality [5]. Tailings left uncovered became acidic (pH = 3.4) after three years. Tailings submerged under a water cover, however, showed little or no evidence of pyrite oxidation. The initial pH of 7.6 in the water overlying the tailings stabilized at 7.3 while the sulphate level remained fairly constant over the five year monitoring period.

Nitrification Rate

The importance of nitrification with regard to nitrogen transformation in lakes has been well documented [6]. The oxidation is largely confined to suspended bacteria in the water column and well oxidized littoral zones [7]. Chemolithotrophic bacteria, particularly Nitrosomonas and Nitrobacter have been recognized as the most significant, although not exclusive, nitrifying organisms; the former oxidizes the ammonium ion (NH^"1") to nitrite ( N 0 2 ~ ) , while the latter converts nitrite to nitrate ( N 0 3

_ ) [8]. According to theory and supported by previous

experimental observations, the nitrification rate should become constant (steady state) provided pH, temperature, and ammonium ion concentration remain constant [9]. Combining the effect of these para­meters, the following functional relationship has been derived for the rate of ammonia oxidation [1]:

r N H 3 = - V

exp (AE/293R -AE/RT) 1 + [H-n/Ki x (7)

K : + c. m

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Where:

V = maximum rate of nitrification, i.e. nitri­fication rate at 20°C, pH = 8.0, ammonia concentration unlimiting (g/m 3-month ammonia-N)

AE = Arrhenius activation energy (J/mole)

R = universal gas constant (J/K)

T = absolute temperature (K) Ki = half reaction rate constant of ammonia oxi­

dation at acidic pH values cvrtj

= ammonia concentration (g/m 3 ammonia-N) JNrl 3

[H +] = hydrogen ion activity [H +] = 10 ^ H

K = Monod (Michaelis-Menten) half saturation constant (g/m 3 ammonia-N)

A series of nitrification tests were performed with water collected from four locations in Quirke Lake. The results are summarized below.

Parameter/Method of Analysis

Arrhenius Activation Energy (AE)/ Linear regression analysis

Maximum Nitrification Rate (V) / Linear regression analysis of steady state nitrification data

Mean (or Maximum Likelihood) Value Range

66.4 kJ/mole

0.62 g/m 3•month (NH 3-N)

60.4 to 72.4 kJ/mole

0.41 to 0.96 g/m 3 tmonth

pKi/ 6.4 6.0 to 6.8 Baysian Statistical Inference (Posterior Likelihood Distribution)

In the water quality model, the rate of ammonia oxidation was evaluated each month as a function of ammonia concentration, temperature, and pH.

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At present, the major source of net cation (i.e. decline due to anion production) is the for­mation of nitrate (N0 3~) from ammonia oxidation. Since ammonia oxidation is pH dependent, this source term is also a function of pH. The rate equation expressed in equivalent/m 3, is given by:

dt dt 2 The calculated coefficient (5 x 10" J is 70 !

of the stoichiometric value of 7.14 x 10" . The value of the coefficient was based upon observed analytical results of nitrate yield and total alkalinity destruction, which equalled 5 mg/L CaC0 3 alkalinity/mg of ammonia.

Bicarbonate - pH Relationship

In Precambrian Shield lakes, the bicarbonate buffering capacity (alkalinity) is characteristi­cally low due to the lack of calciferous rock. Several alkalinity titration curves were derived using Quirke Lake water and combined with field measurements of alkalinity to provide a sufficient pH spread. Linear regression analysis of the data base yielded the following model for calcu­lating bicarbonate concentration:

[HC0 3~] = 1.5 x 1 0 " 8 x 1 0 0 * 5 9 p H (9)

Where:

[HC0 3~] = bicarbonate content (moles/L)

correlation coefficient - 0.96.

Total Dissolved Solids and Radium-226 Mass Transfer

Submerged tailings may become the source (or sink) of radium-226 and total dissolved solids (i.e. calcium sulphate) resulting from dissolution/ precipitation reactions. The general equation describing solubilization is given by the following:

J f = k L ( C * " C h , t ' ( 10 )

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Where:

= flux of dissolved constituent into the water column (pCi/m 2•month or g/m 2-month)

k T = mass transfer coefficient (m/month) Li

C* = equilibrium concentration of the consti­tuent in porewater (125 000 pCi/m 3 for dissolved radium-226 and 2410 g/m 3 for total dissolved solids)

t = concentration of the constituent in the ' hypolimnetic waters (pCi/m 3 or g / m 3 ) .

The mass transfer coefficient, in turn, was related to the diffusivity (D), the eddy velocity (u), and the depth of water column (h) in the following manner:

(11)

Assuming a diffusivity of 7 x 1 0 ~ 6 c m 2 / s (1.8 x 10~ 3 m 2 / m o n t h ) ; an eddy velocity of 0.5 cm/s (1.3 x 1 0 k m/month) and a hypolimnetic water depth of 30 m, the mass transfer coefficient (kL) was estimated to be 0.5 m/month. Consequently, the following relationships were used for calcu­lating the mass flux from the tailings of dissolved radium-226 (in pCi/m 2-month):

J R a = 0.5 (125 000 - C h t ) (12)

and calcium sulphate (in g/m 2«month):

J T D S = 0.5 (2410 - C h ; t ) (13)

Simulation Results

Computer simulations encompassing nine manage­ment scenarios were carried out to investigate the effects on water quality in Quirke Lake and down­stream of several key factors identified for the study. Only the results on Quirke Lake water quality for two scenarios are discussed herein.

The results of Scenario 1 demonstrate the effect of passing all fresh water flow from a watershed of 307.8 km 2 through Quirke Lake, whereas, the results for Scenario 2 reflect the

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7-5

6-5

r 5-5 a.

4-5

3-5 I

4

Z

J 3

E 2

z 0

SCENARIO No. I

3 -

SCENARIO No. 2 7 • • 1 1 1 • I • 1 1 1 1 1 1 1 1 • • 1 1 1 I I I I I I I . I I 1 1 1 1 1 I I

7-5

6-5

5-5

4-5

10 15 2 0 2 5 3 0 3 5 4 0 4 5 5 0 55 60 3-5

\- SCENARIO No. 2

M I L L 1 1 1 1 1 1 1 1 1

i- SENARIO

11 ? iTm I 'u n 1 1 1 1 1 1 1

No. 1

1 1 1 1 1 1 1 1 1 • 1 1 1 I 1 1 '

0 5 10 15 20 25 30 35 40 45 50 55 60

2100

SCENARIO No. 2

0 5 10 15 20 25 30 35 40 45 50 55 60

400

300

200

100

SCENARIO No. 2

0 3 10 15 20 25 30 33 40 45 50 55 60

ELAPSED TIME IN YEARS

Fig.l. Quirke Lake epilimnion water quality simulation profiles.

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effect of reducing the fresh water flow to Quirke Lake by 80% through the implementation of diversion works. Conditions common to the two scenarios which are reflected in the simulation results presented on Figure 1 for the four constituents modelled, include:

i) between years 0 and 8 the results reflect the influence of the tailings effluents from the existing land-based tailings management areas and are indicative of current water quality in Quirke Lake;

ii) commencing in year 9, underwater disposal of mill tailings effluents from the three operating properties is initiated followed by shutdown of two mills in years 15 and 16 and the third mill in year 35;

iii) commencing in year 9 also, the milling pro­cesses employed at two of the mills were assumed to be converted to an alternative process to allow assessment of the effect of reducing the effluent ammonia loading on Quirke Lake water quality;

iv) between years 36 and 59, the results indicate the effect of tailings deposited on the bottom of Quirke Lake during the post-operational period.

The mill discharge tailings characteristics assigned to each operation as input to the model simulations were as follows: total dissolved solids of 3400 to 3900 g/m 3; ammonia (as N) of 8 to 17.5 g/m 3; dissolved radium-226 of 1 250 000 to 1 600 000 pCi/m 3; and net cation content of -0.20 to -0.60 equivalents/m 3. The ammonia levels are indicative of the minewater contribution to the mill dis­charges at the three operating properties.

The results for Scenario 1 indicate a rapid decline in the ammonia level in Quirke Lake from approximately 3.0 to 0.1 g/m 3 following year 9 when the ammonia loading is reduced. The pH is seen to recover from a level of 6.0 to between 6.5 to 7.0 coincident with the reduction in the ammonia level. In contrast, the ammonia level rises in Scenario 2 once underwater tailings dis­posal commences in year 9 and declines very slowly

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during the post-operational period. The slow ammonia depletion rate may be attributed to two factors: less dilution due to the diversion of 80% of the fresh water flow from Quirke Lake; and, minimal ammonia oxidation due to the unfavourable pH level. The pH decline, which stabilizes at 4.5 during the post-operational period, is apparently due to: the reduction of alkalinity input to Quirke Lake as a result of the diversion of fresh water; and, the acid production from the oxidation of ammonia and the pyritic content of tailings depo­sited on the lake bottom.

The total dissolved solids and dissolved radium-226 profiles for Scenarios 1 and 2 indicate a rise on startup of underwater tailings disposal. Whereas the levels for both constituents stabilize in Scenario 1 during the operating period, the levels increase steadily in Scenario 2 to consi­derably higher levels. The difference noted between the two scenarios again reflects the influence of diverting fresh water around Quirke Lake as simulated in Scenario 2. In both scenarios the total dissolved solids profiles are observed to remain at a high level during the post-opera­tional period, reflecting the flux of total dis­solved solids from the tailings deposited on the lake bottom. The dissolved radium-226 profiles, in contrast, decline during the post-operational period. This observation indicates that the flux from the bottom tailings deposit is a less significant source of radium than total dissolved solids.

As previously stated, several other factors were also addressed in model simulations^ The information contained in these simulations provides the mining companies and regulatory agencies with a sound basis for reaching decisions on future tailings management at the Elliot Lake operations. The status of underwater tailings disposal, at this time, has not been resolved.

REFERENCES

[1] HALBERT, B.E., IBBOTSON, B.G., SCHARER, J.M., "Development and Application of a Water Quality Model for Use in an Environmental Assessment", Water Poll. Res. J. of Canada Vol. 15, 1(1980)59-72.

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[2] MOREL, F., MORGAN, J.J., Environmental Science and Technology, 6(1972)58-72.

[3] STUMM, W., MORGAN, J.J., Aquatic Chemistry, John Wiley and Sons, Inc. (1981)

[4] RICCA, V.T., SCHULTZ, R.R., "Acid Mine Drainage Modelling of Surface Mining",(Proceedings of the First International Mine Drainage Symposium Denver, Colorado) (ARGALL, G.O. Jr., BRAWNER, C O . , Eds.), Miller Freeman Publications Inc., San Francisco ( 1 9 7 9 ) 6 5 1 .

[5] MOFFETT, D., "Ultimate Disposal of Uranium Tailings, Part 2: The Pyrite Free Tailings and Flooded Pit Experiment", Internal Research Report R80-8, Rio Algom Limited (1980).

[6] WETZEL, W.B., "Limnology", W. B. Saunders Co., (1975) 166.

[7] CHEN, R.L., KEENEY, D.R., KONRAD, J.G., "Nitrification in Lake Sediments", Jour. Environ. Quality, 1(1972)151.

[8] KUZNETSOV, S.I., "Recent Studies on the Role of Microorganisms in the Cycling of Sub­stances in Lakes", Limnol. Oceanogr. 13(1968)11.

[9] LOEHR, A.C., "Nitrogen and Phosphorus, Food Production, Waste and the Environment", Ann Arbor Science, (PORTER, K.S., ed.) (1975)219.

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HYDROGEOLOGICAL INVESTIGATIONS AND EVALUATION OF THE STANLEIGH MINE TAILINGS IMPOUNDMENT SITE

J.M. BOYD, T.G. CARTER Golder Associates, Toronto, Ontario

R.A. KNAPP SENES Consultants Limited, Toronto, Ontario

K.B. CULVER Rio Algom Limited, Elliot Lake, Ontario, Canada

Abstract

HYDROGEOLOGICAL INVESTIGATIONS AND EVALUATION OF THE STANLEIGH MINE TAILINGS IMPOUNDMENT SITE.

One of the most critical aspects of site investigation for uranium mill tailings facilities is the potential for contaminated groundwater seepage from the impoundment. This paper illustrates the hydrogeological investigation and evaluation process which is currently used to address this question in the Elliot Lake mining area in Ontario, Canada. In particular, the procedures are illustrated by reference to the proposed Crotch Lake Basin which will hold 70 million tonnes of tailings from the recommissioned Stanleigh Mine. The Crotch Lake Basin is rock rimmed and, as a result of metamorphic recrystallization, the intact rocks are intrinsically impermeable. Consequently, potential groundwater seepage from the basin is controlled by joints and other fractures in the rock. Over most of the area, these geological structures are relatively widely spaced and only partly interconnected, and the equivalent hydraulic conductivity of the rock mass is low. It is only in areas of intense fracturing associated with major geological structures (i.e. faults) that hydraulic conductivities and hence seepage fluxes become significant. The investigation phase incorporated aerial photo-interpretation, and topographic and surface geological mapping to identify targets for more detailed evaluation. This phase finished with cored borehole drilling, in situ hydraulic testing, and installation of multi-level piezometers and groundwater geochemistry sampling points. The results of the investigations were used to construct a series of two- and quasi three-dimensional computer models of present groundwater flows which were adjusted until they satisfactorily simulated known surface water occurrences and groundwater conditions monitored in the boreholes. Subsequently, model boundaries were adjusted to reflect changed conditions resulting from tailings deposition in order to enable projections to be made of groundwater flows over the life of the facility. This data was in turn used to examine the impact of see­pages on water quality in the surrounding lakes and streams.

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1. INTRODUCTION

The Elliot Lake Mining camp in northern Ontario, Canada went into initial production in 1955 and by 1958 , consisted of twelve mines with eleven mills. In 1959 , the United States Atomic Energy Commission to which most of the production was contracted announced that it would not extend the contracts beyond 196 2. Consequently, by late 1961 most of the mines were closed. In that short period of operation, the mines had generated approximately 40 million tonnes of tailings which had been depos­ited by discharging into nearby lake basins.

During the 1960's, mining activities continued on some of the properties in the area, and by 19 78 when the market for uranium had recovered due to the requirements of power utilities, a total of 100 million tonnes of tailings had been generated. The increased demand for uranium lead to a require­ment to reopen a number of the old mines and expand a number of the others. The projected tailings to be stored in future in the Elliot Lake area amounts to some 300 - 550 million tonnes to be placed in a combination of existing and future storage areas.

This paper outlines the steps which are now a routine part of the process for investigating, evaluating and licensing one such new tailings facility.

2. INVESTIGATION

The Crotch Lake Basin is situated 3 km south of the town of Elliot Lake (see Figure 1 ) . The basin will be used to store approximately 70 million tonnes of tailings from the recommissioned Stanleigh Mine. The site which covers approximately 36 km2 is characteristic of typical Canadian Shield topo­graphy with rock knolls and ridges divided by lower areas containing swamps, lakes and streams. Generally, the metasedimentary basement rocks which form the area, are exposed on all highlands; and overburden deposits, consisting predominantly of fluvial or outwash silty sands and gravels of glacial origin are restricted to isolated pockets in topographic lows. Site elevation varies from a low of 338 m in the lake bottom to an average lake surface level

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FIG.l. Topography and major geological structures of the Crotch Lake area.

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of 357 m for Crotch Lake to a high of 433 m to the northwest of the lake. The typical topography is shown on Figure 1.

Because of the excellent rock exposure and the isolated nature of the overburden deposits, aerial photo-interpretation was extensively used in the early phases of site investigation. Based on several past investigations in the area it is considered that when intact, the metasedimentary rocks which form the tailings impoundment are intrinsically impermeable (< 1 0 " * 2 m/s) and potential groundwater flow through the bedrock is controlled by joints and fractures in the rock mass .E2! ] site investigation of the Crotch Lake Basin was therefore directed towards locating significant fractures, characterising their hydr­aulic properties by testing in the field and eval­uating their interconnection, orientation and continuity by means of geological interpretation techniques.

Geological maps compiled on the basis of aerial photo-interpretation were taken into the field in order that significant features could be located and examined in situ. Detailed field mapping of lithology and gross structure was supplemented with joint mapping of typical areas, including assessment of joint orientations, apertures, fillings, continuities and roughnesses.

The site is located on the south limb of a large geological structure known as the Quirke S y n c l i n e . T h e syncline axis strikes NW-SE and is located about 2 km north of the area of interest. The beds at the site dip generally at 10 to 2 0 ° to the north and northwest and consist predominantly of lightly metamorphosed polymictic conglomerates. Feldspathic quartzites, dolomitic siltstones and limestones also occur in the parts of the site.

In addition to these metasedimentary rocks, extensive diabase dykes and sills outcrop in the vicinity of the site.

In areas where overburden cover or the lake itself obscured the bedrock, surface geological mapping was supplemented with geophysical investi­gations. These generally comprised refraction

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TABLE I

SUMMARY OF HYDRAULIC CONDUCTIVITIES USED IN HYDROGEOLOGICAL MODELLING

ROCK TYPE HYDRAULIC CONDUCTIVITY m/s

ROCK TYPE

(Range) (Best Estimate)

Unstructured Metasedimentary Rock

Near surface zone At depths < 12 ra

Deep zone Depths 12 m - 90 m

1 x 10~ 5 - 5 x 10~ 7

2 x 10~ 6 - 8 x 10~ 8

1 x 10~ 6

2 x 10~ 7

Diabase Sills K (E-W) max K . (N-S) nun

5 x 10" 6 - 3 x 10~ 8

-7 -9 5 x 10 - 3 x 10

3 x 10~ 7

3 x 10" 8

Major Fault Zones K max (parallel to fault)

K . m m (perpendicular to fault)

1 x 10~ 5 - 8 x 10~ 7

8 x 10~ 6 - 5 x K T 7

5 x 10~ 6

-10* 5 x 10

Minor Fault Zones & Diabase Dykes

K max (parallel to fault)

K . m m (perpendicular to fault)

1 x 10~ 5 - 8 x 10" 8

-6 -8 8 x 10 - 5 x 10

2 x 10" 6

-10* 5 x 10

* Based on hydraulic head measurement computations from piezometers installed across typical fault zone.

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seismic and proton magnetometer surveys on the land area and reflection seismic techniques over water. The land geophysical investigations were also used as an aid in locating later investigation boreholes and for verification of the integrity of the rock rim of the basin.

Once the major structures (primarily faults and dykes) were identified by means of aerial photo-interpretation and field mapping, boreholes were drilled to intersect the features. In addition to providing core for geological identification purposes, these holes allowed the rock mass hydr­aulic conductivity to be evaluated by means of falling head water tests carried out through the drill string using inflatable wireline packers. In general, the holes were tested as they were drilled in order to minimize fracture plugging with drill cuttings and to minimise problems of packer leakage. Tests were typically carried out after every 6 m of advance of the hole.

A total of 1400 m of NQ wireline drilling was required by the investigation with 200 bore­hole packer tests. The test results generally showed that the area could be divided into a number of discrete hydraulic regimes based on hydraulic conductivity as summarized on Table I.

A large part of the Crotch Lake area is com­prised of intact bedrock with only sporadic frac­turing. In the vicinity of diabase dykes and small faults one or more zones of higher conduc­tivity were found to be common. Frequently the core of dyke or sill-like bodies exhibited low conductivities, however the upper portions of such dykes and their margins were generally found to be more weathered and of higher conductivity, (see Table I ) . In addition, conductivity values for these dykes and sills and for the major faults were found to be anisotropic. Such anisotropic characteristics, based on geological orientation data were incorporated into the modelling.

On completion of drilling of the site investi­gation boreholes, most of the holes were instrumented. A total of 52 piezometers were installed in 23 bore­holes. In some locations the instruments consisted of ordinary piezometers, with three or four installa-

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TABLE II

TYPICAL BEDROCK GROUNDWATER CHEMISTRY AT CROTCH LAKE

CONSTITUENT TYPICAL RANGE

PH 6 .5 - 7.5

Calcium 20 - 60 Magnesium 3 - 7 Sodium 5 - 20 Potassium 1 - 4 Chloride 1 - 20 Sulphate 20 - 100 Silica 3 - 8 Alkalinity 50 - 150 (as HC0 3)

Radium- 226 (pCi/L) 2 - 12

Iron 0 . 01 - 0.2 Manganese 0 . 01 - 0.2 Copper 0. 005 - 0.02 Lead 0 . 005 - 0.02 Zinc 0. 02 - 1.0

Nitrate (as N) 0. 2 - 0.6 Ammonia (as N) 0. 4 - 2.0

All concentrations in mg/L unless otherwise noted.

tions per hole packed off at different levels, In other areas, special, chemically inert piezometers were installed to permit the collection of ground­water samples for chemical analyses.

For reliable geochemical monitoring of ground­water it is essential that the drillwater introduced into the formation be identified. Accordingly, the drillwater was tagged with sodium chloride.

In addition to tagging the drillwater it was also necessary to carefully select the materials

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T Y P I C A L G E O L O G I C A L S E T T I N G

MODELLED GROUND

FINITE E L E M E N T M E S H

LAYER 0 WEATHERED SURFACE ROCK: INTENSELY FRACTURED, RELATIVELY HIGH PERMEABILITY

LAYER (| ) UNWEATHERED ROCK: VIRTUALLY UNFRACTURED, MODERATE TO LOW PERMEABILITY

FIG.2. Finite element mesh for fractured rock environment at Crotch Lake.

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to be placed in the boreholes in order to ensure that they did not react with or adsorb any of the constituents to be monitored. The special ground­water sampling piezometer tips were constructed of porous plastic set on CPVC pipes after labora­tory experiments demonstrated that these tips did not interfere with reliable sampling of Radium-226. Within the boreholes the required sampling interval was backfilled with a clean silica sand filter and the holes were sealed off by thick sections of bentonite. Once installed, these tips provided data on both groundwater chemistry and hydraulic head. The natural groundwater which occurs in the bedrock around Crotch Lake has generally low con­centrations of dissolved constituents, (see Table I I ) . The pH of the groundwater typically ranges from 6.5 to 7.5. The natural bedrock groundwater has low activities of Radium-226 ranging from 2-12 pCi/L.

The piezometer readings generally showed that because of the geological and topographical charac­teristics of the site, groundwater heads mirrored the form of the surface topography suggesting that flow is generally towards Crotch. Lake from the surrounding topographic highs with seepage out of the impoundment being restricted to major structural geological features intersecting the basin.

3. EVALUATION

On completion of compilation of the field data, mathematical simulation of the existing groundwater flow pattern was undertaken to enable a projection to be made of the impact of future tailings deposi­tion on both the pattern and quantity of groundwater flows.

Basin simulation was carried out using a quasi three-dimensional numerical model of groundwater flow while selected seepage pathways were compre­hensively studied using two-dimensional models. Details of these models and their capabilities are presented elsewhere.£43 The three-dimensional model allows modelling of regional groundwater flow systems in homogeneous or layered geological materials of different hydraulic conductivities, (see Figure 2 ) . The thickness and position of the geological forma­tions and the major structural features (faults) as

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FIG.3. Equipotentials for current groundwater conditions showing summary of groundwater flows.

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well as the hydraulic conductivity of those forma­tions and features as utilized in the model are specified on the basis of known or "best estimate" values deduced from field investigations of the actual groundwater flow system.

Based on the geological and topographic input data as well as known head conditions under lakes and swamps, the program computes the hydraulic head at specified locations (nodes) and if required provides elevation contours (equipotentials) of hydraulic head. Using the computed gradients and the hydraulic conductivity of the materials, the program also computes the flow entering or leaving the model at specified points in the finite element mesh. These flows can then be summed for the nodes bounding elements of interest in order to determine the total flow into or out of a particular area such as the Crotch Lake Basin.

The model was initially set up to simulate present conditions. The projected hydraulic heads at various points were compared with installed piezometers. Wherever substantial differences occurred, field results were reviewed carefully and the model adjusted to give a better agreement with known conditions. Because of low conductivity and appreciable topographic variations, the piezo-metric levels produced by the model were very sensi­tive to the values of infiltration used.

Once the model was ajusted to faithfully mirror the present conditions (refer groundwater equipoten­tials shown on Figure 3 ) , the topography and dam drainage rearrangement associated with the proposed tailings deposition were altered to ascertain what would happen once additional tailings were deposited in the basin.

The results of the modelling indicated that for existing conditions, groundwater seepage is generally towards the basin from the surrounding higher ground and perched lakes and only nominal groundwater seepage is leaving the basin through two fault controlled valleys (see Figure 3 ) . Under existing conditions, total seepage through the rock into the basin is estimated to be of the order of 11 L/s with total seepage out of the basin being less than about 0.5 L/s.

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FIG.4. Summary of groundwater flows into and out of Crotch Lake under future conditions following additional tailings deposition.

Following development of the tailings area to the present design capacity, the pattern of ground­water flow changes somewhat (see Figure 4 ) . The total seepage into the basin from the north is expected to decrease to about 8.6 L/s. However, seepage out of the basin through the two fault valleys is predicted to increase to about 1.6 L/s towards the south towards Sheriff Lake and to 0.9 L/s to the east towards McCabe Lake. Furthermore, current nominal groundwater flow into the basin from the

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western side of the lake will reverse and will flow away from Crotch Lake at a rate of about 1.2 L/s towards Strouth Lake. Some nominal seepage (0.1 L/s) is also expected to exit to McCabe Lake along another fault located at the east side of Crotch Lake.

On the basis of the results of the geological mapping and 3-D model predictions, specific two-dimensional finite element simulations were carried out along the seepage pathways of most concern. These models were developed to determine the possible subsurface flow paths associated with any seepage. The results of this modelling show that groundwater flow patterns in the bedrock occur as a complex of local, small scale, shallow groundwater systems even within the more permeable fault zones. Flow preferentially takes place within the upper perme­able zone of the rock and tends to occur directly between adjacent lake bodies.

4. IMPACT ASSESSMENT

With the current state-of-the-art in hydro-geological and geochemical modelling, precise predictions of seepage fluxes and characteristics are not practicable, particularly on a local scale. Similarly, precise quantitative modelling of the variations in the flux and quality of the seepage with time is not currently possible. Accordingly, the assessment of the potential effects that see­pages from Crotch Lake would have on surrounding water bodies was carried out on the basis of several extremely conservative assumptions. It was assumed that the chemistry of the groundwater would remain virtually unchanged in its passage from the tailings through the ground to its point of emergence and mixing with surface water. In fact, retardation of radionuclide migration in groundwater flowing through porous media is well documented. While there is less direct evidence, similar retardation is anticipated for groundwater flowing through fractured rock, particularly in fault zones where clay rich gouge materials are present.

Furthermore, assessment was based on pessi­mistic assumptions of tailings porewater chemistry. Seepage quantities several times greater than the model predicted results were utilized to reflect

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TABLE III

SHORT-TERM AND LONG-TERM GROUNDWATER SEEPAGE QUALITIES EXITING FROM TAILINGS BASIN AND PREDICTED

TO OCCUR AT RECEIVING WATER BODIES

WATER QUALITY SEEPAGE CHEMICAL EXISTING PREDICTED PREDICTED SOURCE CONSTITUENT CONDITIONS SHORT LONG

TERM TERM

Tailings TDS - 2300 < 2000 Basin Sulphate - 1600 <1400 (Crotch Ammonia - 3 < 1 Lake) Radium-226 - 500 125

RECEIVING WATER BODY

McCabe TDS 144 147 147 Lake Sulphate 95 97 97 (east of Ammonia 0.1 0.1 0.1 Crotch Lake) Radium-226 7 7.7 7.2

Elliot TDS 80 84 83 Lake Sulphate 31 34 34 (south of Ammonia 0.3 0.3 0.3 Crotch Lake) Radium-226 2 2.8 2.2

Strouth TDS 40 58 55 Lake Sulphate 16 28 27 (west of Ammonia 0.1' 0.12 0.1 Crotch Lake). Radium-226 3 6.9 4.0

All concentrations in mg/L except Radium-226 in pCi/L. Federal drinking standard for Radium is max. 27 pCi/L.

upper bound estimates and, in addition, minimum surface inflow rates were assumed for the receiving bodies of surface water.

Taking cognizance of all of these conservative assumptions, the study determined that environment­ally important chemical constituents, including Radium-226 activities (the critical component) in

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the receiving water bodies, would only increase marginally in the short and long term as shown on Table III. However, it should be noted that nowhere are the levels raised to a point where they would impair the quality of any major receiving stream to such an extent that it would make it unacceptable as a water supply.

5. CONCLUSIONS

The steps which are now routinely carried out in evaluating the groundwater seepage impact of new or expanded tailings facilities in the Elliot Lake area have been described. While it is recog­nized that there are several important uncertainties associated with the prediction of groundwater seepage fluxes and characteristics particularly in a fractured rock environment, the example of the Crotch Lake Basin study presents a completely integrated geological/ numerical approach to the problem.

In view of the possible imprecision of the simulation process, groundwater gradients and sur­face water qualities will be monitored in areas of potential seepage out of the basin during milling operations. The results of such monitoring will: (i) serve as a measure of the performance of

the tailings impoundment; (ii) be invaluable in reassessing local geologi­

cal and hydrogeological conditions of any areas of more significant seepage than predicted; and

(iii) assist in the design of appropriate remedial measures should such measures prove necessary.

REFERENCES

m DAVIS,J.B., Knapp, R.A., Sinclair, K.W., "Seepage Groundwater Control at Elliot Lake Uranium Projects", First International Mine Drainage Symposium, Denver, Colorado, (1979).

121 PULLEN,. P.F. and Davis, J.B., Description of the Panel Mine Tailings Area. NEA Workshop on "Application of Geomorphology to Engineering of Uranium Mill Tailings", Colorado State University, Fort Collins, Colorado, (1981).

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[31 ROBERTSON, J.A., Geology of Township 149 and Township 150, Ontario Department of Mines, Geological Report 57, 162 pp, (1968).

C4D MARLON-LAMBERT, J.M., Manoel, P.J., and Friday, R.G., "The Development of a General Groundwater Computer Modelling Package", Hydrology and Water Resources Symposium, Institute of Engineers, Perth, Australia, Symposium Preprints, p.41-48, (1979).

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CLOSE-OUT CONCEPTS FOR THE ELLIOT LAKE URANIUM MINING OPERATIONS

K.B. CULVER Rio Algom Limited, Elliot Lake, Ontario

JX. C H A K R A V A T T I Denison Mines Limited, Elliot Lake, Ontario

D.M. GORBER, R.A. KNAPP SENES Consultants Limited, Toronto, Ontario

J.B. DAVIS Golder Associates, Toronto, Ontario, Canada

Abstract

CLOSE-OUT CONCEPTS FOR THE ELLIOT LAKE URANIUM MINING OPERATIONS. In the Elliot Lake area, approximately 100 million tonnes of tailings have been generated

and deposited in ten separate management areas covering a total of 460 hectares. With continued placement of tailings into land-based management areas, the ultimate combined area covered with tailings would be in the order of 1500 to 2000 hectares. The principal environmental concerns associated with the land-based management areas in the long term (after mining has ceased), as seen by the Canadian regulatory authorities, are the potential of acid generation from pyrite oxidation, and the release and migration of radionuclides into air and water. The development of close-out criteria and concepts, therefore, has focussed on addressing these concerns. A position paper was issued for comment by the Canadian Atomic Energy Control Board on long-term aspects of uranium tailings management. In response, three of the uranium companies, Rio Algom Limited, Denison Mines Limited, and Eldorado Nuclear Limited, have countered with their own position and supported it with the extensive research on close-out procedures that has been carried out on their properties. The companies' position is that regulations should allow for site specific solutions and that institutional control is a valid long-term control option. As radiological loadings to air and water in the long term will be less than during operations, the only long-term concern in Elliot Lake is pyrite oxidation. Research has indicated that pyrite oxidation can be controlled in the upper zone of tailings. A summary of options available to control pyrite oxidation in this upper zone, including vegetation, limestone addition, pyrite removal, and physical cover is presented as well as preliminary cost estimates of each alternative.

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Introduction

Since the mid-1950's when uranium mining first started in the Elliot Lake area, approximately 100 million tonnes of tailings have been generated. These tailings have been deposited in ten separate management areas as shown on Figure 1, covering a total of 460 hectares representing less than 0.4% of the Serpent River watershed. Processing of currently committed reserves will account for an additional 230 million tonnes of tailings while additional reserves could increase the future tai­lings production to as much as 500 million tonnes. If placement of tailings onto land-based management areas is continued, the ultimate total area covered with tailings could be in the order of 1000 to 2000 hectares.

The principal environmental concerns associa­ted with the land based management areas in the long term (after mining has ceased), as seen by the Canadian regulatory authorities, are the potential for acid generation from pyrite oxidation, and the release and migration of radionuclides into air and water. The development of close-out criteria and concepts, therefore, has focussed on addressing these concerns.

The mining companies in Elliot Lake, Rio Algom Limited and Denison Mines Limited, have expended in excess of five million dollars to conduct research and develop site specific close-out procedures for land-based facilities. These studies have involved extensive field investigations into the geotechnical properties of the basins in conjunction with compu­ter analysis of seepages, seismieity, and other influencing characteristics. Other studies have been conducted into the chemical aspects of ground­water flows, the retardation of radionuclide move­ments in soils and rock, the emission of radon and radioactive dust to the atmosphere, and the esta­blishment of surface covers.

As noted in an earlier paper, in conjunction with investigating land-based options, the first stage of an investigation of the deep lake disposal option has been carried out at the request of the government agencies. The technical information derived from this study provides an important adjunct to the overall assessment of close-out options.

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( N O N - OPERATING)

| | OPERATING TAILINGS AREAS

NON - OPERATING TAILINGS AREAS

• MILL FACILITIES

FIG.l. Elliot Lake area uranium mining properties and tailings management facilities.

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Close-out Criteria

In Canada today there is no legislation specific to the close-out of uranium mine tailings areas. A position paper has been formulated by the Canadian Atomic Energy Control Board (AECB) and issued for comment. In summary, the AECB's position was that numerical limits should be set for radioactive emissions, specific methods of achieving these requirements were given and performance guaran­tees were requested to ensure that requirements would be met in the long term. The government's position was that institutional control was required but it could not be considered as a control measure by itself.

Upon reviewing the position paper and criteria established elsewhere, the mining companies in Elliot Lake developed a set of objectives from which to assess their research and development works related to close-out of their facilities. The following close-out objectives were proposed: . institutional control is required to restrict

land use and site access at a closed out facility and within a reasonable buffer zone around such a facility;

. the close-out of a tailings area is site speci­fic and must be assessed on the characteristics and requirements of a particular location;

. the design of close-out systems should maximize the use of passive or natural systems;

. the annual loadings of any substance to the envi­ronment after close-out, allowing for a transition period, should not be greater than the loading of such a substance during the operating phase of the facility unless it can be reasonably demonstrated by a pathways analysis that a greater annual loading of such a substance would not cause significant harm;

. the ALARA principle should be applied to total radiation exposure to an individual with the recognition that there exists a level below which no further action to reduce exposure is warranted; it is assumed that such a level will be reached when the total radiation exposure is within the normal range of fluctuation of natural background radiation in a given area;

. no practice be adopted unless its introduction produces a net positive benefit.

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The primary differences between these criteria and those proposed by the AECB, is first that cri­teria should allow for site specific solutions and not be restricted to government set emission stan­dards and second that institutional control is a valid means of controlling the use of the property in the long term.

Close-out Concepts

With respect to Elliot Lake operations, several site specific close-out options are available for land-based facilities. As previously discussed, the principal concerns of regulatory agencies with close-out, relate to the long-term generation of acidity and the release of radioactivity to the air and water.

The possible effects that radioactivity released from a tailings area might have on the public is assessed by undertaking a pathways analysis. Such an analysis is used to estimate the exposures that certain critical groups (those most likely to receive the highest exposures) could receive by all of the possible pathways of exposure such as drinking contaminated water, consuming fish from nearby lakes, eating locally grown vegetables, and brea­thing radon or radioactive dust in the air. These results can then be compared with the appropriate standards.

For the mines at Elliot Lake, this type of exercise indicated that exposures to even the most exposed residents living adjacent to tailings areas were less than about 10 mrem/a (about 2% of the public exposure limit) and much smaller than natural variations in background radiation levels in the Elliot Lake area. Research into the emission of radon and radioactive dust from the properties has indicated that levels approaching background are reached at less than 1 km from tailings areas prior to any remedial work being undertaken.

The companies* position that institutional control is a valid means of controlling long-term effects is supported by the U.S. National Academy of Sciences [1]. "if our descendents are sophisti­cated and 'radiation conscious' they would find detection of the source to be very simple, and correction of the condition equally simple. If they are not, it is likely to be because their technology is so regressed that they are subject

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to much more pressing dangers." This leads to the conclusion that by the use of institutional control to prevent the removal of tailings or the construc­tion of homes on tailings, the emission of airborne radioactive material will not pose an environmental or health problem. It has also been demonstrated that short term use of the site for recreational activities will cause no significant harm to the individual.

Research on leaching rates of uranium and radium (the principal radionuclides of concern) has demonstrated that proper grading and contouring of the site to minimize fresh water infiltration into the tailings areas will result in substantially lower loadings in the long term than during the operating phase. The only remaining long-term concern with Elliot Lake tailings is the control of pyrite oxidation (acidity), which is a general problem to most base metal mining operations in the world. Yet the base metal industry is not required to think in terms of hundreds or thousands of years for control of their tailings areas.

As noted in a later paper, an extensive re­search effort on the geochemistry of pyrite oxida­tion in uranium tailings in the Elliot Lake area.has been undertaken over the past few years. Results to date indicate that pyrite oxidation is typically limited to the upper metre or so of the tailings areas. Because of the high rate of rainfall and impermeable nature of the tailings basins, the water table tends to be within a metre or so of the surface. Below the water table, pyrite oxidation is greatly suppressed and limited by the deficiency of oxygen. Therefore, the key to the control of acid production in the tailings basins is the management of the upper layer of tailings. If the pyrite oxidation is prevented in this upper zone, the overall geochemistry of the tailings basin should remain virtually unchanged in the longer term.

Management options have therefore been oriented towards eliminating oxygen and pyrite from the upper zone or by providing natural alkalinity in this zone to inhibit the oxidation of pyrite from producing acidic conditions.

The close-out concepts which currently are being evaluated in Elliot Lake include: . Direct Vegetation which will control wind and water erosion as well as reduce pyrite oxidation

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rates by reducing the quantity of oxygen which reaches the tailings. Considerable research has been done on vegetation of uranium tailings from the Elliot Lake mines since 1970 by both the mining companies and government agencies. Major efforts have been directed towards vege­tating the tailings directly, without the use of imported topsoil or mulch cover, with the intent being to establish a grass cover which will be maintenance-free after five years. Field plots representative of the tailings as a whole, received a limestone application, followed by chemical fertilizer addition, and seeding of various grasses, legumes and miscellaneous annuals. Research to date indicates it does not eliminate pyrite oxidation on the short term, however, continued years of successful vegetation should result in a humus layer on the surface which should inhibit some of the oxygen penetration to the upper zone of tailings.

. Limestone Addition and Vegetation which involves the placement of a tailings cover with limestone in proper ratios to pyrite. Vegetation controls wind and water erosion while limestone will either prohibit or absorb any acidity produced. Lime­stone addition has proved successful in providing a pH suitable for vegetation of the acidic non-operating tailings areas. For operating tailings areas, methods of limestone addition have not been developed, however it is believed this could be achieved by adding crushed limestone directly into the tailings discharge. As pyrite oxidation is limited to the upper zone, a three metre cap with limestone incorporated should adequately control acid production on the long term.

. Pyrite Removal and Vegetation includes the appli­cation of a pyrite reduced tailings cover with small quantities of limestone added to combat acidity resulting from any residual pyrite. This involves the installation of a pyrite flotation circuit in the mill. Experimentation has been conducted on pyrite removal "with good success. It is possible to remove approximately 93-95 percent of the pyrite and approximately 60 percent of the radium. As there is minimal residual calcium carbonate alkalinity remaining in the tailings, it will be necessary to add some lime­stone to combat any potential acidity produced

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from the residual pyrite. The disposal of the pyrite concentrate does represent some concern. However, as this would only be required during the latter years of operation to obtain a three metre cover of pyrite reduced tailings, it may be possible to dispose of the concentrate in worked out areas of the underground mines. Physical Cover and Vegetation includes the addi­tion of a three metre cover of borrow material such as glacial till,sand and gravel or rock. The cover would hopefully control acidity and could reduce radon releases although this is not a primary concern for many areas. Pyrite oxidation is controlled by allowing the water table to rise into the cover material thus minimizing oxygen penetration into the tailings. Borrow material in the Elliot Lake area is very scarce and expensive thus making this alternative very unattractive.

As noted above, vegetation is a component of all close-out concepts. Vegetation includes grading and shaping and the construction of fresh water diversion works where applicable. Therefore, with vegetation there will be control of wind and water erosion as well as a large reduction in seepage flows.

Cost Implications

The costs for implementation of the close-out concepts is highly site specific and is dependent upon a number of factors. For the purpose of comparing the concepts some preliminary estimates have been prepared (in 1982 Canadian dollars) which serve to provide an order of magnitude cost.

Direct vegetation has been applied widely with considerable variations in costs from site to site. A typical cost to grade, shape, vegetate and provide drainage control for a tailings area has been set at $12 500/ha.

Limestone addition costs will be highly depen­dent upon the limestone requirement. Assuming limestone is added at a tonne limestone per tonne pyrite present in the upper three metres of a tai­lings area the limestone cost would be approximately $35 000/ha. Vegetation and drainage control would also be provided giving a total cost of approximately $47 500/ha.

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Pyrite removal costs include the capital cost of equipment, operating the circuit, limestone addi­tion, concentrate disposal and vegetation. Again these costs are highly site specific. Disposal of the concentrate in mined out areas underground is anticipated to cost approximately $1.00/tonne. With an allowance for capital, limestone and vegetation, it is expected a typical cost for pyrite removal will be in the range of $60 000/ha.

Physical cover with overburden will be extre­mely expensive because of its scarcity in the area. Cover material typically costs in the range of $13.00/ m 3 . Therefore the addition of cover with vegetation could cost in the range of $400 000/ha.

Comparison of Existing and Long-Term Emissions

There will be four operating mines in Elliot Lake in 1983. A listing of these mines, together with the estimated loadings of dust and radon emis­sions to the air environment and radium and uranium releases to the water environment prior to close-out from the mining, milling and existing tailings areas is provided in Table I. These estimates are provi­ded as examples and reflect the releases prior to close-out as predicted for the management schemes currently proposed.

The estimated cumulative emissions from the mining properties for the four close-out concepts are presented in Table II. For all concepts, dust emissions will be significantly reduced, radon emissions will be lower, radium concentration levels in effluents will likely increase but the overall loadings reduced, and uranium concentra­tions in effluents will likely remain at or near their operational levels, however total loadings will be substantially lower.

Closure

The implementation of any of the close-out concepts will result in a reduction of loadings in the long term. Direct vegetation is the least expensive option but the ability to control aci­dity is questionable. Both limestone addition and pyrite removal from the upper layers of tailings will control acidity but are more costly than direct vegetation. The addition of cover material is grossly expensive with the major benefit being

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TABLE I

CONTAMINANT LOADINGS PRIOR TO CLOSE-OUT FROM MINE, MILL AND TAILINGS AREAS

RELEASES TO RELEASES TO SURFACE AREA AIR 1 WATER

TAILINGS DUST RADON RADIUM URANIUM MINE (ha) j 7 s ~ yCT7s y c T 7 d ~ kg/d

Denison

Denison Mine 600 180 1390 1220 14.6

Rio Algom

Panel Mine 80 24 260 263 3.2

Quirke Mine 180 440 510 458 5.5

Stanleigh Mine 280 240 290 775 9.3

TOTAL 1140 884 2450 2716 32.6

1 Releases to the a i r include contr ibut ions from mine upcasts, m i l l exhausts and t a i l i n g s areas for each s i t e . The component of radon re leased from t a i l i n g s surfaces was estimated by prorat ing measured data [2] fo r each of the t a i l i n g s areas on the bas i s of ant ic ipated ore grade and surface a rea . The need to consider f a c i l i t i e s on a s i t e spec i f i c bas i s i s ev ident .

a reduction in radon emissions. As long as insti­tutional controls are provided, radon release is not a major concern.

Although direct vegetation cannot be exempted as an option, it appears at this time that the prime close-out concepts for uranium mine tailings areas in Elliot Lake are limestone addition and pyrite removal. Further research is required and specific site studies are necessary to demons­trate which concept is preferred for each site.

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TABLE II

ESTIMATED CUMULATIVE EMISSIONS FOR ELLIOT LAKE OPERATIONS AFTER CLOSE-OUT

LOADINGS

SUSPENDED TOTAL ESTIMATED' MATTER RADON 1 RADIUM 2 URANIUM COST g/s yCi/s yCi/d kg/d ($)

Pre Close-out

Post Close-out

884 2450 2716 32.6

Direct Vegetation Loading Reduction

negligible 2200 2303 10% 15%

5.5 83% 14 300 000

Limestone Addition Loading Reduction

negligible 2200 2303 10% 15%

5.5 83% 54 200 000

Pyrite Removal Loading Reduction

negligible 860 3 2303 65% 15%

5.5 83% 68 400 000

Physical Cover Loading Reduction

negligible 300" 2303 88% 15%

5.5 83% 456 000 000

1 No credit is taken for saturation of tailings on close-out. 2 All runoff from tailings areas on long term as total radium activity

arbitrarily set at 125 pCi/L. 3 Pyrite removal is assumed to reduce specific activity of radium by 60% in top 3 m of tailings.

11 Assumes 3 m of cover and radon flux decrease of 1/e for each 1.5 m of cover

5 In 1982 Canadian dollars

In conclusion, international agencies respon­sible for uranium mining activities must recognize that close-out procedures for uranium mines must be developed on a site specific basis and that institutional control is an appropriate method of controlling land use in the long term. The inter­national agencies must also appreciate that radio­activity may not be a concern after close-out at some operations. Based on our experience at Elliot Lake acid production is seen as a key concern for the long term.

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REFERENCES

[1] NATIONAL ACADEMY OF SCIENCES, "Energy in Tran­sition, 1985-2010", Final Report of the Committee on Nuclear and Alternative Energy Systems of the National Research Council, (1979) .

[2] MACLAREN LIMITED, JAMES F., "Environmental Assessment of the Proposed Elliot Lake Uranium Mines Expansion",Vol. 4 (1978).

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EVALUATION DE DIFFERENTS SCENARIOS DE GESTION D'UN STOCKAGE DE RESIDUS DE TRAITEMENT DE MINERAI D'URANIUM*

N. FOURCADE, P. ZETTWOOG Departement de protection, CEA, Institut de protection et de surete

nucleaire, Centre d'etudes nucleaires de

Fontenay-aux-Roses, Fontenay-aux-Roses, France

Abstract-Risum£

EVALUATION OF VARIOUS SCENARIOS FOR THE MANAGEMENT OF URANIUM MILL TAILINGS.

A mine located in the Bois Noirs (Forez) granitic massif in the centre of France was closed down in 1980 after 20 years of working and the associated milling plant was dismantled. More than two million tonnes of tailings (dry mass) were produced, of which 1.3 million, containing 2200 g of 2 2 6 Ra, were stored behind a retaining barrier. The storage site is described (design, establishment, emplacement of tailings, drainage) and the radioactive, chemical and granulometric composition of the material stored is given. A quantitative evaluation is made of the 2 2 6 Ra transferred to the environment via the aquatic pathway (currently about 10 9 Bq-a - 1 , or 30 mg per year) and of the 2 2 2 Rn transported by diffusion in the atmosphere (currently about 10 1 2 atoms-s - 1). The concentrations of 2 2 6 Ra in the physical and biological host environ­ments and in food chain products originating from such environments were measured. In the food chain it was observed that the concentrations upstream were higher than-those down­stream by a factor generally not greater than 10, except in the case of vegetables where no significant effect was noted. The potential alpha energy from 2 2 2 Rn daughter products was measured continuously. The values obtained are of the same order of magnitude as those recorded in other uranium regions before working. However, we calculate that the few members of the public who comprise the critical group may receive maximum dose equivalent of about 10 /nSv-a"1 through incorporation of 2 2 6 Ra, and of about 500 juSv-a -1 through inhalation of

2 2 2 Rn daughter products. It is not possible to assess experimentally the exact contribution of the storage site since indications of strong external exposure had been recorded before working began but no survey was made of the original conditions. Broadly speaking, it is the wish of the French public authorities that when operations to extract materials from the subsoil have

* Ce memoire est la version condensee d'un rapport interne du Service de protection technique (SPT n° 285) elabore par les memes auteurs et intitule «Methodes devaluation des differents scenarios envisages pour la stabilisation et la gestion d'un stockage de residus de traitement de minerai abandonne d'un million et demi de metres cubes*.

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170 FOURCADE et ZETTWOOG

been completed, every, precaution should be taken to eliminate the danger of personal accidents to the population and that the area be landscaped and the soil restored to allow it to be used again as part of the local economy. Various possible management and stabilization scenarios are examined from the point of view of feasibility and environmental impact.

EVALUATION DE DIFFERENTS SCENARIOS DE GESTION D'UN STOCKAGE DE RESIDUS DE TRAITEMENT DE MINERAI D'URANIUM.

Dans le centre de la France, une mine situee dans le massif granitique des Bois Noirs (Forez) a ete fermee en 1980 apres 20 ans d'exploitation, et l'usine de traitement de minerai associ6e a ete demantelee. Plus de deux millions de tonnes de residus (masse du produit sec) ont ete produits dont 1,3 millions, contenant 2200 g de radium 226, sont stockes derriere un barrage. Le stockage est decrit (conception, implantation, mise en place des residus, drainage) et on donne les compositions radioactives, chimiques et granulometriques des produits stockes. On evalue quantitativement le radium 226 transfere dans 1'environnement par la voie aquatique (actuellement environ 109 Bq-an - 1 soit 30 mg par an) et de radon 222 par diffusion dans l'atmosphere (actuellement environ 10 1 2 atome-s - 1). On a mesure les concentrations en radium 226 dans des milieux recepteurs physiques et biologiques ainsi que dans des produits de la chaine alimentaire en provenance de ces milieux. Dans la chaine alimentaire, on constate que les concentrations sont plus fortes, d'un facteur ne depassant pas 10 en general, en aval qu'en. amont, sauf dans les legumes ou rien de significatif n'apparait. On a mesure en continu l'energie alpha potentielle en descendants du radon 222. Les valeurs obtenues sont en fait du meme ordre de grandeur que celles relevees dans d'autres regions uraniferes avant exploitation. Cependant, on peut calculer que les quelques personnes du public qui constituent le groupe critique sont susceptibles de recevoir au maximum, par incorporation de radium 226, des equivalents de dose de l'ordre de ladizaine de juSv-an - 1, et, par inhalation de descendants du radon 222, de l'ordre de 500 juSv«an_1 environ. II n'est pas possible d'evaluer experimentale-ment la contribution exacte du stockage etant donne qu'avant exploitation des indices de forte irradiation externe avaient ete releves dans la vallee et qu'il n'a pas ete fait d'etat initial. D'une maniere generate, les pouvoirs publics francais souhaitent qu'a la suite des operations d'extraction de materiaux du sous-sol, toutes les precautions soient prises pour que les risques d'accident corporel pouvant survenir a la population soient elimines et que le paysage soit reconstitue et les sols restaurs en vue de permettre la reutilisation dans le cadre de Peconomie locale. Differents scenarios de gestion et de stabilisation sont envisages et etudies sur le plan de la faisabilite et de leur impact environnemental.

1. DESCRIPTION DU STOCKAGE DES RESIDUS DE TRAITEMENT DE MINERAI DE L'USINE DES BOIS NOIRS

De 1958 a 1980, l'usine de traitement installee a proximite du gisement de mineral d'uranium du Limouzat, dans le massif des Bois Noirs, au Nord des MONTS DU FOREZ, a traite 2,4 millions de tonnes de minerai sec produisant 7 500 tonnes d'uranium. On se trouve dans une zone humide et boisee ou 1'altitude varie de 700 a 900 m.

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SICHON BESBRE limagne de l'Allier \ ,

— : —— r.7 v «• •» v limagne-de la Loire

-—sediment recent Chaine des

Puys sediment ancien

2 3

Monts du FOREZ BOIS NOIRS Monts de la MADELAINE

FIG.l. Structure geologique du massif des Bois Noirs.

Le massif des Bois Noirs est l ' un des t r o i s compartiments

d'un horst qui s ' e s t souleve jusqu 'a 1100 m, au t e r t i a i r e ,

entre deux f a i l l e s Nord-Sud actuellement occupees par l es

sediments de l a limagne de l ' A l l i e r a l 'Ouest et de la limagne

de l a Lo i re a l ' E s t . Ces t ro i s compartiments sont separes par

deux v a l l e e s occupees, l 'une par le SICHON, 1'autre par l a

BESBRE (fig.l).

Les dechets so l ides produits par l ' u s ine ont e te , pour un

peu plus de l a moit ie , stockes dans un bass in cree en amont

d'un barrage eleve en travers de l a v a l l e e de la Besbre,

r i v i e r e torrentueuse passant au pied de l ' u s i n e . Le barrage

est du type des grands barrages i n s t a l l e s pour l e s retenues

d'eau creees pour les centrales hydroelectr iques. Sa longueur

est de 500 m, sa largeur 180 m en bas et 10 m en haut, sa

hauteur 41 m environ. Un schema est donne f igure 2.

Sous l e bar rage , l e so l a ete decape jusqu 'au substratum

rocheux du fond de l a v a l l e e . Le decapage concernait l e sommet

d'une couche a l luv ionnai re de 2 metres d 'epaisseur environ,

cette pa r t i e decapee a ete remplacee, pour assurer

l ' e tanche i te entre l e substratum et l a digue, par un para -

f o u i l l e de 6 metres de la rge et constitue d ' a r g i l e compacte.

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FIG.2. Forez, Coupe du barrage et du bassin de stockage des residus de traitement de minerai d'uranium.

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Les sources emergeant a 1'emplacement de l a digue ont ete

captees et co l lectees par 6 drains traversant l a digue; ces

drains co l lectent egalement une par t i e de l ' e au recue par l e

barrage (eau de p lu ie et eau d f i n f i l t r a t i o n venant du b a s s i n ) .

Le fond du bass in n ' a pas f a i t l ' o b j e t d'une preparation

p a r t i c u l i e r e . La surface to ta le est de l ' o r d r e de 20 ha. La

r i v i e r e Besbre a ete deviee dans un canal de 1200 m; l e debit 3 -1

moyen de l a Besbre a ete estime a 1000 m .h , mais i l peut

etre 5 a 10 fo i s plus important.

1.1 Mode de depot et quantite stockee

Apres lavage et addit ion de su l fate de chaux, les residus

de traitement du minerai et les boues chimiques (hydroxydes)

etaient rassemblees et se presentaient sous forme de boues

pompables qui etaient envoyees dans l e bass in .

En fonction des besoins de l a mine, une par t i e de ces

boues e t a i t cyclonee ; l a pa r t i e superieure a 50 urn e t a i t

envoyee dans l a mine souterraine pour le remblayage des vieux

travaux (1 100 000 tonnes) . Les residus f ins restants etaient

d i r i g e s dans le bass in ou i l s sont sedimentes couche par

couche en fonction de l a pos i t ion des buses de r e j e t .

Done, on trouve dans l e bass in , sur une epaisseur de 1 a

19 m :

- 600 000 tonnes, en poids sec, de residus f ins appeles

" f i n e s " stockes dans l a pa r t i e . cent ra l e du bassin,immerges

sous 1 a 11 m d 'eau. Pour 90 % des materiaux, l a granulometrie

est in fer ieure a 50 um ;

- 700 000 tonnes, en poids sec, de produits bruts d 'usine ou

"tout venant" stockes principalement sur les bords du bass in ,

en dehors du plan d 'eau, pour l a plus grande pa r t i e . Pour 90 %

des materiaux, l a granulometrie est in fer ieure a 500 um, et

pour 30 a 40 % in fe r ieure a 50 pm. Ces produits "tout venant"

se presentent comme un beau sable f i n .

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Les eaux de surverse de ce bassin avaient, pendant les 3 -1

travaux, un debit moyen estime a 300 m .h . Le debit actuel 3 -1

est estime a 50 m .h en raoyenne.

1.2 Composition chimique II s'agit de materiaux a base de granit. Le pH de l'eau

de surverse etait de 7 a 8. Des mesures montrent que la quantite de SO^ Ca est repartie de la facon suivante : - pour le "tout venant" :

. 2,8 % dans les particules superieures a 50 urn,

. 97,2 % dans les particules inferieures a 50 um. - pour les "fines" :

. 8,3 % dans les particules superieures a 50 um,

. 91,7 % dans les particules inferieures a 50 um. La masse totale de SO. Ca a ete estimee a 1,4.10"* tonnes.

4

1.3 Estimation de la radiotoxicite potentielle du stockage vis-a-vis du transfert aquatique

1.3.1 Radiotoxicite potentielle volumique_R V

On peut definir la radiotoxicite potentielle volumique vis-a-vis du transfert aquatique comme le volume d'eau susceptible d'etre chargee a la Limite Derivee de Concentration (LDC) par tous les radionuclides presents par unite de volume de source s'ils etaient dissous dans l'eau.

R (m .m source) = A. (Bq.m source)

LDC. (Bq.m" eau) LDC^ limite derivee de concentration pour chaque radionucleide i A^ activite volumique de la source R V volume d'eau ayant une concentration egale a la limite

derivee de concentration

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Calcul de A. :

radionucleide i Pb 210 Ra 226 Po 210 Th 230

LDC publ ic -3

en Bq.m 2 490 8 700 12 500 12 500

v - R pour les f ines :

radionucleide i Pb 210 Ra 226 Po 210 Th 230

R^ (m 3.m 3 ) 2 ,6 .10 4 7,5 .10 3 5,2 .10 3 5,2 .10 3

so i t R V = 4 ,4 .10 4 m3 d' -3 eau . m de source

- R V pour l e " tout venant"

P v - / / ' m 4 3 ,5 .10 7 _ . . i n 4 3 -3 , R = 4,4.10 . = 2,4.10 m d eau.m de source

6 ,5 .10 7

- dans les " f i n e s " qui contiennent, en radium 226, 6.10 Bq O _ 1

(1620 C i ) , l a concentration est de l ' o r d r e de 10 Bq . t " -3 -1

(2,7.10 C i . t ) de produit sec. Le volume est de l ' o r d r e de 3

920 000 m avec une humidite de 50 % en poids et une densite

vo i s ine de 1,3.

On suppose que les Pb 210, Po 210 et Th 230 sont en equ i l i b re

rad ioact i f avec l e Ra 226. A^ = et on neg l ige l ' a c t i v i t e

des isotopes de l 'uranium.

A sera egal a 6 ,5 .10 7 Bq.m" 3 ( 1 , 8 . 1 0 " 3 C i . m " 3 ) . 13

- dans l e " tout venant" qui contient 2,1.10 Bq (560 C i ) ; l a concentration en radium 226 est de l ' o r d r e de 3.10 7 Bq.t

-4 -1 (8.10 C i . t ) de produit sec. Le volume est de l ' o r d r e de

3

600 000 m avec une humidite de 20 % et une densite vo is ine

de 1,5.

A ± sera egal a 3 ,5 .10 7 Bq.m" 3 ( 0 , 9 . 1 0 " 3 C i . m " 3 ) .

Calcul de R V :

Les Limites Derivees de Concentration recommandees par la

Commission Internat ionale de Protection Radioactive (CIPR,

f asc icu le n° 30) sont l es suivantes :

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1.3.2 Radiotoxicite potent ie l l e du stockage R

La rad iotox ic i te potent i e l l e du stockage dans son entier

est

R(m 3 ) = ZrV-v (source) R = 4,4.10 x 9,2.10 + 2,4.10 x 6.10 = 5,5.10

10 3

On pourrait porter a l a LDC eau 5,5.10 m d'eau s i tous

les r a d i o n u c l i d e s du stockage e ta i t dissous.

1.4 Estimation de l a rad io tox ic i te potent i e l l e du stockage

v i s - a - v i s du t ransfert aerien

Etant donne que les residus sont stockes sous l ' e au ou

humides, seul l e t ransfert du gaz radon est a considerer.

Le nombre d'atomes de radon 222 presents dans l e stockage peut

etre calcule a pa r t i r de l a quantite de radium 226 q u ' i l

contient.

Dans l e paragraphe precedent, cette quantite de Ra 226 a

ete estimee a : - 6 . 1 0 1 3 Bq (1620 Ci ) dans les " f i n e s " ,

13

- 2,1.10 Bq (560 Ci ) dans l e "tout venant",

so i t au to ta l 8 , 1 . 1 0 1 3 Bq (2180 C i ) . La production d'atomes de radon 222 par unite de temps

tot 19

13 est done de 8,1.10 et l e nombre d'atomes existants a 1 ' equ i l ib re dans le stockage est 4.10

En prenant comme reference l a LDC du radon 222 dans l ' a i r

indiquee par l 'Agence Internat ionale a l 'Energ ie Atomique -3 -9 -3

(AIEA) , e ' e s t - a - d i r e 110 Bq.m (3.10 Ci.m ) ou encore 7 - 3 12 3 5.10 atome.m , on peut porter environ 10 m d ' a i r a l a LDC

avec l e radon existant a un moment donne dans l e stockage.

2. EXAMEN DES CONSEQUENCES ENVIRONNEMENTALES

2.1 Impact sur 1 ' u t i l i s a t i on des so ls

Le stockage represente, au fond d'une v a l l e e , une emprise

au sol d'une trentaine d 'hectares de bo is analogues a ceux de

l'amont qui n'ont pas ete touches par 1 'exp lo i tat ion.

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2.2 Impact sur l e paysage

Le fond de cette v a l l e e relativement encaissee et sauvage

a ete rehausse, suite a 1 'ed i f icat ion du barrage qui a permis

1 ' i n s t a l l a t i on d'un plan d'eau de 15 hectares entoure de

vegetat ion qui recouvre aussi bien l es berges du bassin que la

digue elle-meme.

La modification contestable du paysage n ' e s t pas due au

stockage lui-meme dans l a mesure ou i l se presente comme un

plan d 'eau, mais a l a presence des batiments indust r i e l s et

des i n s t a l l a t i ons minieres proprement d i tes qui subsistent

apres l a reconst itut ion p a r t i e l l e de ce paysage au niveau des

zones construites : l e s batiments en bon etat ont ete

conserves pour une eventuel le u t i l i s a t i o n dans le cadre de

1'economie l oca l e .

2.3 Impact radiologique

Un etat approfondi de 1'impact de ce stockage a ete f a i t parce q u ' i l e t a i t , a p r i o r i , constitue dans des conditions

defavorables du point de vue des p o s s i b i l i t e s de relachement

des r a d i o n u c l i d e s et de leur accumulation dans l es milieux

physiques avois inants , sauf en ce qui concerne les emissions

de poussieres non re lachab les , l es residus etant satures ou

sous eau.

Bien que les residus soient en grande par t i e sous eau et

que l a source de radon so i t par consequent f a i b l e , on se trouve

dans une v a l l e e frequemment soumise a des phenomenes

d ' invers ion et l e r isque d ' i r r ad i a t i on des populations, par l e

radon, devait etre considere.

La r e a l i t e de cet impact n ' e s t pas actuellement

demontrable experimentalement par l e reseau de mesures en

p lace , et l a theorie indique que,dans l a va l l e e , 1'exces de l a

concentration moyenne en energie alpha potent i e l l e des

descendants du radon se ra i t de l ' o r d r e de grandeur des

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f luctuat ions na ture l l e s . On calcule q u ' i l en r e su l t e r a i t pour

l es personnes habitant l a v a l l e e un equivalent de dose

absorbee supplementaire de l ' o r d r e de 500 uSv.an , du au

radon.

D 'autre pa r t , l e stockage sur un fond de v a l l e e sans

etancheite semblait devoir favor iser les t rans fer ts vers l e

drain naturel constitue par l a couche a l luv ionnai re de

1'ancien l i t de l a r i v i e r e , puis vers l a r i v i e r e elle-meme.

L ' expos i t ion , par ingestion de radium, d'un groupe c r i t ique

constitue d'une ou deux famil ies de paysans et de quelques

pecheurs e t a i t a envisager.

Les resu l ta t s de cet examen,qui f a i t l ' o b j e t du chapitre

suivant, ont montre q u ' i l est poss ib le d 'observer des anomalies

de r ad ioac t i v i t e dans l e proche environnement en fa isant des

analyses en radium 226 dans les milieux physiques et

b io log iques . Mais, en dehors du l i t de l a r i v i e r e et de ses

b i e f s , l es zones agr ico les ou l e radium est en concentration

superieure a la concentration habituellement rencontree

occupent une f a i b l e surface l e long de l a r i v i e r e .

En ce qui concerne l a chafne a l imentaire , on decele une

anomalie de rad ioact iv i te dans l e l a i t d'une vingtaine de

vaches et dans les poissons de l a portion de r i v i e r e situee

immediatement en aval du stockage. I I n 'y a r ien de

s i g n i f i c a t i f dans les legumes.

On doit noter que l es anomalies de rad ioac t iv i t e

observees sur l e s i t e sont aussi bien ce l l e s qui ex is ta ient

avant tous travaux et que l es prospecteurs avaient notees dans

l es re leves radiometriques, que ce l l e s resultant des

operations d 'extract ion et de traitement du mineral. I I n ' es t

done pas poss i b l e , etant donne q u ' i l n 'a pas ete f a i t d ' e ta t

i n i t i a l , de determiner la contribution r e l a t i v e des sources

d ' i r r a d i a t i o n .

Cependant, une va leur superieure de l f e x p o s i t i o n des

personnes du groupe c r i t ique par ingest ion de radium est de

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l ' o r d r e de quelques mrem par an, valeur in fer ieure a la

variance des expositions nature l l es dans l a region.

2.3.1 Taux_de relachement_de la rad iotox ic i te

En ce qui concerne 1'atmosphere, seul l e radon

in te rv ient . La source de radon representee par l e bass in a et 12

estimee au chapitre 3 a 10 atomes par seconde. La quantite d'atomes presents a un instant donne dans l e stockage a ete

„ „ 1 9 precedemment evalue a 4.10 atomes. On a done un taux de

—8 —3 relachement de 2,5.10 par seconde ou bien de 2.10 par

j our .

En ce qui concerne l es t ransferts aquatiques de l a

r ad i o tox i c i t e , l es mesures montrent que l e radium 226 est l e

seul radionucleide qui so i t relache d'une facon notable dans

l ' e au de la r i v i e r e (au minimum 100 fo i s plus que l e plomb).

On ne considere done que l a rad io tox ic i te l i be ree par le

Ra 226 dont la LDC est de 8700 Bq.m" 3 (CIPR n °30 ) . Au chapitre

3, on a estime l es quantites de radium re jetees actuellement.

On estime que l a quantite tota le de radium re jetee est 8 9 - 1 comprise entre 1.10 et 1.10 Bq.an . Ces ac t i v i t e s

permettent de porter a l a LDC un volume d'eau compris entre 4 5 3 -1 1,2.10 et 1,2.10 m .an .

La rad io tox ic i te du stockage a ete estimee, au chapitre „ ^ 10 3

precedent, a 5,5.10 m ; l e taux de relachement est done

compris entre 2.10 ^ et 2.10 ^ an

2.3.2 Indice de confinement

On de f in i t 1 ' indice de confinement d'un radionucleide

comme etant l e rapport entre l a quantite d'atomes qui

s'echappent du stockage par unite de temps et l a quantite

d'atomes qui s ' y produisent par decroissance radioact ive du

generateur.

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TABLEAU I. FLUX D'EMANATION DU RADON 222 (MESURES EFFECTUEES AU FOREZ LE 29/9/81)

CO o

nature du residu flux 2 -1 . s

Rn 222 debit de dose externe*

concentration humidite Ci.m"

flux 2 -1 . s atome. mrd.h 1

en Ra 226 sur poids sec -2 -1 m . s

Bq . t " 1 ( C i . t " 1 ) %

. " f ines" 7,9.10 7 (2 ,1 .10" 3 ) 38,2 3,5. I D " 1 0 6,3.10 6 2,8 a 3

. " f ines" +

"tout venant" 5.7.10 7 (1 ,5 .10" 3 ) 24,4 2,9. I D " 1 0 5,2.10 6 2 a 2,2

."tout venant " 6,4.10 7 (0 ,2 .10" 3 ) 4,8 5,8. I D " 1 1 1,0.10 6 0,6 a 0,7

* mesure avec une chambre d ' ionisation. Au-dessus de la zone de "tout venant", l ' appare i l

recoit egalement les rayonnements gamma des zones environnantes.

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• Cas du radon 222

Le taux de production du radon dans l e stockage est de 13

8,1.10 atomes par seconde, l e debit est au plus de 12

10 atomes par seconde •, on en deduit un indice de confinement -2

de 1.10 au minimum. • Cas du radium 226

13

Le taux de production est de 8,1.10 atomes par seconde,

s i on suppose que l e Th 230 est en equ i l i b re rad ioact i f avec

les autres r a d i o n u c l i d e s ; l e nombre d'atomes sortants 12

actuellement est au maximum de 2,4.10 atomes par seconde 9 - 1

(10 Bq.an ) •, on en deduit un indice de confinement de _2

3.10 . L a fu i te de radium n ' es t pas de nature a modifier

1 ' equ i l i b re entre l e radium et l e thorium dans les res idus .

On notera, par a i l l e u r s , que des etudes de l aborato i re

ont montre que, seu l , au maximum 1 % du radium contenu dans

l es boues e t a i t l i x i v i a b l e par les eaux d ' i n f i l t r a t i o n et

q u ' i l s ' a g i t du radium associe au SO. Ca. 3. ANALYSES QUANTITATIVES DES TRANSFERTS DANS L'ENVIRONNEMENT

ET A LA POPULATION

3.1 Radon 222

Les resu l ta t s r e l a t i f s a l a mesure du f lux in s i tu sont

donnes tableau I . On en deduit , compte tenu des 4 ha de sables

"tout venant" et des 15 ha de " f ines " , que l a source est au

maximum de 1 0 ^ atome.s * (2,2.10^ Bq.s S

3.2 Energie alpha po tent i e l l e

Les mesures f a i t e s a l ' a i d e du dosimetre alpha de s i t e en

continu pendant deux ans en deux l ieux :

- pres du stockage,

- dans l a v a l l e e de l a r i v i e r e , a 2 km en aval du

stockage,

sont donnes tableau I I .

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TABLEAU II. DEBIT D'ENERGIE ALPHA POTENTIELLE INHALABLE

CORRESPONDANT AUX MESURES MENSUELLES (juJ-a - 1 ) EFFECTUEES

PAR DOSIMETRE ALPHA DE SITE a

Implantation station station

pres du bassin 2km aval du bassin

1981 dans la vallee

JANVIER 488 -FEVRIER 554 585

MARS 289 442

AVRIL 408 412

MAI 206 144

JUIN 220 441

JUILLET-AOUT 490 1 016

SEPTEMBRE-OCTOBRE - -NOVEMBRE 440 281

DECEMBRE 207 271

Moyenne annuelle 367 449

Rappel de la moyenne

annuelle 1980 478 554

Remarque: en plus des donnees precedentes, on a obtenu: — la variation des concentrations en Po 212, qui doit mettre en evidence la stabilite verticale de l'atmosphere, Po 218 Po 218 — le rapport des traces , c'est-a-dire des concentrations

Po214-Po218 Pb214+Bi214

qui doit fournir Page apparent du radon 222 produit localement.

a Mis au point par le CEA et presente a la conference internationale: (Radiation hazards in mining. Control, measurement and medical aspects. State of the art of the individual dosimetry in France), Colorado School of Mines, Golden, Etats-Unis (4 -9 octobre 1981).

Page 197: Management of Wastes from Uranium Mining and

Les concentrations moyennes mesurees sont de l ' o r d r e de

grandeur des va leurs trouvees dans des regions urani feres

avant exp lo i ta t ion .

Par un ca lcu l theorique base sur un modele " b o l t e "

representant l ' e space proche du stockage concerne par les

inversions de temperature (longueur 3 km, largeur 1,5 km,

hauteur 100 m) et u t i l i s a n t les donnees meteorologiques

r e l a t i v e s aux periodes d ' invers ion (vo i r f igure 3), on a pu

f a i r e une estimation de 1' influence du stockage. La quantite

d 'energ ie alpha inhalab le a ete trouvee egale a 200 pJ.an ,

en considerant une duree moyenne de chaque periode d ' invers ion

egale a 8 heures, un temps to ta l representant 15 % du temps

annuel et un facteur d ' equ i l i b r e rad ioact i f de 0,5.

3.3 Radium 226

3.3.1 Radium re je te dans 1'environnement

La quantite de radium relache dans 1'environnement a ete

estimee a p a r t i r des c i r cu i t s d'eau ( surverse , dra ins ,

resurgences qui pourraient recuperer de l ' e au d ' i n f i l t r a t i o n ) .

Les resu l ta t s de nos estimations sont donnes tableau I I I ,

en fonction des parametres suivants :

- surverse :

. 4 800 Bq.irf 3 (1 ,3 .10~ 7 C i .m" 3 ) pour les 17 premieres 3 -1

annees avec un debit d'eau de 300 m ,h ,

. 260 Bq.m" 3 ( 7 . 1 0 - 9 C i .m" 3 ) de 1978 a 1981, avec un

debit d'eau de 300 m 3 . h _ 1 , -3 -9 -3

. 150 Bq.m (4.10 Ci.m ) depuis 1982, avec un debit d'eau de 50 m 3 .h ^.

- drains (deb i t 75 m 3 . h - 1 ) : 3 _io -3

. 16 Bq.m (5.10 Ci.m ) actuellement,

. 3 700 Bq.m" 3 (1 .10~ 7 C i .m" 3 ) s i l a retention du Ra 226

par les so ls ne se f a i s a i t p lus .

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FIG.3. Mesures simultanees de la concentration en radon 222, du flux radon 222 et des periodes d'inversion.

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- eaux d ' i n f i l t r a t i o n ou resurgences :

Suite a l a constatation d'anomalies de concentration en

Ra 226 dans l a r i v i e r e et apres etude de diverses hypotheses

de sources pa ra s i t e s , on a estime que l a plus vraisemblable

e t a i t l es eaux d ' i n f i l t r a t i o n qui ne seraient pas captees par

les drains et resurg i ra ient dans l a r i v i e r e en aval du

stockage: -3 -7 -3 . 4 800 Bq.m (1,3.10 Ci.m ) actuellement avec un

debit inconnu.

3.3.2 Radium 226_dans les milieux recepteurs

Une campagne de mesures sur des echanti l lons preleves au

cours de 3 saisons successives a ete effectuee en 1980. Les

echanti l lons ont ete pre leves a proximite du s i t e et de l a

r i v i e r e . Les resu l tats ,dont un ex t ra i t est donne tableau IV;

ont f a i t l ' o b j e t d'une presentation au colloque de Knoxvi l le ,

USA (27-31 j u i l l e t 1981) [ 1 ] .

3.3.3 Indice de rad io tox ic i t e dans l e s _d i f f e rents constituents

de l a chaine al imentaire

Les recommandations de l a CIPR n° 30 de 1980 donnent comme 3 -1

l imite annuelle ingerable (LAI) pour l e radium : 7.10 Bq.an

L'eau n ' e s t pas consommee.

A condition de ne pas avoir d 'autres sources de radium,

l e meme individu peut consommer par an (compte tenu des

va leurs l es plus elevees en aval du stockage) :

. so i t 10 tonnes de t r u i t e s ,

. so i t 10 tonnes de legumes,

. so i t 17 500 l i t r e s de l a i t ,

sans depasser l a LAI.

Les personnes du groupe c r i t i que ont ete informes.Une

f ract ion du l a i t produit est consomme sur place par l e

producteur et sa f ami l l e , 1'autre f ract ion est vendue a des

societes l a i t i e r e s . Au niveau du l a i t commercialise par ces

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TABLEAU III. QUANTITE DE RADIUM REJETE ANNUELLEMENT ( B q - a - 1 )

^ ^ X ^ P e r L ^ ^ exploit avant traitement

(17 ans)

ation apres traitement

(4 ans)

periode d 1 observation

(30 ans)

moyen terme

< 400 ans

rejet evacuateur . soluble . insoluble

drains

resurgence (hypothese)

1,3.10 1 0 (0,34) 0,4.10 1 0 (0,01) 5.10 7 (0,001)

1,5.10 9 (0,04)

7.10 8 (0,02) 7.10 9 (0,18) 5.10 7 (0,001)

3.10 9 (0,08)

5.10 7

negligeable 0,05 a 2,5.10 9

5.10 8

< 1.10 8

negligeable < 1.10 8

< 1.10 8

Remarque : Ces valeurs sont a comparer a la quantite de radium soluble dans la riviere en amont du site : 20 a 40 (Bq.m" 3) x 1000 ( m 3 . h _ 1 ) x 8760 (h.an" 1) = 2 a 4.10 8 Bq.an" 1

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TABLEAU IV. CONCENTRATION EN RADIUM 226 DANS DES MILIEUX

RECEPTEURS

SOLS (Bq.t , sec) : terre de prairies amont 0,12.10**

aval 0,5 a 2,7.10 6

terre de jardin amont 0,09.10

aval 0,10 a 0,21.10

VEGETAUX POUR ANIMAUX (Bq.kg" 1, frais) amont 2,9

aval 12 a 47

CHAINE ALIMENTAIRE lait (Bq.l" 1) amont 0,04

aval 0,12 a 0,23

legumes (Bq.kg" 1, frais) amont 0,7

aval 0,5 a 0,7

truites (Bq.kg" 1 de chair + peau)

amont 0,05 aval 0,7

societes, la concentration en radium n'est pas modifiee par rapport aux valeurs regionales. II a semble inapproprie de rechercher de facon plus approfondie la destination exacte de ces produits, car cela n'aurait abouti qu'a inquieter sans raison valable les populations, ce que nous ne nous sentions pas moralement autorises a faire.

Les calculs precedents sont faits sur les valeurs les plus elevees trouvees actuellement, pour lesquelles on ne

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cormait pas la part due a la radioactivite naturelle, etant donne qu'il n'y a pas eu d'etat initial.

3.4 Irradiation externe Une cartographie gamma faite en suivant les routes

jusqu'a 20 km autour du site montre que le debit de dose par irradiation externe peut, d'un lieu a un autre, varier de 100 a 300 mrad. par an.

4. EXAMEN DES DISPOSITIONS A PRENDRE EN CE QUI CONCERNE LE DEVENIR DE CE STOCKAGE

4.1 Les donnees du probleme

4.1.1 Le contexte administratif et reglementaire La COGEMA, qui est la societe miniere ayant exploite le

gisement d'uranium des Bois Noirs,est restee proprietaire du site de stockage des residus et en est done responsable vis-a-vis de 1'Administration Departementale. Elle a, en particulier, 1'obligation d'en assurer la surveillance, dont elle a confie 1'execution a l'Institut de Protection et de Surete Nucleaire (IPSN) du CEA.

Dans la periode transitoire actuelle, cette surveillance concerne :

- le comportement geotechnique du barrage et notamment les releves piezometriques et le debit des drains, - le relachement du radium et son comportement dans les eaux de surface, et certains indicateurs permettant de suivre la chaine alimentaire locale, - 1'emission du radon et son comportement dans 1'atmosphere.

Cette periode transitoire qui se termine le 30 juin 1983 a ete accordee par 1'Administration a la COGEMA pour lui permettre :

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1 - de f a i r e un constat approfondi des consequences

environnementales de ce stockage dans l a s i tuat ion a c tue l l e ,

2 - d'examiner, compte tenu des d i f fe rents r isques qui sont a

associer dans l ' a v e n i r a ce stockage, d i f fe rentes solutions

v isant a l a suppression de ces r isques et de proposer l a plus

acceptable.

La co l l ec te des donnees necessaires a 1'etablissement de

ce dossier a de nouveau ete confiee par la COGEMA a l ' I PSN .

D'une maniere genera le , 1'Administration en France

souhaite qu 'a l a suite des operations d 'extract ion de

materiaux du sous -so l (mines et ca r r i e re s ) :

1 - toutes les precautions soient pr i ses pour que les r isques

d 'accident corporel pouvant survenir a l a population soient

elimines ;

2 - que le paysage so i t reconst i tue , l e s sols restaures en vue

de permettre l a r e u t i l i s a t i o n dans l e cadre de l 'economie

rura le l o c a l e , et que, s i pos s i b l e , on procede a la

va l o r i s a t i on des modifications apportees a l a topographie du

s i t e .

En ce qui concerne les aspects radiologiques poses par

les stockages de residus de minerals d'uranium, c ' e s t l a

premiere f o i s , a 1'occasion de cette exp lo i tat ion des Bois

Noirs>que le probleme se pose avec une r e e l l e ampleur. I I n 'a

done pas ete mis en p lace , en France, une reglementation

appl icab le a ce type de stockage. I I ex iste b ien sur c e l l e qui

resu l te des d i rect ives generales appl icab les dans l a

Communaute Europeenne en ce qui concerne les rayonnements

ion isants , et des recommandations de l a CIPR. Mais des

ob j ec t i f s plus specif iques r e l a t i f s a l a surete des ouvrages

de confinement et a la protection des populations v i s - a - v i s

des r e j e t s continus ou acc idente ls , a ins i que des reg ies

l imitant ces re j e t s et precisant l a maniere d 'assurer l a

surve i l l ance , n'ont pas encore ete elabore.s. I I est considere

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en France, ou en matiere de reglementation sur 1'environnement

des posit ions pragmatiques ont toujours ete favor i sees , que a

1'occasion de ce dossier des Bois No i r s , l es problemes ree l s

pourront etre concretement i dent i f i e s et t r a i t e s efficacement

sur le plan reglementaire.

4.1.2 Principes de base et hypotheses de t r a v a i l

La co l l ec te des donnees necessaires a 1'etablissement du

dossier que l a COGEMA doit remettre a 1*Administration doit

d'abord comporter un constat de l a s i tuat ion ac tue l l e . Les

aspects radiologiques de cette s i tuat ion ont f a i t l ' o b j e t du

chapitre 2.

Mais i l faut examiner egalement l es solutions

proposables pour l ' a v en i r : a cet e f f e t , i l nous f a l l a i t

necessairement prendre pos i t ion par rapport a l ' un des

problemes qui sont l e plus discutes au niveau des reunions

Internat iona les , ce lu i des d isposit ions q u ' i l convient de

prendre pour assurer des maintenant l a surete et l a protection

a long terme de ces stockages, l e long terme s i gn i f i ant

absence de surve i l lance et p o s s i b i l i t y d'occurence de

modifications geologiques majeures.

Nos re f lex ions nous conduisent a af f irmer les t ro i s

pr incipes ci -dessous :

1 - Tant q u ' i l ex iste un cadre ins t i tut ionne l accepte par

tous, l es problemes de surete et de protection peuvent

etre t r a i t e s de facon parfaitement ra t ionne l l e sur les plans

technique et economique et de facon acceptable par les

populations.Dans ce cadre, des organismes nationaux de gestion

du stockage et de surve i l lance de 1'environnement,qui existent

d ' a i l l e u r s en France, peuvent exercer avec e f f i c ac i t e leurs

competences.

2 - La mise en evidence recente que l a r ad ioac t iv i t e nature l l e

est un facteur b iot ique important, q u ' i l faut prendre en

compte de toute facon au meme t i t r e que la meteorologie par

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exemple, conduit in&luctablement les societes evoluees a

mettre en p lace , et ce de facon de f i n i t i v e , des organismes de

controle de l a r ad ioac t i v i t e des milieux physiques et

b io log iques et des materiaux de construction. La surve i l lance

a long terme de ces stockages par l es generations futures

n ' e s t done pas une charge excessive a leur imposer.

3 - Au cas ou l a s t a b i l i t e des ins t i tut ions ne se ra i t plus

assuree et ou l es organismes en question seraient dans

l ' i ncapac i t e de poursuivre leur mission, e ' e s t de desordres

autrement graves que ceux qui resu l tera ient de l ' o u b l i de ce

stockage dont les generations futures auraient a s o u f f r i r . En

d 'autres termes, l e s societes du futur ont l ' imper ieuse

necess i te , face a un environnement technologique de plus en

plus complexe, de l e mal t r i ser par une organisation po l i t ique

adequate.

Sur l a base de ces t r o i s pr inc ipes , nous avons degage les

hypotheses de t r a v a i l necessaires a l a poursuite de notre

analyse :

- Nous n'envisageons pas que ces stockages puissent etre un

jour abandonnes sans une surve i l lance assuree par des

organismes nationaux competents et e f f i caces .

- C 'est dans un cadre technologique et economique rat ionnel

qui subs istera a long terme que doit etre envisagee

1'optimisation de l a gestion du stockage en ce qui concerne l a

protect ion des populat ions, t e l l e que l e recommande l a CIPR.

- Les ob j ec t i f s de surete et de protection doivent etre

adaptes dans ce cas comme dans tous les autres aux

pa r t i cu l a r i t e s geographiques et humaines du s i t e considere.

4.1.3 Ident i f icat ion_des_r i sques_presentes_£ar_ le_sto

Les r isques que nous avons i dent i f i e s sont l es suivants :

- Le r isque d'enlisement dans l es boues mouvantes qui

constituent les plages de l a retenue d 'eau. Ce r i s que ; qu i

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pourra i t concerner des enfants, des bracormiers et meme des

agents charges de l a surve i l l ance , est un r isque de tous les

j ours .

- L ' inc ident geotechnique sur le bar rage , avec echappement

d'une f ract ion plus ou moins importante des boues f l u i d i s ee s ,

actuellement en amont, est un r isque assez f a i b l e dont la

p robab i l i t e peut etre determinee par reference a des accidents

semblables. En cas de coulees de boues affectant la t o t a l i t e

des produits stockes, l e recouvrement de certaines proprietes

s ituees dans l a v a l l e e se ra i t a craindre et des travaux de

repr i se seraient necessaires pour supprimer l es consequences

radiologiques et restaurer les so l s .

Ce type d ' incident peut resu l te r lui-meme d'un incident

sur l 'ouvrage de deviation amont de l a r i v i e r e ,

particulierement en cas de fortes p lu i e s , e t se t r adu i ra i t en

tout cas par un apport important de radium soluble ou meme de

boues radioact ives dans l a Besbre.

- L ' u t i l i s a t i o n incontrolee des sables qui sont access ib les

sur l es plages en tant que materiaux pour l a construction de

maisons ind iv idue l l es est un r isque d i f f i c i l e a exclure meme

en cas de surve i l l ance . I I en r e su l t e r a i t une i r r ad i a t i on

importante des habitants .

- L ' i n s t a l l a t i o n de locaux a usage indust r i e l ou d 'habitat ion

au bord de la retenue d'eau ou a proximite immediate est tout

a f a i t pensable, surtout a long terme, d'autant plus que l a

municipality souhaite v a l o r i s e r les te r ra ins vo i s ins l a i s se s

disponibles apres l e depart de 1'exploitant. I I en r e su l t e r a i t

de meme une i r r ad i a t i on qui pourrait ne plus etre neg l i geab le .

- La consommation des poissons de l a retenue d'eau que des

braconniers pourraient etre tentes de se procurer est aussi un

r isque d i f f i c i l e a exc lure . La dose co l l e c t i ve qui se ra i t

de l iv ree a des groupes locaux pourra i t etre non neg l i geab le .

De meme l ' a cces pour l 'abreuvage de cette retenue d'eau aux

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troupeaux des p r a i r i e s relativement proches est en pratique un

r isque t res concevable. Compte tenu de l a charge en radium de

cette eau, cela se ra i t une autre voie non neg l igeab le de

t rans fer t du radium dans l a chaine a l imentaire .

- Un accroissement des emissions de radon qui pourrait r e su l t e r

d'un assechement meme p a r t i e l du bassin est poss ib le a moyen

terme malgre l a p luv ios i t e e levee . On a vu que l a source

a c tue l l e , pour ces residus sous eau ou satures ,est au plus 12

egale a 10 atomes par seconde, ce qui ne pourra i t conduire

qu 'a des equivalents de dose au plus de l ' o r d r e de

500 uSv.an 1 pour les habitants les plus proches ; c ' e s t un

niveau qui peut encore etre consider?, comme acceptable par une

population mais qui ne l e se ra i t plus s ' i l devait croxtre

notablement.

- Un accroissement de l a charge en radium dans l a chaine

a l imentaire , a l a suite de l a saturation des ba r r i e r e s qui

assurent encore sa retent ion, t e l l e que l e bar rage , et sans

doute certaines a l luv ions , est egalement un r isque poss ib l e a

l ' e c h e l l e de quelques dizaines d'annees.

4.2 Examen des d i f fe rentes solutions envisagees

4.2.1 Maintien a long terme de l a s i tuat ion t r ans i t o i r e

ac tue l l e ( s tatu quo)

On pourra i t f a i r e une estimation theorique du r isque

d 'appar i t ion des e f f e t s stochastiques pour l es personnes du

groupe c r i t i que en considerant un taux d 'appar i t ion egal a -2 -1

10 • Sv , ce qui conduira i t , au bout de cinquante ans a un -6 -4 r isque in fe r ieur a 5.10 (cas du radium) ou 2,5.10 (cas du

radon) .

Dans l e cadre de l a solut ion du statu quo, bien sur sous

surve i l l ance , ce niveau de detriment indiv idue l pourrait etre

maintenu, ou tout au moins ne pourrait c rott re que lentement,

ce qui l a i s s e r a i t l e temps de prendre les mesures

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conservatoires necessaires. Toutefois, aucun des risques evoques plus haut ne serait reellement pris en compte. De plus 7

le financement d'eventuelles mesures conservatoires, si elles devenaient necessaires a moyen terme, risquerait d'etre difficile a trouver.

4.2.2 Deplacement des residus vers un site de stockage plus approprie et restitution des sols a leur etat initial

Le stockage des residus dans des anciennes carrieres est considere comme le plus satisfaisant par les experts, et une solution de ce type a ete recherchee car elle supprimait tous les risques locaux. Ici cette solution n'est pas possible car il n'y a pas de carriere dans la region capable de recevoir 1 500 000 tonnes de produits et capable d'isoler a long terme ces produits du public.

4.2.3 Stabilisation des boues in situ et reconstitution d'un nouveau paysage apres recouvrement

Deux scenarios de stabilisation sont examines : - couverture generale des residus, - stabilisation chimique de 1'ensemble du stockage ou partiel.

Dans les deux cas, la difficult?, provient de ce que les engins lourds ne peuvent pas manoeuvrer sans precaution sur les boues.

4.2.4 Utilisation des residus et du barrage en tant que materiaux valorisables pour les operations de genie civil et restitution des sols a leur etat initial

Au lieu de chercher a confiner les radionuclides dans la zone de stockage, il s'agit ici d*examiner les conditions dans lesquelles les residus radioactifs pourraient etre disperses de facon controlee sur le territoire regional. On supprimerait par la meme les risques lies a la concentration en un seul point des materiaux radioactifs et les risques lies a la surete du stockage lui-meme. On satisferait les souhaits de

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r e s t i tu t i on du s i t e a son u t i l i s a t i o n pr imit ive exprimes par

1 1 Administration.

C 'est dans cet espr i t qu 'est examinee l a p o s s i b i l i t y de

fabr iquer l es granulats u t i l i s a b l e s en genie c i v i l .

En France, des problemes d 'obtention de materiaux pour

l es travaux de genie c i v i l commencent a se poser par suite des

r e s t r i c t i ons d 'ordre environnemental apporte.es a l ' ouverture

des car r ie res et a 1 'extraction des sables des r i v i e r e s .

Les points a" etudier en de ta i l s concernent :

- l es traitements pa r t i cu l i e r s a mettre en oeuvre pour

s a t i s f a i r e aux exigences techniques,

- l e r isque d 'exposit ion aux rayonnements des t r ava i l l eu r s

pendant les manipulations des produits et ulterieurement pour

les travaux de repr ise et re fect ion des ouvrages,

- l e r isque de l i x i v i a t i o n des produits sur p lace ,

- l e recensement des l ieux d ' u t i l i s a t i o n ,

- l e s couts de transport et de mise en oeuvre.

En France, nous disposons actuellement de 15 mi l l ions de

tonnes de residus de traitement de minerai.

Une var iante de ce type de solution qui aurait pu etre

mise en oeuvre immediatement e ta i t l ' u t i l i s a t i o n en materiaux

de soubassement de route, mais l a r ea l i s a t i on de l ' autoroute

s ituee a proximite est trop avancee pour que les quantites

disponibles soient u t i l i s e e s .

4.2.5 Va lo r i sa t ion des_modifications topographiques apportees

au_s i te par 1 'exp lo i tat ion

I I s ' a g i t i c i de tenter de f a i r e un bien d'un mal.

Une solut ion presentant pour les municipalites loca les un

interet certain est l a transformation du bass in en base

nautique, qui donnerait un a t t r a i t tour ist ique evident a l a

region.

Un certain nombre de travaux seraient necessaires pour

rehausser l e niveau de l ' e au et recouvrir d'eau les plages

http://apporte.es
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actue l les constitutes de residus de traitement. Ceci

supprimerait les r isques d'enlisement et d ' i r r ad i a t i on du

pub l i c . Le recouvrement de 1'ensemble des residus pourrait par

l a suite r a l en t i r l es t rans fer ts vert icaux de radon et de

radium soluble.Des apports de sables de r i v i e r e seraient

necessaires pour reconstituer des plages qui ne presenteraient

plus de r isques d ' i r r ad i a t i on pour l e pub l ic .

Dans cette so lut ion, seuls les risques presentes par les

t ransferts de radium a 1'environnement par i n f i l t r a t i o n dans

l e sous-so l et au travers du barrage ne sont pas p r i s en

compte.On a vu que dans l a s i tuat ion ac tue l l e , l e detriment

radiologique qui pourrait resu l te r de ces i n f i l t r a t i o n s e t a i t

de l ' o r d r e de 10 7 an 1 ce qui est dans l e domaine de

1 'acceptable.

Independamment ou conjointement a cette solution i l est

envisage d ' u t i l i s e r l e bass in comme l a retenue amont d'une

pet i te centrale hydroelectr ique. On va l o r i s e i c i l a capacite

de stockage d 'energie potent i e l l e o f f e r te par l e barrage qui

permet de disposer d'un volume d'eau de l ' o r d r e du mi l l i on de

metres cubes sur une hauteur de chute de 50 metres.

REFERENCE

[1 ] FOURCADE, N., MARPLE, MX., ZETTWOOG, P., <Le radium 226 dans la chaine alimentaire au voisinage d'un site minier d'uranium), Environmental Migration of Long-lived Radionuclides (C.R. Coll., Knoxville, 1981), AIEA, Vienne (1982) 382.

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URANIUM MILL TAILINGS CONTAINMENT SYSTEMS PERFORMANCE AND COST

V.C. ROGERS, K.K. NIELSON, D.C. RICH, M.W. GRANT, M.L. MAUCH, G.M. SANDQUIST, G.B. MERRELL Rogers and Associates Engineering Corporation, Salt Lake City, Utah, United States of America

Abstract

URANIUM MILL TAILINGS CONTAINMENT SYSTEMS PERFORMANCE AND COST. A systems performance and cost model, being developed for the Uranium Mill Tailings

Remedial Action Program, is described. The model can be used to evaluate the effectiveness and cost-effectiveness of remedial action alternatives. Although still in the developmental stage, it incorporates most of the research and development results of the Technology Development Program. Also discussed are research programmes being conducted in the areas of radon emanation coefficients for the tailings, radon transport through tailings cover systems and contaminant leaching from tailings.

1. INTRODUCTION

In the ear ly stages of the development of the uranium mi l l ing industry in the USA that occurred during the 1950s and ear ly 1960s, the U.S. government and industry cooperated in finding and mi l l ing uranium ore in the western U.S. on a very large sca le . While complying with the regulations of those times, the uranium mi l l s l e f t large p i l e s of uncovered mill t a i l i n g s , often in proximity to population centers and in areas of scarce surface water and groundwater resources.

A number of factors have combined to spot l ight the necessity fo r better disposal of the uranium mill t a i l i n g s that were generated during those years . These include:

t Better understanding of the immediate hazards of uranium mill t a i l i n g s .

t Better appreciation of the long-term hazards of the radionuclides in uranium mill t a i l i n g s .

§ S t r i c t e r requirements for disposal of t a i l i n g s and radioact ive waste in general .

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• Shifts in population and increased use of ground and surface waters in the west. (For example, the Vitro mill outside Sa l t Lake City was beyond the l imits of the bu i l t -up area when i t was constructed. Today, i t s t a i l i n g s p i l e is close to the center of the population of the Sa l t Lake Va l l ey . )

As a resu l t of these and s imi lar f ac tors , the inactive Uranium Mill Tai l ings Remedial Action Program (UMTRAP) has been in i t i a ted by the Department of Energy (DOE) to properly s t a b i l i z e and i so l a te the uranium mill t a i l i n g s and former uranium processing s i t e s . An important component of the UMTRAP is the Technology Development Program (TDP)CD. As part of the TDP e f f o r t , a program for t a i l i n g s impoundment sys­tems' performance and cost analysis is being developed by Rogers and Associates Engineering Corporation (RAE). In the develop­ment of the model, research resu l ts from nearly a l l aspects of the TDP are being u t i l i z ed including cover technology, l ine r technology, hydrogeology and e f f o r t s from other basic studies .

2. SYSTEMS PERFORMANCE

The large volumes of t a i l i n g s to be dea l t with d ictate that most of the p i l es be s tab i l i zed in place for cost reasons. Disposal on the ground, in turn, means that health impacts could occur from several credib le pathways to the environment. The major pathways are depicted schematically in Figure 1.

At this time the potential pathways for radionuclide migration from shallow and surface disposal f a c i l i t i e s have been well ident i f ied and have been modeled to some extent. The complexity of the models ranges from simple but adequate repre ­sentations of radionuclide migration through the atmosphere to complex but r e l a t i v e l y unproven models of erosion. The designer of a remedial action disposal f a c i l i t y can co l l ec t these com­puter codes and, running each one separate ly , can try a number of parameters and features until a design that provides s u f f i ­cient protection for a l l major pathways is achieved. This pro­cess is r epe t i t i v e , ine f f i c i ent and usual ly involves the exam­ination of a spec i f ic pathway with l i t t l e regard to the e f fect of the modeled character i s t ics on bar r ie r s to migration by other pathways. Unfortunately, a good design from the point of preventing migration by one pathway may weaken bar r ie rs to migration by another. For example, a moist cover i s des i rab le for preventing radon escape but keeping the cover wet by con­t r o l l i n g the surface i n f i l t r a t i o n of prec ip i tat ion may f a c i l i ­tate migration to groundwater. Thus, the bar r ie rs needed for

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FIG.l. Major exposure pathways to man.

the d i f f e rent pathways can be interdependent. They form a system of ba r r i e r s in which parameter changes to increase ef ­fectiveness in blocking one pathway may reduce ef fect iveness in blocking another.

The systems performance model being developed allows the t a i l i n g s s i t e reclamation design to be treated as a complete, interact ive system. The model wi l l a l low the designer to determine the total performance of the system as well as the e f f ec t of changing one or more parameters on the performance of the s i t e with respect to a l l the s i gn i f i cant pathways.

In addit ion, costs of the ent i re containment system wi l l be determined so that the remedial action s t ab i l i z a t i on sys ­tem can be optimized with respect to costs .

The interact ive nature of the major components of the performance model i s presented in Figure 2. For s impl ic i ty only elements influencing systems performance for the radon and groundwater pathways are shown.

The ca lculat ion begins with an i n i t i a l cover and l i n e r -subsoil spec i f i ca t ion , and then a water balance and equi l ibr ium moisture p ro f i l e s are establ ished for the system. With this information the average radon emanation rate and contaminant leach rates are ca lcu lated . The next step i s a ca lculat ion of radon d i f fus ion through the t a i l i n g s and cover materials with a subsequent comparison of the surface radon f lux to a spec i f ied surface f lux c r i t e r i on . A cover cost optimization rout ine, not shown in the f i gu r e , then a l t e r s the i n i t i a l cover thicknesses to obtain an optimized cover configuration which s a t i s f i e s the f lux c r i t e r i on .

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T A I L I N G S

R A D O N G R O U N D W A T E R

1 1

E M A N A T I O N L E A C H E M A N A T I O N L E A C H

M E T E O R O L O G Y

C O V E R

P A R A M

D I F F U S I O N

N O

WATER B A L A N C E

P R O F I L E L I N E R ,

SUBSOIL

P A R A M

N O

SEEPAGE

F L U X

A Q U I F E R

H Y D R O L O G Y

f C O N T A M I N A N T > / C O N C E N T R A T I O N

OR RELEASE C R I T E R I A

FIG.2. Major component interaction diagram.

The water balance and p ro f i l e are then reca lcu lated , and a groundwater nuclide transport ca lculat ion is performed, with the resu l t ing contaminant concentrations or re lease rates being compared to the relevant c r i t e r i a . I f the c r i t e r i a are s a t i s ­f ied and no l i n e r system is included, then the code passes to the next major component. I f the c r i t e r i a are not s a t i s f i e d , then a separate optimization routine modifies e i ther the l i ne r parameters or the cover parameters, whichever is c o s t - e f f e c t i v e , using the method of steepest descent and subsequently, a f ina l groundwater ca lculat ion is performed before proceeding with the remaining ca lcu lat ions .

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3 . TECHNOLOGY OF SELECTED COMPONENTS

Research and technology development is a l so being per ­formed at RAE on several key components of a t a i l i n g s reclama­tion system. Three of these research areas that w i l l be d i s ­cussed herein a re : radon transport through cover systems, radon emanation from t a i l i ng s and contaminant leaching from t a i l i n g s . The resu l ts of these and other research programs have a lso been incorporated into the systems performance and cost model. A fourth key area for the model, moisture pro­f i l e s and groundwater t ransport , i s a lso discussed in this section.

3 . 1 Radon Diffusion

For the UMTRAP s i t e s , the radon pathway genera l ly dom­inates the potential hazards C 2 J . Thus, as part of the TDP e f f o r t for covers, work on the measurement and modeling of radon attenuation through cover systems has been proceeding under a subcontract to Ba t t e l ! e , Pac i f i c Northwest Laborator­i e s .

In the laboratory work, radon di f fusion coe f f i c i en t s , D, have been determined for several s o i l s obtained in the v i c in i ty of f i ve UMTRAP s i tes C 3 3 . A l i s t i n g of the so i l s and soi l parameters is given in Table I . Also l i s t ed are laboratory measurements of D for each soi l type. Several techniques were used to perform the d i f fus ion coe f f i c ient measurements, inc lud­ing open system f lux and so i l gas p r o f i l e measurements on so i l columns, s ta t i c radon concentrations in closed soi l columns, and time-dependent radon concentrations on small soi l samples in a transient radon test f a c i l i t y . Each of these measurement techniques possesses par t icu la r advantages and disadvantages that influences i t s s u i t a b i l i t y for a spec i f i c app l icat ion . However, the techniques y i e ld consistent values for D. Pre­vious radon di f fus ion coe f f i c ient measurements for representa­t ive western U.S. s o i l s indicated a strong corre lat ion between D and the soi l moisture content C 4 D . However, the data for D at high moistures are sparse. Sample preparation and charac­ter izat ion are d i f f i c u l t at higher moistures, but measurements of D are being made at high moistures. A representative set of high-moisture measurements is shown in Figure 3 for Riverton, Wyoming, s o i l . The measurements have been made with a var iety of techniques, and the result ing values for D are within exper­imental uncertaint ies . The uncertainty in moisture saturation for these measurements is about f i ve percent.

In a re lated program, personnel at RAE have a lso developed a model for ca lculat ing D for porous earthen materials based only upon physical measurements of the material C 5 3 . The model

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TABLE I

RADON DIFFUSION CHARACTERISTICS OF CANDIDATE SOILS

FOR TAILINGS COVERS

Density Moisture Diffusion Coeff. Soil (g/cm 3) Porosity (dry wt. %) D (cm 2/s)

Vitro Soil 1, .62 0 .40 13.1 0.015

Vitro Soil 1. ,81 0, .33 11.6 0.0042

Vitro Soil 1. ,53 0, .43 9.0 0.014

Vitro Clay 1. ,30 0, .52 27.6 0.0052

Vitro Clay 1. .31 0, .51 23.0 0.0058

Durango Clay 1. ,55 0. .43 5.9 0.040

Shiprock Clay 1. ,16 0, .57 20.3 0.026

Shiprock Soil 1. 48 0. ,45 6.0 0.033

Riverton Soil 1. .61 0. ,40 3.4 0.064

Riverton Clay 1. ,33 0. ,51 19.3 0.017

Grand Junction Soil 1. ,72 0. ,36 10.6 0.017

i s based in part upon the pore s ize d i s t r ibut ion of the soi l mater ia l . In addition to being measured d i r e c t l y , th is param­eter can be estimated from e i ther the water drainage curves or from the pa r t i c l e s ize d i s t r ibut ion C6H. The so l id curve in Figure 3 is a ca lculat ion of D for Riverton so i l using the par ­t i c l e s ize analysis and the dashed l ine is based instead on water drainage curves. The agreement with experiment for both curves is general ly within experimental uncerta int ies .

An additional re lated e f f o r t is the development of com­puter codes for ca lculat ing the radon f lux and concentrations through cover mater ia ls . One code, RAEC0, L73 obtains steady-state analyt ica l solutions to the one-dimensional equation using a rapid upper t r iangulat ion and backward solving routine. This code i s incorporated into the systems performance and cost model.

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0 0.2 0 .4 0.6 0.8 1.0

MOISTURE SATURATION, m

FIG.3. Diffusion coefficients for Riverton, Wyoming, soil.

Another code, 3DRD C83 employs a f i n i t e di f ference tech­nique to solve the steady-state three-dimensional radon t rans ­port equation. I t has been used to develop a simple co r r e l a ­tion for estimating the impacts on radon attenuation that occur from cover degradation owing to crack formation and for root and animal penetrations.

Field tests are a l so being conducted to provide benchmark f i e l d ve r i f i ca t ions for the modeling and laboratory radon d i f ­fusion measurements. One major benchmark is the cooperative " j o in t f i e l d t e s t " reported elsewhere in the proceedings of this conference C9D. Other f i e l d tests include 3 and 4m c o l ­umn tests with s ing le earthen cover materials at Grand Junc­t ion , Colorado, and Mexican Hat and Sa l t Lake C i ty , Utah. Character ist ics of these f i e l d tests are given in Table I I . Although the tests are s t i l l in progress , there i s good agree ­ment between the laboratory measured D for the materials and the D deduced from the preliminary radon f lux and concentration

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TABLE II

COMPARISON OF FIELD AND LABORATORY MEASUREMENTS

OF RADON DIFFUSION IN EARTHEN COVERS

D e n s i t y In i t i a l Cover Diffusion Coef f ic ient , D J* Moisture Thickness (cm /s )

Site (g/cnr) Porosity (dry wt.%) {m} Lab Field

Grand Junction, CO 1.3 0.52 7.4 3.7 0.021 0.027

Mexican Hat, UT a 0.33 6.4 3.7 0.013 0.038

Salt Lake City, UT 1.6 0.41 16.6 3.7 0.0074 0.0083

Final density measurement to be made.

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FIG.4. Radon emanation coefficients versus moisture in Grand Junction tailings.

measurements in the f i e l d when di f ferences in moisture and com­paction are taken into account. Radon attenuation is greatest at Sa l t Lake City. The low compaction of the covers at Grand Junction and the low moisture in the cover at Mexican Hat adversely a f f ec t the radon attenuation for the tests at those s i t e s . During the course of the research pro ject , extensive development a lso occurred on several methods for measuring radon f luxes 131.

3.2 Radon Emanation

Recent measurements of the radon emanating power, E, from uranium ores L101 indicated an increase in E of as much as a factor of f i ve with increasing moisture. In the present r e ­search e f f o r t s , values of E have been measured for t a i l i n g s at Grand Junction, Colorado, and Sa l t Lake City , Utah. The Grand Junction r e s u l t s , shown in Figure 4, indicate increases up to about a factor of four with increasing moisture. Increases of a factor of two are observed for the Sa l t Lake t a i l i n g s and help explain di f ferences in previous measurements for these t a i l i ng s £11,1211.

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3.3 Leach Model

Efforts have been made on a contaminant leach model that would e x p l i c i t l y include the e f fects of p rec ip i ta t ion , the i n ­f i l t r a t i o n of p rec ip i ta t ion , and the equil ibrium sorption coef­f i c i en t . The resu l t ing expression for the leach constant i s :

L = leach constant ( a " )

k d = equi l ibr ium sorpt ion c o e f f i c i e n t (m 3 /kg)

x = t a i l i n g s thickness (m)

P = water i n f i l t r a t i on rate (m/a)

km = mass transfer coe f f i c ient ( a - * )

f = f ract ion of year prec ip i tat ion occurs

d = density of the t a i l i n g s (kg/m ) .

So lub i l i t y constra ints , which r e f l e c t the chemical environment, impose upper bounds on the nuclide leach rates . The physical characterization of the t a i l i n g s and leachate, f low condit ions, and laboratory and f i e l d measurements provide guidance in the selection of appropriate values for k .

3.4 Groundwater Transport and Moisture P ro f i l e s

The determination of the groundwater f low patterns for the unsaturated and saturated regimes is extremely complex and s i t e -dependent. The use of a complete but general hydrologic contam­inant migration model is not consistent with the constraints of the systems performance and cost model. Therefore, as a bound­ing estimate of contaminant migration in the saturated and un­saturated regimes, the hydraulic conductivity w i l l be used in the one-dimensional equations for d i spe r s i ve , advective nuclide migration. The analyt ica l expressions for contaminant migration given by Burkholder and Rosinger C133 are used in the systems model. The point source analyt ica l solutions for contaminant migration in the groundwater are numerically integrated over the area of the t a i l i n g s p i l e to account for the spatial dispersion of the nucl ides . In addition major changes in the groundwater pH, i f they occur, are accommodated using the method described in Reference 14.

[ l - exp (-k x f / P ) ] , (1 )

where,

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Efforts are currently underway to develop steady-state models along the l ines of the previous work of McWhorter and Nelson C15I1, Gupta, et al E16D, and Simmons and Gee C17J, for obtaining the moisture p ro f i l e and water balance for a mult i ­layer ta i l ings/cover system. A steady-state formulation should provide adequate data for annual average radon f lux estimates and for long-term equil ibrium hydraulic conduct iv i t ies . The Time-dependent codes C17H wi l l be used to ascertain the degree of v a l i d i t y of the steady-state formulation, given the complex var iat ions in cl imatic conditions.

The equations for the steady-state system bear a strong resemblance to those of References 16 and 17 and l ike the l a t ­t e r , are comprised of a system of f i n i t e di f ference equations. In the present steady-state formulation, the ca lculat ion of the coe f f ic ients is p a r t i a l l y s impl i f ied by the use of approxi ­mate analytical expressions. However, the solution s t i l l en­t a i l s i te rat ion until the moisture p ro f i l e converges.

At present, p ro f i l e s in the cover system for UMTRAP s i tes are estimated from water drainage curves or are approximated with a simple corre lat ion of data from western U.S. uranium mining areas . The co r re l a t i on , appl icab le for areas with an annual preciptation of less than 0.5m and for cover thicknesses exceeding about 1.5m, i s :

M = 19.45p^ - 1.18E + S, (2 )

where,

M = soi l moisture (dry wt. percent)

p = annual prec ip i tat ion (m)

E = annual evaporation (m)

S = soi l index.

The parameter S ranges from over 3.0 for f ine clays to about -1.0 for coarse sand.

4. EXAMPLE ANALYSIS

As an example of the use of the systems performance and cost model in i t s present form, the V i t r o , Sa l t Lake t a i l i n g s p i l e was analyzed for s t ab i l i z a t i on in place with no l i ne r mater ia l , and a cover consisting of a well-compacted clay l ayer , a layer of overburden material and a top layer of 0.15m of top-s o i l . The subsoi ls are saturated, and the calculated leach

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TIME AFTER TAILINGS PLACEMENT (years)

FIG.5. 226Ra concentrations at nearby well.

rates for radium, to 10" 5 per year, well 50m from the The peak in the 2 decay of uranium leached from the dispersion of the t a i l i n g s is a maj the we l l .

-4 thorium and uranium are on the order of 10 The calculated radium concentrations in a

edge of the t a i l i n g s are shown in Figure 5. 2°Ra concentration at 10 5 a a r i ses from the leached from the p i l e . The or ig ina l 2 2 6 R 9

t a i l i n g s decays before reaching the we l l . The contaminant due to the spatia l extent of the

or factor in reducing the concentrations at

Because the radium concentrations at the postulated nearby well are below drinking water standards for the Vitro t a i l i n g s in i t s present condition, the cost optimization centered on the

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Cover Layer

Thickness (m)

D

(10" 2 cm 2 /s )

Exit Flux

(pCi/m 2-s) Cost ($M)

Source Flux entering f i r s t layer 44.2

1 0.42 0.06 6.1 1.47

2 2.43 2.1 2.0 7.22

3 0.15 1.3 2.0 0.50

Total 3.0m $9.19

Other Direct Costs 1.91

Eng. Const Mgmnt 3.33

Contingency 4.33

TOTAL COSTS $18.76

cover. The f inal character i s t ics of the cover and the resu l ts of the radon transport ca lcu lat ions through the cover are given in Table I I I . C r i t e r i a used for this ca lcu lat ion are a maximum surface radon f lux of 2.0 pCi/m^s and a minimum cover thickness of 3m. Unit cost parameters are obtained from a recent Engine­ering Assessment C183.

5. CONCLUSIONS

Character ist ics of the systems performance and cost model and resu l ts of the re lated research and development e f f o r t s are summarized below.

TABLE I I I

VITRO SITE EXAMPLE

Constraints:

1. Maximum Flux = 2.0 pCi/m-s

2. Minimum Thickness = 3.0m

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• Eff luent re leases are evaluated for seven major environmental pathways.

• The interact ive character i s t ics of a t a i l i n g s reclamation design is incorporated into the model.

• Cost estimates and cost optimizations are c a l ­culated with respect to several c r i t e r i a .

• The model is an e f f i c i en t tool for design s tud ies , parameter s ens i t i v i t y studies and program cost -e f fect iveness .

5.2 Supporting Research and Development

• Radon generation and migration models have been developed to provide rap id , accurate ca lculat ions of radon f luxes for complex systems.

• Several so i l s of interest for covers on UMTRAP s i tes have been characterized.

• Several laboratory techniques have been developed for measuring radon di f fus ion coe f f i c i ents .

• Radon di f fusion coe f f ic ients have been calculated for s o i l s using pa r t i c l e s ize d i s t r i bu t i ons , moisture content, porosity and spec i f i c g rav i ty .

• Field tests at many UMTRAP s i tes have provided data to va l idate the models and laboratory measurements.

• A contaminant leach model has been developed which e x p l i c i t l y considers meteorology, prec ip i tat ion i n f i l t r a t i o n ra tes , s o l u b i l i t y l imits and e q u i l i ­brium sorption coe f f i c i ents .

REFERENCES

CD O'BRIEN, P .D . , UMTRAP Technology Development Program, U.S. Dept. of Energy, UMTRA-D0E/AL0-164 (1981).

C23 ROGERS, V.C. , et a l . , Radiation Pathways and Potential Health Impacts from Inactive Uranium Mill T a i l i n g s , U.S. Dept. of Energy, GJT-22 (1978).

5.1 Systems Performance and Cost Model

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Z31 NIELSON, K.K., et a l . , Laboratory Measurements of Radon Diffusion Through Multi layered Cover Systems for Uranium T a i l i n g s , Rogers and Associates Engineering Corp. for Pac i f i c Northwest Laboratory, DOE/UMT-0206 PNL-4107 (1981).

[43 ROGERS, V .C . , et a l . , Characterization of Uranium T a i l ­ings Cover Materials for Radon Flux Reduction, Ford, Bacon & Davis Utah Inc. for Argonne National Laboratory, NUREG/CR-1081 (1980).

E53 ROGERS, V.C. AND NIELSON, K.K., "A Complete Description of Radon Diffusion in Earthen Mater ia ls " (4th Symp. on Uranium Mill Ta i l ings Management, October 26-27, 1981, Fort Co l l i n s , Colorado, USA).

C6: ARYA, L.M. and PARIS, J . F . , A Physicoempirical Model to Predict the Soil Moisture Character ist ics from P a r t i c l e -Size Distr ibut ion and Bulk Density Data, Am. J. Soil Sc i . Soc. 45 (1981) 1023.

C73 ROGERS, V .C . , SANDQUIST, G.M. and NIELSON, K.K., Radon Attenuation Effectiveness and Cost Optimization of Com­posite Covers for Uranium Mill T a i l i n g s , U.S. Dept. of Energy, UMTRA-D0E/AL0-165 (1981).

C83 SANDQUIST, G.M., and ROGERS, V .C . , 3DRD: A Three Dimen­sional Multiregion Radon Diffusion Code, Rogers and Asso­ciates Engineering Corp. report to Pac i f i c Northwest Laborator ies , RAE-9-3 (1981).

E9: HARTLEY, J . N . , et a l . , "Uranium Mill Ta i l ings Remedial Action Project (UMTRAP) Cover and Liner Technology Devel­opment Pro ject" (Proc. Int . Symp. on Management of Wastes from Uranium Mining and M i l l i n g , May 10-14, 1982, Albuquerque, New Mexico, (USA) IAEA-SM-262/39.

CIO: NIELSON, K.K., ROGERS, V.C. and BATES, R.C., A Mathema­t ica l Model for Moisture Effects on Radon Emanation from Uranium Ores, Health Phys. , submitted for publ icat ion.

C113 MACBETH, P . J . , et a l . , Laboratory Research on Ta i l ings S tab i l i za t i on Methods and Their Effectiveness in Radia­tion Containment, U.S. Dept. of Energy, GJT-21 (1978).

E123 RYON, A .D . , HURST, F.J. and SEELEY, F.G. , N i t r i c Acid Leaching of Radium and Other S ign i f icant Radionuclides from Uranium Ores and Ta i l i n g s , Oak Ridge National Labo­ratory , ORNL/TM-7065 (1980).

C133 BURKHOLDER, H.D. and ROSINGER, E .L .J . , A Model for the Transport of Radionuclides and thei r Decay Products Through Geologic Media, Nucl. Tech. 49 (1980) 150.

E143. GEE, G.W., et a l . , " Interact ion of Uranium Mill Ta i l ings Leachate with Morton Ranch Clay Liner and Soil Mate r i a l , " (3rd Symp. on Uranium Mill Ta i l ings Management, Nov. 24-25, 1980, Ft. Co l l i n s , Colorado, USA).

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C15J McWHORTER, D.B. and NELSON, J . D . , Unsaturated Flow Beneath Ta i l ings Impoundments, Proc. Am. Soc. Civ. Eng. 105 (1979) GT11.

[1611 GUPTA, S.K. , et a l . , Fie ld Simulation of Soi l -Water Movement with Crop Water Extraction, U. of Cal . Dept. of Land, A i r and Water Resources, SE No. 4013 (1978).

C173 SIMMONS, C.S. and GEE, G.W., Simulation of Water Flow and Retention in Earthen Cover Mater ia l s , Pac i f i c North­west Laboratory, DOE/UMT-0203 PNL-3877 (1981).

C18J Engineering Assessment of Inactive Uranium Mill T a i l i n g s , Ford, Bacon & Davis Utah I n c . , D0E/UMT-0102 FBDU 360-00 (1981).

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CHARACTERIZATION OF WASTES

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Chairman

J. PRADEL F r a n c e

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HYDROGEOCHEMICAL EVOLUTION OF AN INACTIVE PYRITIC URANIUM TAILINGS BASIN AND RETARDATION OF CONTAMINANT MIGRATION IN A SURROUNDING AQUIFER

N.K. DAVE, T.P. LLM CANMET, Energy, Mines and

Resources Canada, Elliot Lake Laboratory, Elliot Lake, Ontario

A.J. V I V Y U R K A Rio Algom Limited, Elliot Lake, Ontario

N. DUBROVSKY, K.A. MORIN, D.J.A. SMYTH, R.W. GILLHAM, J.A. CHERRY Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, Canada

Abstract

HYDROGEOCHEMICAL EVOLUTION OF AN INACTIVE PYRITIC URANIUM TAILINGS BASIN AND RETARDATION OF CONTAMINANT MIGRATION IN A SURROUNDING AQUIFER.

At the inactive Nordic tailings impoundment in the Elliot Lake uranium mining district, Ontario, hydrogeochemical investigations are being conducted to determine the effects of pyrite oxidation on the chemistry of pore water in the tailings and on the subsurface leaching of metals and radionuclides from the tailings. The tailings have been inactive for more than a decade and in recent years the tailings surface has'supported a cover of grass. Originally the pH of the tailings pore water was about 7, but since the tailings became inactive, near-surface pyrite oxidation resulting from exposure to oxygen and water has caused the pH of pore water above the water table in the tailings to decline to the range of 1.5 to 3, with an associated rise in dissolved iron, sulphate, metals and radionuclides to high concentration levels. The direction of net subsurface water movement in the tailings is downward and therefore the acidic pore water gradually moves downward through the tailings into the permeable sandy groundwater zone beneath the tailings. The rate of this downward migration is controlled by the rate of downward pore water flow and by geochemical processes, primarily those that consume acid, such as reactions involving residual lime-derived carbonate minerals and reactions involving iron and aluminium. In most of the tailings area, the zone of low-pH pore water has not yet reached the bottom of the tailings. In one of the areas where it has passed all the way through the tailings, a plume of tailings-derived water with high iron and sulphate concentrations has

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moved in the sand aquifer a horizontal distance of 400 m beyond the tailings dam. Although the iron-sulphate plume has moved this far, the front of the low pH water is still close to the toe of the tailings dam. Three years of monitoring has established that the low-pH front is advancing in the sand aquifer at a rate that is less than 1% of the groundwater velocity. The rate of acid-front advance is severely retarded because of pH neutralization caused by the. dissolution of trace amounts of carbonate minerals in the sand. Although the plume segment beyond the low-pH front has high concentrations of iron and sulphate derived from the tailings, it does not contain hazardous levels of radionuclides or heavy metals, because these constituents are either insoluble or strongly adsorbed at neutral pH. A narrow zone, near the bottom of the tailings, was observed to have high solid-phase concentrations of various chemical and radioisotope constituents. This is attributed to the settling of fines in the bottom layer containing precipitates of gypsum and metal hydroxides, and co-precipitation and adsorption of trace metals and radionuclides from the residual process water.

INTRODUCTION

The uranium mining industry produces a large volume of low level radioactive waste material which, following milling, extraction and neutralization processes, is deposited in exten­sive tailings impoundments. In many cases the orebodies are associated with metal sulphides such as pyrite, marcasite and pyrrhotite which are not desired products and are released to the tailings as part of the mill wastes. Upon weathering, these metal sulphides are readily oxidized, producing acid mine drain­age conditions from these tailings piles which is of considerable environmental concern.

The oxidation of pyrite and other iron sulphides produces highly acidic conditions within the tailings with the subsequent leaching of the tailings material resulting in highly acidic pore water containing significant concentrations of iron, sulphate, heavy metals and trace radionuclides. The migration of such a poor quality tailings water either by surface run-off or sub­surface groundwater can lead to serious deterioration in the quality of adjacent natural water systems.

During the operating phase of the mine the water quality of the surface and groundwater seepage can be controlled by on-site neutralization and treatment facilities. The potential for pyrite oxidation and acid generation should, however, persist for decades in abandoned tailings. The mining industry is thus faced with the difficult task of devising long term abandonment schemes that minimize pyrite oxidation and prevent the release of contaminants to the environment. These schemes should be cost effective and should require very little future maintenance or monitoring.

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Hydrogeochemical invest igat ions of an inactive py r i t i c uranium t a i l i n g s basin at the Nordic Mine in E l l i o t Lake, Ontario, have been on-going for the past four years , to ident i fy : 1) the zone of act ive pyr i te oxidation; 2) geochemical character i s t ics of the pore water; 3) s o i l gas and so l id phase composition of the t a i l i n g s mater ia l ; 4) migration of contaminants as a sub-surface seepage in the surrounding aqui fer ; and 5) interact ion of the vegetat ive cover with the t a i l i n g s material in r e l a t ion to uptake of radioisotopes and other contaminants. Results obtained to date are b r i e f l y reported here, the de ta i l s of some of the resu l ts can be found elsewhere [ 1 - 5 ] .

GEOLOGY AND HYDROLOGICAL SETTING

The Nordic Mine s i t e is located about 5 km east of the town of E l l i o t Lake. The mine operated from 1957 to i t s closure in 1968. The uranium mined at the s i t e was a metamorphosed quartz pebble conglomerate containing 5-10% py r i t e , 0.11% U 3 O 8 , 0.02% TI1O2 and 0.056% rare earths: yttrium, cerium and neodymium oxides.

The Nordic t a i l i n g s impoundments are shown in F ig . 1. The la rgest impoundment, known as the Nordic main t a i l i n g s , covers an area of 70 hectares and contains approximately 10 mi l l ion tonnes of t a i l i n g s with an average thickness of 12 m. The smaller impoundment situated immediately west of the Nordic main t a i l i n g s , known as the Nordic West-Arm, covers an area of 15 hectares and contains approximately 2 mi l l ion tonnes of t a i l i n g s with an average thickness of 7 m. A peripheral dam of mine waste and overburden, and c ross -va l l ey dams complete the impoundment. The t a i l i n g s impoundments are situated in a g lac iated -valley that runs east to west between bedrock uplands formed from Lower Proterozoic arenaceous sedimentary rocks that s t r ike east-west and dip to the north. The va l l ey f l oor is underlain by Pleistocene sediments that comprise, from the o r i g ina l surface downwards, sand and gravel of g l a c i o - f l u v i a l o r i g in over a layer of sandy, bouldery g l a c i a l t i l l . A layer of black peat , 0.5 to 1 m thick, covers the sand and gravel in much of the va l l ey area in which the t a i l i ng s were deposited. The peat formed in a spruce bog that formerly existed in the area. A dense vegetation cover over most of the t a i l i ng s surface has been establ ished for the past 3-5 years .

The t a i l i n g s area receives approximately 0.8 m of p r e c i p i t ­ation annually, pr imari ly as spring and f a l l ra in and winter snow. The water tab le in the t a i l i n g s ranges in depth from about 1 m to 10 m below ground surface and i t f luctuates by a metre or so with the seasons.

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The Nordic main t a i l i n g s area a l s o r e c e i v e s sur face run -o f f from the rocky h i l l s lope on the northern edge and dra inage from a h igher t a i l i n g s area on the o ther s ide o f the dra inage d i v i d e . Water that does not seep i n t o the t a i l i n g s f l ows eastward across the t a i l i n g s i n t o a l a r g e channel that dra ins from the t a i l i n g s through a decant s t ruc ture t o a seepage c o l l e c t i o n d i t c h beyond the no r th - eas t e rn corner of the t a i l i n g s . The e f f l u e n t from the

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drainage ditch is treated with lime and barium chlor ide to control pH, dissolved metals and radionuclide concentrations. Other than the s ing le decant passageway, the only other out let for water flow from the t a i l i n g s is by way of downward seepage through the t a i l i n g s into the underlying sand and grave l . Groundwater in the t a i l i ng s flows v e r t i c a l l y downward in the upper zone turning gradual ly to a north-south horizontal flow near the bottom of the t a i l i ng s because of the reduced permeabil ity of the peat layer , and coarse and f ine f ract ion interbedding planes.

ORIGIN AND MIGRATION PATHWAY OF CONTAMINANTS

Contaminants that or ig inate in the t a i l i ng s are transported in the flowing pore water towards the bottom of the t a i l i ng s where they enter the latera l ly -moving groundwater in the sand and gravel aqui fer . In the zone above the water tab le in the t a i l i n g s , re ferred to as the Vadose Zone, metals and radionuclides are released from so l ids to the pore water as a resu l t of pyr i te oxidation and subsequent leaching. With recharge events and i n f i l t r a t i o n , the reaction products are gradual ly transported downward into the zone below the water table known as the Phreatic Zone. In this zone, the res idual neutra l ized pore water is thus gradual ly being replaced by the highly ac id i c , high tota l d i s ­solved so l ids recharge pore water. The acid ic pore water jo ins the horizontal flow in the sandy aquifer near the t a i l i n g s impoundment dams and appears as a contaminant plume in the surrounding formation.

For the deta i led invest igat ion of the hydrogeochemical evolution of the py r i t i c uranium t a i l i ng s p i l e , so l id and so lu ­t ion samples were taken from various locations (F ig . 1) and analyzed for chemical and radioisotope consituents. The resu l t s obtained are discussed below.

VADOSE ZONE

Samples for chemical analyses of the s o l i d , l i qu id and gas phases were col lected in deta i led p ro f i l e s above the water table at s i tes T -1 , T-3 and T-5 (F ig . 1 ) . T-1 was representative of areas with shallow water tables and f ine grained t a i l i n g s , T-3 represented medium to f ine t a i l i n g s with a deep water table while T-5 was situated in an area of coarse t a i l i n g s with deep water t ab l e . Sol id phase analyses included so lub le -su lphate , py r i t e , carbonate, Th-228, Th-230, Th-232, Ra-226 and Pb-210; solution phase analyses included pH, e l e c t r i c a l conductance, SOt*, F e ( t o t a l ) , Ca, Na, K, Mg, Pb, Zn, N i , Co, Mn, Cu, A l , C I , Br and Si ; and gas phase analyses included O 2 , N2 and C O 2 . Selected parameters were determined on two occasions, in May and in August, in order to provide some indication of the seasonal v a r i a b i l i t y in the

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T-3

Electrical conductance (yS) mg/L S0 4

5L

FIG.2. Hydrochemical profiles of pH, electrical conductance, SO4, Fe(total), Na, K, Mg and Ca of unsaturated zone at T-3 site on the Nordic main tailings in August 1980.

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T-3 T-3 Soil-Gas Composition Solid-Phase Geochemistry

0 2 A 6 8 10 12 14 16 20% 0 2,C0 2 0 2 A 6 8 10 wt% pyrite, S as SO,,

7 L 7 L

FIG.3. Soil-gas composition and solid-phase geochemistry profiles at T-3 sites on the Nordic main tailings.

profiles. The results for several parameters obtained at T-3 for the August sampling period are included in Fig. 2 and 3. The pH varied from about 3 near the ground surface to a minimum of about 2 at a depth of 1 m, then increased with depth to values near 6 as the water table is approached. Electrical conductance was reasonably uniform throughout the profile, but was at its minimum value (about 2 000 - u S ) near the ground surface, and its maximum value (20 000 u S ) at a depth of about 1 m. SOi* and Fe in the solution phase behaved in a similar manner, varying from maximum values near 1 m depth (9 000 and 3 500 mg/L, respectively) to relatively low values at a depth of 2 m below ground surface, then both show a gradual increase with depth. The O2 profile shows a decrease from about 20% at a depth of 0.1 m below ground surface to about 2% at a depth of 1.0 m, and then relatively constant values at greater depth. The solid-phase analyses show the pyrite concentration to increase from near zero close to ground surface to a value of about 4% by weight at a depth of 1.5 m and then to remain relatively constant with greater depth.

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The low pH, and high sulphate and iron, combined with the decl ine in O2 suggests that pyr i te oxidation is predominantly occurring in a r e l a t i v e l y narrow zone at a depth of about 0.75 to 1.0 m below ground surface. This is a lso consistent with the low pyr i te content near the surface and the r e l a t i v e l y constant values below 1.0 m depth, and the high soluble sulphate observed in the so l id phase p ro f i l e at 0.75 m depth.

Consequently, the major zone of acid generation appears to be at a r e l a t i v e l y shallow depth in the unsaturated t a i l i n g s . Presumably, as the pyr ite continues to be consumed, this zone w i l l move to greater depths with time. Data col lected in May, in the fol lowing year , indicated that the high sulphate and iron peaks had been displaced downwards as a resu l t of the f a l l and spring recharge events. Although this does not a l t e r the major conclusion given above, i t presents a complicating factor in that i t shows that the chemical character i s t ics observed at a pa r t i cu ­la r point and at a par t icu la r time can be the resu l t of not only the loca l geochemical processes, but a lso of translocation processes. Interpret ing trends in chemical p ro f i l e s on a purely equi l ibr ium geochemical bas is could, therefore, lead to inappro­pr iate hypotheses.

Trends observed at T-1 and T-5 were consistent with those presented for T-3. Because of the f iner texture and shallower water t ab l e , the zone of pyr i te oxidation at T-1 appeared to be narrower and at a shallower depth than at T -3 . In contrast , T-5, which was situated in coarse t a i l i n g s , showed the zone of pyr i te oxidation to extend over a zone from near ground surface to a depth of about 2-5 m.

PHREATIC ZONE

In the saturated zone below the water t ab l e , the chemical p ro f i l e s of the t a i l i ng s groundwater show a two layer system in which recharging p rec ip i ta t ion , with high SOi t , Fe and heavy metal concentrations and low pH, has moved downward into the t a i l i n g s , gradual ly displacing the o r i g ina l high pH, low Fe res idual process water as indicated in F ig . 4. Depth of contaminant penetration is control led by the physical properties and hydrologic sett ing of the t a i l i n g s , the greatest penetration occurring in the areas with coarse grained t a i l i n g s and high downward hydraulic gradients . The l imit of the depth of displacement is marked by decreasing concentrations of Fe and SOt*, coincident with increasing concen­trat ions of CI derived from reagents added during ore processing.

The resu l ts a l so show that a decrease in groundwater pH occurs c loser to the surface than the peak concentration of Fe and SOt (F ig . 4 ) . This retardation of the low pH front indicates the

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FIG. 4. Hydro chemical profiles of pH, CI, SO4, Fe(total), Co, and Ra of saturated and unsaturated zones and 02 gas content of unsaturated zone at T-5 site on Nordic main tailings.

presence of H +-consuming processes in the t a i l i n g s . These processes include the d isso lut ion of primary a luminosi l icate minerals and small amounts of carbonate mineral (0.025 weight %) added during neutra l i zat ion of the mi l l e f f luent . P rec ip i ta t ion of s i de r i t e and hydroxides of Fe and Al resu l t ing from the neutra ­l i z a t i on of low pH water during downward migration is suggested by calculated saturation indices .

I t is a lso seen from the resu l ts that typica l heavy metals l ike cobalt in the solution are mobilized in the high Fe recharge water and prec ip i ta te in the neutra l iz ing zone. Data from observed s i t e s indicate that uranium and Pb-210 behave s im i l a r l y , while the highest Ra-226 concentrations are not associated with the peak Fe concentration. P rec ip i t a t ion , co -prec ip i tat ion and sorption of trace heavy metals and radionuclides occur in the neutra l i z ing zone.

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FIG.5. Cross-section of Ra (pCi/L, 1 pCi = 37 mBq) in the plume area and variation of electrical conductance and pH with distance from the dam centre line at the Nordic main site. Locations of monitoring bundle piezometers are shown in the inset.

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ACIDIC SEEPAGE FROM THE TAILINGS

Acidic seepage from the Nordic Main impoundment occurs in three areas as shown in F ig . 1. Area C contains r e l a t i v e l y l i t t l e contaminants compared to areas A and B. Seepage in area B i s at a pH of about 3 and contains high concentrations of contaminants, but is of minor extent. The wel l -developed contaminant plume in area A has been described by B l a i r et a l . [2 ] and examined in de ta i l by Morin et a l . [3 ] and Cherry, Shepherd and Morin [ 5 ] .

The plume or ig inates within the t a i l i n g s near the impoundment dam and moves p a r a l l e l to the water table into the sand aqui fe r . The plume consists of three sections (F ig . 5 ) . The inner core, which is at a pH less than 5, contains several thousand (6 000-10 000) mg/L of Fe and SOi*, over 3 700 mBq/L (100 pCi/L) Ra-226 and r e l a t i v e l y high concentrations of other contaminants. The outer zone, which surrounds the inner core and extends several hundred metres down-gradient, is at a pH greater than 5.7 and contains a few thousand ( 2 000) mg/L of Fe and SOi*, approximately 370 mBq/L (10 pCi/L) of Ra-226, and r e l a t i v e l y low concentrations of other contaminants. The neutra l izat ion zone is the t rans i t ion region between the other two zones.

Groundwater near the dam has a ve loc i ty of about 700 m/a, however, the inner core is moving only a few metres per year (F ig . 5 ) . The zone of low pH is strongly retarded, i t s ve loc i ty being only 0.1 to 0.3 percent of the groundwater flow r a te . This retardation of contaminant movement is caused by pH neu t r a l i s a ­t ion and chemical p rec ip i ta t ion of s i de r i t e and gypsum as ca l c i t e d isso lves in the neutra l i zat ion zone.

DISTRIBUTION OF TAILINGS SOLID PHASE CONSTITUENTS

The so l id phase d i s t r i but ion p ro f i l e s of chemical and r ad i o ­isotope constituents of the t a i l i n g s were measured at various locations in the Nordic Main t a i l i n g s and the Nordic West-Arm. Solid core samples were col lected with s p l i t spoon and modified Shelby tube samplers at various depths and analyzed for moisture content, s o i l pH, loss on i gn i t ion , py r i t e , to ta l and soluble sulphur, S O i t , Fe, Ca, A l , U, Th and radioisotopes Ra-226, Pb-210, Th-228, Th-230 and Th-232. Some of the resu l ts obtained are indicated in F ig . 6. The resu l ts show that within the t a i l i n g s , two d i s t inct zones of s t r a t i f i c a t i o n ex i s t ; an upper zone of s l i gh t l y increasing or uniform concentration of constituents with depth except in the top 1 m or so where the concentrations were low, and a lower zone, approximately 1 m in thickness, near the t a i l i ng s -pea t inter face , where the constituents were concentrated. In the peat layer underneath the t a i l i n g s , the concentrations of various constituents decrease rapid ly with depth. No s ign i f i cant

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FIG.6. Chemical and radioisotope distribution profiles of the tailings solid phase at sites TH-5 on the Nordic West-Arm and T-3 on the Nordic main tailings.

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l eve l s of contaminant penetration below the peat layer were observed. The top 2 to 5 m t a i l i n g s layer has been ac id i f i ed with an average pH in the range of 3 . 8 compared to 5 . 8 - 6 . 5 underneath i t . Ra-226 concentrations measured in the solution phase were in the range of 3 7 0 0 - 5 550 mBq/L ( 1 0 0 - 1 5 0 pCi/L) for the t a i l i ng s pore water and 5 0 - 8 0 mBq/L ( 1 . 5 - 2 . 2 pCi/L) for groundwater beneath the peat layer and near the bedrock contact.

Various poss ib le mechanisms are bel ieved to contribute to the observed trends of so l id phase s t r a t i f i c a t i o n . They are : a) accumulation of f ines ( p a r t i c l e size smaller than 74 ym) contain­ing prec ip i tates of gypsum and metal hydroxides, in the lower zone produced by the se t t l ing process during the i n i t i a l deposition of the t a i l i n g s ; b ) co -prec ip i tat ion and adsorption of major heavy metals and radionuclides from the res idual neutral ized process water in contact with the lower zone; and c) co -prec ip i ta t ion and adsorption of major heavy metals and radionuclides from the neutra l izat ion of the highly ac id i c , high TDS water.

With the vegetative cover on the t a i l i ng s for the past 3 -5 years , a de f in i te s o i l - l i k e p r o f i l e is developing in the top upper layer , approximately 10-20 cm thick, consisting mainly of decomposed organic matter. The vegetation cover has reduced the e f fect of wind and water erosion and probably reduced, to some extent, the amount of water that annually i n f i l t r a t e s to the water table in the t a i l i n g s .

Samples of various species of plants growing on the t a i l i ng s were co l lected at d i f ferent times in a growth cycle ( i . e . , growing, f lowering and seeding) and were analyzed for Ra-226 and other contaminant uptake. Species sampled were the grasses Red Fescue (Festuce rubra L . ) and Red Top (Agrost is a lba L . ) , and a legume, Birds Foot T re fo i l (Lotus corniculatus L . ) . No var ia t ion between species was observed, though various plant par ts , except seeds, showed s l i ght accumulation of Ra-226 ranging from 7 4 -370 mBq/g ( 2 - 1 0 pCi/g) with an average plant concentration of 166 mBq/g ( 4 . 5 pCi/g) dry matter bas is compared to that of 5 550 to 7 400 mBq/g ( 1 5 0 - 2 0 0 pCi/g) in the t a i l i ng s surface layer . In the seeds, Ra-226 concentration was observed to be low, 18 .5 mBq/g ( 0 . 5 pCi/g) dry matter b a s i s . The resu l ts gave, on a dry weight b a s i s , vegetation to t a i l i ng s concentration ra t io (CR) of 0 . 0 3 for Ra-226 with an estimated transfer coe f f ic ient of 6 x 1 0 ~ 6 from so l id to vegetation based on an average dry matter y i e ld of 0 . 0 6 kg/m2 and root penetration depth of 0 . 2 m. No corre lat ion between Ra-226 and other contaminants l ike Fe, A l , Ca and S0i+ uptake can be establ ished from the data.

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SUMMARY

In view of the above invest igat ions , i t can be stated that in py r i t i c uranium t a i l i ng s impoundments the oxidation of pyr i te and other metal sulphides is of considerable environmental con­cern in evaluating suitab le abandonment options under wet c l im­at ic conditions. Pyrite oxidation takes place in a shallow upper zone of the unsaturated t a i l i n g s below which i t is l imited by the a v a i l a b i l i t y of oxygen. The oxidation produces highly ac id ic conditions within the t a i l i ng s which causes leaching of metals and radionucl ides . With i n f i l t r a t i o n and recharge events, the reaction products gradual ly migrate downwards replacing the redisua l neutral ized process water by the acid ic recharge water. With the res idual a lka l ine buffer in the t a i l i n g s , the ac id ic pore water is neutral ized as i t migrates downward, p rec ip i ta t ing hydroxides of Fe, Al and gypsum. Co-precip itat ion and adsorption of heavy metals and trace radionuclides a lso takes place in the neutra l izat ion zone. Acidity is a lso consumed by d isso lut ion of a luminosi l icate minerals and poss ib ly gibbsite(aluminum hydroxide) before the neutra l izat ion zone. For a par t icu la r hydrological s i tuat ion of the impoundment, this acidic pore water enters the hor izonta l ly flowing groundwater near the impoundment dams where i t appears as a major contaminant plume. In the aquifer beneath the dams, the migration of contaminants is appreciably retarded to less than 1 percent of the groundwater flow because of the neutra l izat ion processes involved with ca l c i t e d i sso lut ion .

In the t a i l i ng s so l id phase, depletion of py r i t e , other metals and radionuclides takes places in the shallow oxidation zone with the acidic front progress ive ly moving downwards. A narrow zone, near the bottom of the t a i l i ng s and peat layer i n t e r ­face, was observed to have high concentrations of various chemical and radioisotope constituents which is attr ibuted to the se t t l ing of f ines in the bottom layer , containing prec ip i tates of metal hydroxides, and co -prec ip i tat ion and adsorption of radionuclides from the res idual process water. L i t t l e evidence of contaminant penetration below the peat layer was observed because of the groundwater hydrology of the system and sorption capacity of the peat l ayer .

S tab i l i za t ion of the t a i l i ng s surface with a vegetative cover has reduced wind and water erosion and has developed a top 10 to 20 cm s o i l - l i k e layer . S l ight accumulation of Ra-226 isotope was observed in the vegetation with a vegetation to t a i l i ng s concentra­t ion ra t io (CR) of 0.03 on dry matter bas is and transfer c o e f f i c ­ient of 6 x 1 0 - 6 . No s ign i f icant var ia t ion between plant species or s ign i f i cant accumulation in the seeds were observed.

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REFERENCES

CHERRY, J .A . , BLACKPORT, R .J . , DUBROVSKY, N. , GILLHAM, R.W., LIM, T .P . , MURRAY, D.R., REARDON, E.J. and SMYTH, D.J.A. "Subsurface hydrology and geochemical evolution of inact ive py r i t i c t a i l i n g s in E l l i o t Lake uranium d i s t r i c t , Canada", Uranium Mi l l Ta i l ings Management (Proc. 3rd Symp.) Colorado State Univers i ty , Fort Co l l i n s , Colorado, (1980) 353. BLAIR, R.D., CHERRY, J .A . , LIM, T.P. and VIVYURKA, A . J . , "Groundwater monitoring and contaminant occurrence at an abandoned t a i l i n g s area, E l l i o t Lake, Ontar io" , Uranium Mine Waste Disposal (Proc. 1st In t . Conf. ) Vancouver, B.C. Soc. Mining Engrs. AIME (1980) 411. MORIN, K.A., CHERRY, J .A . , LIM, T.P. and VIVYURKA, A .J . "Contaminant migration in a sand aquifer near an inactive uranium t a i l i n g s impoundment, E l l i o t Lake, Ontar io" , Can. Geotech, J. V9_ 1 (1982). DAVE, N.K., LIM, T .P . , and VIVYURKA, A . J . , "Chemical and radioisotope d i s t r i but ion p ro f i l e s in an abandoned uranium t a i l i n g s p i l e " , Uranium Mi l l Ta i l ings Management (Proc. 4th Symp.) Fort Co l l i n s , Colorado (1981) 343. CHERRY, J .A . , SHEPHERD, T .A . , and MORIN, K.A., "Chemical composition and geochemical behaviour of contaminated ground­water at uranium t a i l i n g s impoundments", Proc. of SME-AIME annual meeting, (1982).

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GEOCHEMICAL PROCESSES IN URANIUM MILL TAILINGS AND THEIR RELATIONSHIP TO CONTAMINATION

G. MARKOS, K J . BUSH Geochemistry and Environmental

Chemistry Research, Inc., Rapid City, South Dakota, United States of America

Abstract

GEOCHEMICAL PROCESSES IN URANIUM MILL TAILINGS AND THEIR RELATIONSHIP TO CONTAMINATION.

A geochemical study of abandoned uranium mill tailings has been in progress since October 1978. Some of the more important aspects of geochemical migration characteristics of the tailings are presented here. Data from the chemical analysis of water and acid extracts show abrupt changes in the concentrations of elements at the tailings/soil interface. They correspond to abrupt changes in the pH and Eh conditions. Isotope analyses of bulk solid samples also show an abrupt decrease in specific activity across the interface. Analyses of the data, thermodynamic calculations, and field observations indicate precipitation of iron, manganese, aluminium, silicon and uranium in a narrow interface zone. Precipitation of these elements apparently scavenges trace metals by co-precipitation, occlusion, and adsorption.

INTRODUCTION

Flowing pore water is the dominant potential means of transport of the toxic components as ionic species from tailings into the surrounding environment. Some of the ions may be present in the mobile aqueous phase, whereas others are partitioned into the immobile phases, thereby unavailable for transport. The partitioning of ions between the mobile and the immobile phases occurs through precipitation-dissolution and sorption reactions that are controlled by the prevailing chemical condition of the system. Occlusion may also play a significant role in immobilizing ions.

An abrupt change in transfer processes of ions between mobile and immobile phases takes place at chemical discon­tinuities: at interfaces between two chemically different conditions, where large changes occur in pH, reduction-oxidation potential, ionic strength, concentration of ion and the type of complexing ligand of the solvent. Evaluating the

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mobility (potential to be transported) and migration (actual occurrence of transport) of contaminants necessitates at least a description or, ideally, a full understanding of transfer processes and the distribution of ions between mobile and the immobile phases.

Field work, sampling and analysis were conducted during the last three years on twenty-four abandoned uranium mill tailings designated for remedial action by Title I of U.S. Public Law 95-604, "Uranium Mill Tailings Radiation Control Act of 1978". Funding for the investigation was from the U.S. Department of Energy.

The main objective of this paper is to elucidate some of the apparently important geochemical relationships in the tailings and surrounding environment system based on the various distribution patterns of chemical components and phases. This report contains a brief summary of results obtained from the detailed investigation of four tailings, with the intention to find answers to two questions: (1) are ionic species available for transport by waters, and (2) what mechanisms determine this availability?

METHODS

The investigation reported in this paper included field observation and sampling, sample preparation, chemical analy­sis, data processing, and interpretation. Methods used in the investigation are routine geochemical procedures as well as procedures developed for the unique questions that the study is attempting to elucidate. The data used in this interpretation has been derived from the chemical analysis of water and hydrochloric acid extractable components, field and laboratory determination of pH and redox potential values.

COMPOSITIONAL CHARACTERIZATION

Soluble Salt Precipitates

Water soluble salts of sulfate and chloride tend to migrate to the surface of tailings where they precipitate as the water evaporates and oversaturation occurs. Salt precipi­tates have also been observed at some locations of the interface with the soil at the base of the tailings. Two types of salts with a large variety of cations were observed:

(1) those dominated entirely by sulfate showing a sulfate/chloride ratio of approximately 600, and

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TABLE I. Enrichment of trace elements in water extractable salts pre­cipitating on the surface relative to the material below the salt crust: Example from Salt Lake City tailings 1/

Sulfate type salt Sulfate-chloride type salt Aver.cone. Aver. zone.

ppm ppm Component Salt in tailings Enrich­ Salt in tailings Enrich­

SLC 2-2 below salt ment SLC 5-3 below salt ment cone. ppm crust factor2/ cone. ppm crust factor 2/

Al 6200 722 5 .84 6700 598 3 .70 As 5.3 1.1 3 .28 12 6 .2 0 .64 Ca 2400 4970 0 33 4700 8300 0 .19

Cd 3.1 0.44 4 .79 2.5 0 .55 1 .50 CI 86 64 0 .91 11500 3013 1 .26 Cr 1.9 0.3 4 31 8.5 0 .50 5 .61

Cu 210 33 4 33 190 36 .7 1 .71 Fe 72 21 2 33 47 28 .8 0 .54 K 26 37 0 48 200 95 .3 0 .69

Mg 3300 416 5 39 4400 530 2 .74 Mn 140 25 3 81 300 40 .8 2 .43 Mo 1.9 0.84 1 54 11 1 .58 2 .30

Na 560 141 2 70 12000 2363 1 .68 Pb. 0.34 0.16 1 45 20 8 .6 0 .77 Se 0.5 0 .25 0 .66

Si 38 23 1 12 35 37 .3 0 .31 SO .... 53200 39100 0 93 91000 | 28775 1 .04 u 4 550 80 4 68 230 41 .8 1 .82 v 24 23 0 71 _ 40 | 2 .5 5 .28 PH 3.0 3.1 3.9 | 4 .0 TDS 66819 45637 131397 | 43879

1/ Data used for calculations are in data file: SLC file of Geochemis­try and Environmental Chemistry Research, Inc.

2/ Calculation of enrichment factor:(TDS-aver./TDS-salt crust) x (ave. cone, component/cone. in salt crust).

(2) salts of sulfate and chloride together with sulfate/chloride ratio of approximately 10.

Eight hand-selected salt groups from the surface of the tailings were analyzed by X-ray diffraction. The dominant salts are gypsum (CaSO « 2H O) and epsomite (MgSO »7H O) with

ft ^ ft 2* the presence of varied amounts of gosslarite (ZnSO «.7H O) ,

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anglesite (PbSO^), celestite (SrSO^). In the salt types abundant in chloride, the dominant salts were identified as halite (NaCl), (NH 4) 2Co(S0 4).2H 20, different alums and their magnesium and iron analogues: (MAI (SO^). 1211^0, M^FeCSO^)^ 6H 20, M 2Mg(S0 4) 2 <6H 20), PbU0 4, gypsum and epsomite. X-ray diffraction analysis did not establish the salts of most trace metals although the chemical analyses show their presence.

Chemical analyses of the water extractable phase of the salt crust show an enrichment for many elements relative to their concentration in the water soluble phase of the tail­ings material below the salt crust. The relative enrichment of metals differs between the two groups of salts, as summar­ized in TABLE I. Maximum enrichment of Al, Mg, Cd, U, Cu, and Cr occurs in the sulfate type salt, whereas Cr, V and Al are enriched in the sulfate and chloride type salts. Increas­ed radioactivity for both types of salts was measured in the field by gross gamma-beta scintillometry. A few salts were analyzed in the laboratory by gamma spectroscopy and they showed an enrichment of radioactive isotopes. A quantitative evaluation of radioactivity and identity of salts has not been made, however.

Vertical Distribution Patterns of Components

Vertical distribution patterns of components were estab­lished from core samples of twelve holes bored through four tailings. The core samples included cover material on tail­ings, where present, and samples from the tailings above and below the interface and subtailings soil. The distribution patterns represent the concentration values of component ele­ments for water and hydrochloric acid extractable phases as the function of depth. The components in water-soluble phases include ions in the mobile and immobile water, ions desorbed and dissolved from easily soluble salts. These components indicate the maximum quantities available for transport by water. The acid soluble phases (HC1 at pH 2) contain the ions dissolved primarily from carbonate, hydrox­ide and oxyhydroxide precipitates: ions which were immobiliz­ed in the interstitial space and unlikely to take part in water transport. Iron, aluminum: and, to a lesser extent, silicon and manganese dominate the acid soluble phase. Many trace metals are associated with the acid soluble phase. A few examples of vertical distribution patterns are shown below.

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R I V 1 4 5 A s C d Se N i ppm

D e p t h , cm

0 r C O V E R

2 0 0

4 0 0

S O I L 6 0 0 L

w a t e r s o l u b l e p h a s e :

HCI s o l u b l e p h a s e :

FIG.L Vertical distributions of some characteristic water and acid soluble components from samples through tailings into the subjacent soil; Riverton, Wyoming site. Solid line indicates data from acid soluble whereas dashed line is that of water soluble phases. Values of Al, Ca and Mg are expressed as log ppm; the other components are shown as ppm.

An example of vertical distribution plot compares water and acid-soluble phases (FIG. 1) representing a tailings (Riverton, Wyoming) where shallow subsurface water may inter­cept the tailings seasonally, although no direct evidence exists to support this interpretation. At another tailings the shallow subsurface water table stands at approximately

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t o

ON

TABLE II. Radionuclide distribution across interface between tailings and

natural qround; values are in pCi/g 1/

Depth | | Sample Type (cm) Ra-226 Th-230 | Th--232 | U-234 1 u-235 | U-238 Po-210 SLC 20-30 tailings 305-320 4370 840 | 1 .41 | 69 | 1 .51 1 4 * 530

-32 soil 320-326 1600 299 1 3 .00 | 72 1 2 .87 1 67 1300 -34 soil 345-350 5.01 4 .55 | 1 .20 1 6 00 | 0.151 1 5 3 3.2

SLC 20-39 soil 381-394 1 .71 1 .51 | 1 .18 1 6 03 1 0 .28 1 6 36 2/ -42 soil 420-432 1 .90 1 .70 | 1 .69 1 1 4 0 1 0 .70 1 1 4 0 1.3 -45 soil 457-464 2 .65 2 .36 1 2 .24 1 1 1 9 1 0 .48 1 11 8 — -49 soil 495-503 2 .0 1 .7 J _ 1 .7 | 1 32 1 0 .227 | 1 35 2.1

SLC 2,1-25 tailings 234-279 1300 410 | 1 .7 | 147 1 5 .3 | 144 — -38 tailings 373-386 1390 962 1 3 .8 | 160 1 5 .8 | 160 1200 -40 soil 391-400 19 .5 13 .7 | 1 .46 | 36 1 | 1 .87 | 36 4 —

SLC 21-42 soil 412-434 0 .69 0 .45 1 0 .31 1 4 7 1 0 .14 1 2 66 1.0 -47 soil 458-480 1 .01 0 .34 1 o .49 1 2 4 1 0 .13 2 44 — -49 soil 480-502 0 .92 1 .44 | 1 .21 1 2 14 1 0 .168 | 1 61 — -53 soil 520-530 1 .68 2 .0 j 1 .17 1 1 13 | 1 .16 1 o 887

1/ Table was reproduced from report [1]. 2/ — indicates that no determination was made. NOTE: Background data is known for radium and total uranium [1]; the values representing soils more

than 30 cm in site SLC 20 and 9 cm in SLC 21 below interface are within the established back­ground limits of 4 pCi/g for radium-226 and 2.7 pCi/g for uranium-238.

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one meter above the base into the tailings at high water season and approximately forty centimeters above the base during the low water season. This water forms a physically continuous body from within the tailings into the subjacent natural soil [1].

The vertical distribution plots shown here are repre­sentative to all of the twelve coring sites evaluated. These plots yield some important information:

(1) There is a relatively sharp discontinuity in the distri­bution pattern of both water- and acid-soluble compon­ents at the base of the tailings.

(2) From approximately thirty to nearly one hundred percent of the sum of water- and acid-soluble concentrations of components are in the water soluble phase within the body of the tailings.

(3) In contrast, nearly one hundred percent of those com­ponents are in the acid-soluble phase in the subjacent soil.

(4) Below the interface layer, all components show concen­trations below those established as the maximum level in the background area in the vicinity of the tailings.

(5) At the base of the tailings two groups of components tend to be grouped: CI, SC>4, Ca, Mg, Cd, Cr, Mo and V are predominantly associated with the water-soluble phase whereas As, Al, Co, Cr, Fe, Ni and U with the acid soluble phase.

The distribution of isotopes with depth across the inter­face were investigated for a sandy and for a slime part of a tailings (Salt Lake City, Utah) (TABLE II). Samples from the two locations extend below the interface into the natural soil to 183 centimeters at the sandy tailings site (SLC 20) and 154 centimeters at the slime-containing site (SLC 21) . The data [1] show a reduction by several orders of magnitude in the specific activities of radionuclides at a distance just below the interface; thirty centimeters at the sandy site (SLC 20) and twenty-one centimeters at the slime-containing site (SLC 21). At both sites the specific activities below the interface are below the maximum value of the range of the statistically established background level.

The important role of pH and Eh as parameters of geo­chemical environments have long been recognized [2] and [3].

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SLC 2 0 SLC 21

GJ 2 6 RIV 145

Or

4 0 0 -

8 0 0 -

I 2 0 0 L

FIG.2. Vertical distributions of pH and Eh values from samples through tailings into the subjacent soil from several different locations. SLC 20 represents a vertical profile from the sandy part of Salt Lake City site. SLC 21 is a location through slime area in the Salt Lake City site. GJ 26 shows an example of "neutralized" sandy part of Grand Junction site. RIV 145 is an example from the Riverton tailings.

In the last few decades, many workers interested in the formal treatment of geochemical processes have applied pH and Eh in thermodynamic calculations. Sillen [4 ] has suggested the use of pH and redox potential as master variables for evaluating the geochemistry of waters.

Vertical distribution of pH and Eh values through the tailings into the subjacent soil were established for core

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samples from the tailings. Four representative distribution patterns are shown in the FIG. 2 . The configuration of values expresses two important relationships:

(1) The pH and Eh values show changes in the opposing directions. This type of change relates to redox reac­tions accompanied by hydrolysis. A characteristic exam­ple of such reaction is the precipitation or dissolution of ferric hydroxide.

(2) An abrupt change takes place in pH and Eh values at the base of the tailings similar to those of ionic com­ponents. The values of both in the subjacent soil are the same as established for the background.

The patterns of distributions: ionic compositions of water- and acid-soluble phases, specific activities of radio­nuclides and their ratios and values of pH and Eh have three important common properties:

(1) Within a few tens of centimeters distance below the tailings in the subjacent soils their values are char­acteristic to the established background.

(2) Within a narrow interface zone, abrupt changes in the chemical conditions take place even under conditions where a continuous body of water transgresses this inter­face zone.

(3) Precipitates on the surface tend to be enriched in trace metals relative to the water-soluble phase within the tailings.

This systematic pattern lends itself to interpretation which can characterize the chemical events involved in migration of contaminants from the tailings to the surrounding soil and the shallow subsurface water environment.

DISCUSSION OF MECHANTiSMS OPERATING AT INTERFACES

The abrupt change in chemical conditions and the accumulation of components at the tailings-subjacent soil interface indicate clearly that transfer mechanisms are oper­ating to repartition of ions among the various phases in a manner that sinks are created for major and trace components. These sinks provide an effective barrier in the possible

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migration path of tailings components. If significant migra­tion of trace metals were occurring a long trail with decreas­ing concentrations should be present along the path of trans­port. This phenomenon, however, has not been detected. Neither surface waters nor shallow subsurface waters adjacent to the tailings have consistently contained contaminants from the tailings at concentrations above the background level for the four sites investigated in detail.

Arsenic, selenium, cadmium, molybdenum and uranium, often considered as the most mobile substances in most geo­chemical environments, are apparently removed from the mobile aqueous phase as indicated by their accumulation at the interface together with the other investigated components. Evidences suggest precipitation reactions and the changes in complexing ligands to be the most significant mechanisms in phase transfer from mobile to immobile and repartitioning of ions.

Thermodynamic calculations show that a large percentage of the soluble metals are complexed by sulfate in the tail­ings. Upon dilution with natural waters dominated by bicar­bonate and hydroxyl, the sulfate complexes break down and, depending upon pH and carbonate concentration, either hydroxyl or carbonate complexes may form. The change in the type of metal complexes combined with a higher pH and lower Eh in the soils than in the tailings, have profound effects on the mobility of ions. Iron together with other electro-active species, manganese, uranium and vanadium, plays a particularly important role in controlling the mobility of trace metals. Iron and manganese are well known scavengers of many trace metals, and precipitation of iron is one of the significant mechanisms to remove many components from the mobile aqueous phase [ 5 ] .

Precipitation reactions of electroactive species are best represented in Eh-pH diagrams. Such diagrams were prepared for iron, manganese, uranium and iron-arsenic relationships. The diagrams reveal several important rela­tionships. The solid species of manganese and uranium are thermodynamically unstable under the chemical conditions of the tailings. The solid species of iron, jarosite and amorphous ferric hydroxide may be stable under some but not other parts of the tailings according to the field data plotted on the Eh-pH predominance diagrams (FIG. 3).

Iron, manganese and uranium form sulfate complexes, according to calculations based on dissociation constants and activity values representative of the tailings [6]. Mangan­ese may also form chloride complexes in the tailings. These

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8 0 0

6 0 0 -

4 0 0 -

2 0 0

0 -

2 0 0

FIG.3. Predominance diagram for the conditions of tailings and background solutions to ther mo dynamically predict precipitates of iron as functions of Eh, pH, and activities of components. Calculations were made with respect to existing conditions in tailings sites.

complexes are stable under tailings conditions and, as a result, high concentrations of these components are present in .the water soluble phase. In contrast, the solid phases are stable under non-tailings conditions.

The diagrams suggest that upon dilution, decreasing the activities of the dissolved ions without an increase in pH, the field of stable dissolved species becomes enlarged. This implies that if tailings solutions mix with a more dilute water, and if the acidic conditions of the tailings prevail, iron, manganese and uranium will remain in solution. The metals and associated contaminants will be susceptible to transport if no significant chemical changes take place along the path of transporting water. However, the vertical distri­bution of pH and Eh data from the tailings into the subjacent soil show an abrupt change at the interface (FIG. 2) . Within a distance of a few centimeters, both pH and Eh conditions assume those which are characteristic to the surrounding environment. The abrupt change in pH and Eh conditions

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indicates well buffered pore water in the subjacent soil to effectively neutralize the acidic tailings solutions and cause the precipitation of iron and perhaps that of manganese and uranium.

The relationships between precipitated iron and trace metals from samples of the tailings in Canonsburg, Penn­sylvania have been investigated in detail. Correlation analy­sis shows high correlations of As, Co, Cr, Ni and U with Fe at 95 percent confidence level [6].

The relationship of arsenic to iron has been investigat­ed in terms of Eh-pH diagrams in view of their good correla­tion in acid-soluble phase. Arsenic could be present as oxy acids either as As(III) or As(V) in the aqueous phase. One possible interaction involves the formation of ferric arsen­ate dihydrate according to the general reaction:

F e 2 + + H A s O „ m - 1 + 2H„0 = Fe (AsOJ; 2H.0 (scorodite) + mH + + e n 4 2 4 2 depending on the many possible aqueous forms of arsenic.

The thermodynamics of the relationship represented by the example in the equation was investigatad and summarized in FIG. 4. Calculations of redox reactions, thermodynamic data, and activities of the species used are given in [7].

As the activity of arsenic increases at Eh values above 600 millivolts by either evaporation or mixing with tailings solutions containing high concentrations of dissolved arsenic the reaction should follow the path of change indicated by A in FIG. 4. Where evaporation causes precipitation the re­sultant solid is ferric arsenate dihydrate. This reaction is independent of the initial concentration of arsenic. Solutions with a high arsenic concentration that undergo a slight increase of pH would result in the same precipitate. At lower arsenic concentrations, amorphous ferric hydroxide is the more likely precipitate as the pH increases. At Eh values below approximately 600 millivolts, ferric hydroxide should precipitate. This condition is indicated by the path of change at B in FIG. 4.

Calculations with high concentrations of iron and arsenic typical of the tailings increase the field of stabil­ity of ferric arsenate dihydrate. Some interstitial solu­tions in the tailings show pFe (aqueous) = 2.5 and pAs(aqueous) = 3.0. The thermodynamic equilibrium relation­ships are shown in FIG. 4B for this condition. Within the tailings where the dominant soluble iron species are iron

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A

2 0 0 1 1 1 1 > l I I

2 3 4 5 6 7 8 9 PH

B

4 0 0

{ 1 1 1 1 1

S j F e ( A s 0 4 ) « 2 H 2 0

1 1

1 S C O R O D I T E -1 t JjAROSITE

P s o 42 - = 1.3

—

^ x l Fe(OH) \ " \

p F e T

= 2 .5

N^amorph.rs. p As

T = 3 .0

A Q U E O U S \ x \

I i i \ i l

2 3 4 5 6 7 8 9

PH

FIG.4. Predominance diagrams for the aqueous and solid species of iron and arsenic as a function of Eh, pH, and activity of components.

sulfate complexes, precipitation of jarosite type minerals is possible.

The precipitation of ferric arsenate dihydrate as pre­dicted by the Eh-pH diagram and the probable formation of solid solutions with other metals are in accordance with the direct quantitative relationship between iron and arsenic concentrations in extracts from the tailings.

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X-ray diffraction analysis of salts from tailings also point toward the occurrence of arsenic iron solid solutions. X-ray diffraction analysis of subsamples of the samples acid extracted and chemically analyzed for iron and trace elements were not available, however, X-ray diffraction analysis on samples from the Salt Lake City tailings show the presence of ferric arsenate dihydrate in samples with high arsenic con­tent. In some other samples from the surface of the tailings the complex salt

PbFe_ (AsO ) (SO.) (OH) _ 3 4 4 6 was identified. This complex salt occurred together with gypsum and a variety of solid solutions of jarosite, whereas the ferric arsenate dihydrate occurred with lead uranate salt.

Reactions with aluminum may also be important at the base of the tailings. In the low pH conditions of sulfate-rich tailings, high concentrations of aluminum are present in the water soluble phase. At the base of the tailings, the breakdown of the sulfate complex and increased pH causes the precipitation of aluminum into many possible forms, depending on the local conditions. Alums, alunite, and alumino-silicate gels were detected by X-ray diffraction analysis but relating them to specific conditions of formation has not yet been established. The amorphous precipitates of aluminum and ferric iron also act on destabilization of colloidal parti­cles [8]. Colloidal precipitates of other trace metals not directly associated with coprecipitation of iron or aluminum are potentially trapped by flocculation. In addition, these precipitates may provide adsorption sites for many metals which do not precipitate under the given conditions.

CONCLUSIONS Data obtained from samples of four uranium mill tailings

show a varied distribution of water-soluble and acid-soluble components through the tailings into the subtailings soil. Distributional characteristics of the components clearly indi­cate the existence of sinks for the investigated twenty-two elements, and indications are for the similar behavior of radionuclides.

Although flowing pore water is the dominant means of transport of the toxic components, geochemical transfer pro­cesses of ions between mobile and immobile phases determine the availability of ions for transport. The mechanisms controlling the transfer processes and the partitioning of ions operate in areas where chemically two different solu­tions are in contact or mix.

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The major mechanism providing sink conditions is the Eh and pH controlled precipitation process of multivalent transi­tion metals, particularly iron. By its scavenging properties iron and perhaps manganese seem to be effective in removing many of the toxic constituents. Dissociation of sulfate and chloride complexes, characteristic to the solutes in the tailings solution, in environments where different ligands predominate, such as bicarbonate and hydroxy1, possibly results in the formation of carbonates, oxides and oxyhydrox-ide precipitates.

These mechanisms become operative where large pH and Eh changes occur accompanied by change in ionic strength and concentration of ligands, such as at the interface between tailings and subtailings soil. Apparently, soils or shallow subsurface waters well buffered with respect to pH offer a development of a protective interface where harmful trace metals from the solution phase in the tailngs become trans­ferred to the immobile phase.

Although these mechanisms were established on the basis of four tailings, experimental investigations are necessary for confirmation of interpretations of field data. Further­more, limit conditions about the effectiveness of various ion transfer mechanisms should be determined experimentally so that conclusive predictions can be made for the varied tailings-surrounding environment relationships.

REFERENCES

[1] MARKOS, G., BUSH, K.J., Geochemical Investigation of UMTRAP Designated Site at Salt Lake City, Utah, UMTRA-DOE/ALO-227 (1981)

[2] ZOBELL, C.E., Studies on redox potential of marine sedi­ments, Assoc. Am. Petroleum Bull. 30 (1946) 477.

[3] BAAS BECKING, L.G.M., KAPLAN, I.R., MOORE, D., Limits of the natural environment in terms of pH and oxidation-reduction potentials, J. Geol. 68 (1960) 243.

[4] SILLEN, L.G., "Master variables and activity scales", Equilibrium Concepts in Natural Water Systems (GOULD, R.F., Ed) Am. Chem. Soc, Washington, D.C. (1967) 45.

[5] JENNE, E.A. , Controls on Mn, Fe, Co, Ni, Cu, and Zn concentrations in soils and water: the significant role of hydrous Mn and Fe oxides", Trace Inorganics in Water (GOULD, R.F., Ed) Am Chem. Soc, Washington, D.C. (1968) 337.

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[6] MARKOS, G., BUSH, K.J., FREEMAN, T., Geochemical Investi­gation of UMTRAP Designated Site at Canonsburg, Penn­sylvania, UMTRA-DOE/ALO-226, GECR #R-811 (1981).

[7] MARKOS, G., BUSH, K.J. Contamination of Ground and Sur­face Waters by Uranium Mining and Milling, Volume II. Field Sampling and Empirical Modeling. U.S. Bureau of Mines, contract #J0295033 (1981) (in press).

[8] WEBER, W.J.,Jr., Physicochemical Processes for Water Quality Control, Wiley-Interscience, New York. (1972).

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RADIONUCLIDES IN PROCESS AND WASTE STREAMS AT AN OPERATING URANIUM MILL

R.J. RING, D.M. LEVINS Australian Atomic Energy Commission

Research Establishment, Lucas Heights Research Laboratories, Lucas Heights, New South Wales

F.J. GEE Queensland Mines Limited, Darwin, Northern Territory, Australia

Abstract

RADIONUCLIDES IN PROCESS AND WASTE STREAMS AT AN OPERATING URANIUM MILL.

A survey was carried out at the Nabarlek uranium mill, located in the Alligator Rivers Region of the Northern Territory of Australia, to determine the distribution of radium-226, thorium-230, lead-210 and polonium-210 in process and waste streams. Particular emphasis was placed on waste treatment processes. The survey showed that 20% of the 2 3 0 Th and only small fractions of the 2 2 6 Ra, 2 1 0 Pb and 2 1 0 Po were mobilized in the leaching circuit. Neutralization of tailings/raffinate slurry to pH 8.5 removed over 99% of the 2 3 0 Th, 2 1 0 Pb and 2 1 0 Po, but the concentration of dissolved 2 2 6 Ra increased. The performance of barium chloride treatment circuits for the removal of 2 2 6 Ra was examined. Under optimum conditions, more than 98% of the total radium was removed from decant tailings water containing 80 to 150 Bq 2 2 6 R a - L - 1 by a mixing tank and a reactor-clarifier. Addition of barium chloride had only a small effect on the long-term concentration of 2 2 6 Ra in the presence of tailings.

1. INTRODUCTION

In many respects, the environmental impact of uranium milling resembles that of any other hydrometallurgical process­ing operation. Process streams and effluents may be highly acidic and contain a high concentration of dissolved salts including heavy metals. A unique feature of uranium ore process­ing is the dissolution of uranium decay products during milling. The most important of these products are the long-lived isotopes, radium-226 ( 2 2 6Ra), thorium-230 ( 2 3 0Th) and lead-210 ( 2 1 0Pb). There have been a number of studies of 2 2 6 R a in mill and waste streams [1,2], but there is little data on 2 3 0 T h and 2 1 0 P b . Some information is available for natural thorium ( 2 3 2Th) [3,4] but this may not be a perfect analogue for 2 3 0 T h because of differences in mineralogy.

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CRUSHED

FIG. 1. Nabarlek flowsheet and location of sample points.

Th is paper summarises the r e s u l t s o f a survey c a r r i e d o u t a t the Queensland Mines L t d uran ium m i l l a t Nabar lek t o determine the d i s t r i b u t i o n o f 2 2 6 R a , 2 3 0 T h and 2 1 0 P b i n p rocess and waste streams. Concent ra t i ons o f po lon ium-210 ( Po) i n a few s e l e c t ­ed streams were a l s o measured. The r a d i o n u c l i d e a c t i v i t y i n s o l i d and l i q u i d phases o f major process streams was measured as a means o f unde rs tand ing the d i s s o l u t i o n and i m m o b i l i s a t i o n processes t a k i n g p l a c e . P a r t i c u l a r emphasis was p l a c e d on the waste t reatment processes - n e u t r a l i s a t i o n and bar ium c h l o r i d e t reatment f o r the removal o f r ad ium. F o l l o w i n g the s u r v e y , p l a n t t r i a l s were c a r r i e d ou t t o o p t i m i s e the performance o f the bar ium c h l o r i d e t reatment c i r c u i t s .

2 . NABARLEK MILL FLOWSHEET

The Nabarlek mill is located in the Alligator Rivers Region of tropical northern Australia. The high grade orebody averaging 2.34% U3O8 was completely mined by open cut methods and stockpiled before the commencement of milling in June 1980. Ore is treated by conventional acid leaching and solvent extraction processes; plant capacity is 240 t ore/day. A simplified mill flowsheet is shown in Figure 1 . Ore is ground to 50 wt % less than 75 ym and leached as a 45 wt % slurry with

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sulphuric acid for 24 h at 40-45°C. Leaching pH is controlled at 1.8 in the first two tanks, but then it is allowed to increase. Pyrolusite is used as an oxidant. The leached solids are separated from the uranium-bearing solution by counter-current decantation (CCD) washing with recycled raffinate. Uranium is recovered from the clarified pregnant liquor by solvent extraction using a tertiary amine and modifier in a kerosene diluent. Uranium is stripped by ammonium sulphate at pH 3.5-4.5 and precipitated as ammonium diuranate (ADU) with ammonia. The ADU is washed, dewatered and calcined at 580°C to produce a high purity yellowcake.

The tailings/raffinate slurry from the CCD circuit is neutralised with lime to pH 8.5 and treated with barium chloride before discharge to the mined-out pit. Decant water from the pit is recycled to the plant via a storage pond. Excess pit water is treated with barium chloride, passed through a clarifier to remove suspended radium, which is returned to the pit, and pumped to an evaporation pond. There is no release of water from the mill.

3. RADIONUCLIDE SURVEY

3.1 Sampling procedures

The survey of the mill was carried out over four days in November 1980. Locations of sample points are shown in Figure 1. Three daily samples of about one litre were taken from all points in the processing circuit. The yellowcake product sample was riffled from a daily composite.

The pH of liquid and slurry samples was measured immedi~ ately after sampling. All samples were filtered soon after collection. Those requiring suspended radium determinations were filtered through a 0.45 um membrane filter; other samples were passed through a Whatman No.541 paper for coarse filtration and then through a membrane filter. Filtrates were immediately acidified with 10 mL of concentrated nitric acid per litre. A composite sample of 500 mL was prepared from the three daily samples. All liquids were analysed for dissolved 2 2 6 R a and sulphate; selected samples were analysed for U, 2 3 0 T h , 2 1 0 P b and 2 1 0 P o . Some solid samples were analysed for U, 2 2 6 R a , 2 3 0 T h and 2 1 0 P b .

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TABLE I DISSOLVED CONCENTRATIONS OF RADIONUCLIDES IN MILL CIRCUIT

Sample No. Description

pH Sulphate (g-L - 1)

Activity (Bq-L 1) Sample No. Description

pH Sulphate (g-L - 1)

U 2 2 6 R a 23 0 T h 2 1 0 P b

1 Recycled process water (ROW) 7.45 4.8 12 17 <0.4 <0.4 2 Slurry feed to leach circuit 7.56 4.7 N.D. 69 11 0.93 3 Slurry from No.6 leach vessel 2.56 35.2 223 000 25 52 200 430 4 Tailings slurry from CCD circuit 2.27 26.4 89 27 33 600 210 5 Raffinate recycle to CCD circuit 2.00 37.2 25 28 42 400 380 6 Slurry from 1st stage neutralisation 3.89 26.4 51 89 6100 280 7 Slurry from 2nd stage neutralisation 7.49 13.9 0.4 210 1.3 8.1 8 Slurry from final stage neutralisation 8.50 12.5 0.2 266 0.2 1.8 9 Tailings slurry after BaCl2 treatment 8.32 12.8 N.D. 40 N.D. N.D. 10 Effluent slurry at entry to pit 8.00 13.4 N.D. 48 N.D. N.D. 11 Decant water from pit 8.06 6.3 0.7 10 0.36 <0.5 12 Pit decant water after BaCl2 treatment 8.08 6.7 N.D. 2.7 N.D. N.D. 13 O/Flow from pit water clarifier 7.71 6.3 0.4 0.9 1.3 <0.5 14 U/Flow from pit water clarifier 7.79 N.D. N.D. 2.6 N.D. N.D. 15 Evaporation Pond 9.40 0.2 1.2 1.3 <0.4 <0.4

N.D. Not determined.

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3.2 Analyses

3.2.1 Radium-226

Liquids were analysed using the ASTM method [5]; this involves sealing the samples to allow ingrowth of 2 2 2 R n which is counted in an a-scintillation cell. Because all samples contained significant radium activity, it was unnecessary to preconcentrate the radium by barium sulphate precipitation. For suspended radium determination, membrane filters and residues were dissolved by repeated contacts with HF/HCI/HNO3, evaporated to dryness and taken up in 30 wt % H N O 3 . The samples were then analysed in the same way as the liquid samples.

Solid samples were sealed for one month so that secular equilibrium was established between Ra and Pb. They were then counted using a Ge(Li) detector to measure the 0.352 MeV y-ray from 2 1 t tPb.

3.2.2 Thorium-250

Thorium-230 was measured using the method of Sill et al. [6], Briefly,this involves precipitation as barium sulphate, redissolution, separation by solvent extraction, followed by a spectrometry. The accuracy of this method varies from about ±5% for high concentrations (>10 Bq«L _ 1) to ±50% near the detection limit (0.4 Bq-L" 1).

3.2.3 Lead-210 and polonium-210

The 2 1 0 P b content was measured indirectly after secular equilibrium had been established with its daughter 2 1 0 B i (half-life 5 days) using the method of Blanchard [7]. The 2 1 0 B i and 2 1 0 P o were deposited onto a nickel disc using hydroxylamine as a reducing agent. Polonium-210 was determined by a counting

210 and the 1.17 MeV 3-particles of Bi were counted using an aluminium absorber to shield out a-particles. Accuracy and detection limits are similar to those for 2 3 0 T h . 3.3 Results and discussion

Dissolved concentrations of U, 2 2 6 R a , 2 3 0 T h and 2 1 0 P b are summarised in Table I. Sulphate concentrations are also reported as they are useful in understanding radium behaviour because of the extreme insolubility of radium sulphate. Previous work has established that sulphate concentration is one of the most important factors controlling the dissolution of radium in uranium mill circuits [8]. Table II shows the radionuclide content of solid samples.

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RADIONUCLIDE CONTENT OF SOLIDS

Sample No.

Description Bq»g -l Sample No.

Description

2 3 8 u 2 2 6 R a 23 0 T h 2 1 0 P b

2 Ore (2.83%U308) 298 314 348 291 4 Tailings 5.3 330 292 300 16 Yellowcake N.D. 0.5 17 0.2

N.D. Not determined.

3.3.1 Leaching and washing aivauits

3.3.1.1 Radium-226

Only a minute fraction of the 2 2 6 R a was mobilised in the 2 2 6

leaching circuit. The dissolved Ra concentration was actually higher in the leach feed than in the discharge from the final leach vessel. This can be attributed to the much higher sulphate concentration in the leaching vessels which tended to suppress radium solubility.

The dissolved 2 2 6 R a in the leach discharge constituted only 0.01% of that in the ore. Previous laboratory studies of ores from.the Alligator Rivers region showed that 0.01-0.03% of the 2 2 b R a dissolved, with the higher grade ores releasing proportionately less radium [8]. Published results are 0.2-0.7% for USA ores [2,9] and 0.09% for Canadian ores [1], One possible reason for the lower radium concentration in solution is the higher proportion of clay minerals in Australian ores which tend to adsorb radium.

The 2 2 6 R a concentrations in the raffinate and underflow from the final thickener were approximately the same as that in the leach liquor. The CCD tails contained 27 Bq 2 2 6Ra«L~ 1

which is only three times the value of 9.3 Bq>L - 1 assumed in the USA generic study [10] for a model mill processing a much lower grade ore (0.1% U 3 O 8 ) .

3.3.1.2 Thorium-230

The dissolved 2 3 0 T h in the leach discharge is equivalent to 18% of that in the ore. This is in good agreement with the value of 20% calculated from the depletion of 2 3 0 T h in the

TABLE II

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tailings assuming 5% of the ore dissolved during leaching. The 2 3 Th concentration in the raffinate and CCD tailings was lower than in the leach discharge because of dilution with wash water.

Previous surveys of acid leaching circuits in the USA and Canada and indirect measurements based on abandoned tailings piles have suggested that 35-85% of the thorium is dissolved during leaching [3,4,11,12]. Laboratory measurements at the AAEC Research Establishment have found 3 0Th dissolutions ranging from 56-80%. When high grade Nabarlek ore was leached at pH 1.3,62% of the 2 3 0 T h was dissolved. The relatively mild leaching conditions during the survey (pH 2.6 in the final tank) were the probable reasons for the low percentage of mobilised 2 3 0 T h .

The CCD tails contained 33 600 Bq«L~1 of dissolved 2 3 0 T h which is only ten times the value assumed in the USA generic study [10], although ore grade at Nabarlek was 28 times greater.

3.3.1.3 Lead-210 and polonium-210

Only about 0.18% of the 2 1 0 P b and 0.37% of the 2 1 0 P o in the ore were dissolved during leaching. The concentrations of 210 210

Pb and Po decreased xn the CCD circuit because of dilution with wash water. The 2 1 0 P o concentrations after leach­ing and in the CCD tailings liquor were 880 and 680 Bq»L - 1, respectively.

3.3.2 Neutralisation

Lime treatment to pH 8.5 precipitated almost all of the dissolved 2 3 0 T h , 2 1 0 P b and 2 1 0 P o :- decontamination factors were 1.5 x 10 5 for 2 3 0 T h , 100 for 2 1 0 P b and 800 for 2 1 0 P o .

The dissolved 2 2 6 R a concentration increased significantly during lime treatment and was higher in the final neutralisation tank than elsewhere in the mill. An increase in radium solubility during lime treatment has been demonstrated in laboratory tests [8] and observed, in practice, at Canadian mills. For Nabarlek ore. Levins et al. [8] found that the maximum radium concentrations was 270 Bq*L _ 1 at pH 6. The phenomenon is not completely understood but can be explained partly by the fall in sulphate concentration (Table I) as calcium sulphate is precipitated. This should lead to dissolution of radium sulphate held on the tailings in accordance with the common ion effect.

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Neutralisation to pH ~8.5 is not an effective method of removing radium from tailings/raffinate slurries. Its value is in its ability to precipitate heavy metals (e.g. U, Pb, Cr, Zn, Cu, Fe) from solution [13].

The effect of pH on the removal of 2 2 6 R a , 2 3 0 T h and 2 1 0 P b from acidic tailings slurries has also been studied at the AAEC Research Establishment. Figure 2 compares results from laboratory studies with those obtained at the Nabarlek mill. The agreement between the survey results and laboratory experiments is reasonable although,for a given pH, the dissolved concentrations of 2 1 0 P b tend to be higher in the survey.

3.3.3 Yellowcake product

The 2 2 6 R a , 2 3 0 T h and 2 1 0 P b contents of the yellowcake were 0.5, 17 and 0.2 Bq^g"1, respectively. These levels are equivalent to 0.005, 0.14 and 0.002% of those in the original ore. A recent survey of three acid leach mills by the US Environmental Protection Agency [14] found that yellowcake

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contained from 0.04-3 Bq 2 2 6Ra.g~ 1/ 12-80 Bq 2 3 0Th-g 1 and 0 .4 -

3 Bq 2 1 0Pb.g~ 1. Compared to these mills, yellowcake produced at Nabarlek contained relatively low concentrations of 2 2 6 R a , 2 3 0 T h and 2 1 0 P b .

3.3.4 Waste ponds

The concentrations of 2 2 6 R a and 2 1 0 P b in the neutralised tailings/raffinate slurry decreased substantially on storage in the tailings disposal pit. The dissolved concentrations of 2 3 0 T h and 2 1 0 P b in the pit, evaporation pond and water recycle pond were below the maximum limits set out in Schedule 6 of the Australian Code of Practice [15] of 74 Bq 2 3 0 T h . L _ 1 and 3.7 Bq 2 1 0 P b - L - 1 . This schedule is essentially a derived drinking water standard for members of the public.

During the survey period, the dissolved 2 2 6 R a concentra­tion in the pit was low (10 Bq-L - 1) compared to that in tailings dams in other countries; for example, neutralised tailings water from low grade Elliot Lake ore contains 15-40 Bq 2 2 6 R a * L - 1 [ 16 ] . However, the concentration of 2 2 6 R a in pit water has fluctuated in the range of 5-160 Bq*L - 1 since milling operations commenced. The 2 2 6 R a level in the evaporation pond indicates that barium chloride treatment has been effective in removing dissolved radium from decant pit water before its discharge to the pond.

4. OPTIMISATION OF BARIUM CHLORIDE TREATMENT CIRCUITS

Following the survey of the mill, plant trials were carried out on barium chloride treatment circuits to analyse their performance and improve the efficiency of radium removal.

4.1 Barium chloride treatment of tailings/raffinate slurry

Barium chloride is added to the neutralised tailings/ raffinate slurry to precipitate radium before discharge to the pit. It is added in a small tank (residence time is 3.5 minutes) where the slurry is also diluted from 32 to 24 wt % by addition of pit water to facilitate pumping a distance of about 800 m to the pit.

In the survey, 2 2 6 R a concentrations were measured in the neutralised tailings, the discharge from the neutralisation pump tank and again just before the tailings entered the pit. The results showed that a barium chloride concentration of 300 mg

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TABLE III RADIUM REMOVAL FROM TAILINGS/RAFFINATE SLURRYC%)

Contact Time (day)

Barium Chloride Dosage (mg«L _ 1) Contact Time (day)

0 35 75 175 350

0.005 22 69 69 78 84 1 87 86 91 96 98 9 94 95 91 98 98

20 97 96 97 99 99 30 97 97 98 99 99

reduced 2 2 6 R a concentration by 85%. A further decrease in 2 2 6 R a occurred in the pit but this was more likely to have been due to slow reactions resulting from lime treatment.

Yourt [17] has claimed that barium chloride treatment is not very effective in the presence of tailings. One explanation for his conclusion is that radium is precipitated from solution by barium chloride, but then further radium immediately dissolves from the tailings to restore equilibrium. In view of the conflicting evidence, further experiments were carried out in July 1981 to establish the merits of barium chloride addition to slurries.

The concentration of barium chloride in the neutralised liquor was varied from 0-400 mg-L"1 in five increments. In each case, the treated slurry was sampled and the dissolved radium concentration determined immediately, and at appropriate intervals for a period of 30 days.

4.1.1 Results and discussion

For the period of the testwork, the average concentration of dissolved 2 6Ra in the tailings slurry after neutralisation was 320 Bq^L" 1. The effects of barium chloride dosage and time on 2 2 6 R a removal are shown in Table III. Dissolved 2 2 6 R a levels decreased with time and increasing barium chloride concentration, although the effect of barium chloride was not very significant after 20 days. For a barium chloride dosage of 175 mg«L - 1, the

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2 2 6 R a concentration was reduced to 2% of the original level in 9 days. Without treatment, 97% of the 2 2 6 R a was removed in 30 days by a slow chemical reaction with lime. During the same period, sulphate concentration decreased from 10.4 to 7.7 g.L - 1. These results establish that while addition of barium chloride is effective in the short term, it has only a small effect on the long-term concentration of 2 2 6 R a in the presence of tailings.

The residual 2 2 6 R a concentrations after 30 days of 3-10 Bq» L - 1 were similar to that in the pit water during the survey. However, measurements in July and December 1981 indicated 2 2 6 R a concentrations in the pit in the range 80 to 150 Bq-L - 1. The reasons for these variations are not completely understood, but significant changes in sulphate concentrations occurred over the same period and there was a correlation between high radium and low sulphate concentrations.

4.2 Barium chloride treatment of decanted tailings water

Barium chloride is used extensively to remove radium from uranium mill effluents. The Canadian target levels for discharge of 2 2 6 R a to the environment are 0.1 Bq-L - 1 (3 pCi-L - 1) dissolved and 0.27 Bq»L~1 (10 pCi-L - 1) total [14]. Although both targets have proved difficult to meet, the limit on total radium has been the most restrictive. In Canada and France [18,19,20], 10-30 mg BaCl2'L - 1 are added and the treated water is discharged to lakes or large ponds to allow sufficient time for the radium-bearing precipitate to settle out. This approach is not completely satisfactory since a wide area of the lake bottom becomes contaminated with radium. Canadian workers have recently completed an extensive study of barium chloride treat­ment using in-plant processes, clarification or filtration, to maximise removal and ensure isolation of the radium precipitate [21,22].

The barium chloride treatment circuit at Nabarlek is similar to one of the options examined in the Canadian study. It consists of a small mixing tank where barium chloride is added, then a clarifier where ferric chloride and flocculant carry down the fine barium-radium sulphate precipitate. The clarification unit is a 6 m diameter Eimco high-rate reactor-clarifier. Ferric hydroxide sludge from the underflow of the clarifier is recycled to aid settling. At the design water flow, of 50 m 3.h _ 1, the residence time in the mixing tank was two minutes and the hydraulic loading in the clarifier was 1.4 m-h" 1

(850 US gallons per day per ft 2).

The efficiency of radium removal is determined by the complex interaction of a number of parameters. These include rates of addition of barium chloride, ferric chloride and

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flocculant, hydraulic loading and the extent of sludge recycle. An experimental program was carried out to optimise the perfor­mance of the clarifier treatment circuit at Nabarlek.. The concentrations of dissolved and suspended 2 2 6 R a in feed and exit streams, and the dissolved 2 2 6 R a immediately after barium chloride addition, were measured.

4.2.1 Results and discussions

Two plant tests were carried out over 2-week periods in August and December 1981. Radium-226 concentrations in the decant pit water feed were 75-150 Bq^L"1 dissolved and 2-20 Bq* L - 1 suspended. The range of variables examined were as follows: barium chloride dosage 25-150 mg^L - 1; flocculant dosage 1-3 mg» L" 1; ferric chloride dosage 10-100 mg'L"1; hydraulic loading 0.85-1.4 m-h - 1; and sludge recycle rate 450-2900 L<h _ 1. The sludge recycle rates corresponded to suspended solids concentra­tions in the feed of 1500-6000 mg'L" 1.

The major findings from the plant investigations are summarised below :

(1) It was essential to maintain a sludge bed depth of 1 to 1.5 m above the water inlet into the settling eone to achieve minimum levels of suspended radium in the clarifier overflow. Changes in hydraulic loading and sludge recycle rate had a significant influence on bed stability which, in the short term, was more important than their direct effect on settling performance.

(2) In general, concentrations of suspended radium in the overflow were greater than dissolved levels. Minor fluctuations in operating conditions had little effect on dissolved radium, but resulted in signifi­cant variations in suspended radium levels.

(3) Most of the radium (>98%) was precipitated in the short residence time mixing tank. Under most conditions, dissolved radium concentrations were further reduced in the clarifier.

(4) Within the range 50-150 mg«L - 1, barium chloride dosage had little effect on dissolved or suspended radium concentrations. Addition of 25 mg-L - 1 barium chloride resulted in increased levels of dissolved radium.

(5) Ferric chloride and flocculant dose rates of 30 and 1 mg«L _ 1, respectively, were sufficient for optimum performance.

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(6) A sludge recycle rate equivalent to 1500-3000 mg-L - 1

of suspended solids in the feed water gave the best and most reliable performance.

(7) The system could be operated consistently to produce 2 2 G R a levels of 0.2-0.5 Bq-L - 1 dissolved and 0.5-1.0 Bq»L _ 1 suspended. The latter corresponded to a suspended solids level of 1.8 to 2.5 ppm.

5 CONCLUSIONS

The major conclusions from the survey and plant tests at the Nabarlek uranium mill are as follows :

Sulphuric acid leaching dissolved 0.01% of the 2 2 6 R a , 20% of the 2 3 0 T h , 0.16% of the 2 1 0 P b and 0.37% of the 2 1 0 P o in the ore.

About 0.005% of the 2 2 6 R a , 0.2% of the 2 3 0 T h and 0.002% of the 2 1 0 P b in the ore reported to the yellow­cake.

Neutralisation of tailings/raffinate slurry with lime to pH 8.5 effectively precipitated almost all the 2 3 0Th, 2 1 0 P b and 2 1 0 P o .

The concentration of 2 2 6 R a increased significantly during neutralisation but decreased on ageing in the tailings pit.

Addition of barium chloride had only a small effect on the long-term concentration of Ra xn the presence of tailings.

Barium chloride treatment of decant tailings water in a mixing tank and clarifier was effective in removing over 98% of the total radium.

REFERENCES

[1] SKEAFF, F.G., Survey of the occurrence of 2 2 6 R a in the Rio Algom Quirke 1 uranium mill, Elliot Lake, Can. Min. Metall. Bulletin, 74 830 (1981) 115.

[2] TSIVOGLOU, E.C., O'CONNELL, R.L., Waste Guide for the Uranium Milling Industry, US Dept. of Health, Education and Welfare, Technical Rep. W62-12 (1962).

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[3] Winchester Laboratory, Topical Report, Jan. 1960, National Lead Co., WIN-112 (1960).

[4] ITZKOVITCH, I.J., RITCEY, G.M., Removal of Radionuclides from Process Streams: A Review, Canada Centre for Minerals and Energy Technology Rep. CANMET 79-21 (1979).

[5] American Society for Testing Materials, "Tentative method for radium-226 in water". Annual Book of ASTM Standards 31 (1976) 682.

[6] SILL, C.W. et al., Simultaneous determination of alpha-emitting nuclides of radium through californium in soil. Anal. Chem. 46 12 (1974) 1725.

[7] BLANCHARD, R.L., Rapid determination of lead-210 and polonium-210 in environmental samples by deposition on nickel. Anal. Chem. 38 2 (1966) 189.

[8] LEVINS, D.M. et al., "Leaching of radium from uranium tailings",Proc. OECD/NEA Seminar on Management, Stabilisa­tion and Environmental Impact of Uranium Mill Tailings, Albuquerque, New Mexico (1978) 271.

[9] CLARK, D., State-of-the-Art: Uranium Mining, Milling and Refining Industry, US Environmental Protection Agency Rep. EPA-660/2-74-038 (1974).

[10] USNRC, Final Generic Environmental Impact Statement on Uranium Milling, US Nuclear Regulatory Commission Rep. NUREG-0706 (1980).

[11] DRESSEN, D.R., Preliminary Evaluation of Uranium Mill Tailings Conditioning, Contract Rep. for USDOE Uranium Mill Tailings Remedial Action Project, Los Alamos National Laboratory (1981).

[12] RYON, A.D. et al.. Nitric Acid Leaching of Radium and Other Significant Radionuclides from Uranium Ores and Tailings, Oak Ridge National Laboratory Rep. ORNL/TM-5944 (1977).

[13] LEVINS, D.M., Environmental impact of uranium mining and milling. Can. Min. Metall. Bulletin, 73 822 (1980) 119.

[14] FORT, C.W. et al.. Radioactive Emissions from Yellowcake Processing Stacks at Uranium Mills. US Environmental Protection Agency Tech. Note ORP/LV-80-3 (1980).

[15] Code of Practice on Radiation Protection in the Mining and Milling of Radioactive Ores, Environment Protection Act 1978. Australian Gov. Publishing Service, Canberra (1980).

[16] MOFFETT, D., The Disposal of Solid Wastes and Liquid Effluents from the Milling of Uranium Ores, Canada Centre for Mineral and Energy Technology Rep. CANMET 76-19 (1976).

[17] YOURT, G.R., "Environmental aspects of the Canadian uranium mining industry", 15th Annual International Conference of the Canadian Nuclear Association, Ottawa, Canada Vol. 5 (1975) 107.

[18] MOFFETT, D., VIVYURKA, A.J., "Control of radium-226 releases in liquid effluents", Proc. OECD/NEA Seminar on Management, Stabilisation and Environmental Impact of Uranium Mill Tailings, Albuquerque, New Mexico (1978) 259.

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[19] LA ROCQUE, E., WEBBER, R., "Waste management at Denison Mines", Ibid, (1978) 215.

[20] FOURNIER, P.M., "Current Research and Development on 2 2 G R a Control at the French Atomic Energy Commission", Proc. of the 2 2 6 R a Workshop, Oct. 17, 1977, CANMET Rep. ERP/MSL 80-14(TR) (1980).

[21] SCHMIDTKE, N.W. et al., "Removal of 2 2 6 R a from tailings pond effluents and stabilisation of uranium mine tailings - bench and pilot plant studies", Proc. OECD/NEA Seminar on Management, Stabilisation and Environmental Impact of Uranium Mill Tailings, Albuquerque, New Mexico (1978) 299.

[22] AVERILL, D.W., et al., Joint Government-Industry Program for the Removal of Radium-226 from Uranium Mining Effluents - Interim Rep. No.2 Process Development, Environment Canada, Wastewater Technology Centre, Burlington, Ontario (1980).

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REVIEW OF THE NON-RADIOLOGICAL CONTAMINANTS IN THE LONG-TERM MANAGEMENT OF URANIUM MINE AND MILL WASTES

R.T. PIDGEON School of Physics and Geosciences, Western Australian Institute

of Technology, Bentley, Western Australia, Australia

Abstract

REVIEW OF THE NON-RADIOLOGICAL CONTAMINANTS IN THE LONG-TERM MANAGEMENT OF URANIUM MINE AND MILL WASTES.

In the management of uranium mine and mill wastes public attention has focussed on hazards associated with radioactivity. However, in many such wastes non-radiological contaminants such as heavy metals, acids, organic complexes, and colloids also form potentially significant long-term health and environmental hazards. The purpose of the present review is to examine in general terms the geochemical basis for management strategies aimed at minimizing the long-term impact of radiological and non-radiological contaminants.

1. INTRODUCTION

The safe management of uranium mining and milling wastes has only comparatively recently become a matter of wide concern. This derives partly from increased public awareness of human responsibility for safe environmental practices, and partly from the increased interest and importance of uranium as an alternative source of energy.

Whereas public concern has tended to focus on the radiological hazard of these wastes it is clear from the breadth of mining experience that the non-radiological contaminants also represent a potentially significant hazard. The purpose in the present Review is to provide an introduction or g e n e r a l o v e r v i e w of the n o n - r a d i o l o g i c a l contaminants and examine in broad terms some of the variables which can affect these contaminants in mill tailings and other mine wastes over the long-term.

This R e v i e w is p r i m a r i l y concerned with the non-radiological contaminants of uranium mining and milling however the general p r i n c i p l e s d i s c u s s e d in the paper apply e q u a l l y w e l l to the radiological contaminants. The close relationship between these two "divisions" of contaminants is assumed implicitly throughout the Review.

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The A t o m i c E n e r g y C o n t r o l Boa rd o f Canada has d i v i d e d the p r o b l e m s o f t a i l i n g s management i n t o t h r e e t i m e p e r i o d s , t h e o p e r a t i o n a l p h a s e , t h e t r a n s i t i o n pha se and a l o n g - t e r m p h a s e ( B r a g g , 1980 ) . T h i s R e v i e w i s c o n c e r n e d w i t h the l o n g - t e r m t i m e p e r i o d . The Boa rd p r o p o s e d t h a t " l o n g - t e r m " s t a r t s a t t he p o i n t i n t i m e a f t e r m i l l i n g o p e r a t i o n s h a v e c l o s e d when n a t u r a l , s y s t e m s , o r s y s t e m s w h i c h a r e c o m p l e t e l y p a s s i v e , b e c o m e t h e o n l y s y s t e m s c o n t r o l l i n g t h e r e l e a s e o f u n d e s i r a b l e m a t e r i a l s . They f u r t h e r p r o p o s e d t h a t t h i s p o i n t can be r e c o g n i s e d i n t h e f i e l d by the e s t a b l i s h m e n t o f a s t a b l e e q u i l i b r i u m " r e l e a s e r a t e " o f c o n t a m i n a n t s f rom the t a i l i n g s ( B r a g g , 1980 ) .

E n g i n e e r i n g s t r u c t u r e s such as dams and c o v e r s must be c o n s i d e r e d as s h o r t - t e r m w i t h a v e r y l o w p r o b a b i l i t y o f c o n t i n u i n g t o p r o v i d e s i g n i f i c a n t p h y s i c a l b a r r i e r s i n t o the l o n g - t e r m . At i t s m e e t i n g o f December 1979 t h e IAEA T e c h n i c a l A d v i s o r y Group on C u r r e n t P r a c t i c e s f o r T a i l i n g s Management p r o p o s e d to i n c o r p o r a t e t h e r e l i a b i l i t y o f man made p h y s i c a l b a r r i e r s i n t o the d e f i n i t i o n o f " l o n g - t e r m " as f o l l o w s : -

" d e s i g n l i f e " ( o f a t a i l i n g s impoundment s t r u c t u r e ) t h e p e r i o d d u r i n g w h i c h t h e t a i l i n g s i m p o u n d m e n t p e r f o r m s a s d e s i g n e d w i t h r e s p e c t t o the r a t e s o f r e l e a s e s o f r a d i o n u c l i d e s and the r e t e n t i o n o f t a i l i n g s m a t e r i a l . ( T y p i c a l l y o f t h e o r d e r o f one hundred t o s e v e r a l , h u n d r e d y e a r s . )

" l o n g - t e r m " t h e p e r i o d , i . e . , b e y o n d t h e d e s i g n l i f e , f o r w h i c h c l i m a t o l o g i c a l and g e o m o r p h o l o g i c a l p r o c e s s e s a r e m o r e o r l e s s p r e d i c t a b l e and d a t a w h i c h a r e u sed i n d e s i g n i n g the impoundment s y s t e m , and f o r w h i c h t h e i n t e g r i t y o f t h e i m p o u n d m e n t s y s t e m d e p e n d s , i s s u b s t a n t i a l l y u n a f f e c t e d b y s u c h p r o c e s s e s . ( T y p i c a l l y o f t he o r d e r o f 1000 t o 10000 y e a r s . )

The l a t t e r d e f i n i t i o n w a s s p e c i f i c a l l y i n t e n d e d no t t o i n c l u d e the p e r i o d beyond the quo t ed p e r i o d o f 1000 t o 10000 y e a r s .

T h e s e d e f i n i t i o n s d e f i n e t h e b e g i n n i n g o f l o n g - t e r m b u t a r e v a g u e i n t h e i r t r e a t m e n t o f t h e d u r a t i o n o r t h e end o f l o n g - t e r m as a p p l i e d t o u r a n i u m m i l l t a i l i n g s . As t h e t i m e i n v o l v e d e x t e n d s i n t o t h o u s a n d s , p o s s i b l y m i l l i o n s o f y e a r s i t can be a r g u e d t h a t any c o n s i d e r a t i o n o f t h e end o f l o n g - t e r m i s l a r g e l y a c a d e m i c .

N e v e r t h e l e s s t h e r e may be some a d v a n t a g e s t o management s t r a t e g i e s i n e x a m i n i n g f u r t h e r t h e c o n c e p t o f l o n g - t e r m a s a p p l i e d t o t h e n o n -r a d i o l o g i c a l c o n t a m i n a n t s .

C l e a r l y r a d i o a c t i v i t y i s not a s a t i s f a c t o r y y a r d s t i c k t o m e a s u r e l o n g -t e r m f o r t h e n o n - r a d i o a c t i v e c o n t a m i n a n t s . L o n g - t e r m f o r t h e s e e l e m e n t s w i l l depend l a r g e l y on the r e s i d e n c e t i m e o f t he c o n t a m i n a n t s i n the w a s t e s .

I t c a n b e p r e d i c t e d f r o m g e o l o g i c a l e x p e r i e n c e t h a t t a i l i n g s w i l l b e h a v e as open s y s t e m s to c o n t a m i n a n t m i g r a t i o n i n t o the i n d e f i n i t e f u t u r e . The v o l u m e o f t a i l i n g s b e i n g g e n e r a t e d i s s o v a s t t h a t s p e c i a l m e t h o d s o f d i s p o s a l b a s e d on c o m p l e t e c o n t a i n m e n t , s u c h a s

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t h o s e p r o p o s e d f o r r e l a t i v e l y s m a l l v o l u m e s o f h i g h l e v e l r a d i o a c t i v e w a s t e s e . g . v i t r i f i c a t i o n and d i s p o s a l i n d e e p g e o l o g i c a l f o r m a t i o n s , a r e n o t p r a c t i c a l and l o n g - t e r m w a s t e management p o l i c i e s f o r m i l l t a i l i n g s b a s e d on " c o m p l e t e c o n t a i n m e n t " wou ld seem to b e u n r e a l i s t i c .

R e s i d e n c e t i m e s f o r e ach p o t e n t i a l c o n t a m i n a n t i n t h e t a i l i n g s depend o n t h e r a t e o f r e m o v a l a n d t h e i n i t i a l c o n c e n t r a t i o n o f t h e c o n t a m i n a n t . T h e c o n t r o l o f t h e r e l e a s e r a t e o f p o t e n t i a l , c o n t a m i n a n t s f rom t h e w a s t e s i s t h e most i m p o r t a n t o b j e c t i v e o f l o n g -t e r m w a s t e management and c o n s i d e r a b l e r e s e a r c h e f f o r t i s p r e s e n t l y b e i n g d e v o t e d to t h i s p r o b l e m , g e n e r a l l y w i t h the a im o f f i n d i n g ways t o r e d u c e r e l e a s e r a t e s o f p a r t i c u l a r s e t s o f c o n t a m i n a n t s . F o r e x a m p l e e x p e r i m e n t s b y M o f f e t ( 1 9 8 0 ) on u r a n i u m m i l l t a i l i n g s f r o m E l l i o t L a k e i n d i c a t e t h a t t a i l i n g s w h i c h h a v e had most o f t h e p y r i t e r e m o v e d s h o w no e v i d e n c e o f a c i d p r o d u c t i o n a f t e r e x p o s u r e t o t h e w e a t h e r f o r a p e r i o d o f two y e a r s , w h e r e a s c o n v e n t i o n a l t a i l i n g s , w i t h a p p r o x i m a t e l y f i v e p e r c e n t p y r i t e , became s t r o n g l y a c i d . W i t h o u t t h e p r o d u c t i o n o f a c i d t h e m o b i l i t y o f c o n t a m i n a n t s ( m a i n l y h e a v y m e t a l s ) i n s o l u t i o n s f rom t h e l o w p y r i t e t a i l i n g s was g r e a t l y r e d u c e d . M o f f e t ( 1 9 8 0 ) a l s o s h o w e d f r o m t h e s e e x p e r i m e n t s t h a t t a i l i n g s d e p o s i t e d u n d e r w a t e r d i d n o t s h o w e v i d e n c e o f p y r i t e o x i d a t i o n o r a c i d p r o d u c t i o n a f t e r f i v e y e a r s and t h a t t h e r e a p p e a r e d t o b e no m i g r a t i o n o f r a d i o a c t i v i t y o r o t h e r c o n t a m i n a n t s f r o m t h e t a i l i n g s t o t h e o v e r l y i n g s o l u t i o n i n t h i s p e r i o d .

W h e r e a s t h e s e r e s u l t s h a v e g e n e r a l i m p l i c a t i o n s t h e e x p e r i m e n t s r e l a t e d i r e c t l y t o E l l i o t L ake c o n d i t i o n s . F u r t h e r i n v e s t i g a t i o n s a r e n e e d e d on t h e c h e m i c a l , and p h y s i c a l p r o p e r t i e s o f t a i l i n g s f r o m d i f f e r e n t o r e t y p e s and c l i m a t i c r e g i o n s t o p r o v i d e i n f o r m a t i o n f o r l o n g - t e r m t a i l i n g s management p l a n n i n g f o r s p e c i f i c s i t u a t i o n s .

2 . NON-RADIOLOGICAL CONTAMINANTS

P o t e n t i a l p o l l u t a n t s a v a i l a b l e f r o m u r a n i u m m i n i n g and m i l l i n g i n c l u d e :

A c i d Manganese Ammonia M e r c u r y A r s e n i c Molybdenum Bar ium N i c k e l B e r y l l i u m N i t r a t e / N i t r i t e Cadmium O r g a n i c s c o m p l e x e s Chromium P h o s p h o r u s C o b a l t S e l e n i u m Coppe r S u l p h a t e C y a n i d e Vanad ium Lead Z i n c

W h e r e a s l i t t l e i s k n o w n a b o u t t h e e n v i r o n m e n t a l i m p a c t o f o r g a n i c c o n s t i t u e n t s f r o m t a i l i n g s i t i s g e n e r a l l y a g r e e d t h a t t h e h e a v y m e t a l s p r o v i d e t h e m a j o r p o t e n t i a l , h a z a r d t o t h e e n v i r o n m e n t and man.

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H e a v y m e t a l s i n t r a c e a m o u n t s a r e n o r m a l c o n s t i t u t e n t s o f l i v i n g o r g a n i s m s and some e l e m e n t s such as z i n c , c o p p e r , c o b a l t and i r o n , a r e a b s o l u t e l y e s s e n t i a l f o r n o r m a l , g r o w t h and d e v e l o p m e n t . T h e s e and o t h e r e l e m e n t s a r e a v a i l a b l e to a q u a t i c l i f e t h r o u g h norma l g e o l o g i c a l p r o c e s s e s o f w e a t h e r i n g and t r a n s p o r t a t i o n . I t i s we l l , known t h a t the a d d i t i o n o f enhanced amounts o f h e a v y m e t a l s and o t h e r m a t e r i a l s t o t h e a q u a t i c e n v i r o n m e n t can h a v e s e r i o u s e f f e c t s on i n d i v i d u a l s p e c i e s and i n d e e d u p s e t the b a l a n c e o f e n t i r e e c o s y s t e m s ( e . g . B r y a n , 1971). I n a d d i t i o n s u c h e n h a n c e d h e a v y m e t a l c o n c e n t r a t i o n s can p o i s o n t h e f o o d and w a t e r i n g e s t e d b y man w i t h p o s s i b l e s e r i o u s c o n s e q u e n c e s ( e . g . B r o w n i n g 1969). W h e r e a s e x a m p l e s o f n a t u r a l p o i s o n i n g o f s o i l s a r e known ( e . g . La*g and B o l v i k e n , 1974) t h e s e a r e r a r e i n c o m p a r i s o n w i t h s o u r c e s o f p o l l u t i o n p r o v i d e d by i n d u s t r y and m i n i n g .

I n o r d e r t o a s s e s s t h e i m p a c t o f p o l l u t a n t s on a q u a t i c l i f e , f i e l d s u r v e y s and l a b o r a t o r y s t u d i e s on t h e b i o l o g i c a l , c h e m i c a l , and p h y s i c a l p a r a m e t e r s o f e c o s y s t e m s a r e r e q u i r e d .

F o o d c h a i n s n e e d t o b e f u r t h e r s t u d i e d . T o x i c i t y t e s t s i n t h e l a b o r a t o r y ( b i o - a s s a y s ) a r e o f g r e a t i m p o r t a n c e i n d e t e r m i n i n g t h e c h e m i c a l , s p e c i e s r e s p o n s i b l e f o r t o x i c e f f e c t s . C l i n i c a l s t u d i e s , e .g . a u t o p s y and b i o p s y , h i s t o l o g i c a l and b i o c h e m i c a l s t u d i e s a r e a l s o n e c e s s a r y t o s e e h o w and w h e r e m e t a l s a f f e c t t h e s t r u c t u r e o f c e l l s and the f u n c t i o n o f o r g a n s .

Me thods f o r t e s t i n g the s e n s i t i v i t y o f a q u a t i c o r g a n i s m s t o p a r t i c u l a r p o l l u t a n t s i n g e n e r a l u se h a v e b een d e s c r i b e d i n a s e r i e s o f a r t i c l e s b y S p r a g u e (1969, 1970 and 1971). The t e s t s u s u a l l y i n v o l v e ( s e e James 1978): ( i ) a s e r i e s o f c o n t a i n e r s each w i t h a d i f f e r e n t c o n c e n t r a t i o n

o f p o i s o n .

( i i ) o b s e r v a t i o n s o f f i s h r e s p o n s e s ( e . g . m o r t a l i t y ) d u r i n g e x p o s u r e s o v e r a p e r i o d o f t i m e ( e . g . b e t w e e n 1 d a y and 1 week f o r a c u t e and l e t h a l t o x i c i t y ) , and

( i i i ) f i n a l r e s u l t s e x p r e s s e d a s c o n c e n t r a t i o n t o l e r a t e d b y t h e m e d i u m o r " a v e r a g e " f i s h , o r a s t h e c o n c e n t r a t i o n t o x i c t o 50% o f t h e p o p u l a t i o n o f e x p o s e d f i s h o v e r a s t i p u l a t e d t i m e . The r e s u l t s o f s u c h t e s t s a r e s h o w n g r a p h i c a l l y i n F i g . 1 ( f r o m J a m e s , 1978). F o r e a c h f i x e d t i m e (96, 48, 24, and 1 h o u r ) t h e p e r c e n t a g e m o r t a l i t y i s p l o t t e d a g a i n s t t e s t c o n c e n t r a t i o n . L e t h a l c o n c e n t r a t i o n s to h a l f t he f i s h ( e . g . 24 h o u r s LC^Q) a r e o b t a i n e d f rom i n t e r p o l a t i o n .

W h e r e a s t h e a b o v e t e s t s a r e t e s t s o f s u r v i v a l i n p a r t i c u l a r c o n c e n t r a t i o n s t h e r e i s i n c r e a s i n g e m p h a s i s on i n v e s t i g a t i o n s o f s u b l e t h a l , e f f e c t s such as r e p r o d u c t i o n s u c c e s s , g r o w t h r a t e , a d a p t i o n t o e n v i r o n m e n t a l s t r e s s , r e s p i r a t i o n r a t e , d i s e a s e r e s i s t a n c e and o t h e r s ( s e e J a m e s , 1978 and S p r a g u e , 1971).

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The i m p o r t a n c e o f t o x i c i t y t r i a l s i n e s t a b l i s h i n g r e a l i s t i c s t a n d a r d s t h a t c o n s t i t u t e s a f e c o n c e n t r a t i o n s f o r t he m a i n t e n a n c e o f s t a b i l i t y i n a q u a t i c e c o s y s t e m s i s r e f l e c t e d i n the amount o f r e s e a r c h i n t h i s f i e l d b e i n g c a r r i e d out i n t h e A l l i g a t o r R i v e r s R e g i o n o f A u s t r a l i a i n p r e p a r a t i o n f o r u r a n i u m m i n i n g and m i l l i n g a t Range r and J a b i r u ( e . g . a n n u a l r e p o r t o f t h e S u p e r v i s i n g S c i e n t i s t 1 9 7 9 - 8 0 ) .

1001-

Concentration

FIG. 1. Method of obtaining LCS0 values from population survival curves. The median lethal concentration (LCS0) is the concentration of a test material that causes death to 50% of a population with a given time period, e.g. 24 h LCSo (from James, 1978).

I n f o r m a t i o n needed to f o r m u l a t e r e l e a s e s t a n d a r d s r e q u i r e s a k n o w l e d g e o f t h e s e n s i t i v i t y o f t h e e c o s y s t e m t o p o t e n t i a l e m i s s i o n s and a k n o w l e d g e o f t h e c o n s t i t u t i o n o f p o s s i b l e e f f l u e n t s . F o r e x a m p l e m e t a l s i n e f f l u e n t s f r o m u r a n i u m m i l l t a i l i n g s c a n o c c u r a s i o n s , m e t a l - o r g a n i c c o m p l e x e s o r i n c o l l o i d a l f o r m s . I t i s w e l l documented t h a t f o r some a q u a t i c o r g a n i s m s , e s p e c i l l y v e r t e b r a t e s , t he t o x i c i t i e s o f h e a v y m e t a l s a r e g r e a t e s t when t h e y o c c u r i n t h e i o n i c f o r m .

A g r e a t d e a l o f i n f o r m a t i o n i s a l r e a d y a v a i l a b l e on m e t a l b e h a v i o u r i n e n i r o n m e n t a l a q u e o u s s o l u t i o n s ( e . g . c h e m i c a l m o d e l l i n g i n A q u e o u s s o l u t i o n s p u b l i s h e d b y t h e A m e r i c a n C h e m i c a l S o c i e t y , 1 9 7 9 ) and s o p h i s t i c a t e d m o d e l s o f s o l u t i o n b e h a v i o u r h a v e b e e n d e v e l o p e d ( N o r d s t r o m e t a l , 1 9 7 9 ; B a l l e t a l , 1 9 7 9 ) . M o d e l s w i l l n e e d t o b e a d o p e d t o d e a l w i t h n a t u r a l and t a i l i n g s s o l u t i o n s f r o m s p e c i f i c t a i l i n g s s i t e s i n c o r p o r a t i n g s i t e s p e c i f i c , c l i m a t i c and o t h e r c o n s t r a i n t s ( e . g . R i t c h i e , 1977 ) .

B a s i c c o n s t r a i n t s on t h e c o m p o s i t i o n and b e h a v i o u r o f e m i s s i o n s f rom t a i l i n g s and w a s t e r o c k a r e imposed by t h e c h e m i c a l and m i n e r a l o g i c a l c o m p o s i t i o n o f t h e o r e and h o s t r o c k and t h e n a t u r e o f t h e m i l l p r o c e s s .

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General Characte r i s t i c s of Uranium Ore Deposits

C o n d i t i o n s s u i t a b l e for the c o n c e n t r a t i o n of uranium may a l s o be favourable for the accumulation of other elements. Consequently i t i s f requently found that uranium is associated with pa r t i cu l a r minerals and s u i t e s of companion e lements in c e r t a i n uranium ore t ype s . Examples of t h i s a re se l en ium in the d e p o s i t s of the Grants Minera l Be l t , arsenic in the deposits in Northern Saskatchewan and vanadium in the c a r n o t i t e d e p o s i t s in Western A u s t r a l i a and the Un i ted S t a t e s . The r e l a t i onsh ip between contaminants and ore types can be examined w i t h r e f e r e n c e to the main uranium ore types r e c o g n i s e d in the IAEA study on the Formation of Uranium Ore Deposits (1974). These are :

( i ) Sedimentary basin and sandstone-type depos i t s .

( i i ) Uranium in quartz pebble conglomerates.

( i i i ) Vein and s imi la r - type depos i t s .

( i v ) Other uranium deposits e . g . magmatic and s u r f i c i a l depos i t s .

Some uranium ore types l i s t e d under " o t h e r uranium d e p o s i t s " e.g. ca l c re te deposites may eventual ly prove important enough to warrant separate ca tego r i e s .

Sedimentary-type Deposits

Sedimentary- sandstone-type deposits comprise 40% of the wo r l d ' s l ow -cost reserves of uranium and approximately two - th i rds of the estimated a d d i t i o n a l p o t e n t i a l (Work ing Group I I , IAEA 1974). There d e p o s i t s are i dent i f i ed predominantly with sedimentary formations of d e t r i t a l cont inenta l , o r i g i n and are a s s o c i a t e d p r i m a r i l y w i t h r educ ing environments in these rocks. Roll front deposits are of this type.

Numerous authors have po inted to the p o t e n t i a l of sandstones containing organic matter, pyr i te or hydrogen sulphide to reduce and c o n c e n t r a t e uranium. Elements such as vanadium, i r o n , molybdenum, copper, sulphur, selenium, arsenic and cobalt can a lso be concentrated in these d e p o s i t s (Harshman, 1974). P a r t i c u l a r l y impor tant in sandstone ores in the centra l USA are concentrations of Se, Mo, As and V ( e . g . Dreeson et a l , 1978).

Proterozoic Quartz - pebble Conglomerates

P r o t e r o z o i c cong lomera te o r e s a re p o t e n t i a l l y the l a rges t source of uranium and p r e s e n t l y con t a in about 40% of the w o r l d ' s low cos t uranium r e s e r v e s ( IAEA, 1974). The cong l omera t e s a lways c o n t a i n a bundan t p y r i t e w h i c h i s b e l i e v e d to o r i g i n a t e m a i n l y by s u l p h i d i s a t i o n of d e t r i t a l m a g n e t i t e and i l m e n i t e . The r e a c t i n g sulphur is thought to be volcanogenic though some pyr i te may a lso have en te red the cong l omera t e s in d e t r i t a l form ( IAEA, 1974). The

3. RELATIONSHIP OF CONTAMINANTS TO URANIUM ORE TYPE

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P r o t e r o z o i c c o n g l o m e r a t e s g e n e r a l l y o v e r l y w i t h m a r k e d u n c o n f o r m i t y t h e metamorphosed A r c h a e a n .

At E l l i o t L a k e t h e o r e body c o n s i s t s o f a q u a r t z p e b b l e c o n g l o m e r a t e s e t i n a s e r i c i t e , p y r i t e ( 5 t o 15%) m a t r i x . P r i n c i p a l o r e m i n e r a l s a r e u r a n i n i t e , b r a n n e r i t e and m o n a z i t e . The i r o n c o n t e n t o f t he m i l l f e e d i s 3%, s u l p h u r i s 3.5% and r a r e e a r t h s 0 .02%. The r e s t i s e s s e n t i a l l y s i l i c a ( M o f f e t t , 1979 ) . H o w e v e r , B l a i r e t a l ( 1 9 8 0 ) a l s o f o u n d s i g n i f i c a n t c o n c e n t r a t i o n s o f N i , Co and Z n , i n t h e t a i l i n g s w h i c h must h a v e been c o n t r i b u t e d by t h e o r e . The h i g h q u a r t z c o n t e n t o f t h e o r e and w a s t e r o c k and t h e c o r r e s p o n d i n g p a u c i t y i n m i c a s , c l a y s e t c h a s i m p o r t a n t i m p l i c a t i o n s f o r w a s t e management .

V e i n - and S i m i l a r - t y p e D e p o s i t s

The v e i n d e p o s i t s o f u r a n i u m a r e t h o s e i n w h i c h u r a n i u m m i n e r a l s f i l l , c a v i t i e s s u c h a s c r a c k s , f i s s u r e s , p o r e s p a c e s , i n b r e c c i a s , s t o c k w o r k s and so on. The s i z e o f v e i n s v a r i e s f rom the m a s s i v e v e i n s o f p i t c h b l e n d e a t J a c h y m o v and P o r t R a d i u m t o t h e m i c r o s c o p i c p i t c h b l e n d e - f i l l e d c r a c k s , p o r e s and d i s s e m i n a t i o n s o f some o f t h e o r e b o d i e s i n n o r t h e r n S a s k a t c h e w a n and n o r t h e r n A u s t r a l i a ( S m i t h , 1974 ) .

V e i n d e p o s i t s o f u r a n i u m a r e f o u n d i n a l l t y p e s o f r o c k s , e . g . t h e g r a n t e s o f t h e V e n d e e , t h e m e t a s e d i m e n t s , v o l c a n i c s and g r a n i t e g n e i s s e s a t B e a v e r l o d g e , t h e m i c a c h l o r i t e s c h i s t s a t J a b i r u . The c h e m i c a l c o m p o s i t i o n o f t h e r o c k thus a p p e a r s t o h a v e l e s s b e a r i n g on t h e d e p o s i t i o n o f v e i n u r a n i u m t h a n d o e s i t s d e g r e e o f c o m p e t e n c y w h i c h p e r m i t s t h e d e v e l o p m e n t o f s t r u c t u r a l t r a p s f o r t h e u r a n i u m -b e a r i n g s o l u t i o n s ( S m i t h , 1974 ) .

V e i n d e p o s i t s c a n c o n t a i n a w i d e and v a r i e d c o n t e n t o f c o n t a m i n a n t e l e m e n t s s u c h a s S e , V , M o , F e , C o , C u , B e , A s . Mn, Zn and c a n c o n t a i n a v a r i a b l e c o n t e n t o f p y r i t e . Davey (AAEC, 1975) r e p o r t e d h i g h Co, Mn a n d Z n and p y r i t e ( ~ 3% S ) i n o r e and w a s t e r o c k f r o m t h e Rum J u n g l e M i n e i n N o r t h e r n A u s t r a l i a and o t h e r v e i n d e p o s i t s i n t h e A l l i g a t o r R i v e r s R e g i o n h a v e v a r i a b l e c o n t e n t s o f h e a v y m e t a l s and p y r i t e ( L e v i n s , 1 9 7 9 ) .

O t h e r U r an ium D e p o s i t s

T h e f o u r t h g r o u p c a l l e d " o t h e r u r a n i u m d e p o s i t s " i n c l u d e s d e p o s i t s w h i c h c a n n o t b e c l a s s i f i e d a s t y p e s 1, 2 o r 3 o f t h e I A E A 1972 c l a s s i f i c a i o n . T h i s g r o u p makes p r o v i s i o n f o r many d i v e r s e t y p e s o f u r a n i u m m i n e r a l i s a t i o n and d e p o s i t s a r e c l a s s i f i e d a c c o r d i n g t o o r i g i n o r t h o m a g m a t i c i n c l u d i n g g r a n i t e s , s y e n i t e s and a l k a l i n e i n t r u s i o n s ; d i a t r e m e s ; s h e a r zones and b r e c c i a s ; s u p e r g e n e - i n c l u d i n g c a l c r e t e d e p o s i t s ; b r i n e s ; m a r i n e .

T h e m i n e r a l o g y and e l e m e n t a l c o n c e n t r a t i o n s a s s o c i a t e d w i t h t h e s e d e p o s i t s a r e n o t d i s c u s s e d i n t h i s p r e s e n t s t u d y a s , i n t e r m s o f t h e o v e r a l l c o n t r i b u t i o n t o t a i l i n g s a c c u m u l a t i o n , t h e y a r e o f m i n o r s i g n i f i c a n c e . H o w e v e r , a s i n t h e m a j o r o r e t y p e s , a n u m b e r o f t h e m i n o r t y p e s l i s t e d a b o v e h a v e a c h a r a c t e r i s t i c m i n e r a l o g y and i n some c a s e s a r e s t r i c t e d s e t o f p o t e n t i a l c o n t a m i n a n t s ( e . g . c o n c e n t r a t i o n o f v anad ium i n c a l c r e t e , Mann and D e u t s c h e r , 1 9 7 8 ) .

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W h e r e a s a k n o w l e d g e o f o r e t y p e can p r o v i d e g e n e r a l i n f o r m a t i o n on t h e l i k e l y c o n t a m i n a n t s i n w a s t e s b e f o r e m i n i n g and m i l l i n g o p e r a t i o n s commence a q u a n t i t a t i v e k n o w l e d g e o f t he m i n e r a l o g y and c h e m i s t r y o f t h e o r e and h o s t r o c k i s e s s e n t i a l f o r e f f e c t i v e l o n g - t e r m management p l a n n i n g .

P a r t i c u l a r l y i m p o r t a n t i s t h e p y r i t e c o n t e n t o f t h e o r e and h o s t r o c k .

The c a p a c i t y o f a t a i l i n g s o r w a s t e r o c k h e a p t o p r o d u c e a c i d i s c r u c i a l t o t h e m a n a g e m e n t o f t h e w a s t e s . As h e a v y m e t a l s a r e p r o g r e s s i v e ! y m o b i l i s e d i n more a c i d s o l u t i o n s the l o n g - t e r m r e l e a s e r a t e w i l l depend t o a v e r y g r e a t d e g r e e on t h e l o n g - t e r m a v a i l a b i l i t y o f a c i d . A u s e f u l , c o n c e p t i s t h e " a c i d g e n e r a t i n g p o t e n t i a l . " o f a s p o i l o r m ine w a s t e w h i c h has b e e n d e s c r i b e d by Le Roux, e t a l ( 1 9 8 0 ) " a s t h e a m o u n t o f a c i d i t y t h a t c a n b e p r o d u c e d , u n d e r f i e l d c o n d i t i o n s , f r o m o x i d a t i o n o f p y r i t e i n t h e s p o i l " . T h e s e a u t h o r s f u r t h e r comment t h a t " s i n c e o t h e r s p o i l component s b e s i d e s p y r i t e a r e i n v o l v e d i n a c i d p r o d u c t i o n and c o n s u m p t i o n r e a c t i o n s and s i n c e h y d r o g e o l o g i c a l and o t h e r p h y s i c a l f a c t o r s a r e i n v o l v e d , a s i m p l e a n a l y s i s f o r t o t a l , p y r i t e i n the spo i l , i s i n a d e q u a t e " as a m e a s u r e o f t he a c i d g e n e r a t i n g c a p a c i t y . Le Roux e t a l ( 1 9 8 0 ) a r e a l s o c r i t i c a l o f u s i n g t o t a l s u l p h u r a s a m e a n s o f e s t i m a t i n g t h e t o t a l a c i d g e n e r a t i n g c a p a c i t y o f m i n e w a s t e s . N e v e r t h e l e s s t h e m o s t common s o u r c e o f s u l p h u r i n u r a n i u m t a i l i n g s i s p y r i t e and w h e r e a s t h e r a t e s o f o x i d a t i o n o f d i s t i n c t p y r i t e f o r m s ( C a r u c c i o e t a l , 1976) w i l l v a r y t h e a s s u m p t i o n can be made t h a t a l l p y r i t e w i l l e v e n t u a l l y b e o x i d i s e d and t h i s r e a c t i o n w i l l p r o v i d e the ma in s o u r c e o f a c i d o v e r t h e l o n g -t e r m .

A l s o c r u c i a l to l o n g - t e r m w a s t e management p l a n n i n g f o r a s p c i f i c o r e d e p o s i t i s an a c c u r a t e k n o w l e d g e o f t h e c o n t e n t and m i n e r a l f o r m o f p o t e n t i a l c o n t a m i n a n t e l e m e n t s .

A u s e f u l p r e l i m i n a r y , q u a l i t a t i v e i n d i c a t o r o f t h e p o t e n t i a l o f a p a r t i c u l a r e l e m e n t i n m ine w a s t e s to c o n t a m i n a t e the e n v i r o n m e n t i s g i v e n by t h e r a t i o o f t h e c o n c e n t r a t i o n o f t h a t e l e m e n t i n t h e o r e o r h o s t r o c k t o t h e c o n c e n t r a t i o n o f t h a t e l e m e n t i n t h e l o c a l e n v i r o n m e n t o r m o r e g e n e r a l l y w i t h r e f e r e n c e t o t h e a v e r a g e c o m p o s i t i o n o f t h e e a r t h ' s c r u s t ( e . g . T a y l o r , 1 9 6 4 ) . S u c h a c o m p a r i s o n w i l l need t o b e u sed w i t h c a u t i o n h o w e v e r a s , un de r c e r t a i n c o n d i t i o n s , w e a t h e r i n g r e a c t i o n s and t r a n s p o r t c o m b i n e d w i t h p y r i t e a c i d g e n e r a t i o n c o u l d remove a l l h e a v y m e t a l s from a t a i l i n g s d e p o s i t .

5 . MILL PROCESSING AS A CONTRIBUTOR AND CONDITIONER OF CONTAMINANTS

M i l l i n g P r o c e s s i n g

The s e c o n d m a j o r i n f l u e n c e on t h e l o n g - t e r m m a n a g e m e n t o f m i l l t a i l i n g s i s t h e m i l l i n g p r o c e s s i t s e l f . M i l l p r o c e s s e s s u c h a s g r i n d i n g , l e a c h i n g and t h e a d d i t i o n o f c h e m i c a l r e a g e n t s , p l a y an i m p o r t a n t r o l e i n d e t e r m i n i n g t h e c h e m i c a l and p h y s i c a l p r o p e r t i e s o f t a i l i n g s and a r e , a s a c o n s e q u e n c e , f u n d a m e n t a l t o t h e b e h a v i o u r o f m i l l , t a i l i n g s o v e r the l o n g - t e r m .

4 . SITE SPECIF IC CHARACTERISTICS OF A URANIUM ORE

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E s s e n t i a l l y m i l l p r o c e s s i n g i s d e s i g n e d t o r e c o v e r the maximum amount o f u r a n i u m and o t h e r d e s i r a b l e e l e m e n t s f rom t h e o r e as e c o n o m i c a l l y a s p o s s i b l e . H o w e v e r , s o m e m i l l s h a v e a d d e d , e i t h e r v o l u n t a r i l y o r t h r o u g h r e g u l a t o r y r e q u i r e m e n t s , a d d i t i o n a l s t e p s d e s i g n e d to r e d u c e t h e e n v i r o n m e n t a l i m p a c t o f t he m i l l t a i l i n g s , e .g . p r e c i p i t a t i o n o f r a d i u m a n d t h e n e u t r a l i z a t i o n o f w a s t e p r o c e s s w a t e r . T h e i n t r o d u c t i o n o f t h e s e s t e p s r e p r e s e n t s a s i g n i f i c a n t a d v a n c e i n management p r a c t i c e to meet s p e c i f i c o b j e c t i v e s . Q u e s t i o n s c o n c e r n i n g t h e l o n g - t e r m e f f e c t i v e n e s s o f such s t e p s , t h e d e s i r a b i l i t y o f a d d i n g to them and the b a l a n c e o f e n v i r o n m e n t a l g a i n s a g a i n s t c o s t a r e b a s i c t o the g e o c h e m i c a l a p p r o a c h t a k e n i n t h i s R e v i e w .

The two p r o c e s s e s used i n u r an ium m i l l i n g a t p r e s e n t a r e :

( i ) t h e a c i d l e a c h p r o c e s s c o u p l e d w i t h e i t h e r s o l v e n t e x t r a c t i o n or i o n e x c h a n g e ;

( i i ) t h e a l k a l i n e l e a c h p r o c e s s c o u p l e d w i t h c a u s t i c p r e c i p i t a t i o n .

T h e r e a r e no i n d i c a t i o n s t h a t t h e b a s i c t e c h n o l o g y a p p l i e d t o u r a n i u m m i l l i n g w i l l b e f u n d a m e n t a l l y a l t e r e d i n t h e n e a r f u t u r e , and a s a r e s u l t c o n s i d e r a t i o n o f t h e c o n t a m i n a n t s and m o d i f i c a t i o n s a d d e d d u r i n g the above p r o c e s s e s w i l l p r o v i d e a r e a s o n a b l y a c c u r a t e p i c t u r e o f t h e c o n t r i b u t i o n o f m i l l i n g t o the c o n d i t i o n o f t he t a i l i n g s .

U r an ium i s a l s o r e c o v e r e d as a b y - p r o d u c t f rom such s o u r c e s as c o p p e r m i n e w a t e r , p h o s p h o r i c a c i d p r o d u c t i o n and h e a p and i n s i t u l e a c h i n g . C h e m i c a l p o l l u t a n t s f r o m t h e s e s o u r c e s c a n d i f f e r f r o m t h o s e f r o m c o n v e n t i o n a l m i l l s though s i m i l a r c h e m i c a l p r i n c i p l e s a p p l y to t h e i r d i s p o s a l .

A c i d L e a c h P r o c e s s

T h e a c i d l e a c h p r o c e s s i s t h e m o s t w i d e l y u s e d t e c h n o l o g y i n t h e i n d u s t r y a c c o u n t i n g f o r m o r e t h a n 80% o f y e l l o w c a k e p r o d u c e d ( U S G e n e r i c E n v . I m p . S t a t e m e n t (NUREG 0 7 0 6 , 1 9 8 0 ) , L e v i n s and R i n g ( 1 9 7 9 ) , Lendrum and McCreedy ( 1 9 7 6 ) and o t h e r s ) .

The US NRC E n v i r o n m e n t a l I m p a c t S t a t e m e n t (NUREG 0706, 1980) d e s c r i b e d the c h a r a c t e r i s t i c s o f o p e r a t i o n o f a model a c i d l e a c h m i l l t r e a t i n g s a n d s t o n e o r e o f an a v e r a g e g r a d e o f 0.16% U 3 0 g . The r e a g e n t s a d d e d d u r i n g the p r o c e s s a r e e s t i m a t e d as shown i n T a b l e 1.

I t i s n o t e d t h a t no a t t e m p t i s m a d e t o n e u t r a l i s e t h e t a i l i n g s b y a d d i n g l i m e o r l i m e s t o n e .

The p r o p o s e d c o n s u m p t i o n o f r e a g e n t s i n a c i d l e a c h m i l l s o f t h e A u s t r a l i a n A l l i g a t o r R i v e r s R e g i o n v e i n t y p e u r a n i u m o r e s i s a s shown i n T a b l e 2 ( L e v i n s , 1979 ) .

B e s i d e s s u l p h u r i c a c i d t h e a d d i t i o n o f p y r o l u s i t e , l i m e , c y a n i d e ( a s s o c i a e d w i t h g o l d r e c o v e r y ) and o r g a n i c r e a g e n t s c o u l d s i g n i f i c a n t l y a f f e c t t h e l o n g - t e r m b e h a v i o u r o f t he t a i l i n g s .

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T a b l e 1

Reagents added during Process

A d d i t i v e s Q u a n t i t i e s kg/Mt o r e

S u l p h u r i c a c i d 4 5 . 0 Sodium c h l o r a t e 1.4 Ammonia 1.1 F l o c c u l a n t 0 . 06 Amine ( l o n g c h a i n ) 0 . 015 A l c o h o l 0 . 0 4 K e r o s e n e 0 . 45 I r o n ( r o d s f o r g r i n d i n g ) 0 . 35

T a b l e 2

P r o p o s e d Consumpt ion o f R e a g e n t s ( t o n n e s / y e a r ) -A l l i g a t o r R i v e r s R e g i o n

A d d i t i v e s Range r I / I M i l l

J a b i l u k a N a b a r l e k a

S u l p h u r i c A c i d 62 100 98 500 6 200 P y r o l u s i t e (75% M n 0 2 ) 9 400 17 500 600 L ime (70% CaO) 23 600 43 800 2 360 Ammonia 1 350 2 550 Amine 27 51 K e r o s e n e 400 740 C y a n i d e 0 146 0

V a l u e s i n f e r r e d from D. L e v i n s u n p u b l i s h e d d a t a ( A A E C ) .

A l k a l i n e L e a c h P r o c e s s

A l k a l i n e l e a c h i n g , w h i c h i s l e s s w i d e l y u s e d t h a n a c i d l e a c h i n g , i s a p p l i e d when t h e h o s t r o c k c o n t a i n s m i n e r a l s t h a t w o u l d c o n s u m e e x c e s s i v e q u a n t i t i e s o f a c i d . L e a c h i n g i s u s u a l l y c a r r i e d o u t i n a h e a t e d p u l p u s i n g ^ 2 0 0 ^ and NaHCO^ w i t h a i r o r o x y g e n as t h e o x i d a n t . C a r b o n a t e l e a c h i n g i s v e r y s e l e c t i v e and an a c c e p t a b l e u r a n i u m c o n c e n t r a t e c a n b e p r o d u c e d d i r e c t l y f r o m t h e l e a c h l i q u o r b y p r e c i p i t a t i o n w i t h sod ium h y d r o x i d e . I n some m i l l s , t h e p r e c i p i t a t e i s r e d i s s o l v e d i n s u l p h u r i c a c i d and r e p r e c i p i t a t e d w i t h a m m o n i a t o p r o d u c e a h i g h e r g r a d e , l o w - s o d i u m , u r a n i u m c o n c e n t r a t e . B e c a u s e c h e m i c a l c o s t s f o r a l k a l i n e l e a c h i n g a r e h i g h , t h e l e a c h l i q u o r i s r e c y c l e d a f t e r c a r b o n d i o x i d e ( u s u a l l y f r o m f l u e g a s e s ) i s a d d e d t o a d j u s t t h e c a r b o n a t e - b i c a r b o n a t e r a t i o (D . L e v i n s , P e r s . Comm. 1980 ) .

C o n d i t i o n i n g o f T a i l i n g s

T h e a d d i t i o n o f c h e m i c a l s t e p s t o t h e m i l l i n g p r o c e s s , d e s i g n e d t o a c h i e v e s p e c i f i c e n v i r o n m e n t a l o b j e c t i v e s , i s w i d e l y p r a c t i s e d i n m i l l s i n some m a j o r u r an ium m i n i n g c o u n t r i e s .

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Main c o n d i t i o n s in t r e a t i n g m i l l i n g was te s have been d i r e c t e d towards:

( i ) recyc l ing of waste waters ;

( i i ) p r ec ip i t a t i on and removal of radium from so lu t ion ;

( i i i ) n e u t r a l i s i n g of t a i l i n g s to cause p r e c i p i t a t i o n of heavy meta ls .

Rega rd ing m i l l i n g p r a c t i c e in Canada, Lendrum and McCreedy (1976) r e f e r to the present pract ice of maximising the recyc l ing of water and s o l u t i o n s , and note that a l l uranium companies now use t o t a l impoundment of s o l i d s , neu t r a l i s e a l l the acid with lime and ox id i se the ferrous i ron to f e r r i c iron by blowing a i r through the pulp p r io r to d i s c h a r g i n g i t to the was te d i s p o s a l a r e a . They f u r t h e r comment that plants use barium chlor ide to coprec ip i ta te radium-226 d isso lved in the t a i l i n g s l iquor to reduce the r a d i o a c t i v i t y of the supernatant l i quor to a low l e v e l .

With reference to the waste management po l icy in Aus t r a l i a Levins and Ring (1979) noted that " a l l proposals in the A l l i g a t o r Rivers region i n c l u d e r e c y c l e of wa te r from the t a i l i n g s dam to m i n i m i s e wate r u s a g e , use of mine wa te r as make-up to the m i l l and s e g r e g a t i o n of r u n - o f f on the b a s i s o f expected con tamina t i on l e v e l s " . No p r o c e s s l i q u i d s w i l l be d i s c h a r g e d by any m i l l and ac id r a f f i n a t e s w i l l be n e u t r a l i s e d w i t h l i m e . Lime t r ea tment to pH 8 w i l l r educe the concentrations of a l l heavy metals except manganese to less than 0.5 mgi - ' ' ' . Levins states that i f manganese in seepage from the t a i l i n g s proves to be a problem i t could be prec ip i tated completely by r a i s i n g the pH to 10. Replacement of manganese in the m i l l p r oce s s by some other oxidant such as sodium chlorate or hydrogen peroxide would be a p o s s i b l e a l t e rna t i v e .

Commendable as these pract ices are they are l a r g e l y aimed at short or medium term was te management o b j e c t i v e s . I t i s impor tant tha t inves t i ga t ions are made of the long-term impl icat ions of adding or not adding l ime , manganese or other material, during the m i l l i n g process. However, to answer such questions i t w i l l be necessary to understand the long-term chemical evolut ion of t a i l i n g s .

6. LONG-TERM CHEMICAL PROCESSES IN MINE AND MILL WASTES

Weathering and Diagenetic Processes

T a i l i n g s and was t e rock can be c o n s i d e r e d as an a r t i f i c i a l sediment w i th s p e c i a l phys i c a l and chemica l p r o p e r t i e s . As soon as the sed iment i s d e p o s i t e d i t i s s u b j e c t e d to w e a t h e r i n g p r o c e s s e s in r e sponse to l o c a l c l i m a t i c c o n d i t i o n s , and to l ong - t e rm d i a g e n e t i c react ions in response to pressure and temperature conditions generated in the individual, depos i ts .

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The ma in c h e m i c a l a g e n t s a r e m e t e o r i c w a t e r , o x y g e n , c a r b o n d i o x i d e , o x i d e s o f n i t r o g e n and s u l p h u r - w h i c h f o r m s t r o n g a c i d s , m i c r o o r g a n i s m s and o r g a n i c m a t e r i a l . C h e m i c a l r e a c t i o n s i n v o l v e h y d r a t i o n , c a r b o n a t e r e a c t i o n s , h y d r o l y s i s and o x i d a t i o n .

The l o n g - t e r m c h e m i c a l b e h a v i o u r o f t h e t a i l i n g s and w a s t e r o c k w i l l depend to a l a r g e e x t e n t on the c o m p o s i t i o n o f t h e p r o c e s s e d r o c k and c h e m i c a l and m i n e r a l o g i c a l c h a n g e s i n t r o d u c e d d u r i n g m i l l i n g . These a s p e c t s h a v e a l r e a d y b e e n b r i e f l y d i s c u s s e d . A l s o c r i t i c a l t o t h e b e h a v i o u r o f t a i l i n g s o v e r t h e l o n g t e r m i s t h e i m p a c t o f t h e l o c a l , c l i m a t e .

The I n f l u e n c e o f C l i m a t e

U r a n i u m m i l l t a i l i n g s a r e g e n e r a l l y d i s p o s e d o f i n impoundments on the s u r f a c e o r r e t u r n e d e i t h e r c o m p l e t e l y o r p a r t i a l l y t o t h e m i n e w o r k i n g s . I n the c a s e o f s u r f a c e dumps t h e t a i l i n g s w i l l b e s u b j e c t e d t o t h e c l i m a t i c c o n d i t i o n s p r e v a i l i n g a t t h e s i t e . D i s p o s a l , u n d e r g r o u n d w i l l i s o l a t e the t a i l i n g s f rom c l i m a t i c a c t i o n ( t o some d e g r e e ) b u t c o u l d l e a d to o t h e r p r o b l e m s such as t h e c l o s e c o u p l i n g o f t h e t a i l i n g s w i t h the g r o u n d w a t e r s y s t e m . C l i m a t i c e f f e c t s c o u l d be e x p e c t e d to be r e l a t i v e l y u n i f o r m f o r t a i l i n g s f rom s p e c i f i c o r e t y p e s i n a u r a n i u m p r o v i n c e such as the A l l i g a t o r R i v e r s R e g i o n i n n o r t h e r n A u s t r a l i a . Howeve r , the e v o l u t i o n o f t a i l i n g s f rom s i m i l a r o r e t y p e s l o c a t e d i n v e r y d i f f e r e n t c l i m a t i c r e g i o n s , s u c h a s n o r t h e r n C a n a d a and n o r t h e r n A u s t r a l i a , w i l l r e f l e c t t he d i f f e r e n t c l i m a t i c c o n d i t i o n s found i n t h e s e r e g i o n s .

I d e a l l y d e c i s i o n s on the l o n g - t e r m management o f u r a n i u m m i l l t a i l i n g s w o u l d t a k e i n t o a c c o u n t l o n g - t e r m c l i m a t i c t r e n d s . H o w e v e r , a s p r e d i c t i o n s on s u c h m a t t e r s a s t h e o c c u r r e n c e o f i c e a g e s o r t h e e f f e c t s on c l i m a t e o f b u i l d u p i n a t m o s p h e r i c CO^ a r e u n c e r t a i n , i t w o u l d seem r e a s o n a b l e t o b a s e l o n g - t e r m w a s t e management d e c i s i o n s on p r e s e n t c l i m a t i c p a t t e r n s .

V e r y l i t t l e i s k n o w n a b o u t t h e e f f e c t s o f c l i m a t e on t h e c h e m i c a l e v o l u t i o n o f u r a n i u m m i l l t a i l i n g s t h o u g h a n u m b e r o f i m p o r t a n t s t u d i e s h a v e b e e n m a d e . F o r e x a m p l e w a s t e r o c k h e a p s , f r o m t h e Rum J u n g l e a r e a i n monsoona l n o r t h e r n A u s t r a l i a , h a s b een d e s c r i b e d i n a s e r i e s o f p a p e r s p u b l i s h e d by t h e A u s t r a l i a n A t o m i c E n e r g y C o m m i s s i o n ( 1 9 7 5 ) .

The Rum J u n g l e r e g i o n i s s e m i - t r o p i c a l w i t h d i s t i n c t w e t and d r y s e a o n s . S e e p a g e f r o m t h e w a s t e s r e d u c e s t o e s s e n t i a l l y z e r o d u r i n g t h e d r y a n d b u i l d s u p s t r o n g l y d u r i n g t h e w e t c o n t r i b u t i n g c o n t a m i n a n t s t o t h e n e a r b y r i v e r . C h a r a c t e r i s t i c a l l y a " s l u g " o f p o l l u t a n t s i s r e m o v e d f r o m t h e w a s t e s b y t h e f i r s t i n t e n s e r a i n s . Howeve r , t he e f f e c t s on the c h e m i s t r y o f t h e m i n e / m i l l w a s t e s o f t h e c y c l i c p a t t e r n o f r a i n w a t e r i n f l u x and c o n t a m i n a n t r e l e a s e f o l l o w e d by a d r y s e a s o n w i t h h i g h e v a p o r a t i o n i s no t w e l l u n d e r s t o o d .

Recen t d e t a i l e d m e a s u r e m e n t s o f w a t e r movement ( D a n i e l e t a l , 1980) and t e m p e r a t u r e d i s t r i b u t i o n ( H a r r i e s and R i t c h i e , i n p r e s s ) i n a " p y r i t e " o v e r b u r d e n h e a p f r o m Rum J u n g l e i n d i c a t e t h a t o x i d a t i o n o c c u r s down t o 15 m e t r e s f rom t h e s u r f a c e o f t h e h e a p b u t no change i n

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rate of oxidat ion was observed from the wet to the dry season. Also these s t u d i e s show that changes in wa te r d e n s i t y from wet to d ry season were l e ss than expected, though there was evidence that drying out of the top 1 to 1.5 met res occur red in the dry season . This work r a i s e s important questions as to the s i gn i f i cance of annual c l imat i c va r i a t i ons on the chemical behaviour of t a i l i ng s/was te rock heaps.

In hot desert areas i t appears that the in f lux of meteoric waters i s i n su f f i c i en t to cause r e l ease by seepage. Markos (1979) observed that acid t a i l i n g s in the dry centra l USA are dominated by hydroscopic and d e l i q u e s c e n t s a l t s which ho ld t i g h t l y to pore w a t e r s s e r i o u s l y l i m i t i n g g rav i ty in f low of ra inwater and outf low by seepage (Bush et a l , 1980). In these t a i l i n g s chemical react ions take place in h igh ly s a l i n e s o l u t i o n s which show l i t t l e i f any s e a s o n a l v a r i a t i o n in concentrat ion.

The wet temperate c l imate at E l l i o t Lake is typical, of uranium mines in Canada and c o n t r a s t s s t r o n g l y w i th the monsoonal c l i m a t e o f n o r t h e r n A u s t r a l i a and the hot d e s e r t c o n d i t i o n s of c e n t r a l USA. Temperatures at E l l i o t Lake ave rage 4°C and annual p r e c i p i t a t i o n i s 966 mm o f w h i c h 210 mm i s due to s n o w f a l l ( M o f f e t t , 1 9 7 9 ) . E v a p o r a t i o n i s n e g l i g i b l e and l a r g e vo lumes of e f f l u e n t s a r e discharged to surface watercourses, p a r t i c u l a r l y in the spring runoff. Ta i l ings are cont inua l ly being permeated by ra in and melted snow and th is condit ion of constant f lushing contrasts with the other examples described and c l e a r l y i s a major factor inf luencing t a i l i n g s behaviour and the residence time of contaminants in the wastes.

7. CHEMICAL-MINERALOGICAL FACTORS IN LONG-TERM MANAGEMENT

Over the long-term the rate of r e l ease of contaminants from t a i l i n g s and waste rock w i l l depend on the chemical and minera log ica l evolut ion o f the t a i l i n g s and c l i m a t i c (and groundwater ) contro l l ed transport mechanisms. The hazard to health and the environment w i l l depend on the r a t e s o f r e l e a s e and the c a p a c i t y o f t he e n v i r o n m e n t to n e u t r a l i s e , absorb or otherwise deal with incoming contaminants and acid. The importance of chemical processes in t a i l i n g s management is i l l u s t r a t e d by the work of M o f f e t t and T e l l i e r ( 1978 ) , Cherry et al (1980), Marcos (1979), Davy (AAEC, 1975) Lush et al (1978), Singer and Stumm (1970) and o t h e r s . A number of a spec t s of the i n t e r a c t i o n of contaminants w i t h the envi ronment have been s t u d i e d . P a r t i c u a r l y r e l e v e n t are those s t u d i e s d i r e c t e d towards the c a p a c i t y of the immediate environment to provide a b a r r i e r to contaminant migrat ion ( e . g . Shepherd and Cherry 1980, Marp l e et a l , in p r e s s , Gee et a l 1980).

Observations on re l a t ionsh ips between physical and chemical processes in t a i l i n g s provide important avenues for invest igat ions for poss ib l e l o n g - t e r m management o p t i o n s . For example in t h e i r s t u d i e s of an abandoned t a i l i n g s dam at E l l i o t Lake M o f f e t t and T e l l i e r (1978) ob se rved that p y r i t e o x i d a t i o n took p l a c e much more r a p i d l y in the c o a r s e t a i l i n g s than in the s l i m e s . The c h a n g e in p y r i t e

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c o n c e n t r a t i o n w i t h depth for the 17 year o ld t a i l i n g s i s shown in F i g u r e 2. The Authors a t t r i b u t e t h i s e f f e c t to r e s t r i c t e d oxygen supply in the sl imes as a r e su l t of saturat ion of the sl imes through greater c a p i l l a r y r i s e in this mater ia l .

These authors a lso observed seasonal changes in the watertab le l eve l in the t a i l i n g s w i th a h igh in s p r i n g t i m e and a p r o g r e s s i v e drop in the summer months. As i l l u s t r a t e d by Lush et a l (1978) the wate r tab le marks a major Eh-pH boundary and this and other boundaries, such as that between coarse and f ine t a i l i n g s and t a i l i n g s to basement, are important to the long-term evolution of the t a i l i n g s .

An example of a major change in pH c o n d i t i o n s at the t a i l i n g s -u n d e r l y i n g so iL boundary has been r e p o r t e d by Marcos (1979) f o r t a i l i n g s in New Mex ico , the Eh-pH d i a g r a m , reproduced in F i g u r e 3, shows that p rec ip i t a t i on of migrating iron would occur immediately the so lut ions crossed the boundary from t a i l i n g s to underlying s o i l s .

I n t e r n a l m i g r a t i o n of m a t e r i a l s and d e p o s i t i o n at p h y s i c a l and chemical boundaries, including the sur face, could over the long term r e s u l t in chemica l l a y e r i n g w i t h i n the t a i l i n g s and i n some c i r c u m s t a n c e s the f o rmat i on of s u r f a c e c r u s t s . These l a y e r s would themselves form physical and chemical boundaries. For example,a layer of f e r r i c hydroxide could have considerab le physical strength and the capacity to absorb heavy metals (Morgan and Stumm, 1965; Co l l ins and Buol, 1970; Means et a l , 1978).

Manganese oxides and clays are noted for the i r absorption capac i t i es and a re impor tant in c o n s i d e r a t i o n s of l o n g - t e r m management of t a i l i n g s . In t h i s r e g a r d Mn02> used as an ox ident in the m i l l i n g of uranium ores in the A l l i g a t o r Rivers Region (Levins and Ring, 1979), may a l so contr ibute to the long-term s t a b i l i t y of the t a i l i n g s .

The o re type and host rock a re c r i t i c a l to the a b s o r p t i o n and n e u t r a l i s a t i o n c a p a c i t i e s of t a i l i n g s . Shepherd and Cherry (1980) po in t out that at E l l i o t l ake the n e u t r a l i s a t i o n (and a b s o r p t i o n , bu f f e r ing ) capacity of the quartz conglomerate ores , which form the major component of the t a i l i n g s , and the underlying c l a y - f r e e s o i l s and c r y s t a l l i n e rock , i s e x t r e m e l y l ow . This i s not the case for ores , such as a number of vein types, which are associated with shales and sch i s t s .

8. BIOLOGICAL PROCESSES

Up to this point processes in the t a i l i n g s have been treated in purely chemical terms. However, i t has become evident that micro-organisms play an important r o l e in weathering processes. Micro-organisms such as y e a s t s , b a c t e r i a and a l g a e are now known to be i n v o l v e d in a w ide r ange of w e a t h e r i n g r e a c t i o n s i n v o l v i n g the breakdown of s i l i c a t e s ( S i l v e r m a n , 1979; Agbim and Dox tade r , 1975) o x i d a t i o n of o r g a n i c ma t t e r ( T r u d i n g e r et a l , 1979; G o l u b i c et a l , 1979) , o x i d a t i o n of s u l p h i d e s (Ra l ph , 1979; Ivanov et a l , 1961) and in the geochemica l processes which a f fect i ron , manganese, uranium, copper, aluminium and other me ta l l i c elements (Ehl ich , 1971).

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0 2 4 6 8 10 12 14

pH

FIG.2. Eh and pH conditions of tailings and soils and their relationship to soluble iron (from Markos, 1979). Precipitation of iron from waters moving downward into underlying soil would also trap other mobile ions by coprecipitation or adsorption.

O r

E 20 -

SANDS

200 -

0.5 1.5 2.5 3.5 4.5 % PYRITE

0.5 1.5 2.5 3.5 4.5 % PYRITE

FIG.3. Typical analysis of pyrite with depth in representative slimes and sands areas from an abandoned tailings site at Elliot Lake (from Moffett and Tellier, 1978).

The fundamental importance of micro-organisms in a f fect ing the rate of s u l p h i d e d e g r a d a t i o n i s i n d i c a t e d by Ralph (1979 ) . Ralph (1979) s ta tes that the involvement of b i o l o g i c a l agencies in the accelerated degradation of sulphide minerals has been unequivocal ly demonstrated by a number of i nves t i ga to r s . Organisms most commonly associated with sulphide degradation are Th iobac i l lus spp., which der ive energy from the o x i d a t i o n o f reduced su lphur compounds and i r o n o x i d i z i n g organisms such as Th iobac i l l u s ferrooxidans and Metallogenium spp.

Singer and Stumm (1970) r e f e r to the importance of the f e r r o u s - f e r r i c oxidat ion as a rate l im i t ing step in acid production during sulphide degradation and note that microbia l mediation acce lerates the f e r rous -f e r r i c oxidat ion at rates 10^ greater than ab io t i c r a t e s .

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T h e n u t r i t i o n a l n e e d s o f p a r t i c u l a r m i c r o - o r g a n i s m s i n c l u d e r e q u i r e m e n t s f o r Eh and pH w i t h i n s p e c i f i c r a n g e s . H o w e v e r , t h e i r m e t a b o l i c a c t i v i t i e s can b r i n g a b o u t c h a n g e s i n t h e s e p a r a m a t e r s . The f i e l d s i t u a t i o n i s dynamic and m i c r o b i a l g e n e r a t i o n o f c h a n g e s i n E h -pH and o t h e r c o n d i t i o n s a r e a c c o m p a n i e d b y t h e d e v e l o p m e n t o f a s u c c e s s i o n o f m i c r o b i a l p o p u l a t i o n s . The e x t e n t t o w h i c h s u l p h i d e d e g r a d a t i o n p r o c e e d s d e p e n d s v e r y l a r g e l y o n t h e s e q u e n t i a l d e v e l o p m e n t o f t h i s m i c r o b i a l , s u c c e s s i o n ( R a l p h , 1979 ) .

I n t a i l i n g s g r a i n s i z e e f f e c t s may l i m i t a c c e s s o f w a t e r , d i s s o l v e d n u t r i e n t s , g a s e s and t h e m i c r o b i a l p o p u l a t i o n s and the r a t e - l i m i t i n g f a c t o r s i n o x i d a t i v e d e g r a d a t i o n may i n f a c t l i e i n t h e d i f f u s i o n c h a r a c t e r i s t i c s o f t h e m a t e r i a l r a t h e r t h a n t h e c h e m i c a l c h a r a c t e r i s t i c s o f t h e m i n e r a l o r t h e b i o c h e m i c a l a b i l i t i e s o f t h e o r g a n i s m s ( R a l p h , 1 9 7 9 ) .

The t e m p e r a t u r e p r o f i l e s o f t h e t a i l i n g s and w a s t e r o c k p i l e s a r e a l s o l i k e l y to a f f e c t and r e f l e c t t he r a t e s o f b o t h c h e m i c a l and m i c r o b i a l r e a t i o n s and t o h a v e c o n s i d e r a b l e i n f l u e n c e u p o n t h e n a t u r e o f t h e m i c r o b i a l p o p u l a t i o n s . D a n i e l e t a l ( 1 9 8 0 ) r e p o r t e d a w i d e r a n g e o f t e m p e r a t u r e s up t o 5 6 ° C i n d r i l l h o l e s t h r o u g h an o v e r b u r d e n dump u n d e r g o i n g p y r i t i c o x i d a t i o n f r o m t h e Rum J u n g l e m i n e i n n o r t h e r n A u s t r a l i a and M u r r and B r i e r l e y ( 1 9 7 8 ) o b s e r v e d t e m p e r a t u r e s up t o 59°C i n a l a r g e s c a l e b a c t e r i a l l e a c h i n g t e s t o f c o p p e r - b e a r i n g w a s t e f r o m t h e K e n n i c o t m i n e . T e m p e r a t u r e s i n e x c e s s o f 8 0 ° C h a v e b e e n o b s e r v e d i n d u m p s o f l o w - g r a d e c o p p e r i n B u l g a r i a ( G r o u d e v e t a l , 1978) and the U n i t e d S t a t e s ( B e c k , 1967 ) .

A m a j o r l o n g - t e r m o b j e c t i v e i n t a i l i n g s and w a s t e r o c k management i s t h e i n h i b i t i o n o f t h e f o r m a t i o n o f a c i d . R e d u c t i o n o f b a c t e r i a l a c t i o n i s an i m p o r t a n t m e a n s o f a c h i e v i n g t h i s . S i n g e r and Stumm ( 1 9 7 0 ) p o i n t t o t h e i m p r a c t i c a l i t y o f s u p p r e s s i n g m i c r o - o r g a n i s m a c t i v i t y by a t t e m p t i n g to s e a l a m ine ( o r m i l l t a i l i n g s o r w a s t e r o c k ) a g a i n s t i n f l o w o f o x y g e n . I n c a s e s w h e r e t a i l i n g s c a n b e l o c a t e d b e l o w the w a t e r t a b l e oxygen c o u l d be e x c l u d e d m a i n t a i n i n g r e d u c i n g c o n d i t i o n s w h i c h w i l l i n h i b i t b a c t e r i a l a c t i o n and Fe o x i d a t i o n . The p o s s i b i l i t i e s f o r a d d i n g s u i t a b l e b a c t e r i c i d e s t o t a i l i n g s , w h e r e s u b m e r g e n c y i s n o t p r a c t i c a l , w i l l n e e d t o b e c o n s i d e r e d a s a l o n g -t e r m s t r a t e g y f o r i n h i b i t i n g b a c t e r i a l , a c t i o n . Ra l ph ( 1 9 7 9 ) r e f e r s t o an i n t e r e s t i n g method o f b i o l o g i c a l c o n t r o l o f i r o n - o x i d i s i n g b a c t e r i a b y t a k i n g a d v a n t a g e o f t h e i n h i b i t i o n o f M e t a l l o g e n i u m p o p u l a t i o n s by i n c r e a s e d f e r r o u s i r o n c o n c e n t r a t i o n ( W a l s h and M i t c h e l , 1975 ) .

CONCLUSIONS AND RECOMMENDATIONS

I n many u r a n i u m m i l l t a i l i n g s t h e n o n - r a d i o l o g i c a l c o n t a m i n a n t s such a s C a , P b , Z n , S e , A s , Mo , C d , a c i d s , o r g a n i c c o m p o u n d s e t c , f o r m a s i g n i f i c a n t , p o t e n t i a l , l o n g - t e r m h a z a r d t o h e a l t h a n d t h e e n v i r o n m e n t .

Over t h e l o n g - t e r m c h e m i c a l p r o c e s s e s t a k i n g p l a c e i n t h e w a s t e s and t h e l o c a l c l i m a t i c and g r o u n d w a t e r c o n d i t i o n s w i l l b e t h e m a i n f a c t o r s c o n t r o l l i n g t h e r e l e a s e r a t e s o f n o n - r a d i o l o g i c a l ( and r a d i o l o g i c a l ) c o n t a m i n a n t s . C o n s e q u e n t l y i t i s o f c o n c e r n t h a t o n l y a f ew d e t a i l e d

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case studies of the chemical behaviour of active and abandoned tailings and waste rock are described in the literature. It is a matter of urgency that relevant information on these wastes is gathered and assimilated in a form which can be used in long-term management strategies.

Special aspects of the problem of the management of non-radiological contminants identified in this present review as deserving further investigation include:

(i) The significance of interfaces and boundaries, which can be static or mobile, between the tailings and underlying rock or within the tailings themselves (e.g. water table).

(ii) The behaviour of bacteria under variable conditions, natural or induced, in tailings and waste rock and the possibility of controlling bacterial, activity by excluding oxygen and water or through the addition of bactericides.

(iii) The effects of addition of chemicals such as limestone, lime, manganese dioxide, organic reagents on the long-term chemistry of the tailings.

(iv) The role of complexes in the transport of materials within and outside of tailings waste rock piles.

(v) Methods of measuring the buffering and neutralisation capacity of tailings and waste rock systems and techniques for using buffering properties to reduce release rates of contaminants.

(vi) The use of physical properties of tailings such as grain size stratification and the shapes of tailings piles, to achieve long-term chemical objectives.

(vii) The influence of climate on the chemical processes in tailings and waste rock, including the question of whether mine/mill wastes could usefully be classified in terms of climatic region.

Real-time experimental work on tailings/waste rock systems present obvious problems. The geological record however provides examples of supergene ore-processes which have relocated and concentrated potentially fugitive compounds, preventing their dispersal, into the surrounding environment. A study of such occurrences and other archaeological and geological analogues to uranium mine/mill wastes will provide valuable time-significant data on chemical processes in situations relative to mine/mill wastes. Experiments under elevated temperatures and pressures may also provide information on long-term processes in tailings.

Reference has been made to the underwater disposal of uranium mill tailings. The advantages and disadvantages of this strategy need to be further investigated.

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The p r e s e n t r e v i e w was s t i m u l a t e d b y the OECD/NEA s t u d y on t h e l o n g -te rm management o f u r a n i u m m i l l t a i l i n g s . I n t e r n a t i o n a l c o o p e r a t i o n i n t h e f o c u s s i n g and c o o r d i n a t i o n o f r e s e a r c h , d i s s e m i n a t i o n o f i n f o r m a t i o n and the e s t a b l i s h m e n t o f d a t a b a n k s i s e x t r e m e l y v a l u a b l e and can o n l y be e n c o u r a g e d .

BIBLIOGRAPHY A g b i m , N .N . and D o x t a d e r , K.G. 1 9 7 5 . M i c r o b i a l d e g r a d a t i o n o f z i n c

s i l i c a t e s . S o i l B i o l . B i o c h e m . 7.> 2 7 5 - 8 0 .

A m e r i c a n C h e m i c a l S o c i e t y , 1 9 7 9 . C h e m i c a l M o d e l l i n g i n A q u e o u s S o l u t i o n s : S p e c i a t i o n ? S o r p t i o n , S o l u b i l i t y a n d K i n e t i c s , ( J e n n e , E .A . ( E d . ) ) , A m e r i c a n C h e m i c a l S o c i e t y , W a s h i n g t o n D . C .

A u s t r a l i a n A t o m i c E n e r g y C o m m i s s i o n , 1975. Rum J u n g l e E n v i r o n m e n t a l S t u d i e s , ( D a v y , D.R. ( E d . ) ) , A u s t r a l i a n A t o m i c e n e r g y C o m m i s s i o n , Sydney , AAEC/E 365 .

B e c k , J . V . 1 9 6 7 . The r o l e o f b a c t e r i a i n c o p p e r m i n i n g o p e r a t i o n s , B i o t e c h n o l . B i o e n g . JJ, 4 8 7 - 9 7 .

B a l l , J . W . , J e n n e , A . E . a n d N o r d a t r o m , D . K . 1 9 7 9 . W A T E Q 2 - A c o m p u t e r i s e d c h e m i c a l m o d e l f o r t r a c e and m a j o r e l e m e n t s s p e c i a t i o n and m i n e r a l e q u i l i b r i a i n n a t u r a l w a t e r s , i n C h e m i c a l M o d e l l i n g i n A q u e o u s S o l u t i o n s : S p e c i a t i o n , S o r p t i o n , S o l u b i l i t y and K i n e t i c s , ( J e n n e , E .A . ( E d . ) ) , A m e r i c a n Chemica l S o c i e t y , W a s h i n g t o n D . C . , 8 0 5 - 8 3 5 .

B l a i r , R . D . , C h e r r y , J . A . , L i m , T . P . a n d V i v y u r k a , A . J . 1 9 8 0 . G r o u n d w a t e r m o n i t o r i n g and c o n t a m i n a n t o c c u r r e n c e a t an a b a n d o n e d t a i l i n g s a r e a E l l i o t L a k e , O n t a r i o . F i r s t I n t e r n a t i o n a l C o n f e r e n c e on U r a n i u m M i n e W a s t e D i s p o s a l , V a n c o u v e r , C a n a d a , May 1980 , 4 1 1 - 4 4 4 .

B r a g g , K. 1980. Long t e rm a s p e c t s o f u r a n i u m t a i l i n g s management ( a n A t o m i c E n e r g y C o n t r o l B o a r d d i s c u s s i o n p a p e r on p r o p o s e d i n t e r i m c l o s e - o u t c r i t e r i a ) . F i r s t I n t e r n a t i o n a l C o n f e r e n c e on U r a n i u m M i n e W a s t e D i s p o s a l , V a n c o u v e r , Canada , May 1980.

B r o w n i n g , E. 1 9 6 9 . T o x i c i t y o f I n d u s t r i a l M e t a l s . B u t t e r w o r t h s . L o n d o n . 383 p p .

B r y a n , G.W. 1971. The e f f e c t s o f h e a v y m e t a l s ( o t h e r than m e r c u r y ) on m a r i n e and e s t u a r i n e o r g a n i s m s . P r o c . R o y . S o c . L o n d . B. 177 , 3 8 9 - 4 1 0 .

B u s h , K . J . , M a r k o s , G . , and S e n g u p t a , S. 1 9 8 0 . I n v e s t i g a t i o n o f p o t e n t i a l c o n t a m i n a t i o n f rom t h e Grand J u n c t i o n t a i l i n g s i n t o t h e C o l o r a d o R i v e r . P r o c . T h i r d S y m p o s . on U r a n i u m M i l l T a i l . i n g s , C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 3 8 7 - 4 0 7 .

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C a r u c c i o , F . T . , G e i d e l , G. a n d S e w e l l , J . M . 1 9 7 6 . The c h a r a c t e r o f d r a i n a g e a s a f u n c t i o n o f t h e o c c u r r e n c e o f f r a m b o i d a l p y r i t e and g r o u n d w a t e r q u a l i t y i n e a s t e r n K e n t u c k y . 6 t h S y m p o s . o f C o a l M i n e D r a i n a g e R e s e a r c h , L o u i s v i l l e , K e n t u c k y , 1 -16 .

C h e r r y , J . A . , B l a c k p o r t , R . J . , D u b r o v s k y , N . , G i l l h a m , R.W. , L i m , T . P . , M u r r a y , D . , R e a r d o n , E . J . and S m y t h , D .J .A . 1 9 8 0 . S u b s u r f a c e h y d r o l o g y and g e o c h e m i c a l e v o l u t i o n o f i n a c t i v e p y i t i c t a i l i n g s i n t h e E l l i o t L ake U r a n i u m D i s t r i c t , Canada . P r o c . T h i r d S y m p o s . on U r a n i u m M i l l . T a i l i n g s M a n a g e m e n t , C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 3 5 3 - 3 8 5 .

C o l l i n s , J . F . and B u o l , S .W. 1 9 7 0 . E f f e c t s o f f l u c t u a t i o n s i n t h e E h -pH e n v i r o n m e n t on i r o n a n d / o r m a n g a n e s e e q u i l i b r i a . S o i l S c i . , UjO, 1 1 1 - 8 .

D a n i e l , J . A . H a r r i s , J .R . and R i t c h i e , A . I . M . 1 9 8 0 . T e m p e r a t u r e d i s t r i b u t i o n s i n an o v e r - b u r d e n dump u n d e r g o i n g p y r i t i c o x i d a t i o n , i n B i o g e o c h e m i s t r y o f A n c i e n t a n d M o d e r n E n v i r o n m e n t s , ( T r u d i n g e r , P . A . , W a l t e r , M.R. and R a l p h , B.J. , ( E d s . ) ) , A u s t r a l i a n Academy o f S c i e n c e , C a n b e r r a , 6 3 0 -6 .

D r e e s o n , D .R . , M a r p l e , M.L . and K e l l e y , N. E d . 1 9 7 8 . C o n t a m i n a n t t r a n s p o r t , R e v e g e t a t i o n , and T r a c e E l e m e n t S t u d i e s a t I n a c t i v e U r a n i u m M i l l T a i l i n g s P i l e s . P r o c . F i r s t Symp. on U r a n i u m M i l l T a i l i n g s Management , C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 1978, 1 1 1 - 1 3 9 .

E h l i c h , H.J.L. 1971. B i o g e o c h e m i s t r y o f t he m i n o r e l e m e n t s o f s o i l i n S o i l B i o c h e m i s t r y , ( M c L a r e n , A . D . a n d S k u j i n s , J . , ( E d s . ) ) , 2, 3 6 1 - 8 4 .

G e e , G .W. , C a m p b e l l , A . C . , O p i t z , B .E . and S h e r w o o d , D.R. 1 9 8 0 . I n t e r a c t i o n o f u r a n i u m m i l l t a i l i n g s l e a c h a t e w i t h M o r t o n Ranch C l a y l i n e r and so i l , m a t e r i a l . P r o c . T h i r d Sympos . on U r a n i u m M i l l T a i l i n g s M a n a g e m e n t , C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 3 3 3 - 3 5 3 .

G o l u b i c , S. , K r u m b e i n , W. and S c h n e i d e r , J . 1979. The c a r b o n c y c l e i n B i o g e o c h e m i c a l C y c l i n g o f M i n e r a l f o r m i n g E l e m e n t s , ( T r u d i n g e r , P . A . and S w a m e , D . J . , ( E d s . ) ) , E l s e v i e r , 2 9 - 4 5 .

G r o u d e v , S . N . , G e n c h e v , F .N . a n d G a i d a i j i e v , S . S . 1 9 7 8 . O b s e r v a t i o n s on t h e m i c r o f l o r a i n an i n d u s t r i a l c o p p e r dump l e a c h i n g o p e r a t i o n , i n M e t a l l u r g i c a l A p p l i c a t i o n s o f B a c t e r i a l L e a c h i n g and R e l a t e d M i c r o b i o l o g i c a l Phenomena , ( M u r r , L.E. , T o r m a , A .E . and B r i e r l e y , J . A . , ( E d s . ) ) , A c a d e m i c P r e s s , New Y o r k , 2 5 3 - 7 4 .

H a r r i s , J .R . and R i t c h i e , A . I . M . The u s e o f t e m p e r a t u r e p r o f i l e s t o e s t i m a t e t h e p y r i t i c o x i d a t i o n r a t e i n A W a s t e R o c k Dump f r om an Opencut M i n e , W a t e r , S o i l and A i r P o l l u t i o n , 25^ ( i n

P r e s s 57 : —

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Harshman , E .N . 1 9 7 4 . D i s t r i b u t i o n o f e l e m e n t s i n s o m e r o l l - t y p e u r a n i u m d e p o s i t s i n F o r m a t i o n o f U r a n i u m O r e D e p o s i t s . IAEA , V i e n n a , 1 6 9 - 1 8 3 .

I n t e r n a t i o n a l A t o m i c E n e r g y A g e n c y , 1974. f o r m a t i o n o f U r a n i u m Ore D e p o s i t s . P r o c e e d i n g s S e r i e s - S T I / P U B / 3 7 4 , A t h e n s , May 1974 .

I v a n o v , V . I . , N a g i r n y a k , F . I . and S t e p a n o v , B.A. 1 9 6 1 . B a c t e r i a l o x i d a t i o n o f s u l f i d e o r e s , I . The r o l e o f t h i o b a c i l l u s f e r r o x i d a n s i n t h e o x i d a t i o n o f c h a l c o p y r i t e and s p h a l e r i t e . M i k r o b i o l o g i y a , 30 , 6 8 8 - 9 2 .

James , R.D. 1 9 7 8 . E f f e c t s o f h e a v y m e t a l s on a q u a t i c l i f e . C S I R O R e v i e w P u b l i c a t i o n . J a n . 1978 . 79 p p .

L § g , J . and B o l v i k e n , B. 1 9 7 4 . Some n a t u r a l l y h e a v y - m e t a l p o i s o n e d a r e a s o f i n t e r e s t i n p r o s p e c t i n g , s o i l g e o c h e m i s t r y , and g e o m e d i c i n e . N o r g . G e o l . U n d e r s . N o . 3 0 4 , 7 3 - 9 6 .

Lendrum, F .C . and M c C r e e d y , H.H. 1 9 7 6 . R e c e n t t r e n d s i n C a n a d i a n u r a n i u m p r o c e s s i n g i n U r an ium Ore P r o c e s s i n g , IAEA, V i e n n a , 1 3 - 2 1 .

L e R o u x , N .W. , D a c e y , P .W. and T e m p l e , K.L . 1 9 8 0 . The m i c r o b i a l r o l e i n p y r i t e o x i d a t i o n a t a l k a l i n e pH i n c o a l m i n e s p o i l , i n B i o g o c h e m i s t r y o f A n c i e n t a n d M o d e r n E n v i r o n m e n t s , ( T r u d i n g e r , P . A . , W a l t e r , M.R. and R a l p h , B . J . , ( E d s . ) ) , A u s t r a l i a n Acadamy o f S c i e n c e , C a n b e r r a , 5 1 5 - 2 0 .

L e v i n s , D.M. 1979. E n v i r o n m e n t a l i m p a c t o f u r a n i u m m i n i n g and m i l l i n g i n A u s t r a l i a . C a n . I n s t . M i n . M e t . P r o c . , 9 t h A n n . H y d r o m e t a l l u r g i c a l M e e t i n g , T o r o n t o , 1978 .

L e v i n s , D.M. and R i n g , R .J . 1 9 7 9 . P r o c e s s i n g o f u r a n i u m o r e s i n A u s t r a l i a . The Chem. E n g . , A u g u s t , 5 8 0 - 4 .

L o u d e r b a c k , T. 1 9 7 5 . S e l e n i u m and t h e E n v i r o n m e n t . M i n . I n d . R e s . B u l l . 1_8, 1 - 1 4 . ( P u b l i c a t i o n o f t h e C o l o r a d o S c h o o l o f M i n e s . )

L u s h , D . , B r o w n , J . , F l e t c h e r , R. , G o o d e , J a n d J u r g e n s , T. 1 9 7 8 . An a s s e s s m e n t o f t h e l o n g t e rm i n t e r a c t i o n o f u r a n i u m t a i l i n g s w i t h t h e n a t u r a l e n v i r o n m e n t . P r o c . o f OECD/NAE S e m i n a r on M a n a g e m e n t , S t a b i l i s a t i o n and E n v i r o n m e n t a l I m p a c t o f u r an ium M i l l T a i l i n g s , A l b u q u e r q u e , New M e x i c o , 3 7 3 - 9 8 .

Mann, A . W . and D e u t s c h e r , R .L . 1 9 7 8 . G e n e s i s p r i n c i p l e s f o r t h e p r e c i p i t a t i o n o f c a r n o t i t e i n c a l c r e t e d r a i n a g e s i n W e s t e r n A u s t r a l i a . E c o . G e o l . , 7 3 , 1 7 2 4 - 3 7 .

M a r k o s , G. 1979. G e o c h e m i c a l m o b i l i t y and t r a n s f e r o f c o n t a m i n a n t s i n u r a n i u m m i l l t a i l i n g s . P r o c . Second Sympos . on U r an ium M i l l T a i i n g s M a n a g e m e n t . C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 5 5 - 9 .

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M a r p l e , M .L . , L o u d e r b o u g h , E . T . , P o t t e r , L . D . , D r e e s o n , D.R. and C o k a l , E.J. A b s o r p t i o n o f s o l u b l e c o n t a m i n a n t s f rom u r a n i u m m i l l t a i l i n g s b y m a r i n e s h a l e s . 1980 A n n . R e p t . o f t h e US D e p a r t m e n t o f E n e r g y , D i v . o f B i o l o g i c a l and E n v i r o n m e n t a l R e s e a r c h .

Means, J . L . , C r e r a r , D.A., B o r c s i k , M.P. and D u g u i d , J . O . 1 9 7 8 . Adsorption of Co and selected actinides by Mn and Fe oxides in soils and sediments. Geochim. Cosmochim. Acta., 4 2 , 1 7 6 3 - 7 3 .

Moffett, D. 1 9 7 9 . Characterisation and disposal of radioactive effluents from uranium mining. Bull. Can. Inst. Mining. 1 5 2 - 1 5 6 .

M o f f e t t , D. 1 9 8 0 . U l t i m a t e d i s p o s a l o f u r a n i u m t a i l i n g s - P a r t 2 : The p y r i t e f r e e t a i l i n g s and f l o o d e d p i t e x p e r i m e n t . R i o A lgom L t d . , E l l i o t L ake p a p e r , R 8 0 - 0 8 .

M o f f e t t , D. and T e l l i e r , M. 1 9 7 8 . R a d i o l o g i c a l i n v e s t i g a t i o n s o f an abandoned t a i l i n g s a r e a . J . E n v . Q u a l i t y , 7_, N o . 3 , 3 1 0 - 4 .

M o r g a n , J .J . and Stumm, W. 1965. The r o l e o f m u l t i v a l e n t m e t a l o x i d e s i n l i m n o l o g i c a l t r a n s f o r m t i o n s as e x e m p l i f i e d by i r o n and m a n g a n e s e . A d v . W a t e r P o l l u t . R e s . , 1 , 1 0 2 - 1 8 .

M u r r , L . E . and B r i e r l e y , J . A . 1 9 7 8 . The u s e o f l a r g e - s c a l e t e s t f a c i l i t i e s i n s t u d i e s o f t h e r o l e o f m i c r o o r g a n i s m s i n c o m m e r c i a l l e a c h i n g o p e r a t i o n s , i n M e t a l l u r g i c a l A p p l i c a t i o n s o f B a c t e r i a l L e a c h i n g a n d R e l a t e d M i c r o b i o l o g i c a l P h e n o m e n a , ( M u r r , L . E . , T o r m a n , A .E . and B r i e r l e y , J .A . , ( E d s . ) ) , A c a d e m i c P r e s s , New Y o r k , 4 1 9 - 5 1 8 .

N o r d s t r o m , D.K. e t a l , 1 9 7 9 . A c o m p a r i s o n o f c o m p u t e r i z e d c h e m i c a l m o d e l s f o r e q u i l i b r i u m c a l c u l a t i o n s i n aqueous s o l u t i o n s , i n C h e m i c a l M o d e l l i n g i n A q u e o u s S o l u t i o n s : S p e c i a t i o n S o r p t i o n S o l u b i l i t y and K i n e t i c s , ( J e n n e , E .A . ( E d . ) ) , A m e r i c a n Chemica l . S o c i e t y , W a s h i n g t o n D.C., 8 5 7 - 9 2 .

R a l p h , B . J . 1 9 7 9 . O x i d a t i v e r e a c t i o n s i n t h e s u l f u r c y c l e , i n B i o g e o c h e m i c a l C y c 1 i n g o f M i n e r a l f o r m i n g E l e m e n t s , ( T r u d i n g e r , P .A . and S w a i n e , D . J . , ( E d s . ) ) , E l s e v i e r , 3 6 9 -4 0 0 .

R i t c h i e , A . I . M . 1 9 7 7 . H e a p l e a c h i n g : a g a s d i f f u s i o n r a t e - l i m i t e d m o d e l . R e p o r t o f t h e A u s t r a l i a n A t o m i c E n e r g y C o m m i s s i o n , S y d n e y , AAEC/E, 4 2 9 .

S h e p h e r d , T .A . and C h e r r y , J . A . 1 9 8 0 . C o n t a m i n a n t m i g r a t i o n i n s e e p a g e f r o m u r a n i u m m i l l t a i l i n g s i m p o u n d m e n t : an o v e r v i e w . P r o c . t h i r d S y m p o s . on U r a n i u m M i l l T a i l i n g s M a n a g e m e n t , C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 2 9 9 - 3 3 1 .

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S i l v e r m a n , M.P. 1 9 7 9 . B i o l o g i c a l and o r g a n i c c h e m i c a l d e c o m p o s i t i o n o f s i l i c a t e s , i n B i o g e o c h e m i c a l C y c l i n g o f M i n e r a l - F o r m i n g E l e m e n t s . ( T r u d i n g e r , P .A . and S w a i n e , D . J . , ( E d s . ) ) . S t u d i e s i n E n v i r o n m e n t a l S c i e n c e , 3. E l s e v i e r , New Y o r k .

S i n g e r , P .C . and S t u m m , W. 1 9 7 0 . A c i d i c m i n e d r a i n a g e : t h e r a t e -d e t e r m i n i n g s t e p . S c i e n c e , 167 , 1 1 2 1 - 1 1 2 3 .

S m i t h , E .E .N . 1 9 7 4 . R e v i e w o f c u r r e n t c o n c e p t s r e g a r d i n g v e i n d e p o s i t s o f u r a n i u m i n F o r m a t i o n o f U r a n i u m O r e D e p o s i t s . IAEA, V i e n n a 1974, 1 6 9 - 1 8 3 .

S p r a g u e , J . B . 1 9 6 9 . M e a s u r e m e n t o f p o l l u t a n t t o x i c i t y t o f i s h - I . B i o a s s a y methods f o r a c u t e t o x i c i t y . W a t e r R e s . , 3 , 793 .

S p r a g u e , J . B . 1 9 7 0 . M e a s u r e m e n t o f p o l l u t a n t t o x i c i t y t o f i s h - I I . U t i l i z i n g and a p p l y i n g b i o a s s a y r e s u l t s . W a t e r R e s . , 4 , 3 .

S p r a g u e , J .B. 1971. M e a s u r e m e n t o f p o l l u t a n t t o x i c i t y t o f i s h - I I I . S u b l e t h a l e f f e c t s and " s a f e " c o n c e n t r a t i o n s . W a t e r R e s . , 5, 245 ,

S u p e r v i s i n g S c i e n t i s t f o r t h e A l l i g a t o r R i v e r s R e g i o n . Annua l R e p o r t 1 9 7 9 - 8 0 . A u s t r a l i a n G o v t . P u b . S e r v . C a n b e r r a 1 9 8 0 . 148 p p .

T a y l o r , S.R. 1964. Abundance o f c h e m i c a l e l e m e n t s i n t h e c o n t i n e n t a l c r u s t : a new t a b l e . Geoch im. Cosmochim. A c t a , ^ 8 , 1 2 7 3 - 8 5 .

W a l s h , F. and M i t c h e l l , R. 1975. M ine d r a i n a g e p o l l u t i o n r e d u c t i o n by i n h i b i t i o n o f i r o n b a c t e r i a . W a t e r R e s . , 9 , 5 2 5 - 8 .

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IMPLICATIONS OF ALTERNATIVE GEOCHEMICAL CONTROLS ON THE TEMPORAL BEHAVIOUR OF ELLIOT LAKE TAILINGS

W.J. SNODGRASS* D.L. LUSH, J. CAPOBIANCO Beak Consultants Limited, Mississauga, Ontario, Canada

Abstract

IMPLICATIONS OF ALTERNATIVE GEOCHEMICAL CONTROLS ON THE TEMPORAL BEHAVIOUR OF ELLIOT LAKE TAILINGS.

An assessment of the major minerals and probable radioisotope associations which are typical of the Elliot Lake, Canada, mining district have been made using mill operating data, laboratory and field observations, and equilibrium chemistry calculations. The majority of the 2 3 8 U series and one-half of the 2 3 2 Th series are postulated to have been chemically leached and reprecipitated with gypsum, jarosite and hydroxides and carbonates of calcium and iron during the milling and tailing neutralization processes. It is hypothesized that gypsum dis­solution controls the mobilization of radioisotopes within the tailings except for jarosite associated radium mobilization and acidification control on thorium. Treating a typical tailings area as homogeneous and with a typical drainage area, it is estimated that the time to leach all buffer from the tailings is 100 to 150 years, the time to oxidize all pyrite is 200 years and the time to dissolve all gypsum is 400 to 1000 years for the base tailings management case. For alternative management schemes of tailings hydrology, with or without pyrite removal, the errors in estimates of radionuclide concentration and pH in the tailings pore water and a downstream lake are modelled and assessed. The major errors are the proportion of radium in jarosite and gypsum, the adsorption coefficient in the tailings and the time history of the solubility product of the mill-formed and in-situ-formed minerals. The time scales of this model are compared to those of major hydrological and geological phenomena of the Elliot Lake area. The closest time scales (infilling of Lake Erie, the next glaciation age) appear to be longer than those of concern for dosimetry calculation.

1. Introduction

Uranium mining and milling is the first step used in pro­ducing a fuel for generating electricity from nuclear reactors and for producing material suitable for military uses. In Canada, the two main mining areas are located in Northern

* To whom correspondence should be addressed. Mailing address: Department of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, Md 21218, United States of America.

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Saskatchewan and in the E l l i o t t Lake d i s t r i c t of Ontario; other areas show the potent ia l fo r development (see Hamel and Howieson, 1982). The former area has been developed only most recent ly . Mining and smelting which began in the E l l i o t t Lake d i s t r i c t ca 1954 has produced about 100 mi l l i on tonnes of t a i l i n g s to date; i t i s estimated that up to another one b i l l i o n tonnes could be mi l led before mining in this d i s t r i c t ends (Cherry et a l . , 1980). Past "d i sposa l " techniques have often consisted of depositing the waste rock and t a i l i n g s in compoundments behind leaky, v a l l e y dams in lake, bog or stream v a l l e y s . Present designs include l ine r s in impounding dams, and vegetated cover; a l te rnat ive methods under consideration include deep lake d i s ­posal ( e . g . , see BEAK, 1981, Halbert et a l . , 1982).

Contaminants which can be mobilized and transported through aquatic and atmospheric pathways pose potentia l dangers to the ecosystem and to human health. Ta i l ings ac id i f i ca t i on due to py r i t e oxidation lowers the pH and mobil izes trace metals both of which may cause toxic e f fects upon f i s h and other b io ta . Ionizing rad iat ion may induce health ef fects in humans i f they are exposed to radioact ive isotopes through ingestion or through external exposure.

Objectives for rad iat ion protection include dose l imitat ion and optimization (Osborne, 1982). An optimization approach i s b a s i c a l l y s imi lar to c l a s s i c a l econometric techniques of bene f i t -r i sk analyses subject to the constraint that no individual i s unacceptably exposed to rad ia t ion . Quantitat ive ly , this t rans ­lates into the optimum point of management being that degree of protection at which any addit ional degree of protection would be attained at an addit ional cost that was greater than the perceived value of the reduction in the r i sk from rad ia t ion . This optimiza­t ion procedure i s commonly re ferred to by the acronym ALARA. I t has been applied to gaseous ef f luents from nuclear f a c i l i t i e s (Osborne, 1982). I t i s desired to develop a set of examples capable of demonstrating the app l i c ab i l i t y and the l imitat ions of ALARA to low leve l wastes, in pa r t i cu l a r to t a i l i n g s p i l e s .

I t i s the goal of this paper to present the concepts used in estimating the biogeochemical evolution of the t a i l i n g s p i l e used in the Canadian example. Other papers in th is volume present work re lated to dose commitment ca lcu lat ions from the Canadian, Austra l ian and American examples and of preliminary resu l t s from appl icat ion of ALARA ( e . g . , Lush et a l . , 1982; Osborne, 1982). For the Canadian example, a study was sponsored by the Atomic Energy Control Board of Canada for making dose commitment ca lcu ­la t ions fo r a generic uranium mi l l t a i l i n g s s i t e in Northern Ontario, Canada. The study object ives were to formulate and tes t methodologies ( i ) for predict ing the quantity of radioisotopes

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transported out of a uranium mi l l t a i l i n g s p i l e and ( i i ) fo r r e l a t ing these transport rates to the dose commitment received by humans through aquatic and atmospheric pathways.

I dea l l y , one des i res to measure the quantity of radioisotopes entering a water body. Over the short-term, ongoing monitoring programs can be used to measure the quantity of contaminants re leased from the t a i l i n g s to the natural environment. I f the impact i s deemed excessive, engineering pract ices can be brought to bear to r e c t i f y the problem e i ther through structura l modi f i ­cation or through treatment of the seepage. An example i s the present ly mandated treatment of t a i l i n g s ' pond overf low with BaCl2 to p rec ip i t a te Ra-226. Over the longer term, i t i s d i f ­f i c u l t to assess the future without resor t to some method for predict ing future conditions. Mathematical modelling, incorpor­ating the p r inc ip les of mass and energy balances, provides a tool f o r estimating future conditions. I t incorporates present knowledge of the major biogeochemical and hydrological processes in both the t a i l i n g s and receiving waters into a set of mathematical equations capable of being used fo r quantifying the expected future rates of contaminant loss from the t a i l i n g s mass.

However, the construction and use of mathematical models i s fraught with many problems and dangers. As Osborne et a l . (1981) note, the transport through the environment of many chemicals i s not wel l known or can be predicted only with con­s iderab le uncertainty. The e f fect of poss ib le management s t ra teg ies ( e . g . of engineered impoundments) on the long-term d ispersa l of wastes i s not wel l known. The e f fects of chemicals upon humans i s not p rec i se ly known although those for r ad io ­nucl ides are probably among the best documented. The under­standing of long-term biogeochemical processes i s not wel l known. The quandary then i s that wastes from U mining and mi l l ing ex i s t and that reasonable and acceptable decisions concerning the i r long-term management have to be made in the face of th i s uncertainty.

The approach of the work i s to bu i ld mathematical models of the major processes and the i r interact ions . I t i s useful to describe such models as having one of three purposes: d iagnost ic , simulation, and p red i c t i ve . While use of such a model fo r dose commitment ca lcu lat ions may be described as a simulation use, th i s paper uses i t in a diagnostic sense. The modelling philosophy used i s to bu i ld and tes t simple models incorporating the apparently main mechanisms. These models are then tested with ava i l ab l e data and updated to the degree that test ing proves such models inadequate.

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The object ives of th is paper are the fo l lowing: (1) to hypothesize poss ib le geochemical and biogeochemical mechanisms which may control the behavior of major radionucl ides and other contaminants in the so l i d phase and pore water of the t a i l i n g s , ( i i ) to se lect the major mechanisms suggested by the l i t e r a t u r e of the f i e l d , ( i i i ) to examine the time trend of major r ad i o ­nucl ides and ( i v ) to examine the t ime-scales of concern resu l t ing from the interact ion of d i f f e rent mechanisms. This paper p a r t i c u l a r l y emphasizes the t imes-scales of geochemical processes in the t a i l i n g s as re la ted to other relevant v a r i a b l e s .

Contaminants of concern fo r the management of U-mil l t a i l i n g s t yp i ca l l y include U-238 decay ser ies (U-238, U-234, Th-230, Ra-226, Pb-210, Po-210) and Th-232 decay ser ies (Th-232, Ra-228, Th-228) isotopes, heavy metals ( e . g . , Fe, Mn, Co, Cr, N i , Pb, Ba ) , and ac id i t y . This work evaluated the forms, controls and pathways of the radionucl ides and ac id i ty . Dose commitment ca lcu lat ions show that Ra-226 and daughters are the main radioisotopes of concern; Th-230 i s of some importance as a source of Ra-226 for t ime-scales of 1000 years . Hence th is paper i s mainly l imited to considering the implications of geochemical controls for Ra-226 transport .

2. Development of Ta i l ings Model

2.1 Ta i l ings Hydrology

A va l l ey dam was selected as typica l of past uranium-mill t a i l i n g s management pract ices in the E l l i o t t Lake area . A schematic c ross -sectional drawing of the chosen synthetic s i t e i s shown in Figure 1. Phys ica l ly , the s i t e comprises 4.2 X 106 t of t a i l i n g s below a sur ­face area of 40 ha with a maximum depth of approximately 10 m. I t over l i e s a peat layer underlain by a l l u v i a l v a l l ey f l oo r mater ia l . The dam i s broad (2000 m wide, 10 m high) with a shallow length of t a i l i n g s (400 m) ; th i s compares with the Nordic mass which i s more square, 1460 m by 550 m and has a dam length of approximately 2000 m. The to ta l catchment area upstream of the va l l ey dam comprises an area of 160 ha, fo r a catchment bas in : t a i l i n g s area r a t i o of 4 : 1 . Groundwater inflow from the catch­ment to the t a i l i n g s area and outflow downgradient of the dam i s considered. The to ta l annual p rec ip i ta t ion in the area i s 80 cm/a with the e f fect ive y i e l d from the drainage basin being 26 cm/a.

Management pract ices suggested three poss ib le long-term a l t e rna ­t i v e s . Case I (base case) i s unvegetated and al lows i n f i l t r a t i o n and watershed flows to pass through the t a i l i n g s mass. A co ro l l a ry , Case IA, bypasses watershed f lows; the long-term maintenance (> 100 a ) of such a condition requires invest igat ion due to

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QT ( 6 )

T A I L I N G S

HYDROLOGY Flow Rate (10 5 m3/a)

Case Description QT(1) QT(2) QT(3) QT(4) QT(5) QT(6) QT(7) QT(8) QT(9)

1 Porous Dam 3.96 5.49 0 .072 .336 4.22 0 .264 1.6

2 Porous dam 3.96 4.95 0 .072 .336 4.22 0 .264 1.06 8c Vegetation

3 Impermeable 0 .0003 4.22 .264 .0002 4.22 3.96 .264 0 Dam

FIG.1A. Schematic cross-section and hydrology of synthetic tailings site.

10m

IOm

FIG. IB. Schematic geometry of tailings.

beaver dams, etc. Case II is similar to Case I but vegetated, reducing infiltration quantities. Case III, an impermeable dam, causes a marsh (or lake) to form behind the dam and reduces flows through the tailings mass to 5 percent of Case I.

This site and its characteristics do not correspond directly to any existing or planned site, but rather incorporate a composite of variables from many older sites. The physical dimensions of the

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va l l ey dam are abstracted by examining the structure of the Nordic t a i l i n g s area ( e . g . , B l a i r et a l . , 1980) while estimates of the groundwater f low through consolidated materials are abstracted from deta i led groundwater modelling work (MacLarens 1977) with su i tab le modification for a v a l l e y dam structure . Estimates of i n f i l t r a t i o n character i s t ics are based upon the revegetation studies carr ied out by CANMET over the past several years .

The t a i l i n g s mass i s underlain by a peat layer (1-1.5 m thick) formed by a marsh, which i s underlain by g l a c i a l t i l l s comprised of basal t i l l and g l a c i o - f l u v i a l outwash sand and g rave l . Ta i l ings accumulate behind a dam a f ter s e t t l ing out of the m i l l ' s s l u r ry . In r e a l i t y , the coarse sand-sized f ract ion se t t l e s out in proximal pos i t ion to the ou t f a l l while f i ne r f ract ions ( s i l t - s i z e p a r t i c l e s , s ludge, e tc . ) are carr ied further before s e t t l i ng . Continual pumping bu i lds the t a i l i n g s up, causing a heterogeneous " t a i l i n g s " mass with d i s t inct layers of d i f f e rent materia ls caused by the segregat ion. For this synthetic t a i l i n g s , they are assumed to be homogeneous with f ines , coarse pa r t i c l e s and sludges uniformly interspersed.

Two hydrological questions of concern are the long-term pathways of drainage basin runoff and the presence of a marsh in Case 3.

In our discussions with various people, a debate centered over whether drainage basin f low would pass through the t a i l i n g s mass or whether i t s d ivers ion around the t a i l i n g s could be assured over the long-term (100-10 000 a ) . The Nordic s i t e at present has much of the drainage basin f low from two small streams diverted around i t . After consideration of the state of t a i l i n g s abandonment a f te r 20 years of construction, including the e f fects of beaver dams in channels, f a l l i n g t rees , etc . blocking up the channel, i t was concluded that the future continuity of the diversion could not be assured. Accordingly, i t was concluded that most of the drainage basin s u r f i c i a l runoff could flow through the t a i l i n g s mass and that a l l drainage basin groundwater would f low as groundwater under the t a i l i n g s mass. With these assumptions, the di f ferences between Case 1 and Case 2 are small because drainage basin flows are 2.5 to 3 times l a rge r than i n f i l t r a t i o n from d i rect r a i n f a l l to the t a i l i n g s mass.

The decisions concerning the hydrology of Case 3 are po tent i a l l y the most controvers ia l . An impermeable dam i s defined for th i s study as having hydraulic character i s t ics which are s imi lar to those of consolidated mater ia l s ; these are the character i s t ics which cause marshes and lakes to form in the Canadian Sh ie ld . Given the f low from the drainage basin, a marsh or shallow pond has to form behind an impermeable dam, depending upon the height of the dam and the time of year .

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IAEA-SM-262/54

Table 1. Summary of Ta i l ings Composition

MATERIAL QUANTITY

I Solid Formed in Mill Gypsum 545 mol/t Ca(OH, CO3) 116 mol/t Jarosite 2 mol/t (Ba, Ra) SO4 0.5 mol/t

II Radioisotope Concentration Associated with Gypsum or Jarosite

U-238 21 g/t U-234 1.1E-3 g/t Th-230 1.65E-2 g/t Ra-226 3.22E-4 g/t Pb-210 4.2E-6 g/t Po-210 7.2E-8 g/t Th-232 1.78E+2 g/t Ra-228 7.2E-8 g/t Th-228 2.4E-8 g/t

III Radiosotope Concentration Remaining in Host Mineral

U-238 53 g/t U-234 2.8E-3 g/t Th-230 8.6E-4 g/t Ra-226 1.7E-5 g/t Pb-210 2.2E-7 g/t Po-210 3.8E-9 g/t Th-232 1.9E+2 g/t Ra-228 7.5E-8 g/t Th-228 2.5E-8 g/t

Hydraulic Characteristics of Tailings Porosity (E) 0.4 _2

Hydraulic Conductivity 3150 m/a (1 X 10 cm/s) Density of Tailings 2 g/cm3

Bulk Density of Tailings 1.6 g/cm3

Hydraulic Detention Time of Tailings Pore Water

Case Detention Time (a)

1 2.6 2 2.8 3 53

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During spring melt, a lake could ex i s t . With evaporation and low flows during the summer, the water depth could decrease but s t i l l provide water cover over a l l the t a i l i n g s mass. Accordingly fo r a r e l a t i v e l y f l a t surface with a dam height of 0.5 m above the t a i l i n g s , Case 3 i s described as a t a i l i n g s mass which i s always saturated with water.

The major water flows for Case 1 and 2 are drainage basin sur­face runoff, d i rect r a i n f a l l i n f i l t r a t i o n , and outflow being through the dam. For Case 3, i t i s assumed ( i ) that no surface water from the drainage basin enters the t a i l i n g s mass and ( i i ) that groundwater flows from the drainage basin are the only s i gn i f i cant flows passing through the t a i l i n g s mass. Accordingly, the major di f ferences in pore water detention time (see Table 1) are due to the order of magnitude di f ference in f low rates through the t a i l i n g s mass. The corresponding hydraulic gradients of water flowing through the t a i l i n g s are 0.0089 and 0.0080 for Case 1 and 2 respect ive ly , values which are quite typica l of those of Nordic (0.0065-0.0071). Because Case 3 i s a f looded t a i l i n g s mass, the piezometric gradient across the bulk of the t a i l i n g s i s approximately 0.

2.2 Ta i l ings Chemistry

For estimating the f lux of radioisotopes out of the t a i l i n g s mass, i t i s essent ia l to know the major associations of r a d i o ­isotopes with d i f ferent minerals, the r e l a t i v e f ract ion in the par t i cu la te and soluble phases, and the mechanisms which control the mobi l izat ion of the radio isotopes . The approach used was to make mass balances on the ore fed to the mi l l and chemicals added in the mi l l to determine major so l i d f ract ion forms. Then the l i t e r a tu r e was used to determine major mineral - radioisotope assoc iat ions .

Geochemical mechanisms which need to be considered are re la ted to forms of the radioisotopes upon leaving the mi l l and to reactions which occur in the t a i l i n g s . Over 90 percent of r ad i o ­isotopes leaving the mi l l are associated with p a r t i c l e s . They may be as a coprec ip i tate , as a p rec ip i t a te , adsorbed or in the leached host conglomerate. Radium i s hypothesized to be coprecipitated mainly with gypsum, other metal su l fa tes ( e . g . , j a r o s i t e , KFe3(SO4)2(OH)6) with minor influences of such prec ip i ta tes as A1(0H)3.) Thorium i s an example of a p rec ip i t a te formed during f i n a l neutra l izat ion (Th(0H)4) and enmeshed or associated with prec ip i ta tes such as gypsum. In the t a i l i n g s , the main mechanisms of interest are p rec ip i ta t ion -d i s so lu t ion react ions , pyr i te oxidation, adsorption onto surfaces, so l id state d i f fus ion , pore water d i f fus ion , pore water complexation and hydrological transport .

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The major re levant observations which have been discerned from the l i t e r a tu r e and pract i t ioners in the f i e l d ( researchers , engineers, hydrogeologists , geochemists) are as fo l l ows . In the m i l l , 95 percent of uranium and 50 percent of Th-232 minerals are mobilized in the acid leach process — the di f ferences occur due to the a b i l i t y of the minerals bearing the d i f f e rent isotopes to r e s i s t leaching during su l fu r i c acid attack. I t i s probable that a l l U-238 decay ser ies isotopes and Th-232 decay ser ies isotopes that are leached are in secular equi l ibr ium with U-238 and Th-232 respect ive ly . Observations on U-238, Th-230 and Th-232 in mi l l water suggest that these mater ia ls remain in the mi l l water unt i l f i n a l neut ra l i za t ion . However, no more than approximately 5 percent of Ra-226 i s found in the acid leach l iquor ( I tzkovitch and Ritcey, 1979). Hence, i f 95 percent of the Ra-226 i s leached from i t s host mineral, i t must come into solution and then go back into the so l i d phase in the leaching process . The transport of thorium species through the mi l l i s consistent with formation of thorium hydroxide p rec ip i ta tes in f i n a l neutra l i zat ion upon adjustment of the pH from 2 to 8 or 9.

Kaiman (1977) observed that approximately 50 percent of radium was associated with j a r o s i t e and 50 percent was associated with gypsum in a Nordic t a i l i n g s sample. Jaros i te can be formed in the acid leach ( i t i s s tab le from pH of 0.5 to 2.0) and in the t a i l i n g s p i l e due to the production of f e r r i c and su l fa te ions by ac id i f i c a t i on reactions resu l t ing from bacter ia l ly - induced oxidation of py r i t e minerals . The formation of j a r o s i t e in the mi l l may be several orders of magnitude f as te r due to the higher temperatures and higher su l f a te concentrations; however i t s formation in the t a i l i n g s i s equal ly probable i f pH conditions are low enough since the length of time ava i l ab le (years—decades) would be su f f i c i ent time f o r the slower k inet ic rates to cause mineral formation. Gypsum can form in the pa r t i a l neutra l i zat ion tank (pH i s adjusted from approximately 0,5 to 2,0 by addit ion of CaO and CaCOs) and in the f i n a l neutra l i zat ion tank of the m i l l . Our thermodynamic s t a b i l i t y ca lcu lat ions indicate that both j a r o s i t e (KPe3(S04)2COH)6) and gypsum should form in the leaching pachucas. Given the kinet ics of j a r o s i t e , i t i s our conclusion that radium i s leached and coprecipitated with j a r o s i t e as i t forms in the leaching pachucas. The remainder of fadium leached i s probably absorbed to var ious surfaces in the pachucas; upon movement to the p a r t i a l neutra l i zat ion tanks, th i s absorption i s probably redisturbed, al lowing the remaining radium to coprecip i tate with gypsum. I t i s assumed that 50 percent o f radium leached i s coprecipitated with j a r o s i t e and 50 percent with gypsum.

The other components of the t a i l i n g s chemistry are the fo l lowing .

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1. Aqueous forms of U-238, U-234, Pb-210 andPo-210 in the mi l l c i r cu i t coprecipitates with gypsum formed in the f i n a l n eu t r a l i z a ­t ion basin while Th species form hydroxide p rec ip i ta tes enmeshed in gypsum.

2. The o r i g ina l ore contains 6 percent py r i t e and other iron sulphide minerals . During the mi l l ing and leaching process , 20 pe r ­cent of the iron su l f ides are d isso lved, re leas ing ferrous iron into so lut ion . The remaining iron su l f i de which i s pyr i te (5 pe r ­cent of t a i l i n g s ) i s disposed in the t a i l i n g area e s sent i a l l y unaltered by acid leaching.

3. The f i na l neut ra l i za t ion , accomplished by the addit ion of excess lime, provides a reserve buf fer ing capacity equivalent to the capacity to neut ra l i ze 116 moles of H2SO4 per tonne of t a i l i n g s .

4. The t a i l i n g s are deposited such that they are phys ica l ly uniform with respect to process p r ec ip i t a t e , res idual mineral d i s t r i but ion and gra in s i z e . Consequently permeabi l i t ies are uniform in a l l d i rec t ions . A l l f low has v e r t i c a l and horizontal components through the t a i l i n g s towards a seepage creek at the toe of the reta in ing v a l l e y dam. The r e l a t i v e l y impermeable peat layer below the t a i l i n g s mass al lows l i t t l e seepage into the underlying permeable g l a c i a l sands and g rave l s . This i s an over - s impl i f i ca t ion of the actual f i e l d case in which slimes and sands are in te r - f ingered resu l t ing in heterogeneous chemical d i s t r i but ion and marked di f ferences in spat ia l permeabi l i ty .

5. In the t a i l i n g s , radionucl ides weakly and reve r s i b ly adsorb onto the surface of res idua l and mi l l formed minerals and onto coatings of gypsum or other metal sulphates or hydroxides formed in the t a i l i n g s .

6. Acid i s produced at an annual ra te of 6.8 mol H + /m 3 • a in the unsaturated zone of the t a i l i n g s due to pyr i te oxidat ion. This rate was determined from lysimeter studies made on old Nordic and fresh t a i l i n g s (Schmidke et a l n , 1978; S i l ve r and Ritcey, 1980). This acid i s neutra l ized by the buf fer ing capacity of the saturated and unsaturated zones of the t a i l i n g s u n t i l i t i s expended. A s l i g h t l y modified theory i s used to estimate the ac id i f i ca t i on rate of the saturated zone (Klapwijk and Snodgrass, 1981).

The composition of these generic t a i l i n g s are given in Table 1. These chemical propert ies are used fo r Cases 1, 2, and 3. For three other engineering a l te rnat ives (Cases 4, 5 and 6, corresponding to Cases 1, 2 and 3 r e spec t i v e l y ) , 90 percent of the Ra-226 and Th-230 i s removed by engineered methods (see Osborne, 1982). Due to unknown transients in future meteorology, e t c . , the physical

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propert ies of the t a i l i n g s are assumed constant into the future . This resu l t s in the fo l lowing set of assumptions:

1. The reta ining v a l l e y dam and underlying a l l u v i a l sands and grave ls are assumed to re ta in the i r i n i t i a l chemical and physical propert ies throughout the time of in te re s t . A l l transport of contaminants from the t a i l i n g area i s v i a solut ion t ransport .

2. No physical changes within the t a i l i n g s mass i t s e l f occur as a r e su l t of chemical d i s so lut ion .

3. A l l impinging environmental cont ro l l e r s such as p rec ip i ta t ion and annual temperature regimes are held constant throughout the period of ana lys i s .

In summary, the main assumption of the model, p a r t i cu l a r l y re la ted to radium are the fo l lowing : 1. Ra-226, associated with gypsum is coprecipitated with gypsum in the m i l l . I t d i s ­solves at the same rate as gypsum in the t a i l i n g s . 2. Ra-226 associated with j a r o s i t e i s coprecipitated with j a r o s i t e in the m i l l . 3. Jaros i te remains s tab le at ac id ic pH's but transforms to an iron hydroxide ( e . g . , goeth i te ) at neutral pH. Goethite so lub i l i z e s at ac id ic pH. 4 . Pyr i te oxidation occurs in the porous zone. I t produces H + , Fe, and S04^~, consuming base ( e . g . , CaC03) formed in the m i l l . 5. The pore water i s always saturated with respect to gypsum. 6. Weak adsorption occurs. 7. Hydrological flows through the t a i l i n g s are governed by the t a i l i n g s surface area, the watershed area, and the management p rac t i ce . The major associat ions of the radionucl ides with major minerals i s summarized in Figure 2.

Model Character is t ics

The character i s t ics of the t a i l i n g s model are described in two ways. F i r s t l y , the major mechanisms are described for Case 1 and Case 3, using the predicted pore water concentrations of Ra-226 for descr ipt ive purposes. Then the d isso lut ion rates of gypsum for d i f f e rent periods are described quant i ta t ive ly .

The predicted pore-water concentration of Ra-226 for Case 1 i s given in Figure 3. Four d i s t inc t time periods are apparent. The f i r s t period (0-160 a ) produces SO4 from py r i t e oxidat ion, Ca from neutra l i zat ion react ions , and CaS(>4 from gypsum d isso lut ion ; the plateau i s the steady-state concentration corresponding to a gypsum d isso lut ion rate of 0.9 mol/t-a. Ja ros i te remains s tab le in the porous zone, but slowly transforms to goethite in the saturated zone. At the start of the second per iod, the saturated zone goes ac id i c . During the second period (160-186 a ) , gypsum disso lut ion

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Jarosite—Ra-226

Gypsum -U-238/234 -Th-230/232/228 -Ra-226/228 -Pb-210 -Po-210 LEACHED HOST CONGLOMERATE

FIG.2. Conceptual sketch of tailings particles.

E

CO

T I M E (YEARS)

FIG.3. Tailings pore water concentration. (Base case - 226Ra.)

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200 1400 2600 3800 5000 6200 7400 8600 9800

TIME (YEARS)

FIG.5. Radioisotope concentration in gypsum fraction. (Case 3 - Ra.)

increases (1.4mol/t-a) and goethite dissolution in the saturated zone is initiated, giving the peak in radium concentration. At the end of the second period, all pyrite is consumed. Thereafter (186 a-386 a ) , the pH returns to *v 5-6 and gypsum dissolution (1.75 mol/t-a ) maintains saturation conditions. In the fourth period, all gypsum is exhausted — the only source of radium is that absorbed.

The predicted pore water concentration of Ra-226 is given in Figure 4 for Case 3. That for Case 2 is not too different from Case 1 and hence is not included. Two distinct periods are apparent. The first (0-6500 a ) is controlled by gypsum dissolution. Thereafter (> 6500 a ) , the Ra-226 concentration approaches zero due to gypsum having been exhausted from the solid phase. There is no peak observed similar to Figure 3 because the pH remains near neutral throughout the entire period, preventing dissolution of any goethite formed from jarosite and its associated Ra-226 contents. The pore water concentration peaks at a concentration which is approximately 50 percent larger than that for Case 1. This results from Ra-226 ingrowing from Th-230 in the gypsum fraction becoming significant over a 1000 a time frame. This is demon­strated in Figure 5. The peak Ra-226 concentration in the gypsum fraction occurs at approximately 1500 years.

In more descriptive terms, the processes involved in Case 1 may be described as follows. As water moves through the unsaturated zone, it forms a film around the pyrite particulates within this zone. Oxygen in the pore spaces diffuses into this fiim, allowing the chemical oxidation of the pyrite and bacterial oxidation of the

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Table 2. Dissolution Rate of Gypsum, FeS, and Oxides and Hydroxides of Calcium. 0 0

P E R I O D

Time = 0 to time = TA Time=TA to TIME=TPYR TIME > TPYR

Case

Maximum Gypsum

Dissolution Rate

Length of

Time Rate of

Consumption (mol/t*a) Length Consumption of Time (mol/f a)

Time Period

Rate of Consumption

(mol/t-a)

(mol/t-a) (a) CaO FeS2 Gypsum (a) FeS2 Gypsum (a) Gypsum

1 2 3

1.75 1.58 0.0842

160 120

10 000

0.834 0.834 0.916 0.962 0.962 0.618 0.0136 0.0136 (2)

36 0.834 1.39 66 0.962 1.17

T > 186 T > 186 -

1.75 1.58

Notes:

(1) TA = Time of Ac id i f i ca t ion ; TPYR = Time to Consume Pyrite (a).

(2) This gypsum dissolut ion i s 0.0706 mol/t-a for 6500 years after which it is 0.

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Table 3. Ca lcu lat ion : Time History of Gypsum Dissolut ion

Case Time Period

Gypsum Disso lut ion Rate

mol/t-a

Gypsum Remaining at End of Period

mol/t

1 0 0.0 545 0 - 160 0.916 398

160 - 186 1.39 351 186 - 386 1.75 0

2 0 0.0 545 0 - 120 0.618 471

120 - 186 1.17 396 186 - 437 1.58 0

3 0 0.0 545 0 - 6500 0.0842 0

reduced su l f ide to cause acid production. As i n f i l t r a t i n g water moves down through the ta i l ings , i t atta ins a bas ic pH because of excess lime not yet leached from the system. As water i n f i l t r a t e s , i t d isso lves gypsum in order to maintain saturation conditions with respect to gypsum in the t a i l i n g s pore water. As the acid production and consequent neutra l i zat ion of lime proceed, the d isso lut ion rate of gypsum proceeds very slowly because of calcium and su l f a te d issolved from so l i d calcium minerals and oxidized p y r i t e . Consequently there i s a very slow rate of loss of rad ionuc l ides .

During the i n i t i a l per iod , the pore water remains basic near pH 7-8 at which pH j a r o s i t e i s thermodynamically unstab le . Accordingly, a certa in f ract ion of the j a r o s i t e i s transformed to f e r r i c hydroxide (goethite ) by several react ions , with the goethite reta in ing the radium.

When the e lut ion of the excess lime added during the o r i g ina l neutra l i zat ion processes i s complete, the bas ic t a i l i n g pore water becomes ac id ic (pH ^ 2 ) . During th is second per iod , the so lub le calcium concentration in pore water produced by calcium oxide d isso lut ion drops, al lowing an increase in gypsum s o l u b i l i t y . Sul fate production a lso continues from the py r i t e oxidation react ions . Dissolut ion of gypsum and of the iron hydroxide, occurs during ac id ic condit ions, re leas ing radionucl ides into the pore

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water. The peak concentration occurs during this period due to dissolution of goethite and its associated Ra-226 contents. Upon completion of tie oxidation of pyrite, no more sulfate is produced leaving gypsum dissolution as the only significant sulfate source. Also at this point, the tailings pH returns to more neutral conditions. With the exception of thorium, which is postulated to form a soluble thorium sulphate complex at pH values below 4,5,all of the radionuclides released reversibly absorb to the surface of residual mineral particles.

The rates of dissolution of the various minerals and the time history of gypsum are given in Tables 2 and 3 for Cases 1-3. These tables provide exact confirmation regarding the time history predicted by the model for the different cases. Cases 1 and 2 follow a similar pattern, but a shorter time period exists to completely consume the neutralizing capacity of the tailings due to the deeper unsaturated zone producing a larger flux of acid. The numbers given, while described by 2-3 figure accuracy, must be viewed as nothing other than relative numbers describing order of magnitude time scales.

Comparison of Tailings Time-Scales to Geochemical Time-Scales

This section calculates the time to mobilize all Ra-226 associated with gypsum for various alterations in the geochemical mechanisms of Case 1 assuming that this represents the only significant source of geochemically mobilizable Ra-226. Then it compares these time scales to long-term geological and hydrological time scales.

The time scales of gypsum dissolution and pyrite oxidation are given in Tables 4-8. The calculated times to dissolve all gypsum (TGYP), assuming no pyrite oxidation (Table 4) ranges from 310-6500 years depending upon management scenario. Various studies suggest time scales ranging over two orders of magnitude are required to consume all pyrite (TPYR; Table 5) in the unsaturated zone. More work is required to obtain insight into the obvious effects of aging of pyrite surfaces upon pyrite oxidation rates. Of the geochemical mechanisms considered, alteration of the solubility product (10 percent of standard) causes the most pronounced effect in alterating the time scale (Table 6 ) , Alteration of the reversible, linear adsorption coefficient has a lesser effect. Alteration pf the irreversible adsorption assumes that irreversible adsorption of Ra-226 is permanent for all time. The predicted pore water concentrations over time due to the altered adsorption coefficient is given in Table 7.

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Table 4. Time Scales for Hydrology — Time to Dissolve all Ra-226 from Gypsum Fraction, Assuming No Pyrite Oxidation.

Case Description of Case Origins of Flow TGYP

1 Base Case - Valley Dam, Unvegetated Surface

Watershed; direct rainfall 310 a

1A Base Case Direct rainfall only 1100 a

2 Vegetated Surface Watershed; direct rainfall 360 a

3 Impermeable Dam Structure

Watershed; direct rainfall 6500 a

Table 5. Time Scales for Unsaturated Zone-Time to Consume all Pyrite (5 percent Pyrite Content, 5° C ) .

Data Source TPYR

Lab Data (Halbert et al., 1982, Fresh Tailings) 4-13 a

Lysimeter Data (Silver and Ritcey, 1980; Fresh Tailings) 9 a

Lysimeter Data (Schmidke et al., 1978; 20 year old Tailings) 186 a

All time scales of concern for gypsum dissolution are short compared to major geological and hydrological time scales (see Tables 8, 9 ) . The time scale to fill most of the Great Lakes is of the order of 50-100 millenia. Lake Erie is the shortest (7000 a ) . The time scales for most major physical and chemical agents to remove the tailings mass is of the order of 100-800 millenia. All calculations (Table 9) are made assuming a constant rate over time. The shortest time scale for major agents acting on the tailings mass is the time for development

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Table 6. Time Scales for Various Geochemical Mechanisms - Time Required to Dissolve All Ra-226 in Gypsum for Change in Various Mechanisms (Standard used is Case 1 ) .

TGYP (a)

Case 1 390

Solubility Product divided by 10 1100

Adsorption Coefficient increased by 10 600

Irreversible Adsorption 390

Mill Fractionization of Ra-226 Between Gypsum and Jarosite 390

Table 7. Time Scales for Ra-226 Tailings Coefficient (F) -Sensitivity of Pore Water Concentration to Change in F.

Relative Radium Concentation in Porewater

Time (a) Base Case F X 10*

5 0.21 0.21 100 0.50 0.37 180 2.5 1.0 200 1.2 1.0 380 1.0 1.0 400 0.13 0.8 500 0.00003 0.28 600 0.09

1000 0.001

* F X 10 means that the tailings coefficient P is increased by 1 0 .

of the next glaciation age. The major geological or hydrological phenomena which could affect the tailings mass and hence the time for Ra-226 mobilization is the next glaciation age. The infilling of Lake Erie is only a constraint for dosimetry calculations (removal of food sources such as fish consumption), as it is probable that a river could continue to connect Lake Huron to Lake Ontario.

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Table 8. Time Scales for Filling of Lakes - Time to Fill Various Lakes Given Present Estimates of Sedimentation Rates.

Lake Superior 150 000 years

Lake Michigan 80 000

Lake Huron 40 000

Lake Erie 7 000

Lake Ontario 60 000

North Atlantic 100's Million

Table 9. Times Scales for Forces Acting on Tailings Mass-Time Required to Completely Remove Tailings Mass by Agent Acting on It (Agent is Assumed to Have a Constant Rate).

Time to Remove

1. Wind Erosion* 200 000 a

2. Chemical Weathering* 600 000 a

3. Erosion CEast. Sea. Rate)* 700 000

4. Suspended Solids in Runoff from Tailings Mass (a) 10 mg/L 800 000 (b) 50 mg/L 200 000

5. Wind Erosion, Chemical Weathering and 25 mg/L in Runoff 90 000

6. Next Glaciation Age ^ 1 0 000 ?

*Wind Erosion uses rate of 2 X 10-6 g/m 2 s. Chemical Weathering is rate of solution transport from an Appalachian Mountains (New Hampshire), 55 year old forested ecosystem (Likens, et al., 1977). Erosion is the Eastern Seaboard erosion rate.

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1. Pyrite Oxidation in Porous Zone 100-200 a

2. Pyrite Oxidation in Saturated Zone 10 000 a

3. Hydrology* - Intimate Contact 400 a

Impermeable Dam 7000 a

4. Chemical Mechanisms:* Relative Time 390 a

No Pyrite Oxidation t = -70 a

Adsorption Coefficient X 10 t = +200 a

Solubility Product Divided by 10 t = +700 a

Irreversible Adsorption t = 0

5. Time Scales Constraints

Loss of 10 percent of Tailings Pile by

Wind Erosion, Weathering, etc. 10 000 a

Lake Erie Filling Time 7 000 a

Next Glaciation Age * 10 000 a ?

*Time Scale is time to dissolve Ra-226 in gypsum fraction.

Implications of Time Scales on Controlling Tailings Geochemistry

There are several implications for modelling, research, dose commitment calculations and management resulting from this work. The implications are assessed assuming that the time scale of concern for dosimetry calculations is defined as the time to dissolve and to transport all Ra-226 in the gypsum fraction from the tailings.

1. For modelling and dosimetry calculations, time scales of concern are of the order of 400-1000 years for the base case but are of the order of several millenia for an impermeable dam (see Table 10). In the unsaturated zone, the time scale of

Table 10. Summary Time Scales in Tailings.

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pyrite oxidation affects such calculations for a decade to a century, while the time scale for pyrite oxidation in the saturated zone is estimated to be much longer than the time scale for dosimetry calculations.

2. It is doubtful that major geological and hydrological changes will affect the time scale for dosimetry calculations as the nearest time scale (infilling of Lake Erie) is equal or longer than the time used for such calculations. Further Lake Erie processes are a constraint as its main effect is upon food sources, not upon the tailings mass. The major geological change of concern is the time of the next glaciation age.

3. Time scales for dosimetry calculations for present management techniques are of the prder of one millennium. Present management options for valley dam storage areas are best described by a hybrid of a Case 2 equivalent of 1A (vegetated cover; bypassing surface runoff around the tailings mass) and of Case 3. The term "storage" is differentiated herein from "disposal" due to potential erosion of valley dam structures. The long-term effect of bypassing surface runoff around the tailings given present designs cannot be assured due to beaver dams, etc.

Table 11. Relative Pore Water Concentrations caused by Alterations in Cheoical Mechanisms (Plateau of Base Case is used as Standard)*

Base Case Peak 2.5

Plateau 1.0

Adsorption Coefficient X 10 1.0

Solubility Product/10 0.4

Hydrological Flow/20 1.5

Initial Radium Fractioniz. in Gypsum - 10 percent 0.2

1 percent 0.02

Irreversible Adsorption 90 percent 0.1

*Plateau Value Unless Noted.

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4. The long-term predicted pore water concentrations of Ra-226 are approximately an order of magnitude higher than presently observed concentrations. If the model assumptions (initial mill forms of Ra-226 and solid state diffusion acting to essentially distribute Ra-226 uniformly throughout the gypsum fraction) are approximately valid, the long-term Ra-226 concen­tration from seepage in receiving waters can be expected to significantly increase above what is presently observed. This has significant implications for management as the long-term concentrations (if BaCl treatment does not continue for a millennium) in lakes below existing tailings areas could increase by an order of magnitude. For presently observed concentrations over the short-term, mechanisms which retain Ra-226 in the solid form are more dominant than used for the base case. Such mechanisms include a smaller initial fraction of mobilizated radium in gypsum (1-5 percent) formed in the mill, irreversible adsorption (see Table 11) and occlusion.

5. Observations (e.g., Cherry et al., 1980) indicate that the pH of pore water in various saturated zones is approximately 2-3, only 5-20 years after tailings placement. Either all calcium hydroxides and oxides are not consumed due to the presence of surface coatings (e.g., iron and manganese coatings) preventing their dissolution or higher pyrite oxidation rates than used in. the above model (see Table 5) have already consumed most of base neutralizing capacity of the tailings.

Acknowledgements

This study was initiated by and financially supported by the Atomic Energy Board of Canada. It will form a portion of the Canadian example for a NEA study whose objective is to test the applicability of the ALARA principle of the ICRP system of dose limitation to the management of uranium mill tailings. Financial support of The Johns Hopkins University (USA) to the senior author for writing and presenting this paper is gratefully acknowledged. Also conversations with R. V. Osborne, K. Bragg, E. Joe, J. Coady, A. Vivyarka, C. Wong and E. Barnes, related to this work are gratefully acknowledged.

BIBLIOGRAPHY

BEAK (1981) A qualitative Evaluation of Long-Term Processes Governing the Behayiour of Uranium Mill Tailings Placed in Deep Lakes. Report to Atomic Energy Control Board of Canada. 300 pp.

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BEAK (1982) Dose Commitment Calculations for a Generic Uranium Mill Tailings Site in Northern Ontario. Report for Atomic Energy Control Board of Canada. 200 pp.

Blair, R., J. A.Cherry , T. P. Lim, and A. J. Vivyarka (1980). Groundwater Monitoring and Contaminant Occurrence at an Abandoned Tailings Area, Elliott Lake, Ontario. Proc. First Inter. Conference on Uranium Mine Waste Disposal, AIME, 36 pp.

Cherry, J. A., R. J. Blackport, N. Dubrovsky, R. W, Gillham, T. P.Lim,D. Murray, E. J. Reardon, and D. J. A. Smyth (1980). Subsurface Hydrology and Geochemical Evolution of Inactive Pyritic Tailings inlhe Elliot Lake Uranium District, Canada. Proc. 3rd Symposium on Uranium Tailings Management, CSU, Fort Collins, .^Colorado, Nov., Session 5.

Halbert, B.E., J. M. Scharer, J. L. Chakravatti, and E. Barnes (1982). Modellingdof the Underwater Disposal of Uranium Mine Tailings in Elliot Lake. Proceedings International Symposium on Management of Wastes from Uranium Mining and Milling, Albuquerque, New Mexico. Paper No. 1AEA-SM-262-4.

Hamel, P., J. Howieson (1982). "A Summary of the Canadian Uranium Mill Tailings Situation." Proceedings International Symposium on Management of Wastes from Uranium Mining and Milling, Albuquerque, New Mexico, Paper No. IAEA-SM-262-61.

Itzkovitch, L. J., and G. M. Ritcey (1979). Removal of Radio­nuclides from Process Streams - A Review. CANMET Report 79-21 Canada Department Energy Mines and Resources Ottawa. 171 pp.

Kaiman (1977). Mineralogical Examination of Old Tailings from the Nordic Lake Mine, Elliott Lake, Canada. CANMET Paper.

Klapwijk, A., and W. J. Snodgrass (1981). Measurement of Sediment Nitrification and Denitrification in Hamilton Harbour, Canada. Proc. Fresh water - Sediment Interactions Conference Junk (in press).

Likens, G. E., F. H. Bormann, R. S. Pierce, J. S. Eaton, and N. M. Johnson (1977). Biogeochemistry of a Forested Ecosystem. Spring er-Ver1ag.

Lush, D., J. Brown et al. (1978). An Assessment of the Long-Term Interaction of Uranium Tailings with the Natural Environment. Management, Stabilization and Environmental Impact of Uranium Mill Tailings, Albuquerque USA-NEA Workshop. OCED pp. 373-400.

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Lush, D. L., W. J. Snodgrass, and P. McKee (1982). Aquatic Pathway Variables Affecting the Estimation of Dose Commitment from Uranium Mill Tailings.Proceedings International Symposium on Management of Wastes from Uranium Mining and Mill, Albuquerque, New Mexico. Paper No. IAEA-SM-262/9.

MacLarens (1977). Environmental Assessment of the Proposed Elliot Lake Uranium Mines Expansion. Report to Denison Mines Ltd. and Rio Algom Ltd., Toronto, Ont (M5H 1C2) 4 Volumes.

Osborne, R. V. (1982). Optimizing Radiation Protection in the Management of Uranium Mill Tailings. Proceedings Inter­national Symposium on Management of Wastes from Uranium Mining and Milling, Albuquerque, New Mexico. Paper No. IAEA-SM-262-30.

Osborne, R. V., M. J. Clark and J. H. Snihs (1981). "NEA Program on the Long-Term Aspects of Uranium Mill Tailings Management." Chapter 3 in Principles and Methods, Task 2 of WG 1 Study. Atomic Energy of Canada Ltd. Paper.

Schmidke, N. M., D. Averill, D. N. Bryant, P. Wilkinson and J. W. Schmidt (1978). Removal of Ra-226 from Tailings Pond Efficients and Stabilization of Uranium Mill Tailings — Bench and Plot Scale Studies. Proc. NEA Seminar, Management, Stabilization and Environmental Impact of Uranium Mill Tailings, pp. 299-317.

Silver, M., and G. M. Ritcey (1980). A simulated study of the effects of Bacteria, Organics and Salt Solutions on Uranium Mill Tailings from Elliott Lake, Ontario. Proceedings 2nd International Symposium on Waste Treatment and Utilization. 17 pp.

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WASTE WATER TREATMENT AND TAILINGS CONDITIONING

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Chairman

H.I. LINDHOLM Sweden

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URANIUM MILL TAILINGS CONDITIONING TECHNOLOGY*

D.R. DREESEN, E.J. COKAL, L.E. WANGEN, J.M. WILLIAMS Los Alamos National Laboratory, Los Alamos, New Mexico

P.D. O'BRIEN Sandia National Laboratories, Albuquerque, New Mexico

E.F. THODE Department of Management, New Mexico State University, Las Cruces, New Mexico, United States of America

Abstract

URANIUM MILL TAILINGS CONDITIONING TECHNOLOGY. Conditioning of uranium mill tailings involves the physicochemical alteration of tailings

to remove or immobilize mobile radionuclides and toxic trace elements before disposal in a repository. The principal immobilization approach under investigation is sintering tailings at high temperatures (1100—1200°C) to radically alter the structure of tailings. This thermal stabilization at 1200°C reduced radon emanation power for tailings sands by factors of 20 to 200 and for tailings fines by factors of 300 to 1100. Substantial reductions in the leachability of most contaminants have been found for thermally conditioned tailings. Obvious mineral transformations occur, including an increase in amorphous material, the conversion of gypsum to anhydrite and its subsequent decomposition, the disappearance of clay minerals, and some decrease in quartz content. A conceptual thermal stabilization process has been developed wherein obsolete coal-fired rotary cement kilns perform the sintering. An economic analysis of this conceptual process has shown that thermal stabilization can be competitive at certain tailings sites with other remedial actions requiring the excavation, transportation, and burial of tailings in a repository. An analysis of the long-term radiological hazard posed by untreated tailings and by tailings conditioned by radionuclide removal has illustrated the necessity of extracting both 2 2 6 Ra and 2 3 0 Th to achieve long-term hazard reductions. Sulphuric acid extraction of residual mineral values and important radionuclides from tailings has been investigated. Concentrated H 2 S0 4 can extract up to 80% of the 2 2 6 Ra, 70% of the Ba, and 90% of the 2 3 0 Th from tailings in a single stage extraction. An economic analysis of a sulphuric acid leach process was made to determine whether the value of minerals recovered from tailings

* Supported by the United States Department of Energy, Uranium Mill Tailings Remedial Action Project.

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would offset the leaching cost. For one relatively mineral-rich tailings pile, the U and V values would more than pay for the leaching step and would contribute about 60% of the costs of moving and burying the tailings at a new site.

1. I N T R O D U C T I O N

The proper disposal and long-term management of uranium mill tailings in the US was mandated in the Uranium Mill Tailings Radiation Control Act of 1978 (Public Law 95-064) by the US Congress. This act directed the US Department of Energy to dispose of uranium mill tailings from inactive uranium ore processing sites and to clean up contaminated land and buildings. The initial standards for remedial action proposed by US Environmental Protection Agency required adherence to strict radon flux and water pollution standards, which would necessitate very stringent control measures [1]. The development of technologies to assure long-term stabilization of tailings is being supported by the US Department of Energy under the Uranium Mill Tailings Remedial Action Project (UMTRAP) . As part of the overall technology development program, Los Alamos National Laboratory is investigating tailings conditioning as a means of attaining long-term reduction in emissions of 2 2 2 Rn gas and release of leachable contaminants from tailings.

The conditioning of uranium mill tailings can be broadly defined as any modification of the composition or structure of tailings to limit the release of contaminants. In essence, such modifications are aimed at controlling contaminant mobility on the micro or particle scale versus more typical disposal scenarios using barriers to isolate the entire tailings mass from the environment. The types of conditioning that we have evaluated are (a) the immobilization of contaminants by altering the structure (i.e., mineralogy) of tailings by thermal treatment at high temperatures (~1200°C) - "thermal stabilization" and (b) the removal of hazardous radionuclide and toxic metal contaminants using concentrated or strong aqueous sulfuric acid phases.

Laboratory studies have been performed to determine the technical feasibility of each conditioning method and their efficacy in limiting contaminant release. The long-term radioactive hazard of tailings conditioned to remove long-lived radionuclides has been assessed to determine the long-term benefits to be gained by radionuclide removal. Conceptual conditioning processes have been conceived to evaluate the engineering feasibility as well as to estimate the costs of large-scale conditioning operations.

2. T H E R M A L STABILIZATION

Determining the efficacy of thermal stabilization as a conditioning process requires an evaluation of changes in structure (mineralogy), reductions in 2 2 2 Rn emanation power, and decreases in contaminant leachability. The long-term stability of thermally stabilized tailings (TST) has been assessed by simulating weathering caused by particle degradation and repeated water leaching. A preliminary conceptual thermal stabilization process has been developed to assess engineering and economic feasibility; refinement of these concepts is underway on a site specific basis for those sites given high priority for remedial action.

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2.1 Mineralogy and surface area of original and thermally stabilized tailings

The mineralogy of tailings from inactive sites at Salt Lake City (SLC), Utah, Shiprock (SHIP), New Mexico, Durango (DGO) , Colorado, and Ambrosia Lake (AML) , New Mexico has been determined by powder x-ray diffraction technqiues [2]. The predominant minerals found are as follows:

(a) quartz (Si0 2 ) contents are 70-90% for tailings sands and 20-60% for fines (sands are classified as being greater than 50% sand-sized particles);

(b) gypsum (CaSO 4»2H 20) - a major constituent of sulfuric acid leached tailings (SLC, SHIP) with contents of 5-35%;

(c) clays (illite and kaolinite) - found at 10-30% in the tailings fines;

(d) feldspars - major constituents of tailings fines (~20%) and the predominant mineral type in Durango fines;

(e) other identified minerals - calcite (AML) , barite (DGO) , and clino-chloroapatite and a-hematite in the SLC vanadium ("ferrophos") tailings.

After tailings have been thermally treated at temperatures ranging from 500 to 1200°C at 100° intervals, the following principal changes in mineralogy occur:

(a) quartz is not affected until 1200°C where some reduction is noted; cristobalite, calcium silicates, or amorphous material are thought to be forming;

(b) gypsum dehydrates at low temperature (163°C) to anhydrite; anhydrite is appreciably reduced at 1000°C and by 1200°C is reduced by ~75%; anhydrite is thought to be decomposing to calcium oxide or reacting directly with silicates or aluminosilicates;

(c) clay minerals have disappeared by 900°C; kaolinite is not even found at 500°C; clay minerals may transform to feldspars or, at high temperatures, to amorphous (vitrified) material;

(d) original plagioclase-type materials are somewhat reduced at 1100°, but substantially reduced by 1200°C; these reductions may indicate transformations to new feldspar minerals or conversion to amorphous glass;

(e) the amount of amorphous material shows a substantial increase at 1100°-1200°C; tailings containing appreciable clay or feldspars show the greatest amount of amorphous content in TST.

Thermally stabilized and untreated SLC tailings (-20 mesh, <0.8 mm) were measured for surface area by the nitrogen BET 1 method; the surface area of untreated tailings was 15-17 m2/g and tailings sintered at 1200° (which were slightly fused) had surface areas of less than 0.1 m2/g.

1 Brumauer-Emmet-Teller method of nitrogen adsorption.

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q\ 1 I 1 1 1 1 1 1

500 700 900 1100 SINTERING TEMPERATURE (°C)

FIG.l. Per cent reduction in 222Rn emanating power as a function of the sintering temperatures used in thermal stabilization.

2.2 Emanating power of thermally stabilized tailings

The 2 2 2 Rn emanating power (as defined by the activity, pCi/g, of 2 2 6 Ra contributing 2 2 2 Rn to the pore atmosphere) of 4 types of tailings has been determined for materials heated from 500° to 1200°C at 100° intervals. These results are shown in Fig. 1 and illustrate that to achieve substantial reduction (i.e., >95%) in emanating power requires treatment at temperatures of 1100° to 1200°C. This temperature range corresponds with the thermal treatments necessary to produce large increases in amorphous material and large reductions in surface area. Thus, it appears that substantial reductions in emanating power result from greatly reduced surface area, mineral transformation and lattice rearrangements, and increased vitreous (amorphous) material sealing or joining mineral grains.

A variety of tailings materials from the 4 inactive sites was sintered at 1200°C to investigate the general utility of thermal stabilization in reducing 2 2 2 Rn emanations. The coarse tailings sands with high quartz contents originally had emanating powers of 40-140 pCi/g; thermal stabilization reduced the emanating power to 0.4-1.3 pCi/g (i.e., reductions of 97 to 99.5%). The tailings fines had initial emanating powers of 125-550 pCi/g, which were reduced to 0.3-1.6 pCi/g (i.e., reductions of 99.6 to 99.9%). As mentioned in section 2.1, the finer tailings tended to become more amorphous upon sintering and formed slags at 1200°C; thus, it appears that slagging causes a greater percentage reduction in 2 2 2 Rn emanation than can be achieved by the slight fusion of quartz grains as observed with tailings sands.

2.3 Effect of thermal stabilization on leachable contaminants

Another measure of the efficacy of thermal stabilization as a remedial action technology is the reduction in contaminant leachability. Batch leaching tests (25 g tailings/125 mi H 20) were

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TABLE I

COMPOSIT ION OF LEACHATES FROM UNTREATED A N D

T H E R M A L L Y STABILIZED TA IL INGS

A M L Alkaline Fines* SLC Acid Sands" SHIP Acid Fines' Proposed

Thermally Thermally Thermally Standard

Element Units Untreated Stabilized Untreated Stabilized Untreated Stabilized Vitrified'1 US EPA

pH _ 9.1 7.5 3.3 8.2 3.2 6.8 9.8

As mg// 1.03*e 0.01 0.009 0.04 0.04 0.002 0.020 0.05

Ba mg// 0.03 0.009 0.037 0.47 0.03 0.14 0.013 1.0

Cd mg// <0.002 <0.002 0.08* <0.003 0.088* <0.005 <0.002 0.01

Cr mg// <0.004 <0.004 <0.004 0.016 <0.004 <0.004 <0.004 0.05

Mo mg// 0.84* <0.004 0.027 0.82* 0.10* 0.47* 0.02 0.05

Pb mg// 0.02 <0.01 0.08* <0.01 0.36* <0.01 <0.04 0.05

Se mg// 1.27* <0.01 <0.01 <0.01 0.33* 0.15* 0.02* 0.01

U mg// 0.21* 0.002 8.5* 0.017 0.73* 0.002 0.001 0.03 J " R a pCi// 264* 3.0 71 * 21 * 32* 40* 6 * 5.0

SO? mg// 76 56 1600 950 2000 1700 1 -Ca mg// 4 22 550 350 470 650 7 -SiO z mg// 43 12 54 15 63 5 53 -Na mg// 130 3 3 2 66 1 12 -Mg mg// 0.2 0.7 11.8 0.4 91 1.2 0.5 -Fe mg// 2.2 0.04 0.73 <0.01 2.5 <0.04 0.04 -V mg// 1.8 <0.3 <0.1 <0.1 2.0 <0.1 0.4 -Al mg// <0.1 <0.1 11 0.1 16 <0.1 0.3 -

Zn mg// 0.01 <0.01 2.8 <0.01 1.16 <0.01 <0.01 -Mn mg// <0.01 <0.01 2.8 <0.01 3.1 0.01 <0.01 -Ni mg// <0.01 <0.01 0.63 <0.01 0.80 <0.01 <0.01 —

"Ambrosia Lake tailings (carbonate leach) dHeated to 1400°C, glass formed bSalt Lake City tailings (H 2 S0 4 ) '* indicates concentration in excess of proposed standard cShiprock tailings (H 2 S0 4 )

performed on both untreated and thermally conditioned (1200°C) tailings. The concentrations of hazardous constituents and major ions in these leachates are presented in Table I. The first nine elements in Table I (As —*• 2 2 2 Ra) represent most of the contaminants for which the US Environmental Protection Agency has proposed water contamination standards related to tailings disposal [1]. Concentrations for the untreated tailings leachates exceed the standards for many of the elements including As, Cd, Mo, Pb, Se, U, and 2 2 6 Ra. The thermal stabilization treatment reduces the leachability of most of these contaminants; however, Ba, Mo, and 2 2 6 Ra are apparently more leachable in some of the thermally stabilized acid tailings (SHIP and SLC). Acid mobile species (e.g., Cd, Pb) are well retained in TST; whereas, alkaline mobile elements (e.g., Mo and Se) are still readily leached from TST, which are all neutral to alkaline. Uranium exhibits a very large decrease in leachability as a result of thermal conditioning. After thermal treatment, barium leachability increases by factors of 5 to 10 for acid tailings; however, 2 2 6 Ra exhibits minor increases or substantial decreases in leachability for these materials. Thus, the aqueous leachability of Ba is not analogous to Ra in these leaching experiments.

When considering the other elements listed in Table I, the most noticeable change as a result of thermal stabilization for the alkaline tailings is a pronounced decrease in sodium leachability, probably resulting from the incorporation of sodium into silicates or

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aluminosilicates. The substantial amount of leachable iron in the untreated alkaline tailings suggests the presence of Fe(II). Thermal treatment could oxidize Fe(II) or cause its incorporation into silicates, making it immobile. Vanadium also exhibits a substantial decrease in leachability; the formation of water insoluble calcium vanadates or uranates may occur during thermal treatment as it does in the salt roasting of uranium ores [3]. The untreated acid tailings leachates are dominated by C a + 2 and SC^2. However, when heated to glass forming temperatures (>1200°C), anhydrite apparently decomposes to CaO and sulfur oxides. Acid mobile constituents such as Fe, V, Al, Zn, Mn, and Ni, are virtually immobilized in the TST as a result of the neutral or alkaline character of these leachates or the incorporation of these elements into insoluble minerals or glasses.

2.4 Experimental assessment of the long-term stability of thermally stabilized tailings

2.4.1 Changes in emanating power

A preliminary assessment of the effects of weathering TST was performed to evaluate whether physical degradation and leaching would increase radon emanation. Physical degrada­tion was simulated by pulverizing crushed (<6 mm) sintered tailings to <0.85 mm. A split of the pulverized material was leached with deionized water. Emanating 2 2 6 Ra was measured on (a) untreated tailings, (b) crushed sintered tailings (<6 mm), (c) pulverized sintered tailings (<0.85 mm), and (d) leached pulverized sintered tailings (<0.85 mm). Reduction factors for crushed (<6 mm) and "weathered" (pulverized and leached) sintered tailings compared with emanation power of untreated tailings are presented in Table II. In addition, Table II presents radon emanation ratios that illustrate the effects of "weathering" on thermally stabilized tailings.

Sintered tailings crushed to <6 mm have radon emanation reduced by factors of 100 to 2300. The levels of emanating 2 2 6 Ra in the thermally stabilized tailings that were pulverized and leached range from 0.3 to 11 pCi/g corresponding to reduction factors of 20 to 300.

The effects of pulverizing the sintered tailings on radon emanation are illustrated in the pulverized/sintered (P/S) column of Table II. The tailings sands, which retained a sandy texture after thermal stabilization, show P/S ratios of 1.2-1.6. Thus, the pulverizing had a relatively small effect on the sandy or slightly fused sands produced by thermal conditioning. The tailings fines that formed slags or the glass (SHIP Fines, 1400°C) showed an appreciably greater effect from pulverization; P/S ratios ranged from 2.3-4.3. Pulverization obviously causes a greater alteration in the structure and surface area of slags than for tailings that have not undergone melting and have retained a sandy texture. Thus, if increases in radon emanation power are used as a measure of the extent of weathering, slags from thermal stabilization will be more greatly altered by a given amount of physical degradation than will granular materials.

The effect of leaching on radon emanation is illustrated by the ratios in the pulverized and leached/pulverized (PL/P) column of Table II. Two groups can be discerned from these results: a low initial gypsum (<7%) group in which sands have PL/P ratios of 1.2-1.3 and fines (slags) have ratios of 1.7-1.8; a high initial gypsum (15-35%) group in which sands have a ratio of 2.3 and fines have a ratio of 4.7. Tailings with high initial gypsum contents contain appreciable anhydrite (CaS0 4 ) after sintering in oxidizing conditions. Possibly, the initial presence of large amounts of gypsum (dehydrated to anhydrite by heating) may cause structural damage within the sintered material as a result of the rehydration of this mineral. Some evidence of this mechanism is seen in the glass produced from high gypsum fines that had been heated

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TABLE II

E M A N A T I O N REDUCTION FACTORS FOR T H E R M A L L Y STABILIZED TA IL INGS (1200°C); RATIOS OF E M A N A T I N G POWER SHOWING

THE EFFECTS OF G R I N D I N G A N D L E A C H I N G

Initial Initial

Texture* Gypsumb S c U/S U/PL P/S PL/P PL/S

Sands 15% 1.2 100 34 1.3 2.3 3.0

< 7 % 0.2 - 0.4 100 -450 5 1 - 2 4 0 1.2-1.6 1.2-1.3 1.4-2.0

Fines 35 % 0.9 230 20 2.5 4.7 11.6

[0.2] [1200] d [170] [4.3] [1.7] [7.3]

<7 % 0.2 - 0.5 370 - 2300 9 5 - 3 0 0 2 .3-4 .3 1.7-1.8 3.9 - 7.5

"Tailings with >50% sand-sized particles = sands bGypsum content as determined by x-ray diffractometry cEmanating power (pCi/g) of

U = Untreated tailings S = Sintered 1200°C, crushed <6 mm P = Sintered 1200°C, pulverized <0.85 mm PL = Sintered 1200°C, pulverized <0.85 mm, leached

d [ ] indicates vitrified material = glass

sufficiently to completely decompose anhydrite as shown by the very small amounts of leachable C a + 2 and SO~4

2 and the absence of any anhydrite peaks in the x-ray diffraction patterns. The increase in emanation for this glass because of leaching, i.e. the PL/P ratio, is 1.7 and similar to those of low gypsum slags. Thermally conditioned (1200°C) tailings having high gypsum levels not only show the greatest increase in emanation because of leaching, but also contain the most leachable C a + 2 and SO42 of all the sintered tailings.

The combined effects of both pulverization and leaching are given as the pulverized and leached/sintered (PL/S) ratios in Table II and can be used as a measure of weathering potential. Low weathering potential, PL/S <2 (i.e., greater stability), is seen for low gypsum sands. Moderate weathering potential, PL/S = 3-7.5, is found for high gypsum sands, low gypsum fines, and the glass (high initial gypsum, low final anhydrite). High weathering potential, PL/S = 11.6, is found only for the high gypsum fines.

2.4.2 Changes in leachable constituents

Untreated and thermally stabilized tailings were batch leached 3 times in succession to assess the dissolution of major constituents (e.g., gypsum/anhydrite) and contaminants resulting from the equivalent of approximately 30 pore volumes of water (assuming 50% pore volume) contacting these materials.

For untreated acid tailings the pH rose from 1/2 to 1 unit after 3 leaches. Calcium and sulfate continued to be highly leachable with concentrations still controlled by the solubility of

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TABLE III

RATIO OF TOTAL AMOUNT OF ELEMENT EXTRACTED FROM UNTREATED TAILINGS DIVIDED BY TOTAL EXTRACTED FROM

THERMALLY STABILIZED TAILINGS (3 SUCCESSIVE BATCH LEACHES)

Ratio Final

Site Material pH' Ba Ca Mg so;2 Si02 Pb Mo V U

SHIP Sands 4.5/7.8 0.1 14 24 18 2 >8 <0.2 0.3 45

SHIP Fines 3.8/6.7 0.3 0.9 53 1.0 7 >14 <0.2 >23 190

SLC Sands 3.7/7.5 0.1 3 18 3 3 >4 <0.1 - 590

SLC Fines 3.4/6.9 0.3 9 71 14 5 >60 1.6 >54 330

SLC Ferrophos 8.1/7.8 ~1 35 34 165 5 _b 1.8 91 4

D G O LP Fines 9.3/7.9 0.8 6 6 2 0.9 - - 12 58

D G O SP Sands 9.1/7.2 3 5 13 48 4 - 0.1 13 64

DGO SP Fines 8.4/7.6 0.1 7 10 10 6 - 4 25 170

A M L Fines 9.3/7.4 12 0.6 0.7 1.5 20 >5 >9 >9 230

*pH of third leach of untreated tailings/pH of third leach of TST bConcentration less than detection limit

gypsum. The concentrations of Mg, Pb, and U dropped substantially for the acid tailings (excluding the SLC ferrophos material, pH = 8.1). In addition, V and Mo levels decreased rapidly in the 3 successive leaches of the acid tailings fines.

The thermally treated tailings leachates (SLC and SHIP) have neutral to alkaline pH values and exhibit reduced C a + 2 and SC^ 2 concentrations in the successive leaches, except for the SHIP Fines. As seen in Table III, up to 18 times more SCT 2 is leachable from untreated acid tailings than from TST. Mo leachability from TST decreased rapidly in most cases, although more Mo was leached from TST than from untreated tailings. The amounts of Mg, V, and U leachable from TST tailings are small compared" to the amounts extracted from untreated tailings (see Table III). The SHIP Fines, high in anhydrite after thermal treatment, exhibit no decreases in leachable constituents with repeated leaching, except for Mg.

These alkaline tailings generally show a pattern of much more leachable Ca, SO?, Mg, V, and U in the untreated tailings than in the thermally stabilized material. The untreated A M L Fines contain little leachable Ca, SCTj2, or Mg, but substantial Si0 2 ; thermal treatment causes a substantial decrease in Si0 2 concentrations with a moderating of pH to near neutrality.

The results summarized in Table III substantiate the conclusion that Mo and Ba are the only elements identified that exhibit increased leachability from thermally conditioned tailings. However, the Ba levels are initially below the US EPA standard and the Mo in almost all materials drops below the standard after the first leach of TST.

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2.5 Conceptual thermal stabilization process

2.5.1 Process design

The preliminary conceptual design of the thermal stabilization process was developed around the use of an obsolete coal-fired rotary cement kiln to perform the thermal treatment. Such a kiln would have to be moved to the tailings site and appropriate feed apparatus and particulate and gaseous emissions control equipment would have to be installed. The sintered product or slag would be piled on site and covered with a 0.5 m layer of earth to attenuate the gamma field and to aid revegetation [4].

Because the cost of coal is a substantial portion (up to 20%) of the overall cost, alternative fuel sources are being evaluated. In those cases where the tailings pile is near a large population center (e.g., Salt Lake City), municipal refuse or dewatered sewage sludge could be used as alternative fuels. Codisposal offers the economic advantage of an investment in capital equipment that can be used for the incineration of municipal wastes long after the thermal treatment of tailings is completed; the energy output in the form of steam, steam-generated electricity, or low-Btu gas could be diverted to off-site uses at the completion of thermal stabilization. Initial engineering evaluation of existing technologies indicates that it is not currently possible to achieve a one-stage simultaneous waste incineration/tailings conditioning process. Thus, the present focus of these efforts is to evaluate the prospects of a two-stage process; the first stage would pyrolyze municipal waste into low-Btu gas,which would fire the second stage kiln or furnace where the tailings would be thermally treated.

2.5.2 Thermal stabilization cost estimates

Cost estimates have been calculated on the basis of the coal-fired rotary kiln concept for remedial action at Shiprock, Salt Lake City, and the residues at Canonsburg, Pennsylvania [4]. The estimated cost for performing thermal stabilization at Salt Lake City is $32.00/t for a 450 t/d facility; the overall cost would be $76 million. A comparison of a 450 t/d and a 900 t/d facility was made for the Shiprock site; the overall costs were determined to be equivalent at $17.50/t or a total of $27 million. The lower cost at Shiprock results from lower coal, electricity, and manpower costs than at Salt Lake City. The cost of thermal stabilization at Shiprock is approximately the same as moving the pile a moderate distance (~10 km), but appreciably more than covering the existing pile in place. The estimated costs of thermal stabilization of Canonsburg tailings is significantly higher, $45.50/t, because of the large capital expense involved with treating a relatively small amount of tailings ( ~ 180 000 t). Thus, the site specifics are very important in determining the costs of thermal stabilization.

3. R A D I O N U C L I D E R E M O V A L

Another approach to the conditioning of uranium mill tailings involves the removal of radionuclides from the tailings to enable the disposal of an innocuous large volume waste and the stringent management of a small volume of highly radioactive residues. The advantages of radionuclide removal can be seen in an evaluation of the long-term radiological hazard posed by

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to o

I 10 I0 2 I0 3 I0 4 I0 5 I0 6 I0 7

YEARS AFTER RADIONUCLIDE SEPARATION

FIG.2. Relative hazard index as a function of time.

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tailings with varying radionuclide contents. This analysis encourages the development of conditioning techniques that remove a substantial portion of the long-lived radionuclides (i.e., 2 3 8 U , 2 3 4 U , 2 3 0 Th, 2 2 6 Ra, 2 1 0 Pb, 2 3 5 U , 2 3 1 Pa ) ; a concentrated sulfuric acid method shows promise. If valuable metals can be recovered as a byproduct of a radionuclide removal process, some of the reprocessing costs can be offset.

3.1 Long-term radiological hazard after radionuclide removal

The removal (and separate disposal) of residual actinides and radium has been considered as a means of reducing the radiological hazard associated with uranium mill tailings [5,6,7]. Early in the U M T R A P conditioning technology program, a study was conducted to determine the effect of thorium and radium separation on long-term radiological hazard. Hazard was quantified in terms of an index calculated by summing the quotients of the activities and maximum permissible concentrations (MPCs) of the radionuclides present in the material of interest; thus,

The hazard index (H in cubic liters) is the number of unit volumes of water required to dilute a standard quantity of ore or tailings so that the concentrations of the various radioisotopes are individually equal to the MPCs.

Hazard indices for times up to a million (10 6) years were calculated for uranium ore, typical tailings, and conditioned tailings from which arbitrary2 fractions of 2 3 0 Th and 2 2 6 Ra have been removed. In Fig. 2, hazard indices relative to uranium ore are plotted for various initial concentrations of uranium, thorium, and radium. It is seen that the relative hazard index at 100 years is almost completely determined by the initial radium concentration; at 104 years, initial 2 3 0 Th concentration dominates; and at 106 years and beyond, only the initial 2 3 8 U concentration is important. Further, both thorium and radium must be removed in order to effect a long-term reduction in hazard index.

It should be noted that, regardless of the benefits that may accrue from radionuclide separation, the concentrated process residues constitute a new waste product whose disposal must be considered in assessing the cost of this tailings management option.

3.2 Radionuclide extraction with concentrated sulfuric acid.

One of the more difficult technical obstacles in achieving radionuclide removal is the extraction of 2 2 6 Ra from a sulfate-rich matrix such as tailings. Such extraction can be achieved with multi-stage leaching with strong nitric acid [6], hydrochloric acid, or chelating agents [5]. The approach for 2 2 6 Ra removal, which we have investigated, has much in common with early radium extraction methods using concentrated sulfuric acid [9].

2 Arbitrary in the sense of being selected to illustrate the effect, but without regard for the existence of a practical separation process that will produce the assumed mix of radionuclides. Landa has summarized the separation efficiencies attainable in various leaching processes [8].

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TABLE IV

EXTRACTION OF RADIONUCLIDES AND OTHER ELEMENTS BY CONC. AND ION H 2S0 4

U 2 3 0 Th 2 2 6 Ra Ba 2 1 0 Pb Pb

% Extracted by Cone. H 2S0 4

SHIP 0 85 80 70 20 40 SLC 60 90 75 30 55 30 DGO 55 80 70 70 50 55

% Extracted by ION H 2S0 4

SHIP 35 55 0 0 20 30 SLC 70 65 0 0 0 60 DGO 90 60 0 0 0 15

Table IV presents the percentage extraction of radionuclides from tailings fines by both concentrated and 10N H 2 S0 4 . The extraction observed seems consistent with the proposition that concentrated H 2 S 0 4 is an effective solvent of aqueously insoluble sulfate salts, such as BaS0 4 , RaS0 4 , and PbS0 4 [10]. Concentrated sulfuric acid also extracts substantial U and 2 3 0 Th, as does 10N acid. These results indicate that concentrated H 2 S 0 4 is effective in extracting the long-lived radionuclides. A major technical problem is to achieve a solid/liquid separation with a very viscous liquid like concentrated H 2 S0 4 . Until this technical obstacle and other technical difficulties are resolved, a conceptual radionuclide removal process can not be developed.

3.3 Recovery of mineral values

The recovery of mineral values from SHIP, SLC, and D G O tailings has been assessed using strong H 2 S 0 4 leaches [10]. the Shiprock tailings contain negligible values; the V and Mo in the fines have a value of approximately $6.00/t. The Salt Lake City fines have appreciable recoverable Mo and U worth about $29.00/t; the ferrophos material has significant residual V values, as well as minor amounts of U, Mo, Cr, Mn, Ni, and Cu, for a total value of approximately $20.00/t. The Durango tailings contain substantial residual U and V values worth about $11.00/t for the sands and $39.00/t for the fines. In addition, the Durango fines have appreciable extractable Co, as well as minor amounts of Mn, Cu, and Zn.

An economic analysis of reprocessing the Durango tailings has been performed; percolation H 2 S 0 4 leaching of tailings in excavated leach tanks was the conceptual process that was evaluated [4]. It is estimated that $32 million of U and V could be recovered from these tailings with an incremental cost because of the leaching steps of $19.5 million. Therefore, over $12

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million could be gained to offset the overall cost of remedial action. The net cost of such a reprocessing scenario would be less than the total cost of reshaping, stabilizing, and covering the existing tailings in place.

Reprocessing tailings for metals recovery will remove some residual U and 2 3 0 Th, but not 2 2 6 Ra; thus, the long-term radiological hazard is not appreciably reduced. However, reprocessing can remove potential leachable contaminants, such as Mo and U, and therefore lessen the overall hazard of these materials. In conclusion, if the value of the materials recovered equals or exceeds the incremental cost of adding the leaching step, reprocessing should definitely be considered as part of the overall remedial action.

4. CONCLUS IONS

Immobilization of contaminants by thermal stabilization appears to be a technically effective remedial action technology. Costs of this type of conditioning are high; the primary energy source will be coal or combustible wastes. In comparison, petroleum-based liquid fuels are the primary energy sources for remedial actions requiring the transportation of tailings and excavation of burial pits. Thermal stabilization may be cost competitive with other remedial actions and may yield better long-term hazard reduction depending on site specifics.

The possibility of removing long-lived radionuclides with concentrated H 2 S 0 4 before tailings disposal is probably technically feasible. However, the practical engineering and economics of such a conceptual process can not be analyzed until technological advances are achieved. Some tailings materials contain sufficient residual mineral values to offset the cost of reprocessing steps. It is recommended that serious consideration be given to reprocessing as part of remedial action at those sites with substantial residual values.

REFERENCES

[1] Draft Environmental Impact Statement for Remedial Action Standards for Inactive Uranium Processing Sites (40CFR192), Office of Radiation Programs, U.S. Environmental Protection Agency, Washington, D.C., EPA 520/4-80-011 (1980).

[2] DREESEN, D.R., WILLIAMS, J.M., COKAL, E.J., "Thermal stabilization of uranium mill tailings," Uranium Mill Tailings Management (Proc. 4th Symp., Fort Collins, Colorado, 1981) Colorado State University, Fort Collins, Colorado (1981), 65.

[3] MERRITT, R.C., The Extractive Metallurgy of Uranium (Colorado School of Mines Research Institute), Johnson Publishing Co., Boulder, Colorado (1971).

[4] THODE, E.F., DREESEN, D.R., "Technico-economic analysis of uranium mill tailings conditioning alternatives," Uranium Mill Tailings Management (Proc. 4th Symp., Fort Collins, Colorado, 1981), Colorado State University, Fort Collins, Colorado (1981), 155.

[5] B O R R O W M A N , S.R., BROOKS, P.T., Radium Removal from Uranium Ores and Tailings, Bureau of Mines Report of Investigations 8099 (1975).

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[6] R Y O N , A.D., HURST, F.J., SEELEY, F.G., Nitric Acid Leaching of Radium and Other Significant Radionuclides from Uranium Ores and Tailings, Oak Ridge National Labor­atory report ORNL/TM-5944 (1977).

[7] RAICEVIC, D., "Decontamination of Elliot Lake uranium tailings," Canadian Institute of Metallurgy Bulletin (1977), 109.

[8] L A N D A , E.R., Isolation of Uranium Mill Tailings and Their Component Radionuclides from the Biosphere - Some Earth Science Perspectives, U.S. Geological Survey Circular 814 (1980).

[9] L A N D A , E.R., " A Historical Review of the Radium-Extraction Industry in the United States (1906-1926) - Its Processes and Waste Products," Uranium Mill Tailings Management (Proc. 4th Symp., Fort Collins, Colorado, 1981), Colorado State University, Fort Collins, Colorado (1981), 3.

[ 10] WILL IAMS, J.M., COKAL , E.J., DREESEN, D.R., "Removal of radioactivity and mineral values from uranium mill tailings," Uranium Mill Tailings Management (Proc. 4th Symp., Fort Collins, Colorado, 1981) Colorao State University, Fort Collins, Colorado (1981), 81.

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A STUDY ON THE DEVELOPMENT OF A PROCESS FOR TREATING URANIUM MILL EFFLUENTS

J.L. KHARBANDA, P.K. PANICKER, K. BALU Waste Management Division, Bhabha Atomic Research Centre, Bombay, India

Abstract

A STUDY ON THE DEVELOPMENT OF A PROCESS FOR TREATING URANIUM MILL EFFLUENTS.

The acidic solid/liquid tailings from the mill are neutralized with lime and transferred to the tailings pond. The overflow waters released from the pond at the point of discharge contain manganese and radium in quantities that exceed drinking water tolerance. This paper describes the results of studies carried out on the concentration/removal of the pollutants from mill effluents, particularly from the barren solutions and from the tailings pond overflow waters. Factors influencing solution conditions and the pollutants in the pond are discussed. Insolubilization/stabilization of M n 2 + by oxidation to higher oxides and radium by co-precipitation have also been investigated.

1. INTRODUCTION

In India uranium is mined mainly at Jaduguda, Bihar. A uranium mill is operating on a commercial production basis at the mining site. The mill processes low-grade ore and produces magnesium diuranate as concentrates. Uraninite as dissemination is the chief uranium mineral of the ore. Toxins such as arsenic, copper, selenium, cobalt and cadmium are present in the ore in small amounts. Uranium is extracted by leaching the ore with sulphuric acid using pyrolusite and is recovered by the ion-exchange process. After leaching almost the entire feed is rejected as solid waste. Apart from solid tailings the mill generates about 3 m 3 of liquid effluents per tonne of ore processed. The solid/liquid tailings are neutralized with lime and are transferred to the tailings pond located near the mill. On decantation the pond waters are allowed to flow into a public stream.

Neutralization of the tailings helps in precipitating most of the radioactive and chemical toxins, which settle and remain confined as sediments in the

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impoundment area. However, it is observed that, although radium and manganese are also carried by the sediments to an appreciable extent, their remaining traces in the pond waters at the point of discharge are in excess of drinking water tolerance.

In order to reduce the long-term environmental impact of the tailings, laboratory investigations were undertaken to evolve methods for more efficient decontamination, primarily of the barren solutions and also of the overflow streams. Further efforts were directed towards insolubilization/stabilization of the contaminants prior to their transfer to the pond.

2. NATURE OF EFFLUENTS

After uranium leaching, solids are treated with lime and are segregated as sand and slimes with the help of hydrocyclones [1 ] . Sand and gravels are used as backfill material and slimes are discarded in the tailings pond.

Barren solutions from ion-exchange recovery process and other process waters such as supernates from diuranate precipitation, filter back washings, floor washings etc. constitute liquid tailings. Barren solutions contain all the acid soluble chemicals and radioactive impurities dissolved from the ore and the oxidant.

Overflow waters from the tailings pond are near neutral and contain large amounts of calcium and magnesium sulphates. Typical analyses of the liquid effluents are shown in Table I.

3. TAILINGS POND

Neutralized barren solutions along with other process waters and the slimes, separated from the solid tailings, are discharged to the tailings pond through a pipe-line. The tailings pond at the mill site occupies an area of about 30 acres in natural depression formed by two hills with an opening on one side. An earthen dam constructed with boulder foundation on the opening side converts the enclosed area into a pond. Figure 1 shows the location of the pond and its environment [2] .

3.1. Behaviour of manganese and radium

In the pond, solid debris settles and the supernatant solution flows out continuously through decantation wells located in the pond and joins the natural streams of the local environment.

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S.No. Components analysed Effluent streams

S.No. Components analysed Barren solutions

Tailings pond waters

1. pH 2.0 7.2

2. TDS (g/L) 19.6 3.6

3. SS (g/L) 5-10 5

4. Mn (mg/L) 560-800 0.4-10

5. Fe (mg/L) 700-900 -6. S0 4 (g/L) 10-11 1.5-2.0

7. Total hardness (mg/L) 3625 1775

8. Gross beta (pCi/L) 82 000 16 000

9. Gross alpha (pCi/L) 21 000 270

10. Radium-226 (pCi/L) 1300 150 (max.)

TDS = Total Dissolved Solids; SS = Suspended Solids.

0 WELLS

FIG. 1. Location of tailings pond.

TABLE I. NATURE OF LIQUID EFFLUENTS

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On neutralization manganese precipitates as Mn (OH) 2 . It however reappears in the supernatant liquids and overflow waters. Partial solubilization of manganese may be attributed to in-situ reactions in the pond resulting in a change in solution conditions. Although discharges from the mill into the pond are highly alkaline (pH 10.5), the overflow waters are normally near neutral. This change in pH is possibly responsible for its redissolution. Neutralization of atmospheric carbon dioxide with soluble lime seems to be primarily responsible for the decrease in the pH-value. This was verified experimentally by taking barren solutions neutralized to pH 10.5 with lime and exposing them to atmosphere. The change in the pH-value of the supernatant liquid was followed with time and it was found that the value decreased to 7.5 within a period of 12 days. At this stage the supernate contained 8 mg/L of manganese. In addition, bacterial action may also contribute to some extent to this effect.

4. SOURCE CONTROL

4.1. Neutralization of barren solutions

Since the liquids are acidic, the first step towards their disposal essentially involves neutralization. Radium and manganese are of prime interest and hence their behaviour under different conditions of pH-value and neutralizing agents was studied. Lime and caustic were used for this purpose. It was observed that, irrespective of the neutralizing agent used, manganese precipitation is complete only when the pH-value is 10.5 and above, as shown in Fig.2. Under these conditions, gross activity (DF = 300) and radium (DF = 28) are also carried by the precipitates to an appreciable extent. This shows that separating the sludge will facilitate decontamination. Data on sludge collected are as follows:

Sludge volume (overnight settling): 50 vol.% of the liquid treated Sludge density: 1.0267 g/L Dry extract: 66 g/L Amount of wet cake (on filtration under vacuum): 198 g/L

It was estimated that filtration would generate about 100 kg of wet cake per cubic metre of barren solutions. Economics of sludge handling and final disposal has to be looked into.

4.2. Radium removal using barytes and pyrolusite

Barytes and pyrolusite, naturally occurring minerals of barium and manganese, respectively, are often suggested for use in the treatment of waters contaminated with radium activity [3] . Their use for the concentration of radium from barren

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TABLE II. TREATMENT OF BARREN SOLUTIONS WITH BARYTES AND PYROLUSITE

Range of Barytes treatment Pyrolusite treatment particle size (mm) Radium-226 Removal Radium-226 Removal

(pCi/L) (%) (pCi/L) (%)

0.37-0.25 286 78.0 _ _

0.25-0.15 254 80.5 470 64.0

0.15-0.10 234 82.0 - -0.10-0.075 182 86.0 290 77.5

0.075-0.05 159 88.0 230 84.0

0.037 - - 97 92.5

solutions was examined. The important factors studied were the effects of contact time, particle size, concentration of the minerals and method of contact on the extent of radium uptake. Results of these studies showed that the radium removal increases with decreasing particle size and with increasing mineral concentration (Table I I ) . This indicates that radium uptake is mainly controlled by surface adsorption mechanisms.

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TABLE III. BARIUM CHLORIDE-LIME TREATMENT OF BARREN SOLUTIONS (Initial 2 2 6 Ra : 1300 pCi/L, Lime: 12g/L,pH: 10.5)

Barium Final Removal (mg/L) 226Ra (%)

(pCi/L)

0 48.0 96.31 10 23.0 98.23 25 6.5 99.50 50 5.6 99.57 75 6.8 99.48 100 5.2 99.60

In equilibrium tests, radium removal up to 88% was obtained on contacting 2 g/L of barytes (0.075 mm—0.05 mm size) for one hour. Feasibility of its use as column material was also examined. Results, however, were not promising.

A removal efficiency of 92% was obtained on contacting the solution with 2 g/L of powdered pyrolusite (0.037 mm size). A clear solid/liquid separation in this case was obtained only after about 12 hours of settling. Freshly prepared manganese dioxide precipitates were also tried for this purpose and, under similar conditions of concentration and time of contact, 96% radium uptake was obtained.

4.3. Barium chloride treatment

Radium removal from acidic barren solutions by coprecipitation with barium sulphate was studied by introducing BaCl 2, the amounts ranging between 10 to 200 mg/L of B a 2 + . It was observed that a maximum of 75% radium could be concentrated on barium sulphate without altering the solution conditions. Increase in the pH-value improved the removal of radium, and about 99% was concentrated in the precipitate using 25 mg/L of Ba 2 + at pH 5. Sludges produced under these conditions amounted to about 8% of the volume of the liquid. Controlling the pH-value thus helps in restricting the precipitation of inactive components and in concentrating radium on minimum amounts of precipitates.

4.4. Stabilization of radium and manganese

Radium is the only important radioactive contaminant that remains soluble to some extent in pond waters. Barium chloride, in combination with lime, was used to insolubilize radium more efficiently. The quantity of Ba 2 + required for

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10

0-1 1 1 < . . I 1 1 r

2 3 4 5 6 7 8 9 10 II P H

FIG.3. Treatment of barren solutions.

maximum coprecipitation of radium was optimized (Table I I I ) . Results of lime treatment with and without barium as shown in Fig.3 indicate that, as expected, radium is concentrated in the precipitates more effectively in the presence of barium salt. This further indicates that barium containing precipitates should have better radium retention capacity in the pond as sediments, where conditions continue changing depending upon different factors including climate. In order to ascertain this aspect, the radium retention capacity of these precipitates was tested. Slurries, both with and without barium, were filtered and the solids (30—40 wt%) were contacted separately with deionized water and sulphate solution with gentle agitation. Results in Table IV show that release of radium from solids containing barium is negligible as compared with radium release

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TABLE IV. LEACHING OF 2 2 6 Ra FROM PRECIPITATES

Time Per cent radium leached

(h) Deionized water Sodium sulphate (3M)

Lime Barium-lime Lime Barium-lime

1 6.8 0.8 2.3 0.07 2 8.4 1.2 2.9 0.13 4 9.7 1.6 3.5 0.18 24 10.6 1.3 3.6 0.20 48 10.9 1.8 3.8 0.21

from solids containing no barium. Sulphate suppresses the release of radium to a significant extent. Thus, the use of barium together with lime stabilizes radium activity in the sediments and minimizes its concentration in the overlying waters.

It was further noticed that the sequence of chemical addition plays an important role. Barium should be introduced first and should be thoroughly mixed before lime is added.

During this process, manganese precipitates as hydroxide and, under neutral conditions, has appreciable solubility. Higher hydrated oxides of manganese are practically insoluble over a wide range of pH-values [4] . It was, therefore, considered that a change in chemical state may help in stabilizing manganese by rendering it more insoluble. Oxidation of the hydroxide slurries is necessary to achieve this objective. Methods such as air oxidation and permanganate treat­ment were tried for this purpose.

Under alkaline conditions Mn(OH) 2 has strong affinity to react with oxygen to form higher oxides. In view of the large quantities of manganese involved, supply of oxygen from external sources is necessary for its complete conversion to higher oxides. Air digestion of the neutralized slurries was studied in this respect. It was observed that, as aeration proceeds, the precipitates change from dirty brown to greyish black in colour. The extent of stabilization was deter­mined by acidifying the aerated slurries to pH 2 to 3, and analysing the supernate for manganese. Results are shown in Fig.4. Oxidation accelerates after a time lapse of about one hour indicating that once the higher oxides are formed, they exert a catalytic effect and enhance the rate of reaction. Air digestion for about six hours resulted in over 99% conversion of manganese to higher oxides.

Permanganate reacts with M n 2 + both under slightly acidic as well as alkaline conditions to produce hydrous Mn0 2 . The quantity of permanganate required for the complete precipitation of manganese was determined experimentally.

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An estimate made in the precipitates showed that more than 98% of the radium was concentrated on these precipitates. After overnight settling sludges amounted to about 4 to 5 vol.%.

5. TREATMENT OF TAILINGS POND OVERFLOW WATERS

Radium removal from overflow waters was studied by coprecipitation on barium sulphate and sorption on barytes and pyrolusite minerals. Coprecipitation efficiency was evaluated for different concentrations of barium. About 90% removal was obtained by the addition of 10 mg/L of barium. Precipitates are very fine and settle with difficulty. Settling was found to improve with increasing pH-value.

As regards the use of barytes for the concentration of radium from these waters, a maximum of 45% removal was obtained with 4 g/L of barytes (0.075 mm size), the contact period being four hours. Removal was reduced to 25% for the same contact period when 0.37 to 0.25 mm size mineral was used.

When pyrolusite was used, about 90% removal was obtained with 1.5 g/L of the mineral (0.037 mm size), the contact period being one hour. Supernate was clear after 24 hours. The slurries were reused for the treatment of fresh solution. It showed that their capacity to concentrate radium practically remained unaffected, suggesting their use for repeated treatment. Results are shown in Table V.

Some field studies on the use of these minerals in contact beds have also been carried out by the Health Physics Division, BARC, at the mill site [5 ] .

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TABLE V. TREATMENT OF OVERFLOW WATERS WITH PYROLUSITE (0.037 mm size)

Treatment-I Treatment-!!3

(mg/L) Final 2 2 6 Ra (PCi/L)

Removal (%)

Final 2 2 6 Ra (PCi/L)

Removal (%)

100 3.84 68 4.20 65

200 2.88 76 2.64 78

500 1.88 85 2.04 83

1000 1.32 89 1.68 86

1500 0.96 92 1.20 90

2000 0.76 92 1.08 91

Treatment II: Slurry from Treatment I contacted with fresh overflow waters.

TABLE VI . TREATMENT OF OVERFLOW WATERS WITH PERMANGANATE

Treated effluents Potassium permanganate (mg/L)

Manganese (mg/L)

Radium-226 (pCi/L)

20

25

30

0.08

Not detected

Not detected

0.35

0.30

0.29

The experimental setup was located near the pond. An overall maximum containment up to 90% of radium and up to 95% of manganese was achieved in the initial stages. Efficiency, however, decreased considerably both for radium and manganese as time progressed. This is possibly due to the silt deposition in the bed as well as to biological growth.

As regards manganese, its concentration in these waters is large enough to permit its precipitation and subsequent removal as hydroxide. Laboratory tests showed that raising the pH-value to 10.5 with lime results in its complete precipitation. The precipitates coagulate, and settle rapidly. There has been no significant change in radium activity.

Another alternative is to insolubilize and separate manganese as M n 0 2 . Permanganate could be employed without altering the solution conditions. Changes in solution conditions involve additional cost and, therefore, only

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permanganate oxidation was tried and conditions such as amounts, time of contact, and settling periods etc. were optimized. It was observed that permanganate action produces fine precipitates that are slow in settling. A period of 24 hours is necessary for the supernatant solution to be clear for decantation. Addition of 25 mg/L of potassium permanganate was sufficient to completely precipitate soluble manganese. The settled sludge amounts to 0.5% of the liquid volume. Radium activity was also reduced considerably in the treated effluents. Results shown in Table V I indicate that the treated effluents are free from manganese and that the residual radium is much below the permissible limits.

6. FUTURE RESEARCH AND DEVELOPMENT WORK

Effectiveness of reverse osmosis

Membrane processes in recent years have found application in the treatment of waters and waste waters including radioactive liquids. In view of this, it is proposed to initiate studies on the use of reverse osmosis in the treatment of tailings pond waters. Laboratory experiments are being carried out with asymmetric cellulose acetate membranes.

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BARREN SOLUTION

OTHER PROCESS WATER

MIXING 4 BoCI2 MIXING BoCI2

- I i NEUTRALIZATION Ca(OH) 2 PH IO-5 Ca(OH) 2

SLURRIES

I - SETTLING

RAW SLUDGE

AIR DIGESTION

I DIGESTED SLUDGE

TAILINGS POND

± OVER FLOW

MIXING KMn0 4 MIXING KMn0 4

3! I SETTLING

SUPERNATANT

Mn02 FOR U LEACHIN6

Mn0 2 SLURRY DE WATERING

SUPERNATANT

FOR DISPOSAL I t

FOR REUSE AS PROCESS WATER IN THE MILL

DECONTAMINATED WATERS

FOR DISCHARGE

INTO ENVIRONMENT

FIG.6. A scheme for the treatment of uranium mill effluents.

Preliminary studies were carried out with simulated effluents [6] . Radium and manganese retention was evaluated-and the results are shown in Fig.5. Studies using other commercially available membranes with respect to various parameters such as operating pressure, feed composition and the extent of membrane porosity etc. are currently under investigation.

7. CONCLUSION

Lime treatment of barren solutions followed by separation of the resulting precipitates substantially reduces the concentration of radium, manganese and other heavy metal toxins. The process of solid separation would generate huge amounts of concentrates, requiring further processing and handling for their disposal. It would warrant further working out of an economical and safe

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scheme for ultimate disposal. Among other methods investigated coprecipitation with barium sulphate, sorption on barytes and pyrolusite may prove useful in concentrating radium from acid solutions in relatively smaller volumes, leaving the bulk of the chemical impurities in solution. Permanganate treatment to precipitate hydrous M n 0 2 from acid solutions may find application in con­centrating and removing both radium and manganese in a single step.

In order to avoid solid/liquid separation it may be desirable to continue using tailings ponds as permanent reservoirs for slurries and pollutants. The risk of environmental contamination in this case may be minimized by chemically stabilizing the pollutants in a form that desists from redissolving and becoming water-borne in the pond. Barium sulphate-lime treatment insolubilizes radium to an appreciable extent. Combined treatment followed by air digestion of the slurries stabilizes manganese as hydrous M n 0 2 that can withstand changes in pH conditions in the pond waters. In addition it aids in scavenging the remaining traces of radium. Residual manganese and radium contamination of the overflow waters, if any, could be successfully removed by treatment with permanganate solutions and separating the resulting radium-bearing precipitates before release into the environment. A treatment scheme as shown in Fig.6 has been formulated on these lines. Feasibility of the implementation of the scheme is being looked into.

REFERENCES

[1] FAREEDUDDIN, S., SEN, S., "Recent developments in metallurgical science and technology", Proc. Silver Jubilee Symposium, Indian Institute of Metals, New Delhi (1972) 279.

[2] KAMATH, P.R., et al., "Non-radioactive effluents from nuclear installations", Environmental Surveillance around Nuclear Installations (Proc. Symp. Warsaw, 1973) Vol.2, IAEA, Vienna (1974).

[3] TYRINA, A.P., et al., At. Ehnerg. 18(1965)487. [4] NORDELL, E., Water Treatment for Industrial and other Uses, Reinhold and Co.

(1961)405. [5] MARKOSE, P.M., et al., Symp. Application of Nuclear and Allied Techniques in Public

Health and Pollution Control, Bombay (1981). [6] MISRA, B.M., KHARBANDA, J.L., Bhabha Atomic Research Centre, Bombay,

unpublished data (1981).

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CONCENTRATIONS AND OBSERVED BEHAVIOUR OF 2 2 6Ra AND 2 1 0Po AROUND URANIUM MILL TAILINGS*

S.A. IBRAHIM, SX. FLOT, F.W. WHICKER

Department of Radiology and Radiation

Biology,

Colorado State University,

Fort Collins, Colorado,

United States of America

Abstract

CONCENTRATIONS AND OBSERVED BEHAVIOUR OF 2 2 6 Ra AND 2 1 0 Po AROUND URANIUM MILL TAILINGS.

This study was designed to determine 2 2 6 Ra and 2 1 0 Po concentrations in soil and native plants from various sites around a conventional acid leach uranium operation in the western USA, and to estimate plant/soil concentration ratios. Soil and vegetation samples were collected from exposed, weathered tailings, near the edge of a tailings pond, from a reclamation area, and at several background (control) locations. The mean concentrations of 2 2 6 Ra and 2 1 0 Po in background soil were within the reported range for normal background locations in the United States of America. Concentrations of these radionuclides in soil and vegetation were elevated above background in the perturbed sites. The highest vegetation concentrations of both radionuclides were found in mixed grasses and forbs which had invaded exposed, weathered tailings. Mean plant/soil concentration factors varied significantly among sites and between radionuclides, but few significant differences between plant groups were found. In general, concentration factors for plants growing on exposed tailings and at the edge of a tailings pond were significantly greater than for those in background and reclamation areas. Concentration factors for 2 1 0 Po were usually considerably greater than for 2 2 6Ra. Frequency distributions of concentration factor values were highly skewed, with arithmetic mean values 3 to 4 times larger than modal values. The results of a leaching study indicated that both 2 2 6 Ra and 2 1 0 Po in uranium tailings from the sulphuric acid leaching process are highly insoluble in water, and the resulting ecological mobility appears significantly reduced as a result.

1. INTRODUCTION

Uranium mi l l ing waste contains several natura l ly -occurr ing radionucl ides in r e l a t i v e l y large concentrations and quant i t i e s . M i l l t a i l i ng s from conventional acid leach processes contain near ly a l l of the o r i g ina l a c t i v i t y of 2^^Th, 2 2 6 R a , and progeny of 2 2 2 R n (notably 2 1 0 P b and 2 1 0 P o ) .

* This work was funded primarily by the United States Department of Energy under Contract DE-AC02-79EV10305 to Colorado State University.

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Although the vast majority of tailings are adequately confined and controlled, experience clearly indicates that some tailings and associated radioactivity can be expected to elevate levels in soil, water and biota immediately adjacent to areas where ore and tailings are stored. This study was designed to delineate the quantities and geographical extent of these radionuclides and to study their ecological transport in the environs of a uranium mine and mill complex. This document provides a status report on findings to date. The studies reported are being conducted at a uranium mine* located in the southeastern high plains region of Wyoming at an elevation of about 7000 feet. The area under investigation is a semi-arid land dominated by a grassland-sagebrush association. This site was chosen for investigation because it is rather typical of many uranium production operations in the western U.S.A.

This report focuses on but one aspect of the overall study, namely the levels of 226*Ra a n ^ 210p o £ n s o i i s & n & plants, and the biological mobility of these radionuclides when derived from mill tailings. Of specific interest were the relative levels of 2 2 ^ R a and 2 1 0 P o at different sites on and near tailings systems, the comparison of sites, plant groups, and radionuclides in plant/soil concentration factors, and the leachability or solubility of these radionuclides in tailings materials.

2. MATERIALS AND METHODS

2.1. Sample collection and preparation

Soil and vegetation samples were collected in natural, undisturbed areas 0.8 km northwest, 5.6 km northwest, and 16 km southwest of the mine site to estimate background levels of 226 r & and 210p o < Other samples were collected from sites on the reclamation area, directly on exposed, weathered tailings that had stabilized in the lee of tailings pond dams, and near a tailings pond at distances of .05, 0.6, 1.2, 1.8, 6.1, 9.1 m from the edge. Sampling sites other than background are designated S r , S ., S p in Figure 1. The current annual aboveground growth of vegetation was clipped by hand to provide 15-50 g of dry matter. Plant groups [1, 2] sampled were mixed grasses (Genera: Agropyron, Koeleria. Poa, Hordeum and Oryzopsis); sagebrush (Genus: Artemisia); and forbs (Genera: Melilotus, Kochia, and Salsola). Soil samples of about 1 kg (dry) were collected by trowel from the major root zone (0-20 cm) areas of the specific plants which were sampled. Samples were individually bagged to minimize cross-contamination.

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FIG.l. Approximate 1981 configuration of the study area. Soil and vegetation sampling locations shown are the reclamation area (STJ, exposed tailings (St), and tailings pond edge (SpJ. Background sampling locations are off the map to the west.

Vegetation was washed ultrasonically (model 32 Bransonic) for 10 min. in mild detergent (high sudsing, Type 1 from White King, Inc., Los Angeles, California) and then two times in distilled water for 10 min. each. Such washing was done to assure the removal of most of the surficial dust and associated radioactivity. Samples were then oven-dried at 70°C for about 12 hours and the dry weight was recorded. Soil samples were oven-dried at 70°C for 12 hours and then allowed to equilibrate with the room air for another 12 hours before the dry weight was recorded. A few one-liter water samples taken from a tailings pond were filtered the same day as collected through a 0.45 um pore filter; the pH was then measured and the sample was acidified with 10 ml concentrated HC1.

Decomposition of soils and tailings prior to analysis for radium was carried out using pyrosulfate fusion in platinum containers to ensure complete matrix dissolution [3]. Decomposition prior to analysis for polonium was carried out using hydrofluoric and nitric acids to eliminate its volatilization [ 4 ] . Vegetation was wet-ashed using a mixture of concentrated nitric and perchloric acids. Water samples were evaporated to near dryness and the organic matter was ashed using concentrated nitric-perchloric acids.

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2.2. Radionuclide Analysis

2.2.1. Determination of 2 2 6 R a

For tailings and other samples containing comparatively high levels of 2 2*>Ra, a gamma spectrometry method was used. The method involved sealing the processed sample in a gas-tight container to allow 2 2 2 R n and daughters to grow into equilibrium with 2 2 6 R a (97% ingrowth after 20 days). The 1.76 Mev gamma ray of the daughter 2^^Bi was then measured using either shielded 4 x 8 inch Nal or coaxial GeLi (30% efficiency relative to a 3 x 3 inch Nal) crystals. The net count rate in the 1.76 MeV photopeak region was converted to pCi of 2 2 ^ R a by comparison to a standard tailings sample containing a known amount of 2 2*>Ra.

For low-level 2 2*>Ra analysis, the radon emanation technique was used [5, 6 ] . The method involves chemical isolation of radium on barium sulfate, emanation of 2 2 2 R n from the 2 2 6 R a in solution, entrapment of radon in a Lucas cell, and counting the Lucas cell after ingrowth of the radon daughter products. The chemical yield, determined by gamma counting of Ba-133 tracer, was close to 86%. Relative counting errors for 2 2 ^ R a (standard deviation/mean) ranged from < 1% to 16%, depending on sample activity.

2.2.2. Determination of 2 1 0 P o

Samples were analyzed for 2*0po using a technique developed earlier [7]. In this method, polonium was extracted into 30% aliquot-336 (mixed trioctyl and tridecyl methyl ammonium nitrate) in benzene from 2 M hydrochloric acid, and then back-extracted using 5% perchloric acid. 2 l u P o was then plated by spontaneous deposition onto a nickel disk and measured by alpha spectrometry. 2 ® 9 p 0 tracer was used to determine the chemical yield.

The minimum levels of detection for 2*0po and 2 2 ^ R a measured by the radon emanation method were about 0.05 pCi/sample, based on the computational procedure outlined by Currie [8], acid blanks activity, and background count rates of the detectors. Most of the samples analyzed in this study contained activity well above the minimum detection limits. However, all measured values were used in computations of results regardless of their relationship to the critical level. Relative counting errors for 2*0po ranged from 3-24%.

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2.3. Leaching Methods

Three tailings samples were collected from dry tailings areas and analyzed for initial 2 2 6 R a and 2 1 0 P o activity. Fifty grams of each tailings sample was then subjected to 15 consecutive extractions (10 min each) using 50 ml of distilled water (pH 7) at room temperature for each extraction. Each leachate fraction was analyzed for pH, 210p o a n ( j 226g a using the methods described previously.

2.4. Data Treatment

Data on soil and vegetation concentrations and concentration factors were expressed as arithmetic means ± one standard error of the mean (sample standard deviation/ VTT, n being the sample size). The number of independent samples was also provided with the tabular data. A concentration factor (CF) was determined for each pair of soil and vegetation samples. It is defined by:

Cp = pCi/g dry vegetation pCi/g dry, underlying soil

Statistical comparisons were based on standard analysis of variance procedures [9], implemented by a computerized statistical package [10].

3. RESULTS AND DISCUSSION

3.1. 2 2 6 R a and 2*°Po Concentrations in Soil and Vegetation

Mean concentrations of 2 2*>Ra and 2 1 0 P o in soil and various groups of vegetation from different areas within and near the uranium production operation are given in TABLE I. The levels of both radionuclides in soil and vegetation from disturbed areas near the operation were significantly elevated over background. This was fully expected in the case of exposed tailings areas, and the area at the edge of the tailings pond. Fresh tailings sediments contained roughly 300-400 pCi/g of both 2 2 6 R a and 2 1 0 P o . Exposed tailings on which plants were sampled contained somewhat less activity due to a higher content of sand and depleted amounts of finer 'slimes' which are known to contain more radioactivity. The soil at the tailings pond edge is natural, except that it was saturated with the pond-derived water, which was very acidic (pH - 1.8) and contained elevated concentrations of radionuclides (~ .3 pCi 2 2 6 R a / m l and ~ 8.5 pCi 2 1 0 P o / m l ) .

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TABLE I . 2 2 6 R a AND 2 1 0 P o CONCENTRATIONSa IN VARIOUS PLANT GROUPS AND SOILS FROM VARIOUS SITES. MEANS ± STANDARD ERRORS (NUMBER OF SAMPLES)

0-20 cm so i l Mixed grasses Sagebrush Forbs

226 Ra:

Natural Background 2.54 ± .63 (4) .075 ± .027(4) .19 ± .10(4)

Reclamation Area

( S r ) b 9.73 ± 2.07(11) .25 ± .19 (3) 1.38 ± .04 (2)

Exposed Ta i l ings

( S t ) 64.9 ± 6.3 (11) 12.2 ± 2.4 (3) 9.52 ± 3.54(5)

Ta i l ings Pond Edge ( S p ) 4.65 ± .46 (11) 1.26 ± .33 (7) 1.52 ± .49(6)

210 Po:

Natural Background 2.42 ± .40 (4) 1.79 ± .09 (3) .87 ± .08(4)

Reclamation Area

( S r ) 9.22 ± 1.93(7) .76 ± .29 (3) .82 (1) .28 ± .06 (2)

Exposed Tai l ings

( S t ) 105 ± 13 (9) 22.0 ± 7.5 (3) 29.9 ± 10.7(6)

Ta i l ings Pond Edge ( S p ) 6.04 ± 1.33(10) 6.66 ± .58 (7) 11.1 ± 4.0(7 )

Concentrations given in pCi/g dry weight

Map Location (Figure 1)

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The elevated soil concentrations in the reclamation area were probably the result of naturally higher levels in the overburden material now on the surface, but the area sampled may not be representative of the reclamation areas in general. The area sampled was reclaimed in (1972) and did not contain a topsoil cap as does the more recently reclaimed areas. Apparently it is not uncommon for 2 2*>Ra to be depleted from the surface and enriched in the substrata because of downward migration from leaching [11]. Background levels of 2 2*>Ra and 210p 0 £ n Soil were within the range reported for various background locations in the United States [12, 13].

Concentrations of 2 2*>Ra in vegetation samples varied from a minimum of 0.03 pCi/g in the reclamation area location to a maximum of 20 pCi/g for a sample growing directly on exposed tailings. In the case of 2*0po, concentrations in plants varied from a minimum of 0.22 pCi/g in the reclamation area to a maximum of 72 pCi/g on exposed tailings. Since the vegetation samples were ultrasonically washed to remove surficial dust prior to radioassay, these values likely represent activity primarily absorbed through the roots. With a few exceptions, plant concentrations of 2^°Po were generally higher than 2 2<>Ra concentrations, even though soil concentrations of these nuclides were more closely comparable.

There was a mild tendency for levels of 2 2*>Ra and 2l0po in soil and vegetation to decrease as a function of distance from the edge of the tailings pond. However, the data showed considerable variability which probably obscured any real trend. A probable source of variability was the several sampling dates that were used to obtain the samples, and possible temporal fluctuations in the water level of the tailings pond.

3.2. Plant/soil Concentration Factors

A summary of mean concentration factors for 2 2 ^ R a a n < j 210p o j,y collection site and plant group is provided in TABLE II. A group of statistical comparisons of the CF data in TABLE II is provided in TABLE III in order to objectively contrast sites, plant groups, and radionuclides. The observed distributions in CF values for both nuclides are shown as frequency histograms in Figure 2.

The observed data appears to demonstrate substantial differences between collection sites in mean CF values, with a general tendency for relatively low values in the background and reclamation sites, and comparatively high values at the tailings pond edge (Figure 2, TABLE II). The individual

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TABLE II. 2 2 6 R a AND 2 1 0 P o CONCENTRATION FACTORS 8 , FOR VARIOUS PLANT GROUPS AND SITES. MEANS ± STANDARD ERRORS (NUMBER OF SAMPLES).

Mixed grasses Sagebrush Forbs All plants

226 Ra: Natural Background .035 ± .011 (4) .087 ± .035 (4) .061 ± .020 (8) Reclamation Area ( S r ) b .035 ± .017 (3) .66 ± .02 (2) .28 ± .15 (5)

Exposed Tailings (S t) .23 ± .04 (3) .15 ± .06 (5) .19 ± .04 (8)

Tailings Pond Edge (S p) .28 ± .07 (7) .33 ± .10 (6) .31 ± .06 (13)

All Sites .17 ± .04 (17) .24 ± .07(10) .30 ± .10 (7) .22 ± .04 (34) 210 Po:

Natural Background .66 ± .01 (3) .40 ± .09 (4) .51 ± .07 (7) Reclamation Area (S r) .10 ± .05 (3) .19 (1) .045 ± .009(2) .097 ± .030(6)

Exposed Tailings (S t) ,25 ± .09 (3) .27 ± .09 (6) .26 ± .06 (9)

Tailings Pond Edge (S p) 1.4 ± .3 (7) 2.6 ± .8 (7) 2.0 ± .4 (14)

All Sites .82 ± .20 (16) 1.7 ± .6 (12) .21 ± .07 (8) .96 ± .22(36) Concentration factor = Activity/g dry plant * Activity/g dry soil Map location (Figure 1)

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TABLE I I I . STAT IST ICAL COMPARISONS OF MEAN PLANT/SOIL CONCENTRATION FACTORS BETWEEN S I T E S , PLANT GROUPS, AND RADIONUCLIDES.

S i g n i f i c a n t a t P r o b a b i l i t y L e v e l

C o m p a r i s o n s 2 2 6 R a 2 l 0 p o

Be tween S i t e s :

a l l s i t e s , m ixed g r a s s e s b a c k g r o u n d v s . r e c l a m a t i o n , m ixed g r a s s e s b a c k g r o u n d v s . e x p o s e d t a i l i n g s , m i x e d g r a s s e s b a c k g r o u n d v s . t a i l i n g s pond e d g e , m ixed g r a s s e s b a c k g r o u n d v s . t a i l i n g s pond e d g e , s a g e b r u s h b a c k g r o u n d v s . t a i l i n g s pond e d g e , m ixed g r a s s e s

+ s a g e b r u s h b a c k g r o u n d + r e c l a m a t i o n v s . e x p o s e d t a i l i n g s

+ t a i l i n g s pond e d g e , m ixed g r a s s e s r e c l a m a t i o n v s . e x p o s e d t a i l i n g s , m i x e d g r a s s e s r e c l a m a t i o n v s . e x p o s e d t a i l i n g s , f o r b s r e c l a m a t i o n v s . e x p o s e d t a i l i n g s , m ixed g r a s s e s

+ f o r b s r e c l a m a t i o n v s . t a i l i n g s pond e d g e , ' m i x e d g r a s s e s e x p o s e d t a i l i n g s v s . t a i l i n g s pond e d g e , m i x e d g r a s s e s

Be tween P l a n t G r o u p s :

m i x e d g r a s s e s v s . s a g e b r u s h , b a c k g r o u n d m ixed g r a s s e s v s . s a g e b r u s h , t a i l i n g s pond e d g e m i x e d g r a s s e s v s . s a g e b r u s h , b a c k g r o u n d + t a i l i n g s

pond e d g e m i x e d g r a s s e s v s . f o r b s . , r e c l a m a t i o n m ixed g r a s s e s v s . f o r b s , e x p o s e d t a i l i n g s m ixed g r a s s e s v s . f o r b s , r e c l a m a t i o n + e x p o s e d

t a i l i n g s

Be tween R a d i o n u c l i d e s :

a l l s i t e s , m i x e d g r a s s e s a l l s i t e s , a l l s p e c i e s b a c k g r o u n d and t a i l i n g s pond e d g e , s a g e b r u s h e x p o s e d t a i l i n g s , f o r b s

*NS - n o t s i g n i f i c a n t l y d i f f e r e n t

statistical comparisons suggest numerous significant differences, but the overall pattern is complex (TABLE III). The most complete site comparisons could be made with data for mixed grasses, since this group occurred and was sampled at all locations. For 2 2 <>Ra j n mixed grasses, there was a clear distinction between the background and reclamation sites as contrasted to the exposed tailings and pond edge sites. This comparison did not yield a significant difference for 2^®Po,

.05 N S * .01 .05 NS

.05

.01

.05 NS NS

. 0 1 05

.01

.05

.01

NS NS .05

NS .05 NS

NS .05 NS

NS NS

NS NS

NS .01 NS

NS .01 NS

NS NS

.01

. 01

.05 NS

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ARITH. MEAN* 0.22 GEOM. MEAN » 0.11 MODE » 0.07

.2 .3 4 .5 CF INTERVAL

210 p 0

SITE DESIGNATION

Background

Reclamation

^ Exposed Tailings

1UD Tailings Pond Edge

ARITH. MEAN » 0.96 GEOM. MEAN* 0.43 MODE~ 0.23

2 3 4 5 6 CF INTERVAL

FIG.2. Frequency distributions of the plant/soil concentration factors observed for 226Ra and 210Fo at four collection sites.

however. This and other individual comparisons demonstrates factor interactions among sites, plant groups and radionuclides. It is possible that the acidity or other properties of exposed tailings as well as of the saturated pond edge tend to enhance the solubility of the radionuclides and hence their uptake by plants.

The frequency histograms (Figure 2 ) demonstrate substantial skewness in the data, with most observations falling well below the arithmetic mean, and a very few observations falling considerably above the mean. The modal (most frequently observed) values were a factor of 3 -4 times lower than the arithmetic means. The geometric means, which describe the most probable values for log-normally distributed data, fall between the actual modal values and arithmetic means. These distributions typify the substantial and real variability in CF values, and reflect the many factors which influence such values.

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The statistical comparisons contrasting plant groups indicated few demonstrable differences between groups (TABLE III). Mixed grasses and forbs growing on the reclamation site provided the only exception to the general rule. The lack of plant group differences was generally a reflection of small differences between CF means and large variance terms. Any real differences in CF means between plant groups are likely small in comparison to site differences and the overall variability within populations.

Overall, there was clear indication that 2l°Po concentration factors were significantly higher than CF values for 2 2 ^ R a . The only case in which this was not observed was for forbs growing on exposed tailings and on the reclamation area. The sample sizes for forbs were particularly small, so little can be concluded either way. The reason for the apparently reduced uptake of 2 2*>Ra in contrast to 2*°Po is not clear. However, we speculate that in the case of sulfuric acid leached tailings-derived material, 2 2 <>Ra is largely sequestered as a sulfate, which is extremely stable and insoluble. This may also occur for 2*°Po, bu+ probably not to the same extent.

3.3. Leachability of 2 1 0 P o and 2 2 6 R a from Tailings

In order for elemental root uptake in plants to occur, a soluble species must exist adjacent to the root membrane. Thus a major factor governing element availability to plants in soils is solubility. Results of the water leaching experiment showed that the pH increased gradually in the leachate fractions from about 4 to 6 after five consecutive extractions and then remained almost unchanged for the following fractions. The total activity of 2 1 0 P o and 2 2 6 R a removed by the sum of all leaches remained very small and averaged 0.12% and 0.24% of the original sample activity, respectively.

Soil characteristics such as particle size, organic matter content, and exchange capacity are important factors in interpreting such results. Nevertheless, the predominant radium compound in tailings from the sulfuric acid process is radium sulfate. Radium sulfate is probably the most insoluble radium compound known; its solubility is 2.1 x 10~4 g/100 ml of water [5]. Polonium and lead exhibit similar behavior as illustrated by the coprecipitation on barium and radium sulfate. These results indicate that radium and polonium in uranium tailings from sulfuric acid leaching are highly insoluble in water, and the resulting ecological mobility appears reduced.

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4. COMPARISON TO EARLIER WORK

A recent and generally comparable study was conducted around alkaline-leached tailings in the Grants Mineral Belt in New Mexico by Marple [14]. Using similar species and plant washing methods, Marple found 2 2 ° R a concentration factors ranging from 0.01 to over 1.0 and averaging roughly 0.6, 0.4 and 0.2 for natural, reclamation, and tailings areas, respectively. The values presented by Marple are within the expected range of concentration factors for 2 2*>Ra as reviewed by Menzel [15] . These values compare favorably with the overall mean CF for 2 2*>Ra of 0.2 which we observed. Moffett and Tellier [16] measured a 2 2 ^ R a CF value for grasses on uranium tailings of 0.03, which is considerably lower than most other reported values. Earlier work at Wyoming uranium mills resulted in 2 2*>Ra cp values that were generally higher than reported herein, but the vegetation samples were not cleansed of surficial dust in those studies [17].

Our observation of higher concentration factors for 2 * u P o compared to 2 2*>Ra would not have been predicted on the basis of findings from two other investigations [16, 18]. Concen­trations of 2 1 0 P o reported by Moffett and Tellier [16] in four grass species growing on tailings are probably aberrant, since the plants were dry-ashed at 750°C which would volatilize a significant fraction of the polonium. The plants studied by D'Souza and Mistry [18] were cultured in a nutrient solution, thus root uptake would be the only plausible contamination mechanism. It is possible that our higher concentration factors for 2*0po may be due to the potential for foliar absorption in addition to root uptake. Other work related to both 2 * u P o and 2 2*>Ra uptake by plants was recently reviewed by Rayno [19].

Overall, it is clear that there is at least a one order of magnitude uncertainty in concentration factors for 2 2 ^ R a and 210pOf a n<i that continued investigation is warranted to fully elucidate the sources of this uncertainty.

ACKNOWLEDGEMENTS

Thanks are due to S. White, G. B. Kuzo, C. Domingue and A. Whicker of Colorado State University for their assistance on various phases of the work.

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REFERENCES

[1] WEBER, W. A., Rocky Mountain Flora, Colorado Associated University Press, Boulder, Colorado (1976).

[2] HARRINGTON, H. D., Manual of the Plants of Colorado, Sage Books, Denver (1954).

[3] SILL, C. W., Simultaneous determination of U-238, U-234, Th-230 and Pb-210 in uranium ores, dusts and mill tailings. Health Phys. 33 5 (1977) 393.

[4] FIGGINS, P. E., The Radiochemistry of Polonium, National Academy of Sciences, Nuclear Science Series NAS-NS 3037 (1961).

[5] KIRBY, H. W., The Radiochemistry of Radium, National Academy of Sciences, Nuclear Science Series NAS-NS 3057 (1964).

[6] HARLEY, J. H., 'Procedures Manual', U. S. Department of Energy Report HASL-300 (1977).

[7] WHICKER, F. W., Radioecological Investigations of Uranium Mill Tailings Systems, Second Technical Report, Dept. of Radiology and Radiation Biology, Colorado State University, Fort Collins, Colorado, DOE/EV/10305-2 (October 1981).

[8] CURRIE, L. A., Limits for quantitative detection and quantitative determination. Anal. Chem. 40 (1968) 386.

[9] SNEDECOR, G. W., Statistical methods (5th ed), Iowa State Univ. Press, Ames (1956).

[10] RYAN, T. A. JR., JOINER, B. L., RYAN, B. F., Minitab student handbook, Duxbury Press, North Scituate, Mass. (1976).

[11] OSBURN, W. S., Primordial radionuclides: Their distribution, movement and possible effect within terrestrial ecosystems, Health Phys. 11. (1965) 1275.

[12] NCRP, National Council on Radiation Protection Measurements, Report #50 (1976).

[13] MYRICK, T. E., BERVEN, B. A., HAYWOOD, F. F., State background radiation levels: Results of measurements taken during 1975-1979, ORNL/TM 7343 (1981).

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[14] MARPLE, M. L., Radium-226 in vegetation and substrates at inactive uranium mill sites, Report LA-8183-T, Los Alamos Scientific Labortory (1980) .

[15] MENZEL, R. G., Soil-plant relationships of radioactive elements, Health Phys. 11 (1965) 1325.

[16] MOFFETT, D., TELLIER, M., Uptake of radioisotopes by vegetation growing on uranium tailings. Can. J. Soil Sci. 57 (1977) 417.

[17] WHICKER, F. W., Biological interactions and reclamation of uranium mill tailings, Uranium Mill Tailing Management (Vol. 1 ) , Civil Engineering Dept., Colorado State University, Fort Collins (1978).

[18] D'SOUZA, T. J., MISTRY, K. B., Comparative uptake of thorium-230, radium-226, lead-210, and polonium-210 by plants, Rad. Botany 10 (1970) 293.

[19] RAYNO, D. R., Estimated dose to man from uranium milling via the terrestrial food-chain pathway. Dept. ANL/ES-125, Argonne National Laboratory (1982).

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DEVELOPMENT OF A PRECIPITATION AND FILTRATION PROCESS FOR RADIUM-226 REMOVAL D.W. AVERILL , J.W. SCHMIDT Environment Canada, Wastewater Technology Centre, Burlington, Ontario

D. MOFFETT Eldorado Nuclear Limited, Ottawa, Ontario

R.T. WEBBER Denison Mines Limited, Elliot Lake, Ontario

E. BARNES Rio Algom Limited, Elliot Lake, Ontario, Canada

Abstract DEVELOPMENT OF A PRECIPITATION AND FILTRATION PROCESS FOR RADIUM-226 REMOVAL.

A physical/chemical wastewater treatment process has recently been developed for the removal of radium-226 from the effluents of uranium mining and milling operations. The process consists of barium-radium coprecipitation in stirred-tank reactors and solid/liquid separation in chemically-aided dual-media filters. Over a period of several months, the process was demonstrated at pilot scale to provide an effluent meeting the following programme goals: 10 pCi/L (0.37 Bq/L) total radium-226 activity and 3 pCi/L (0.11 Bq/L) dissolved radium-226 activity. The first full-scale treatment process designed on the basis of this development programme is currently being built by Rio Algom Limited in Elliot Lake, Ontario, Canada. The Stanleigh Mine Tailings Effluent Treatment Plant will treat a maximum flow of 31.8 m3/min (8400 US gpm). Its estimated capital cost is $7.2 million (Canadian) based on first quarter 1981 prices.

1 . INTRODUCTION

In Canada, dissolved radium-226 is removed from uranium mining and mi l l ing ef f luents by the addition of barium chlor ide to sulphate-bearing wastewaters to prec ip i ta te barium-radium sulphate [ (Ba,Ra)S04J. The treatment process, which has been in use since 1965, consists of mixing a barium chlor ide solution with the t a i l i n g s basin e f f luent in a pipe or open channel, followed by so l i d/ l i qu id separation in s e t t l i ng ponds. Dissolved radium-226

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a c t i v i t i e s are general ly reduced e f f ec t i ve ly in these treatment systems. However, barium-radium sulphate is a f i ne , s l ow - se t t l ing c r y s t a l l i n e so l i d which is not ea s i l y removed by sedimentation. Thus, appreciable quantit ies of par t icu late radium-226 were often present in the ef f luents discharged to surface watercourses. In 1974, the Radioactivity Sub-group of a government-industry Metal Mining Task Force recommended that research be directed toward upgrading the performance of ex is t ing treatment systems and developing more e f f ec t ive methods for the removal of total radium-226 [ 1 ] . More recent ly , the addition of chemical coagu­lants or the use of s e t t l ing ponds with up to several weeks of residence time have given a marked improvement in e f f luent qua l i ty . A second area of concern with regard to s e t t l i ng pond systems was the d i f f i c u l t y of recovery and disposal of the accu­mulated prec ip i tate or sludge [ 2 ] .

A bench-scale study was undertaken by Environment Canada in 1976 and 1977 to examine the f e a s i b i l i t y of upgrading the e x i s t ­ing process technology [ 3 ] . The successful completion of the study led in ear ly 1978 to the establishment of a "Joint Govern­ment-Industry Program for the Removal of Radium-226 from Uranium Mining E f f luents " . The principal goal of the Joint Program was to develop a physical/chemical wastewater treatment process to reduce the radium-226 content of uranium mining and mi l l ing ef ­f luents . Target a c t i v i t i e s of 10 pCi/L (0.37 Bq/L) total radium-226 and 3 pCi/L (0.11 Bq/L) dissolved radium-226 were e s ­tabl ished for the program.

2. EXPERIMENTAL PROGRAM

Bench scale experiments u t i l i z i ng both batch and continuous-flow techniques were conducted at the Wastewater Technology Centre in Burl ington, Ontario. Ta i l ings basin e f f luent samples were ob­tained from an acid leach mi l l ing process; the character i s t ics are summarized in Table 1. The bench scale experiments i dent i ­f ied optimum operating conditions for the coprecipitat ion of radium with barium sulphate and for chemical coagulation and f locculat ion of the (Ba,Ra)S04 suspension.

P i l o t sca le experiments were undertaken a t the Quirke Mine of Rio Algom Limited in E l l i o t Lake, Ontario, using a mobile physical/chemical wastewater treatment plant with a nominal capacity of 23 L/min (6 US gpm)1. The objectives of the p i l o t -sca le process development experiments were to ver i fy the results of the bench scale process development t e s t s , to ident i fy s ca l e -up re lat ionships and to continue the optimization of process

1 gpm = gal/min.

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Parameter Mean Value Range No. of Samples

Total Radium-226 (pCi/L) * > 2 1 070 590 - 1 850 80 pH 2 9.4 8.8 - 10.2 160 Suspended so l ids (mg/L) 2 3.1 0.7 - 9.7 76 Calcium (mg/L) 3 617 449 - 703 15 Sul fate (mg/L) 3

3 1 340 1240 - 1 500 13 A lka l in i ty (mgCaC03/L) 92 36 - 152 14 Potassium (mg/L) 3 152 114 - 168 14 Magnesium (mg/L) 3 5.4 3 8 14 Chloride (mg/L) 3 16 13 20 14 TKN (mg N/L> 43 41 45 5

1 Approximately 90% in dissolved form (<0.45 urn). 2 Sampling period 16 October, 1979 to 15 August, 1980. 3 Sampling period 17 March, 1980 to 6 August, 1980. k Sampling period 30 July, 1980 to 6 August, 1980.

TKN = Total Kjeldahl Nitrogen.

var iab les in i t i a t ed in the laboratory . Process demonstration experiments were subsequently conducted using steady-state operating condit ions.

Two wastewater treatment processes were invest igated at p i l o t s ca l e . Both processes incorporated barium-radium copre­c ip i t a t ion in series-connected s t i r r ed tank reactors . In the c l a r i f i c a t i o n process, coprecipitat ion was followed by rapid mixing of a chemical coagulant, f locculat ion in series-connected mechanical f loccu lators and so l i d/ l i qu id separation in a c l a r i f i e r . In the f i l t r a t i o n process, barium-radium coprec ip i ­tat ion was fol lowed d i rec t ly by so l i d/ l i qu id separation using chemically-aided granular media f i l t r a t i o n .

3. RESULTS

In short term tests during the process development phase of the program, both the c l a r i f i c a t i o n and f i l t r a t i o n processes produced total radium-226 a c t i v i t i e s of less than 10 pCi/L and dissolved radium-226 a c t i v i t i e s approaching or equal to 3 pCi/L. Both processes operated at hydraulic loads equal to or greater than those employed in conventional wastewater treatment processes [ 4 ] . The c l a r i f i c a t i o n process subsequently proved to be unre l iab le during the process demonstration phase of the program. Although some operational problems were experienced,

TABLE I . TAILINGS BASIN EFFLUENT CHARACTERISTICS

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INFLUENT-

|—BARIUM CHLORIDE nj m PRECIPITATION REACTORS

SLUDGE TO DISPOSAL

-POLYMER FILTRATION AID

DUAL MEDIA FILTER

•EFFLUENT

BACKWASH

FIG. 1. Coprecipitation and filtration process for radium-226 removal.

TABLE I I . DATA BASE FOR PROCESS DESIGN

Barium dose rate 16 mg/L

Bari um

Radium

Copreci­

p i tat ion

Precipitat ion reactors : ( a l t e rnat ive systems) No. of CSTR units and Volumetric residence time

3 at 26.7 = 80 min 4 at 15.0 = 60 min 5 at 11.0 = 55 min

Precipitat ion power input 6 x 10"2kW/m3

F i l t e r aid dose rate l 0.01 mg/L

Granular

Media

F i l t r a ­

F i l t ra t ion rate (design) (maximum)

6.5 L/m2.S

9.8 L/m2-s

tion F i l t e r bed depth (anthrac i te ) (sand)

0.5 m 0.5 m

F i l t e r media e f f ec t ive s ize (anthrac i te )

(sand) 1.2 mm 0.4 mm

1 Continuous flow of high molecular weight anionic polymer

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FIG.2. Performance of the barium-radium coprecipitation system.

the f i l t r a t i o n process was demonstrated to produce an e f f luent meeting the program ob ject ives . The f i l t r a t i o n process is i l l u s t r a t e d in Figure 1. The principal design parameters are summarized in Table I I .

The barium-radium coprecipitat ion system consisted of series-connected continuous-flow s t i r r ed tank reactors (CSTR's ) . A barium chlor ide solution was added to the sulphate-bearing wastewater in the f i r s t reactor to coprecipitate radium with barium sulphate. The optimum precipitant dosage was determined to be 16 mg/L as Ba. Su f f i c ient mixing was provided by mechan­ical ag i ta tors to disperse the prec ip i tant and suspend the pre ­c i p i t a t e . The goal of the operation was to produce a dissolved radium-226 ac t i v i t y (0.45 um f i l t e r ) of 3 pCi/L, or as low as practical considering the total radium-226 target of 10 pCi/L. The reactor system employed during the process demonstration phase consisted of 5 CSTR's with a total volumetric residence time of 70 minutes. The mean dissolved radium-226 ac t i v i t y in the e f f luent of the f i f th reactor was 5 pCi/L (Figure 2 ) . The recommended coprecipitat ion systems (Table I I ) are based on the performance of the f i r s t four p i l o t sca le reactors which pro­duced a mean disso lved radium-226 ac t i v i ty of 6 pCi/L. I t is

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300-

250-

200-

150

100-1

40 -

z s

Q

20-

10-

® ® ® © ©

Z TARGET

FEB 1980

MAR APR MAY JUN JUL AUG

NOTES:

1. DEMONSTRATION PERTOO MTIATED WITH NEW MEDIA. 2. SODIUM CHLOROE WASH WITH AR SCOUR TESTED FOR

REMOVAL OF POLYMER FROM MEDIA. SOME IMPROVEMENT IN TERMNAL HEADLOSS CONDITIONS OBSERVED.

a MEDIA EXPANSION AND NTERMIXNG WERE OBSERVED UNTL THS TME. THE MEDIA WERE REMOVED FOR EXAMINATION AND CLEANING TESTS.

4. DEMONSTRATION PERIOD RESUMED WITH NEW MEDIA AND WITH NCREASED AK SCOUR DURING BACKWASH. POLYMER DOSE OPTMZATION RESULTED IN UNACCEPTABLE RADIUM ACTIVITY IN SOME RUNS.

5. RESUMPTION OF STEADY-STATE POLYMER DOSAGE. START OF PROBLEMS RELATED TO ALGAE IN THE INFLUENT AND BARIUM-RADIUM COPREOPITATION SYSTEM UPSET.

6. TERMINATION OF DEMONSTRATION PERIOD AND INITIATION OF SENSITIVITY TESTING.

FIG. 3. Performance of dual-media filter during the demonstration period.

antic ipated that equivalent performance would be achieved in f u l l - s c a l e reactors for the same wastewater, or s imi lar waste­waters , providing that the prec ip i tant dosage and the hydraulic behaviour of the reactor systems are the same.

So l id/ l iqu id separation was achieved using a constant - rate , dual-media f i l t e r with an anionic polymer (Percol 727) as a f i l t r a t i o n a i d . For approximately three months during the demon­strat ion phase of the program, the f i l t e r produced a mean total radium-226 ac t i v i ty of only 3 pCi/L a t a f i l t r a t i o n rate of 6.5 L/m^-s (9.6 US gpm/ft2) as i l l u s t r a t e d in Figure 3. The corresponding e f f luent suspended so l ids concentration was 0.4 mg/L. The resu l ts of an extended f i l t e r run are presented

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0 10 20 30 40 TWE (h)

FIG.4. Extended filter run at 6.5 L/m2-s.

in Figure 4. Furthermore, the f i l t e r demonstrated l i t t l e sens i ­t i v i t y to varying loading conditions and tended to f a i l by plugging rather than by so l ids (o r radium) breakthrough. There­fo re , the f i l t e r was considered to be very r e l i a b l e . A maximum f i l t r a t i o n rate of 9.8 L/m2-s (14.4 US gpm/ft2) was shown to be f e a s i b l e .

Scale formation on the f i l t e r media and apparatus is an operational problem associated with this process. The use of sulphuric acid in the mi l l ing process and lime addition to the t a i l i n g s promote the formation of gypsum and calcium carbonate s ca l e . The coprecipitat ion operation resu l ts in the formation of barium sulphate s ca l e . I t was shown that washing the appa­ratus with a 2% (V/V) hydrochloric or n i t r i c acid solution w i l l

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remove the sca le and ensure continued r e l i a b l e operation of the process. Acid washing necessitates the use of a c i d - r e s i s t an t materials of construction. The period between acid washes was demonstrated to be at l eas t three months.

The p i l o t scale f i l t e r consisted of a p l a s t i c column 20 cm in diameter and approximately 4 m in height. An experimental unit of that s ize w i l l predict f u l l - s c a l e performance with respect to the f i l t r a t i o n phase of the f i l t e r cyc le , but not the backwash phase [ 5 ] . I n i t i a l l y , the backwash routine used at p i l o t scale was selected to represent typical f u l l - s c a l e con­d i t i ons : a i r scour at 1.2 m3/min-m2 (4 ft3/min-ft2) in con­junction with s u b s i d i z a t i o n backwash, followed by backwash to 30% bed expansion. However, f i l t e r bed i n s t a b i l i t y (media in te r ­mixing and expansion) was experienced during the process development phase and part of the demonstration phase of the program. The bed i n s t a b i l i t y problem was associated with e r r a t i c , but general ly increasing, headloss (Figure 3 ) . This operational problem was thought to be the r e su l t of polymer and scale accumulation on the media. The a i r scour rate was i n ­creased to 6.1 m3/min-m2 (20 ft3/min-ft2) during the second part of the demonstration phase. The media i n s t a b i l i t y and headloss problems were consequently overcome, but sca le formation on the media was not ent i re ly el iminated. Therefore, i t is ant ic ipated that a s imi la r , good e f f luent qua l i ty w i l l be obtained from dual-media f i l t e r s at f u l l - s c a l e , although the backwash requi re ­ments can not be scaled-up accurately and some backwash f l e x i ­b i l i t y should be designed into f u l l - s c a l e p lants .

Bench-scale sludge character izat ion and dewatering tests were completed as part of the process development program [ 6 ] , However, p i l o t - s c a l e work was deferred pending ident i f i ca t ion of su i tab le sludge disposal options. Invest igat ions conducted by others have indicated that blending the sludge with mill t a i l i ng s would not adversely a f f ec t the s t a b i l i t y of radionuclides in the t a i l i ng s or sludge [ 7 ] .

4. FULL-SCALE

The f i r s t f u l l - s c a l e coprecipitat ion and f i l t r a t i o n process based on the design data generated at p i l o t sca le is currently being b u i l t by Rio Algom Limited in E l l i o t Lake, Ontario [ 8 ] . The Stanleigh Mine Tai l ings Eff luent Treatment Plant w i l l have a maximum capacity of 31.8 m-fymin (8 400 US gpm). The estimated capita l cost is $7.2 mi l l ion (Canadian) based on f i r s t quarter 1981 pr ices . S i te preparation began in the f a l l of 1981 with s ta r t -up operations scheduled for September and October of 1982.

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The Stanleigh mine and mill were o r i g i n a l l y operated during the 1950's. The mi l l ing process included acid leaching and ammonia prec ip i tat ion operations; the t a i l i n g s were neutra l ized with lime and discharged to a nearby lake where the so l ids se t t l ed out of the suspension. The l i qu id e f f luent was d i s ­charged without radium control into the Serpent River System. The renovated mill w i l l include the LAMIX process. The ex is t ing t a i l i n g s disposal area w i l l be used but the total lake outflow w i l l be treated in the new e f f luent treatment p lant .

The Stanleigh Mine Tai l ings Eff luent Treatment Plant con­s i s t s of two structures , a pretreatment bui lding and a f i l t e r bu i ld ing , s i tuated on a h i l l s i d e to u t i l i z e the topography for gravity flow from the t a i l i n g s basin to the point of discharge (Figure 5 ) . The pretreatment bui ld ing contains a pH adjustment tank, the coprecipitat ion reactors , the f i l t e r d i s t r ibut ion chamber and the fol lowing chemical feed systems: lime for pH adjustment, barium chlor ide and polymer. Neutra l izat ion of the in f luent w i l l be required i n i t i a l l y because the water in the ex is t ing t a i l i ng s basin is a c id i c . The f i l t e r bu i ld ing , located a t a lower e levat ion , contains seven dual-media f i l t e r s , backwashing equipment, f a c i l i t i e s for n i t r i c acid cleaning of the f i l t e r s and miscellaneous anc i l l a ry equipment. Space is provided for future i n s t a l l a t i on of one additional f i l t e r . The prec ip i ta te backwashed from the f i l t e r s w i l l be pumped back to the t a i l i ng s basin in s lurry form. The designers ant ic ipate an e f f luent qua l i ty including a mean total radium-226 ac t i v i ty of less than 10 pCi/L and a dissolved radium-226 ac t i v i ty of less than 10 pCi/L and often approaching 3 pCi/L [ 8 ] .

The deta i led design of the Stanleigh plant was based on the Joint Program resu l ts but with two notable d i f ferences : the total volumetric residence time in the coprecipitat ion reactors w i l l be 27 minutes and the average f i l t r a t i o n rate w i l l be 5.4 L/m 2-s (8.0 US gpm/ft 2 ) . Based on ava i l ab l e data, the average dissolved radium-226 ac t i v i t y in the coprecipitat ion system e f f luent w i l l not be less than 12 pCi/L. However, during the p i l o t p lant study, i t was observed that appreciable dissolved radium-226 ac t i v i t y could be removed by the f i l t e r , a t l eas t during short-term excursions from normal operating condit ions. Therefore, although the design of the Stanleigh coprecipitat ion system is less conservative than the Joint Program recommenda­t ions , both the dissolved radium-226 removal capacity of the f i l t e r s and the reduced f i l t r a t i o n rate proposed for the f u l l -scale plant should act as compensating f ac tors . A l so , the p i l o t p lant produced a total radium-226 ac t i v i ty appreciably less than the target value. Assuming that the e f f luent of the LAMIX process is not detrimental to the coprecipitat ion operation, the 10 pCi/L performance expectation for total radium-226 appears to be reasonable.

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FIG.5. Stanleigh Mine Tailings Effluent Treatment Plant.

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TABLE I I I . JOINT GOVERNMENT-INDUSTRY PROGRAM - LIST OF PARTICIPANTS

Part ic ipat ing Organization

Repre­sented

on

Contributing

Part ic ipat ing Organization

Man

agem

ent

Pan

el

Wor

kin

g G

roup

Fin

anci

al

Su

ppor

t

Pil

ot

Pla

nt

Sta

ff

Lab

ora

tory

S

ervic

es

Sit

e S

ervic

es

AMOK Limited * * Atomic Energy Control Board * * Denison Mines Limited • * * * * * Eldorado Nuclear Limited * * * * * * The E l l i o t Lake Centre * Energy, Mines and Resources Can. * * Environment Canada * * * • * Gulf Minerals Canada Limited * Key Lake Mining Corporation * * Madawaska Mines Limited * * Rio Algom Limited * * * * * *

5. CONCLUSION

A j o i n t l y managed and funded government-industry program has successfu l ly developed a t p i l o t sca le a physical/chemical t r e a t ­ment process to reduce the radium content of uranium mining and mi l l ing e f f l uents . The program target of an e f f luent containing less than 10 pCi/L total radium-226 ac t i v i ty was achieved. The f i r s t f u l l - s c a l e coprecip itat ion and f i l t r a t i o n process is currently being constructed in E l l i o t Lake, Ontario, Canada.

ACKNOWLEDGEMENTS

The part ic ipants in the Jo int Program are acknowledged in Table I I I . This paper is based in part upon the f inal report (current ly in preparat ion) on the Joint Government-Industry Program for the Removal of Radium-226 from Uranium Mining Effluents by D.W. A v e r i l l , D. Moffett , R.T. Webber, L. Whit t le , and J.A. Wood. The cooperation of Rio Algom Limited with respect to the Stanleigh p lant , and the assistance of many people in the par t i c ipat ing organizations are g ra te fu l l y acknowledged.

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REFERENCES

[ 1 ] ANON, Report of Radioactivity Sub-group to the Mining Task Force for the Development of Eff luent Guidelines and Regula­tions for the Canadian Mining Industry, Environment Canada (1974).

[ 2 ] INTERNATIONAL ATOMIC ENERGY AGENCY ( IAEA) , Management of Wastes from the Mining and Mi l l ing of Uranium and Thorium Ores, Safety Series No. 44, IAEA, Vienna (1976).

[ 3 ] WILKINSON, P., COHEN, D.B. , "The optimization of f i l t e r e d and unf i l te red 226Ra removal from uranium mining e f f l uen t s , status report (1976 - 1977)" , Proc. 226Radium Workshop, 1977, (MCCREEDY, H.M.,SMITH, W.H., Eds ) , Energy, Mines and Resources Canada Rep. ERP/MSL 80-14 (TR) , Canada (1980).

[ 4 ] AVERILL, D.W., MCCLURE, R., MOFFETT, D., WEBBER, R., Joint Government-Industry Program for the Removal of Radium-226 from Uranium Mining Ef f luents , Interim Report No 2, Environment Canada (1980) .

[ 5 ] U.S. ENVIRONMENTAL PROTECTION AGENCY, Process Design Manual for Suspended Sol ids Removal, Technology Transfer Manual EPA 625/l-75-003a (1975) .

[ 6 ] CAMPBELL, H.W., SKEAFF, J .M. , "Characterization of Ba/RaS04

sludges from uranium mining e f f l u e n t s " , paper presented a t 14th Mid-Atlantic Conference, Maryland, (1982).

[ 7 ] IEC, INTERNATIONAL ENVIRONMENTAL CONSULTANTS LIMITED, Place­ment of Radium/Barium Sludge in Tai l ings Areas, Atomic Energy Control Board Rep. INFO 0019, Canada (1980) .

[ 8 ] AQUATECHNICS CONSULTING LTD., Rio Algom Limited Project 231-Stanleigh Mine Area 761 - Tai l ings Eff luent Treatment Plant Design Report, Internal Report, Canada (1982).

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DECOMMISSIONING AND REHABILITATION TECHNOLOGY DEVELOPMENT

Page 380: Management of Wastes from Uranium Mining and

Chairman

D.H. GROELSEMA United States of America

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TAILINGS TECHNOLOGY Decommissioning and rehabilitation remedial action technology development

R.W. RAMSEY, Jr. United States Department of Energy, Washington, DC, United States of America

Abstract

TAILINGS TECHNOLOGY. DECOMMISSIONING AND REHABILITATION REMEDIAL ACTION TECHNOLOGY DEVELOPMENT.

This paper is to provide an overview of technology requirements for long-term uranium mill tailings disposal and remedial actions for existing tailings to ensure their adequate disposal. The paper examines the scientific disciplines that are the basis for the technology of uranium mill tailings stabilization and the design of barriers to control radiological exposure or environmental degradation at the location of tailings disposal. The discussion is presented as a hypothetical course of instruction at a fictitious university. Features of six mechanisms of dispersal or intrusion are examined with brief discussion of the applicable technology development for each. The paper serves as an introduction to subsequent specific technology development papers in the session.

Introduction

The unique problems related to their long-terra radioactivity require that the decommissioning or rehabilita­tion of uranium mill tailings disposal areas draw upon an unusual blend of scientific and engineering disciplines. The technology that must be developed must provide stable impedances or barriers to all forms of transport. They must be tailored to a wide range of characteristics of the tailings material, the geography of their location and the potential for instability in these characteristics as well as man-made intrusions in the long term.

In developing effective technological solutions to the problem of decommissioning or rehabilitating tailings piles for their stable, long-terra disposal, it is useful to first catalog the scientific and technical disciplines that can contribute mitigating measures and then to draw upon these for approaches to technological development. In the following discussion I have attempted this by postulating a Tailings

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Institute of Technology or "Tailings Tech" whose course of instruction leads to the education of competent engineers who are capable of designing reliable and cost effective processes and structures for the disposal of radioactive ore tailings. I then examine the various technical approaches for establishing barriers or controls that provide long-term stability. Please note that much of what I describe as fact is hypothetical and may not actually exist, however the purpose is not to report actual technological development but to suggest directions and emphasis for such development in this field.

A Hypothetical Course of Instruction in Tailings Technology

At "Tailings Tech" the prerequisite course of instruction consists of preparation in the fundamental sciences of physics and chemistry augmented with an understanding of the earth sciences-geology, ecology, etc. Special emphasis is given to the fundamental physics of nuclear decay and the properties of the various radioactive species that compose the natural decay chain. Among the fundamental courses of instruction are labora­tory work in radiation measurement and assay of radioactive materials. These include both laboratory and practical field exercises to gain experience in the gathering and interpretation of data using standardized and calibrated instruments and tech­niques.

Course work is also included in the measurement and interpretation of data for assessment of radiological health impacts from the various exposure mechanisms that are peculiar to uranium mill tailings. The concept of risk assessment and risk benefit is introduced as are various manipulations to calculate cost/benefit ratios of tailings stabilization measures.

The special chemical characteristics of the various species of uranium daughters and how they are influenced in extraction process must also be well understood. One of the first exercises is to determine the extractability and the economics associated with several advanced secondary processing techniques that have been proposed to remove radium or recover residual uranium from existing tailings and at the same time leave them in a more easily stabilized form. The possibility of converting tailings to forms suitable for disposal as roadway fill or for the construction of dams or filling and contouring of land surfaces is also assessed both technically and economically.

Special emphasis is also given to soil chemistry and hydrology as well as the fundamental ecology of soil systems and how they

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may be influenced by the chemical constituents found in processed ores. This provides the basis for understanding the first con­sideration in design of the stable long-term tailings disposal— the physical, chemical, and radiologic characterization of the tailings materials and their potential for interaction with the host systems. It also provides understanding of the features that comprise the host system or the natural environment of the disposed tailings materials. The critical elements of such characterization relate to the potentials for transport and interaction in a manner that can either directly or indirectly produce exposure to life forms that can be regarded as unacceptably damaging and hence require mitigating measures. These ultimately derive the criteria or standards for long-term stabilization to be achieved either by natural or design augmented control measures.

Natural control measures include the geographic features of the site, its remoteness from populations, its topography, geology, hydrology, and climatic factors.

The augmented control measures are the barriers that are incorporated into the tailings stabilization by design. The term "design" is used to connote that sufficient development has been accomplished to provide specification of the composi­tion, compatibility, and transport attenuation factors of barrier materials to allow their selection. At "Tailings Tech" the most developed of the techniques have been reduced to a very useful working Handbook which is constantly referred to in the engineering applications part of the course.

There are six mechanisms of transport considered in selection and design of disposal. Because of natural barriers not all of them must be discretely augmented in the tailings disposal design,yet each one requires an analysis to ensure an effective system. These are:

1. Wind borne erosion and transport. 2. Water borne erosion and transport. 3. Groundwater (surface, perched or subsaturated and

water table) dissolution and transport. 4. Noble gas emanation. 5. Intrusion by ecological agents—plants or animals. 6. Man-made intrusions either inadvertent or purposeful.

The first two are kinetic processes for which control is accomplished by barriers consisting of:

1. subgrade burial or contouring to a relief that is stable against erosion,

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2 . emplacement of materials of suitable composition and thickness or,

3. processing the tailings to consolidate them into forms that are not transportable by the normal intensity of wind or interaction with water.

They may also be augmented by the selection of the location away from potential drainage conduits and with topographic features that protect the integrity of the pile. The long-term aspects of this technology are the realm of geomorphology which is part of the advanced course of study at "Tailings Tech."

The design of barriers against dissolution and transport are taught as a combination of hydrology and physico-chemistry unique to the tailings materials. In addition to leaching by surface waters and the customary ion exchange interactions with soil materials several other geophysical and chemical phenomena are important. Transport by capillary effects with transpiration and recrystallization can be an important mechanism in a variety of conditions. Hence, it may be necessary to provide barriers above the tailings investment to serve as a block against upward mobilization by this mechanism or provide some "getter" material to retain recrystallized material in a subcover layer and pro­vide a discontinuous pathway to the surface. The normal gravity driven transport of leached materials is controlled by the selection of liner materials. These can be natural materials such as clays, useful because of their low porosity and high ion exchange capacity; impervious membranes of synthetic materials or the design of either or both with control of any water that can intrude into the tailings. Such techniques as clay grout curtains to intercept and divert the movement of groundwater or the use of very permeable materials around or under the tailings to provide a low impedance pathway for the passage of groundwater without intrusion into the tailings material is possible. At Tailing Tech, libral use is made of the "Handbook of Barrier and Liner Materials" which contain tables of the composition and attenu­ation factors and other parameters associated with a variety of tested designs.

This brings us to the consideration of that most maligned of transport phenomena, the emanation of radioactive species of noble gas. It is particularly necessary to understand the interaction of radon with the atomic scale environment where it is born and attempt to identify any possibility for influencing the in situ retention, diffusion and emanation. Among the basic considerations are the peculiar properties of anisotropic

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diffusion and streaming of radon. Various models have been developed into a general theory of radon transport that provides a model for analysis. The model however includes a number of terms that account for weak interactions, the effects of which are observed but not readily accountable. It is necessary to therefore include these as empirical factors in the equations for predicting the performance of barriers.

Despite the absence of a satisfying theory and model there has been assembled in the "Handbook of Barrier and Liner Materials" a tabulation of all known candidate emulsions, membranes, cover soils and composite soils with binders complete with half value attenuation thicknesses plotted as a function of the temperature and barometric pressure. These have developed from the efforts of several eminent laboratories who have explored the effectiveness of a complete range of potential barriers. Work continues on the development of climatic or lifetime stability factors.however, the most used design function is an extrapolation in both directions from the basic three meters of compacted clay soil covered by properly sized monolyths for kinetic transport protection.

The final element of barrier design relating to intrusion by plants, or other ecological species including man has been investigated. At "Tailings Tech" the research has been worked from both directions with somewhat inconclusive results. For example in the United States it has been found that most of the tailings sites are located in the arid climates where it is nearly impossible to establish a vegetation with sufficient vigor to contribute to the stabilization of tailings. Yet even in these locations tailings stabilization may be endangered by the intrusion of plants and biobarriers of herbicidal materials have been tested with inconclusive results. Some forms of vegetation or small animals are able to intrude to surprising depths.

The final concern is intrusion by man and this is the most difficult to provide a barrier against. If the tailings pile is an observable feature someone will want to move it and even if it can't be observed someone someday will want to build on it. This area of study is now under the newly found Department of Philosophy and Theology at Tailings Tech. The Department provides a course on institutional control beyond the horizon of governmental bodies and is taught by an ecumenical group of theologians who have the unique experience to address this problem.

I hope that you have found some benefit from this tongue-in-cheek discussion and that it is useful in considering the technological needs and opportunities of mill tailings management in spite of the obvious extrapolations I have made.

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WATER QUALITY AND HYDROLOGIC IMPACTS OF DISPOSAL OF URANIUM MILL TAILINGS BY BACKFILLING

B.M. THOMSON, R J . HEGGEN

Department of Civil Engineering,

University of New Mexico,

Albuquerque, New Mexico,

United States of America

Abstract

WATER QUALITY AND HYDROLOGIC IMPACTS OF DISPOSAL OF URANIUM MILL TAILINGS BY BACKFILLING.

Backfilling of the sand portion of spent uranium mill tailings has been practised for years in the Grants Mineral Belt of New Mexico, USA. Until recently, it has been limited to abandoned stopes requiring roof support to enable continued ore production. Recent environ­mental regulations of surface disposal make backfilling an increasingly attractive alternative for disposal of a greater fraction of the tails. This paper discusses the impacts of the backfill process on groundwater resources. Immediate and long-term hydrologic effects are evaluated. Whereas backfilling does lead to some changes in minewater flows, these changes are localized, of slight magnitude, and of short duration. In the long term, backfilling will have inconsequential impact on regional hydrology. Short- and long-term water quality impacts are considered. In general, backfill decant is contaminated with the same constituents found in normal mine wastewater, but at elevated concentrations. During the backfill process, backfill decant is returned to the surface and treated along with dewatering discharge. In the longer term, there may exist some potential for contaminants mobilized from backfill media in a flooded mine to migrate into the surrounding aquifer. It is predicted that low groundwater velocities and geochemical interactions including precipitation will together prevent any backfill-caused deterioration of regional groundwater quality.

INTRODUCTION

Back f i l l ing , the disposal in empty mine stopes of the sand fraction of t a i l i n g s generated by uranium mining and mi l l i ng , has been practiced for over a decade in the Grants Mineral Belt of northwestern New Mexico, USA. Backf i l l ing has genera l ly been limited to those mines which are located imme­d ia te ly below major aquifers where the confining layer sepa­rat ing the ore formation and the aquifer might be breached. Backf i l l ing is employed to prevent co l lapse of the stope roof and subsequent hydraulic connection with overlying aqui fers , increasing mine dewatering requirements. Currently, there are about six operating mines which practice back f i l l ing or have plans t o .

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Backf i l l ing is accomplished by returning a s lurry of t a i l i n g s sands and treated mine water from the surface into abandoned stopes. The s lurry is t yp i ca l l y 70 percent so l ids on a weight basis or 50 percent so l ids by volume. Bulkheads (timbers lined with burlap to provide drainage yet retain the sand) are constructed at each access d r i f t to retain back­f i l l . A map of a typical backf i l l s i t e showing the location of bulkheads, vert ica l shafts ( r a i s e s ) , and adjacent backf i l l is presented in Figure 1.

Present backf i l l practice is limited to disposal of the sand fraction (greater than 200 mesh). Consequently, the pro­cess is also known as s and f i l l i n g . This f ract ion typ i ca l l y accounts for roughly 70 percent of the total t a i l i n g s produc­t ion , the remainder consisting of s i l t s and c l ays , termed " s l imes" . When the slimes are included with the sand, the backf i l led material w i l l not adequately dra in , remaining in the stope as a s t ructura l l y unstable mud. Backf i l l ing only the sand fraction of the t a i l i n g s resu l ts in rapid dewatering; drainage from the f i l l is e s sent i a l l y complete in a matter of hours.

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Additional s t ab i l i z a t i on with time has been observed resu l t ing from interpar t icu la te cementation. Stopes back­f i l l e d years ago revert to a rock - l ike consistency.

To the present, back f i l l ing has been primari ly a s t ruc ­tural concern. Today, however, the mining industry is facing increasingly stringent regulations on the surface disposal of uranium mill t a i l i n g s . Consequently, there i s increasing interest in the potential application of backf i l l as a d i spo ­sal a l ternat ive for a s i gn i f i cant portion of the t a i l i n g s gen­erated. The potential advantages include less interaction of the t a i l i n g s with the biosphere, additional roof support and associated reduced subsidence, reduced mine dewatering r e ­quirements, and lower vent i lat ion requirements in operating mines. Disadvantages include higher costs and potential for groundwater contamination. This paper describes invest iga ­tions currently in progress at the University of New Mexico deal ing with the ef fects current back f i l l operations have on groundwater resources.

HYDROLOGIC EFFECTS

As potential pol lutants associated with uranium mining are in large part water borne, the hydrologic impact of back­f i l l i n g may conceivably have s ign i f icant environmental conse­quences. Such impact must be assessed at least on two l e ve l s : the immediate ef fects in and around the mine during and f o l ­lowing backf i l l operation, and the long-term ef fects in the surrounding aquifer after mining ceases.

Immediate Hydrologic Effects

An a r t i f i c i a l l y dewatered mine is r a re ly a dry environ­ment. Delayed y ie ld ( g rav i ty drainage of groundwater tempo­r a r i l y retained above the f a l l i n g water t ab l e ) and fau l t s or shafts extending r a d i a l l y into the drawdown cone sustain substantial flows along mine shaf ts . Backfi l l decant may s i g ­n i f i c an t l y increase this flow along the most d irect channel from the backf i l l s i t e to the mine sump. Such an increase i s l oca l i zed , however. From the perspective of total mine de-watering, backf i l l return is l i ke l y to be less s i gn i f i c an t , comprising less than 5 percent of total pumping requirements in mines examined to date. This increase, of course, does not r e f l e c t a greater rate of aquifer dewatering, but rather a r e ­cyc le , as backf i l l s l u r r i e s are prepared using treated mine water.

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In the backfi11-to-sump pathway, the water t rave ls in two phases: seepage through and sheet flow over the backf i l l media, and channelized open-channel flow (with l i ke ly i n f i l ­t ra t ion ) to the sump. The seepage phase, by which the back­f i l l s lur ry is dewatered, is ana ly t i ca l l y akin to that of groundwater inflow into an excavation. Ibrahim and Brutsaert [ 1 ] provide a predict ive analysis for estimating the drainage time for long, l i n ea l , horizontal excavations f i l l e d with i so t rop ic , homogeneous media. Such ca lculat ions indicate that the backf i l l wi l l dewater more than 90 percent within 10 min­utes after back f i l l ing ceases . The seepage rate from the drain face wi l l decrease in this period to less than 5 percent of the drainage rate during back f i l l i ng .

Whereas this analysis perhaps is extended here beyond i ts intended application (c lean, uniform sand has a s i gn i f i c an t l y higher hydraulic conductivity than that associated with exca­va t i ons ) , the results are roughly ver i f i ed by observation. Within 30 minutes after backf i l l ceases, outflow from the drainage face becomes n e g l i g i b l e .

This immediate flow phase can be broken into two compon­ents: surface and subsurface discharge. The f i r s t , l i ke ly a substantial portion of the t o t a l , flows as r i v l e t s over the deposited surface. Travel time is no more than minutes. For percolated f low, the second component is also rap id . Travel time may be on the order of half an hour. Near the drainage face , ve loc i t i e s may be su f f i c i en t l y high to create turbulent porous media f low, ca l l ing into question precise answers based on Darcy's Law. One general conclusion can be drawn about back f i l l hydraul ics : decant drainage is rapid compared to most other groundwater systems.

In the immediate second phase, channelized flow from the back f i l l drain face to the mine sump, backf i l l water intermin­gles with other mine seepage. A portion of this flow may r e i n f i U r a t e into the mine f l oo r . If the drainage ways are kept reasonably c lear of rubble , the backf i l l decant w i l l be in the sump within an hour as haulage d r i f t slopes within the mine are nominally 1 percent. If stope and haulage grades are f l a t , ponding may increase this detention time several f o ld .

Long-Term Hydrologic Effects

The overal l hydrologic impact of uranium mine dewatering can be large scale and long term. Drawdown may be measured in hundreds of meters over thousands of square kilometers. Whereas these hydrologic consequences of mining are substan­t i a l , the marginal long-term quantative hydrologic consequence

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of back f i l l i ng is n e g l i g i b l e . Drawdown gradients and rates w i l l not be measurably affected by back f i l l i ng .

In that backf i l l decant w i l l have d i f fe rent qua l i ty char­ac te r i s t i c s than natural groundwater, i t is necessary to hydro log ica l ly predict pathways of the decant. As long as the mine is being dewatered, the water - tab le gradient precludes any escape from the mine's cone of depression. Should the dewatering cease, however, groundwater recovery wi l l begin. After a period of tens of years water would begin passing through the backf i l l into the neighboring aqui fer . Whereas the actual flow may vary s i gn i f i c an t l y with location and time, a typical upper l imit on anticipated escape ve loc i ty would be in the order of mil l imeters per day. Given hydrologic uncer­ta int i es there may be cases where ve loc i t i e s are in the centimeters-per-day range.

Potential for rapid subsurface flow would ex ist i f deep water wel ls were placed in the aquifer near abandoned, back­f i l l e d stopes. Such a well could have high spec i f ic capacity, hydrau l ica l ly prof i t ing from the proximate, t a i l - f i l l e d l a t ­eral g a l l e r i e s . The same (or even better productiv ity ) could be achieved i f the shafts were not back f i l l ed . For water qua l i ty reasons, such well placement would be i l l - a d v i s e d in either instance.

In general , the quantitat ive management of groundwater resources is not appreciably influenced by back f i l l i ng . There are numerous cautions and tradeoffs to be weighed, but no more, and in no greater degree, than must be considered for mining without b a c k f i l l .

WATER QUALITY

A major concern about the backf i l l process is the e f fects i t w i l l have on subsurface water qua l i ty . This is of special s igni f icance in New Mexico where groundwater resources are the major source of domestic, municipal, indust r i a l , and ag r i cu l ­tural supply. Table 1 compares state groundwater standards with native groundwater qua l i ty in the Westwater Canyon Member of the Morrison Formation, the principal ore-bearing s t r a ta , and the average reported concentrations of t a i l i n g s decant from the s t a te ' s acid leach mill t a i l i n g s disposal ponds.

Most water qua l i ty problems associated with the uranium industry are due to the extensive sh i f t s in acid-base and oxidation-reduction chemistries effected by mining and mi l l ing

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Table 1. Comparison of New Mexico groundwater standards, undisturbed aquifer qua l i ty , and mill t a i l i n g s decant so lut ions . Al l concentrations in mg/L except as noted.

Constituent

As

Ba

Mo

Se

SO 4

TDS

U

V

pH (pH units)

Ra-226 (pCi/L)

Gross a radio­activity (pCi/L)

Notes:

New Mexico Groundwater Standards

0.1

1.0

0.05

600 3

1000 3

5.0

6-9 3

30

Undisturbed Aquifer

<0.005

0.13

<0.01

<0.005

37

363

<0.005

<0.010

12

160

Median Acid-Leach Mill Tailings Decant

Solution 2

1.3

0.26

0.9

0.21

29,700

39,800

15

74

1.05

70

38,000

1. Data from Perkins and Goad (1981). 2. Data compiled by Bruce Gallaher, N.M. Environmental

Improvement Division (1981). 3. Standards for human consumption. 4. Combined Ra-226 and Ra-228.

operations. As discussed by Brookins [ 2 ] , uranium deposits are associated with strongly reducing conditions near neutral pH. Figure 2 presents a summary of the acid-base and redox chemistry of uranium in the form of a pE-pH diagram where pE is the negative logarithm of the free electron ac t i v i ty . Large values of pE correspond to highly oxidizing condit ions.

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20

pE

- 5

-10

-15

. SURFACE WATER

uo 2 ( c o 3 ) ,

_i i i i i i_

1-4

1-2

10

0-8

0-6

0-4

0-2

0 0

-0-2

0-4

-0-6

0-8

Eh

6 8

PH

FIG. 2. Summary of oxidation-reduction and acid base chemistry of uranium. The figure is constructed for conditions of a dosed system, total dissolved uranium of 10~6M, total dissolved CO^ of 10~3M, and a concentration of H^iO^ of 10~XlM.

These diagrams are often referred to as Eh-pH diagrams, the di f ference being a simple scale factor [ 3 ] . For convenience both scales are included. Mine operations introduce oxidizing conditions to the strata by providing vent i lat ion for the miners, exp los ives , and extensive f racturing of the host rock. Longmire et a l . [ 4 ] have prepared pE-pH diagrams for most of the species of in te res t .

Short-Term Water Quality Effects

While the mine is in operation, water i s continual ly removed from the sumps in the lowest region of the mine. Al l water draining from the back f i l l s i t e w i l l thus eventually flow to the sumps and be pumped to the surface, treated to achieve compliance with surface water discharge standards, and discharged. Short-term water qua l i ty problems associated with back f i l l material w i l l therefore be associated with the sur­face discharge and wi l l be limited to the duration of the mine operation.

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Table 2. Results of monitoring program during backf i l l event. All units in mg/L except as noted.

Constituent Mine Water Slurry

Backmix Drainage

Commingled Water

Surface Discharge

As 0.056 0.023 0.022 0.015 0.021

Ca 219 390 - - 32.0

Fe 0.17 0.06 0.13 0.12 0.042

Mn <0.1 <0.1 <0.1 <0.1 -

Mo 46 6.0 8.9 37 8.9

N0 3(N) 6 24 28 7 <1

Se 2.6 0.91 1.8 2.8 0.17

SO 4 1680 2120 2390 1960 555

TDS 3090 3560 3800 3190 1210

U-238 101 20 74 63 1.1

V 0.81 0.27 0.49 0.55 0.075

pH (pH units) 7.3 7.3 6.6 7.5 8.2

Q ( m V n r ) 1 2 31 - 20 360

Flows inside mine estimated by use of sharp crested weirs.

Tai l ings as discharged from the mill are in a strongly acidic solution of extremely poor qua l i ty (Table 1 ) . Subse­quent reintroduction of backf i l l ed t a i l i n g s into the mine might introduce highly contaminated solutions to the subsur­face environment. There are a number of factors which mi t i ­gate this contamination. F i r s t , the sands are separated from the slimes hydraul ica l ly and much of the contamination, in ­cluding the high ac id i ty , is washed with the slimes to the disposal p i l e . Second, the s lurry amounts to a r e l a t i v e l y small fraction of the total flow seeping into the mine, t y p i ­c a l l y less than 5 percent over a 24-hour period when b a c k f i l l ­ing is in progress. F ina l ly , while the mine is in operation, v i r t u a l l y al l of the l iquid associated with the backf i l l s lurry flows back to the mine sumps and is removed with the mine inf low.

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The resu l ts of an 8-hour sampling program for a typical backf i l l event are presented in Table 2. Samples were c o l ­lected from the s lurry p ipe l ine , at the bulkhead through which the backf i l l drained, upstream and downstream from the bulk­head (normal mine drainage and commingled water, respect ive ­l y ) , and at the surface water discharge. Flows were measured by use of rectangular weirs . Note the near neutral values of pH of the s lurry and the rapid neutra l izat ion achieved in the commingled water. The high value of su l fates (SOi;) is an indirect indicator of highly oxidizing condit ions, as are the low concentrations of iron and manganese which form insoluble prec ip i tates under oxidizing conditions above pH 7.

The ef fect of the back f i l l ing on the qua l i ty of the sur ­face discharge has not been found to be s i gn i f i c an t , primari ly due to the r e l a t i v e l y small volume of water associated with the backf i l l s lurry compared to the total mine dewatering r e ­quirements. The two mines which have been monitored to date t yp i c a l l y backf i l l during two s h i f t s , or a tota l of about 12 hours per day, at a flow rate of 0.008 m 3 /s. Mine dewatering r a t e s , on the other hand, average about 10 m3/s (1 600 ga l/ min) over a 24-hour period. These observations are consistent with those reported by Perkins and Goad [ 5 ] and Longmire et a l . [ 4 ] . Furthermore, d i lut ion and treatment of the commin­gled water pumped from the mines is provided at the surface before discharge. Normal treatment consists of processes for removal of suspended so l ids and radium, and recovery of d i s ­solved uranium (Thomson and Matthews [ 6 ] ) .

Long-Term Water Quality Effects

Long-term ef fects of back f i l l ing on water qua l i ty are considered to be those ef fects occurring after f i l l i n g is t e r ­minated and drainage from the stope has ceased. While the mine continues in operation the t a i l i n g s wi l l remain p a r t i a l l y saturated, containing a mixture of the or ig ina l s lur ry water and seepage from the roof. After dewatering operations end, the stopes wi l l become saturated as the aquifer is recharged. The principal concern is whether there wi l l be contamination of the aquifer as a result of the b a c k f i l l . Potential sources of contaminants include retained s lu r ry water and leachate from the backf i l l ed sands.

I n i t i a l l y , the l iquid associated with the sand has high concentrations of su l f a te , pr imari ly due to the acid leach process used in mi l l ing the ore . So lub i l i t y ca lculat ions p re ­d ict the prec ip i tat ion of calcium ions under such conditions with the formation of gypsum (CaSOt^HaO) (Figure 3 ) . This i s consistent with observations of cementation occurring in old

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log [CcTl

- I I I i — -i • • -i

CoS0 4- 2H 20 ( S ) -

(GYPSUM) -

C a C 0 3 <s) (CALCITE)

X & / / / / / / / / / / / / / / / / y k ; \ 1 i , i J... —i 16 1

10

FIG.3. Solubility diagram of calcium for an open system with a total sulphate concentration of!0~2M, andPco of 3.3 X 10~A atm.

backf i l l ed stopes. This prec ip i tat ion has benef ic ia l conse­quences. F i r s t , i t w i l l reduce porosity and the hydraulic conductivity of the f i l l . Second, i t is l i ke ly that many con­taminants wi l l be removed from solution through the process of coprecipitat ion in the same manner that radium is removed from mine water by coprecipitat ion with barium su l fa te pr ior to discharge.

The mine wi l l f i l l with native groundwater which has a substant ia l l y d i f ferent oxidation potential ( E n ) than that of the backf i l l f l u i d . Longmire et a l . [4] have concluded from thermodynamic considerations that most contaminants w i l l p rec ip i ta te under the highly reducing conditions found in the native groundwater. Species which may remain in solution include uranium (as a carbonate complex), selenium, and manganese. Also of relevance are the reduced su l fate concen­trat ions found in the native groundwater. If the cementation i s , in f ac t , due to su l fate p rec ip i t a tes , part ia l d issolut ion of this phase may occur as the sul fate concentration drops. One of the biggest uncertainties when dealing with oxidat ion-reduction reactions is the reaction k inet ics . Thermodynamic considerations are val id for equil ibrium ca lcu la t ions . Often, however, species such as sulfur may remain in a metastable equi l ibr ium. Conditions of low En should resu l t in the f o r ­mation of e ither elemental sul fur or su l f i d e s , yet high con­centrations of sul fates remain. Sat is factory incorporation of chemical kinetics into the speciation models are d i f f i c u l t due to lack of suf f ic ient data.

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Another feature of the backf i l l system which wi l l act to l imit potential long-term contamination is interaction of the dissolved contaminants with the soi l matrix. Potential i n t e r ­actions include ion exchange, adsorption, and microbial up­take. Movement of ions through the soi l column is analogous to the movement of a solute front through a chromatograph. The part i t ioning between the l iquid and sol id phases is de ­scribed by the d is t r ibut ion coe f f i c ient which can be used to ca lcu late the retardation ve loc i ty . Thomson and Heggen [ 7 ] have investigated the interaction between contaminants and so i l s in the Grants Mineral Belt and have found that a l l species wi l l have a migration ve loc i ty of from 0.01 to 10" 5

times that of the l iquid ve loc i ty depending on the soi l type and the chemical speciat ion. At such low migration ve l oc i t i e s i t is extremely unlikely that s ign i f i cant regional contamina­tion of the formation would occur.

CONCLUSIONS

1. Though the l iquid associated with the backf i l l s lu r ry i s of genera l ly poor qua l i ty , commingling with mine water d i lutes the contaminants by at least one order of magnitude.

2. Drainage from the backf i l l flows to the mine sump and i s rap id ly pumped to the surface, t reated, and discharged without measurable short-term ef fects on aquifer qua l i ty .

3. Cementation of the backf i l led material occurs, po s s i ­b ly through the formation of su l fa te or carbonate p rec ip i ­t a t e s .

4. Long-term ef fects on aquifer qua l i ty are predicted by thermodynamic considerations to be minimal. Predictions do not include possib le kinetic l imi tat ions .

5. Due to interaction with the soi l column, long-term e f fects on aquifer qua l i ty wi l l remain loca l ized even i f pre ­c ip i ta t ion of contaminants does not occur.

ACKNOWLEDGMENTS

Joe Black of Kerr-McGee Nuclear Corporation provided invaluable assistance in sample co l l e c t i on . Financial a s s i s t ­ance has been provided by the New Mexico Energy and Minerals Department. Much of the analytical data presented was per ­formed by Kerr-McGee Nuclear Corporation.

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REFERENCES

[ 1 ] IBRAHIM, H. A . , BRUTSAERT, W., Inflow hydrographs from large unconfined aqui fers , J. I r r i g . Drain. Div . , Am. Soc. Civ. Eng. 91 (IR2) (1965) 21-38.

[ 2 ] BROOKINS, D. G., "Uranium Deposits of the Grants Mineral Be l t : Geochemical Constraints on Or ig in" , in Rocky Mountain Association of Geologists , symposium, (1977) 337-352.

[ 3 ] STUMM, W., MORGAN, J. J . , Aquatic Chemistry, 2nd Ed., Wi ley- Intersc ience, New York, (1981) 423.

[ 4 ] LONGMIRE, P. A . , HICKS, R. T . , BROOKINS, D. G., "Aqueous geochemical interactions between groundwater and uranium minestope back f i l l ing - -Grants Mineral Be l t , New Mexico: Application of Eh-pH diagrams", Uranium Mill Tai l ings Management (Proc. 4th Conf., Fort Co l l ins , CO, 1981) 389-414.

[ 5 ] PERKINS, B. L., GOAD, M. S. , Water Quality Data for Discharges from Uranium Mines and Mi l l s in New Mexico, N.M. Health and Environment Department, Santa Fe, NM (1980).

[ 6 ] THOMSON, B. M., MATTHEWS, J. R., Water and Wastewater Treatment Alternatives for the Uranium Mining Industry in New Mexico, Rep. to N.M. Envi. Imp. D iv . , Santa Fe, NM, 155 pp. (1981).

[ 7 ] THOMSON, B. M., HEGGEN, R. J . , "Contaminant transport from uranium mill t a i l i ng s in Ambrosia Lake, New Mexico, Uranium Mill Tai l ings Management (Proc. 4th Conf., Fort Co l l i n s , CO, 1981) 415-438.

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AN ECOLOGICAL APPROACH TO THE ASSESSMENT OF VEGETATION COVER ON INACTIVE URANIUM MILL TAILINGS SITES

M. KAL IN , C. CAZA

Institute for Environmental

Studies,

University of Toronto,

Toronto, Ontario,

Canada

Abstract

AN ECOLOGICAL APPROACH TO THE ASSESSMENT OF VEGETATION COVER ON INACTIVE URANIUM MILL TAILINGS SITES.

Vascular plants have been collected from abandoned or inactive uranium mill tailings in three mining areas in Canada. The collection was evaluated to determine some characteristics of vegetation development and to identify the plants which will persist on the sites. A total of 170 species were identified. Many of the species are widely distributed in North America, none have been reported as rare in any of the locations from which they were collected. Species richness was highest on Bancroft sites and lowest on Uranium City sites, though values were variable between sites. Forty-four per cent of the total number of species were found on only a single site. Only seven species occurred on more than half of the tailings sites and in all three mining areas. There was no difference between amended and unamended sites in terms of either species richness or species composition. There was no apparent relationship between species richness and either site size, site age or amendment history. The results of this survey suggest that the uranium mill tailings sites are at an early stage of colonization where the seed input from surrounding areas and the heterogeneity of the sites are factors determining species composition and species richness. The fate of an individual once it has reached the site will be determined by its ability to establish on the sites. A perennial growth habit and the ability to expand clonally are important characteristics of the species on the tailings. The species on the tailings are commonly found in a variety of habitats. Consistent with the observation that the tailings sites are at a stage of early colonization, we find that the few species widely distributed across sites are all characteristic pioneering species with wide environmental tolerances. These species included Populus tremuloides, P. balsamifera, Scirpus cyperinus, Equisetum arvense, Betula papyrifera, Achillea millefolium and Typha spp. The vegetation on the tailings is likely to be characterized by these species for a long period of time.

I N T R O D U C T I O N

In the early 1960s tailings slurries discharge ceased from many uranium operations in the Provinces of Saskatchewan and Ontario (Canada). Some of the tailings sites were abandoned at that time and have since received no amendments of any kind. Other tailings sites have been amended and revegetated and are currently maintained.

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These areas are referred to as inactive tailings. During the last two decades volunteer vegetation has colonized sites of both types. It is generally assumed that both seeded and volunteer vegetation will eventually form the basis of a self-sustaining ecosystem on the tailings [1,2]. Vegetation develops slowly in harsh environments and changes in the composition of plant associations may only be apparent over long periods of time. Identification of the vascular plants presently on the tailings sites provides information on the stage of development of vegetation on the tailings and on the composition of this vegetation in the future.

Uranium mill tailings, unlike tailings from other milling operations, contain long-lived radionuclides which will persist in the environment. Identification of persistent vegetation on the tailings is necessary for the long-term assessment of radionuclide transport from the tailings to plants growing on these wastes.

In this study vascular plants were collected from 13 inactive or abandoned tailings sites in Canada. The plant collection was evaluated by comparing tailings sites, mining areas and the composition and richness of the flora on individual sites. The objective of the investigation was to characterize the ecological processes relevant to colonization on the tailings and to identify persistent plant associations significant to the future develop­ment of vegetation on the sites.

DESCRIPTION OF STUDY AREAS Map I illustrates the locations of the three mining districts in Canada. Both the

surrounding flora and the climate of the regions will influence the vegetation colonizing tailings sites. The Bancroft tailings are located in south-central Ontario in an area of mixed deciduous-coniferous forest referred to as the Great Lakes-St. Lawrence Forest Region. The forest of this area is transitional between the boreal forest to the north and deciduous forest to the south. The Elliot Lake tailings are located in central Ontario, still within the Great Lakes-St. Lawrence Forest Region, but much closer to the southern limits of the boreal forest.

The Uranium City tailings in northern Saskatchewan are located on the north shores of Lake Athabasca. These sites are surrounded by boreal forest, a mosaic of woodlands and barren country. The boreal and mixed deciduous-coniferous forests are characterized by different tree species. The dominant trees in the Boreal Forest Region are coniferous species while there is an increasing number of deciduous trees in the Great Lakes-St. Lawrence Forest Region [3].

The climatic regimes of the three mining areas are different. The average annual precipitation is 879.8 mm for Bancroft, 926.3 nun for Elliot Lake and 354.1 mm. for Uranium City. The Uranium City area receives less total precipitation than either Ban­croft or Elliot Lake. Furthermore, approximately half of the precipitation falls as snow in northern Saskatchewan compared to about one-third for Ontario. The period avail­able for plant growth in the three areas is also different. The growing season is shortest in the Uranium City area and longest in the Bancroft area [4,5].

The physical and chemical characteristics of the tailings vary both within and between sites [6,7]. The available information is not detailed enough to relate the phy­sical and chemical characteristics of the tailings to species richness or composition on the sites. The tailings sites, however, do share some properties which are relevant to vegetation development. In all cases, the mills ground the uranium ore to a particle size of 50 percent under 200 mesh and used an acidic leaching process to extract the

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MAP 1: The location of the tailings areas investigated in this study and the distribution of the forest regions of Central Canada. Modified from Scudder, 1980 [3].

uranium oxide [8). The tailings slurries were neutralized before discharge into the tail­ings areas in all operations, with the exception of the slurries from the Gunnar mill in Uranium City. At present the Gunnar tailings are neutral, as are those in the Bancroft area. In Elliot Lake, due to the pyrite content of the ore, the tailings are acid generat­ing. Neutralization of these surfaces with lime has generally ameliorated their acidity. Information on site history and some surface characteristics relevant to the develop­ment of vegetation on tailings are summarized in Table I. Detailed descriptions for each site, in addition to selected chemical and physical characteristics of the abandoned or inactive tailings have been reported elsewhere [6,7,11,12,13].

METHODS

The 13 abandoned or inactive tailings sites surveyed in this study covered an area of approximately 320 ha (Table I). Plant collections were made during the 1979-1981 field seasons. Specimens were collected throughout these years from each site at different times of the growing season. Bancroft and Uranium City sites were smaller than Elliot Lake sites and open areas on the former facilitated collection of specimens. Dense vegetation cover in Elliot Lake, resulting from seeding with cultivated species, made it difficult to ensure the collection of all species represented by at least one indivi­dual.

The distribution of vascular plants within a tailings site was rarely homogeneous. Consequently, two sampling approaches were adopted. Site edges, or areas with hetero­geneous surfaces were sampled repeatedly to ensure specimens of all species present

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Table I . Site history and descriptions of abandoned or inact ive uranium mill t a i l i nq s u> J CO

Name of ta i l ings s i t e

Site Codes

Dry surface area 1

(ha)

Operation of t a i l ings

( a )

Year amendment in i t iated 1 *

Amendment measures

Seeding mixtures

Estimated area with vegetation

(%)

5 Comments

Bancroft Area: B 25

Madawaska B-l 16 1957-1964 1978 waste rock overburden

grass & legumes

80 -3/4 of s i t e covered, sampled only from exposed ta i l ings areas.

Auger Lake B-2 2 1957-1963 unamended - none 70 -vegetat ion belts on beaches & fores t edge.

Bicro f t Proper B-3 4 1956-1957 unamended - none 50 -bare areas in centre of s i t e

Dyno B-4 3 1957-1960 unamended - none 90 -3/4 o f s i t e wetland not sampled

E l l i o t Lake Area: E 248

Williams E-l 2 19592 1976 g lac ia l t i l l top soi l

grasses & legumes

100 - t a i l i n g s beach, cat ta i l stand

Nordic E-2 101 1957-1968 1970 neutral ization grasses & legumes

80 -roadways of waste rock on s i t e

Crotch E-3 53 1957-1964 1970 neutral ization mulching

grasses 30 -extensive bare areas, experi­mental plots with vegetation

Stanrock Main E-4 63 1958-1964 1978 neutral ization none 20 -extensive bare areas : moist areas vegetation

Olive E-5 5 1958-1959 1977 neutral ization grasses & legumes

80 - t a i l i n g s beach, cat ta i l stand

Lacnor

Uranium C i A r e a :

E-6

U

24 1957-1960 1978 neutral ization grasses & legumes

80 - roadways of waste rock on s i t e

Gunnar Main U-l 45 1955-1964 unamended - none 60 -moist areas dense vegetation, ca t ta i l stands

Langely Bay U-2 11 1959-19643 unamended - none 60 - t a i l i n g s beaches, denser vegetation

Gunnar Central U-3 12 1955-1964 unamended - none 70 -denser vegetation on forest edges

ibased on aerial photographs, f l i gh t s in 1973 for E l l i o t Lake, Bancroft 1977 and Uranium City 1976. 2 s p i l l a g e 3 [ 9 ] '•[lO] 5 estimate does not r e f l e c t % vegetation cover.

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U. Ci ty

FIG.l. Numbers of species collected in three mining areas and on each tailings site.

where collected. Larger homogeneous tailings areas, which were either barren or densely covered with seeded vegetation, were sampled by randomly placed transects covering an area proportional to the area of the site.

Voucher specimens were deposited in the vascular plant herbarium at the Univer­sity of Toronto, Department of Botany.

RESULTS A total of 170 different vascular plant species were identified on the tailings. A

complete species list is given in Table II. All of these plants have a wide geographical distribution and none of the species have been reported in the literature as rare in the locations from which they were collected [15,16,17,18,19,20]. Lower plants such as algae, bryophytes and fungal sporocarps were also present on the sites [13,21], however this investigation dealt only with vascular plants. The percentage vegetation cover by species on the tailings exhibited large variation. Some species were represented by only a few scattered individuals on a site while other species formed populations with 100 percent cover on tailings areas where they occurred.

Species richness values, or the number of species per site and per area are presented in Figure 1. The values are arranged in order of decreasing species richness. The largest number of species 123, or 76 percent of the total was collected in the Ban­croft area and on individual Bancroft sites. This was twice the number of plants col­lected in Elliot Lake and four times that found in Uranium City. The Bancroft tailings had small surface areas which had been undisturbed for a long period of time. The sites were relatively moist with extensive tailings beaches (Table I). In addition, these sites were in an area of high precipitation and had a longer growth period than either

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Table II. List of vascular plants identified on 13 uranium mill tailings sites in Canada

Abies balsamea (L.) Mill.

Acer rubrum L.

A. saccharum Ma rs h.

Achillea millefolium L. Agropyron repens (L.) Beauv.

A. sp. Gaertner

A. trachyaaulum

var. unilatevale (Cassidy) Matte.

Agrostis gigantea Roth.

A. hyemalis (Watt.) BSP

A. hyemalis

var. tenuis (Tukerman) Gleason

A. tenuis Sibth

Alnus crispus (Ait.) Pursh.

Amelanchiev spioata (Lam.) K. Koch

Anaphalis margaritacea (L.) Benth. & Hook.

Aralia nudicaulis L.

Aster junciformis Rydb.

A. simplex Willsd. si.

A. umbellatus Mill.

Beokmannia syzigaohne (Steud.) Fern.

Betula papyrifera Marsh.

Bidens cernua L.

B. tripartita L.

Bromus inevmis Leysser

Calamagrostis canadensis (Michx.) Beauv.

C. inexpansa Gray

Carex adusta Boott.

C. aquatilis Vahl.

C. brunnescens (Pers.) Poir.

C. communis Bailey

C. crawfordii Fern.

C. crinita var. gynandra (Schw.) Schw. & Torr.

Carex interior Bailey

C. merritt-femaldii Mack.

C. pseudo-cyperus L.

C. rostrata Stokes.

C. scoparia Schk.

C. stipata Muhl.

C. vulpinoidea Michx.

Cerastium vulgatum L.

Chaenorrhinum minus (L.) Lange

Chamaedaphne calyoulata (L.) Moench.

Chenopodium album L.

Chrysanthemum leucanthemum L.

Cirsium vulgare (Savi.) Ten.

Cirsium arvense (L.) Scop.

Conyza canadensis (L.) Cronq.

Danthonia spicata (L.) R. & S.

Deschampsia cespitosa (L.) Beauv.

D. flexuosa (L.) Beauv.

Dianthus armeria L.

Drosera rotundifolia L.

Dulichium arundinaceum (L.) Britt.

Eleocharis cf. o%ivacea Torr.

E. palustris (L.) R. & S.

Elymus canadensis L.

Epilobium angustifolium L.

E. ciliatum Raf.

Equisetum arvense L.

E. hymale L.

E. palustre L.

E. variegatum Schleich

Erigeron acris L.

E. phi lade Iphicus L.

Eupatorium perfoliatum L.

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Table II- List of vascular plants identified on 13 uranium mill tailings sites in Canada cont'd.

Festuoa elatior L. F. rubra L. Fragaria vesca L. F. virginiana Duchesne

Galium trifidum L. Gypsophila paniaulata L.

Hordeum jubatum L. Hieracium auranticum L. H. floribundum Wimmer. & Grab. H. pratense Taush. Hypericum perforatum L.

Junous alpinus Vi 11-J. baltiaus Wi1 Id. J. breviaaudatus (Engelm) Fern. J. bufonius L. J. effusus L. J. nodusus L. J. pelooarpus Meyer. J. tenuis Wi1 Id.

Larix larcina (DuRoi) K. Koch Ledum groenlandicum Oeder. Lepidum densiflorum Schrader Linnaea borealis L. Lotus cornioulatus L. Lyoopodium clavatum L. Lyaopus americanus Muhl. L. uniflorus Michx. Lysimachia terrestris (L.) BSP

Malaxis unifolia Michx. Medioago saliva L. Melilotus alba Desr. M. officinalis (L.) Desr. Mentha arvensis L.

Myrica gale L.

Oenothera biennis L-0. parviflora L •

Parnassia palustris L. Piaea glauca (Moench) Voss Pinus strobus L. Phalaris arundinaoeae L. Phleum pratense L. Phragmites australis (Cav.) Trin. Plantago major L. Poa eompressa L. P. pratensis L. Polygonum aviculare i L. P. cilinode Michx. P. persicaria L. Populus balsamifera L. P. grandidentata Michx. P. tremuloides Michx. Potentilla norvegica L. Prunus pennsylvanica L. P. virginiana L. Pteridium aquilinum (L.) Kuhn. Puccinellia distans (L.) Pari.

Querous rubra L.

Ztosa acicularis Lindl. Rubus sp. L. R. strigosus Michx. Rumex aoetosella L. R. erispus L. i?. mexioanus Meissr. R. oocidentalis Wats.

Salix bebbiana Sarg. 5 . discolor Muhl.

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Table II. List of vascular plants i sites in Canada cont'd.*

Salix glauaa L.

S. humilis Marsh.

S. interior Row!ee

S. luaida Muhl.

S. petiolaris Sm.

S. pyrifolia Anderss.

Sagina nodosa (L.) Fenzl.

Sarraoenia purpurea L.

Sairpus cyperinus (L.) Kunth

S. validus Vahl.

Scutellaria galericulata L.

Solidago canadensis L.

S. decwnbens

var. oreophila (Rydb.) Fern.

S. graminifolia (L.) Salisb.

S. hispida Muhl.

S. juncea Ai t.

S. nemoralis Ait.

Sonchus arvensis L.

Sparganium americanum

Spiraea latifolia (Ait.) Borkh.

S. tomentosa L.

Spiranthes cernua (L.) Rich.

S. lacera (Raf.) Raf.

S. romanzoffiana Cham.

Taraxacum officinale Weber.

Thuga occidentalis L.

Tragopogon dubius Scop.

Triadenum fraseri (Spach.) GL

Trifolium agrarium L.

T. hubridum L.

Triglochin palustre L.

Tsuga canadensis (End!.) Carr.

Tussilago farfara L.

ified on 13 uranium mill tailings

Typha angustifolia L.

T. latifolia L.

Typha spp. L.

litmus americana L.

Vaccinium sp. L.

Verbascum thapsus L.

Nomenclature follows: Gleason & Cronquist, 1963 [14] and Scoggan, 1978 [15].

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-,n=74

40 ,

3 0 .

in 0)

1 2 3 4 5 6 7 8 9 10 11 12 13 N u m b e r of S i t e s

FIG.2. Frequency distribution of species occurring on one or more tailings site. 94% of the species identified were collected from fewer than 50% of the sites.

Elliot Lake or Uranium City, both factors favouring the presence of more species on the Bancroft sites. The climatic conditions, the size of the sites and the water regimes, however, may influence species richness only to a limited extent. The species numbers of Nordic (E-2), Stanrock Main (E-4) and Gunnar Main (U- l ) , all relatively large and dry sites, were comparable to that of Bicroft Proper (B-3) and Dyno (B-4), small and extremely moist sites.

A comparison of species richness (Figure 1) and the history of the sites (Table I) indicates that the number of species on a site was not related in any apparent way to the age, the amendment history or the area of a tailings site. For example, the species rich­ness of Stanrock Main (E-4), which has been neutralized but not revegetated, was identical to that of Lacnor (E-6), which was revegetated in the same year (Table I).

In Figure 2 the presence of species has been plotted as a frequency of their occur­rence on the tailings sites. Forty-four percent of all species identified were collected from only one site. This highly skewed distribution of the species occurrences also sug­gests there is no relationship between species richness and the previously discussed parameters.

Only a small number of species were found on more than six sites. These are characteristic pioneer species or weedy species that frequently colonize waste places [14,15]. The tree species, Betula papyri/era Marsh (White birch), Populus tremuloides Michx. (Trembling aspen), and P. balsamifera L. (Balsam poplar) were generally res­tricted to dry areas on the tailings, as were the herbaceous dicots Anaphalis margaritacea (L.) Benth. & Hook. (Pearly everlasting) and Achillea millefolium L. (Common yarrow).

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7 0 _

0>

o

2 - H e r b a c e o u s D i c o t s

0,6 0 ^ a

V)

o ^ 0 <D

Xl E

l l l l l l l l l l l

5 0 3-j j/Vo^ody S p e c i e s

o 0

- 40

2 5 «

tl 11 11 11 11 tl 11 l 0

^ ° 3 0 4 - P t e r i d o phy t e s -

tfi n «-i •n fri L ti IT 1 2 3 4 1 2 3 4 5 6 1 2 3

B a n c r o f t E l l i o t L a k e u. C i t y

r-15

0

S I T E S

FIG.3. Representation by taxonomic groups on each of the 13 tailings sites expressed both as percentages and actual numbers of species. Open bars represent numbers of species, closed bars represent percentages of total numbers of species.

Agrostis gigantea Roth. (Redtop) the only commonly occurring grass species on the tail­ings was also collected in drier areas. Scirpus cyperinus (L.) Kunth (Wool-grass) and Equisetum arvense L. (Common horsetail) were found in both moist and dry areas on the tailings. Typha spp. (cattails) were collected from wet tailings areas.

In Figure 3 the plant collection has been grouped into four broad categories: her­baceous monocots (grasses, sedges and rushes), herbaceous dicots (all non-woody dicots), woody species (trees and shrubs) and pteridophytes (ferns and horsetails). Both actual numbers and percentage of the total number of species have been graphed for each category and for each site.

The range in the numbers of species within one category on the 13 tailings sites was greatest for the herbaceous dicots. There were no species from this group on Gun­nar Central (U-3) in contrast to the 41 species on Madawaska (B-l). The range in numbers was considerably smaller for the other sites. Sites in the Uranium City area had a higher percentage of herbaceous monocots, compared to Elliot Lake and Bancroft sites, but the woody species and the pteridophytes represented similar fractions of the total species richness when compared with other sites. The apparent increase in woody

1 - H e r b a c e o u s M o n o c o t s

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species on the Bancroft sites may be due to identification of all Salix (Willow) speci­mens to the species level in this area only. Accurate identification to species in the Salix genus generally requires flowering specimens. Only in the Bancroft area was it possible to obtain flowering individuals. In general, the taxonomic groups in Figure 3 were represented in similar proportions across sites and areas. Of particular interest is the observation that these proportions did not change appreciably on the revegetated sites in Elliot Lake.

Table III illustrates the distribution across the three mining areas of those plant families containing the largest numbers of species on the tailings. If presence or absence of species on the tailings is related to their ability to establish on these wastes then certain taxonomic groups may have greater representation on the tailings. In total 38 families were represented on the sites, though most contained only one or two species in an area. The examination of species richness and composition at the plant family level indicates that only a few species occurred on sites in all three mining dis­tricts.

The Compositae (the Composite Family) was the family with the largest represen­tation on the tailings. There were 30 composite species constituting 18 percent of the total number of species identified on all sites. The only composite collected in all three areas was Achillea millefolium L.

The family with the second largest number of species was the Graminae (the Grass Family). Fourteen percent (n=24) of all species identified were grasses. Although grasses were found on all the sites surveyed, a single grass species was rarely collected from more than one or two sites. The exception to this was Agrostis gigantea Roth, which was found on eight sites. This species was one of the grasses seeded in the Elliot Lake area. None of the 23 grasses were collected in all three mining areas.

The Cyperaceae (the Sedge Family) with 18 species was the third largest family on the tailings sites. Of the 18 sedges identified 13 belonged to the large and taxonomi-cally complex genus of Carex. Only three members of the genus were collected from more than one site and none were found on more than four sites. Scirpus cyperinus (L.) Kunth was the only sedge found in all three mining areas.

The remaining families in Table III, though they contained less than five percent of the total number of species in the collection, were found in all three mining areas. Within these families were the most frequently occurring pioneer or weedy species. These included the trees, Populus tremuloides Michx, P. balsamifera L, Betula papyrifera Marsh and the weedy species Equisetum arvense L, E. hyemale L. (Scouring rush) and Epilobium angustifolium L. (Fireweed).

The presence of these few species on more than half of the tailings sites and in all three mining areas may be explained by their life history characteristics and their extremely wide ecological tolerance. Species-specific life history characteristics will be of primary importance in the establishment of an individual on the tailings. Selected life history characteristics of most of the species collected on the tailings are summar­ized in Table IV. Approximately 75 percent of the plants identified on the tailings were native species. Most the introduced species are now naturalized in this country and have been extending their ranges since their introduction [16,18]. Some were seeded onto the tailings sites in vegetation programs. Another characteristic shared by most of the species found on the tailings was a perennial habit. Eighty-nine percent of all species on the sites were perennials. In addition, 58 percent of the species on the tail­ings commonly undergo clonal expansion, either by rhizomes or stolons.

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Table I I I . Families containing more than f ive percent of the total number of species or containing species in a l l three mining areas

ON

Family % of total

species

number of

species

species in

B. only

species in E.L. only

species in U.C. only

species in B. &

E.L.

species in B. &

U.C.

species in E.L. & U.C.

species in all three

areas

COMPOSITAE 18 30 14 1 3 10 2 0 1

GRAMINAE 14 24 5 4 4 7 3 1 0

CYPERACEAE 10 18 8 5 2 1 1 0 1

SAL ICACEAE 6 11 5 0 1 1 2 0 2

R0SACEAE 6 11 6 1 1 1 1 1 0

JUNCACEAE 5 8 2 0 1 3 0 2 0

CARYOPHYLLACEAE 2 4 1 2 1 0 0 0 0

LABIATAE 2 4 2 0 1 1 0 0 0

BETULACEAE 12 2 0 0 1 0 0 0 1

ONAGRACEAE 2 4 1 0 0 2 0 0 1

EQUISETACEAE 2 4 1 0 1 0 0 0 2

POLYGONACEAE 4 7 0 0 2 4 1 0 0

TYPHACEAE* *Typha spp. occurred in all three mining areas.

B. - Bancroft, Ontario. E.L. - Elliot Lake, Ontario. U.C. - Uranium City, Saskatchewan.

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Table IV. Selected character i s t ics of species col lected on 13 uranium mil l t a i l i n g s

Characteristics Number of species % of total

number of species

1. Native species 126 75

2. Introduced species (includes natural­ized species) 41 25

3. Perennial species 148 89

4. Biennial species 5 3

5. Annual species 14 8

6. Species with clonal growth (rhizomes or stolons) 92 58

7. Referenced habitats: 1

• roadsides, old fields, waste places 53 32

• sandy areas, well-drained soils. 20 12

• water edges, wet soils, marshes 35 21

• woodlands, meadows, moist soils 27 16

• bogs, peaty soils 15 9

• wide range of habitats (including most of the above) 15 9

Note: Information was unavailable for several species. 1[14,15,16,17,18,19].

In Table IV the types of habitats in which the tailings species have commonly been found off-tailings have been summarized. The species were characteristic of many habitats, ranging from waste sites, open fields, meadows and woodlands to marshes, lake shores and bogs. All of these were relatively common throughout the three min­ing areas.

DISCUSSION Species richness in natural ecosystems is influenced by a large number of interact­

ing factors. Major long-term factors include speciation and the immigration and extinc­tion of species within an area. These in turn, are related to the dynamics of popula­tions, competition, climatic regimes, soil properties and ultimately the life history

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characteristics of a species. In disturbed ecosystems, in addition to these factors, the physical and chemical characteristics of the soil resulting from disturbance strongly influence species richness.

Tailings areas are frequently treated as disturbed lands or ecosystems [22]. How­ever, it is more accurate and useful for the study of vegetation development to treat them as areas of sterile, abiotic material. Uranium mill tailings lack many of the characteristics of disturbed soils, particularly soil structure, nutrient content [1] and the remnants of former faunal and floral populations. Species richness alone, as it is influenced by many factors in natural and disturbed ecosystems, is of limited value in predicting vegetation development in these systems. On tailings however, which pos­sess different characteristics than either of these ecosystems, it is a useful indicator of early colonization by vascular plants.

Increases in species richness with the age of a disturbed site might have been expected. On lead and zinc tailings in Wisconsin and on post-fire sites in northern Ontario, such a relationship is observed for the first ten years after disturbance [23,24]. Species numbers on the uranium mill tailings sites did not vary sufficiently to suggest that species richness was indicative of changes with time on the tailings.

The uranium mill tailings areas surveyed in this study had different amendment histories, ages and surface characteristics (Table I). The similarity in species numbers on Stanrock Main (E-4) and Lacnor (E-6) which were both ameliorated in 1978, and Gunnar Main (U- l ) and Dyno (B-4), sites which have been abandoned for several decades, indicated that species richness on these sites was independent of site age, sur­face area and amendment history (Figure 1). Furthermore, changes in species richness with time were not affected by revegetation or neutralization. Similar numbers of species were found on both Nordic (E-2) and Williams (E-l ) , though areas of the former have been the object of vegetation programs since 1970, while Williams received glacial till and overburden prior to seeding in 1976 (Table I) [11].

A relationship between species richness and the geographical location of the tail­ings sites was indicated by the decrease in numbers of vascular plants from the most northerly tailings in Uranium City to the most southerly in Bancroft. However, if species richness is strongly related to geographical location then those sites in closest proximity to each other might be expected to exhibit greater similarity in species com­position than sites more distant. This was not supported by a comparison of species composition on sites both within and between areas. Twelve of the sites, for example, shared the greatest number of species with- Bancroft area sites, mainly Madawaska and Auger. Similarly, many of the families in Table III were represented by species occur­ring on only a single site within the mining area in which they were collected. These observations suggest that similarities and differences in composition were more closely related to species numbers than site location.

As Figure 2 indicates, a very small number of species (n=9) were found on more than six sites. The majority of all vascular plants collected on the tailings occurred on only one or two of the 13 sites surveyed. This highly skewed distribution of species occurrence suggests that the introduction of species onto the tailings sites is primarily a process of chance. Bauer [25], investigating early colonization of coal-mining wastes in the Cologne Lignite District (FRG), also concludes that initial plant settlement is the result of a chance combination of species.

The colonization of tailings by vegetation is dependent on the resources of the surrounding flora. Tailings sites will receive seeds and other propagules from species in

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the surrounding area. In an analysis of seed input into post-fire sites in northern Saskatchewan by Archibold [26], only 18 species were present in the wind dispersed seed population. Wind-dispersed seeds represent the greatest source of species avail­able for site colonization. The composition of the seed populations reported by Archi­bold [26] is in agreement with the frequency of herbaceous dicots, monocots, woody species and pteridophytes identified on the uranium mill tailings (Figure 3).

Kimmerer [27] reported that many of the species occurring on lead and zinc tail­ings during the first ten years of colonization are annuals. This observation differs from that on the uranium mill tailings where the majority of species on all sites were perenni­als. However, the lead and zinc tailings are located in agricultural lands which support many annual species. The observation does support the conclusion that seed input from the surroundings is an important resource for the colonization of tailings.

Although species richness is related to seed input only a few of the species intro­duced by seed are established on the sites. Seedling establishment is difficult on severe sites. It is the characteristics of the wind dispersed species that are important to suc­cessful establishment of individuals on the tailings. Clonal growth permits expansion through the lateral spread of roots and sucker production. This characteristic has been reported as important to the persistence of plants in stressed environments [28,29]. After initial establishment, the majority of the perennial species on the uranium mill tailings are able to grow clonally (Table IV).

The majority of species on the tailings are indigenous to North America and have been recorded in a variety of habitats (Table IV). However, it is of interest to note that at this time few of the species characteristic of the forests surrounding the tailings [3] are either present or well represented on the tailings sites. The presence of species from different types of habitats indicates that a wide range of environmental conditions exist on the tailings sites. Species richness and composition may also be related to the spatial heterogeneity of the tailings environment. Similar observations have been made in other environments [25,30,31]. Comparisons of species richness values on the uranium mill tailings with other harsh environments indicate that actual numbers are quite similar [23,24,31,32].

At present, the tailings areas appear to exhibit some characteristic typical of early stages of colonization by vascular plants in relatively heterogeneous environments. These studies also suggest that changes in species richness during primary colonization may not occur for decades or millennia [23,25,30].

After major environmental disturbances (such as fires or volcanic eruptions), bryophytes are usually among the first colonizers [31,32]. Sixteen terrestrial bryophytes have been identified on the 13 uranium mill tailings sites [21]. Several of these mosses covered significant areas on the tailings, particularly in the vicinity of the pioneering tree species (Trembling aspen, Balsam poplar and White birch). These bryophyte popu­lations may play an important role in the colonizing process of the sites and the long-term development of the terrestrial tailings plant community. Bryophyte carpets, as well as dense seeded grass covers on the tailings may have a significant effect on long-term changes in species richness. Vogel and Berg [33] have reported on competition between seeded herbaceous vegetation and Black Locust seedlings on coal-mine spoils in eastern Kentucky. The presence of dense ground vegetation may inhibit the establishment of other plants.

The pioneering species (trees, cattails and wool-grass) which were identified on many of the tailings sites have broad ecological tolerances and were able to establish on

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the tailings despite harsh conditions for plant growth. At present, these species do not provide a significant vegetation cover, but will likely dominate the vegetation develop­ment on the tailings for a long period of time. An evaluation of their growth and interactions with other colonizing plants (particularly bryophytes) will lead to a more comprehensive assessment of the long-term development of vegetation in the tailings environment.

ACKNOWLEDGEMENTS This work was supported by the Atomic Energy Control Board, Saskatchewan

Environment, Environment Canada and the Department of Energy, Mines & Resources Canada.

The authors wish to thank P. Stokes for her helpful comments on the manuscript, G. Brumelis and the staff of the herbarium at the University of Toronto for the identification of the plants, K. Frerot for the preparation of the manuscript and N. Chudzinski for the graphic work.

R E F E R E N C E S

[1] MURRAY, D.R., "Pit Slope Manual, Supplement 10-1 - Reclamation by Vege­tation: Vol. 1 - Mine Waste Description and Case Histories.'' CANMET Report 77-31 (1977) 120 p.

[2] MURRAY, D.R. & TURCOTTE, M., "Tree Growth Studies on Uranium Mill Tailings." CANMET, Div. Report MRP/MRL 82-19 (TR) (1982) 25 p.

[3] SCUDDER, G.G.E., "Present patterns in the fauna and flora of Canada", Canada and its Insect Fauna. Danks, H.V. (ed.). The Entomological Society of Canada, Ottawa (1980) 87.

[4] ATMOSPHERIC ENVIRONMENT SERVICE, Ontario Temperature and Pre­cipitation 1941-1970 Normals. Atmospheric Environment Service, Downsview, Ontario (1971a).

[5] ATMOSPHERIC ENVIRONMENT SERVICE, Prairie Provinces Temperature and Precipitation 1941-1970 Normals. Atmospheric Environment Service, Downsview, Ontario (1971b).

[6] KALIN, M., "Long-term Ecological Behaviour of Abandoned Uranium Mill Tailings: 1. Synoptic survey and identification of invading biota." EPS (Ottawa) Final Report (1982). In press.

[7] KALIN, M, "The Environmental Conditions of Two Abandoned Uranium Mill Tailings Sites in Northern Saskatchewan." Submitted to: Saskatchewan Environ­ment, March 1982.

[8] GRIFFITH, J.W., "The Uranium Industry - Its History, Technology and Pros­pects." Canadian Dept. Energy, Mines and Resources, Report No. 12, Ottawa, Canada (1967) 335 p.

[9] BOTSFORD, J.B., Kesmark Ltd., Willowdale, Ontario, Canada. Former Mine Manager of Gunnar Mines.

[10] RIO ALGOM LIMITED & DENISON MINES LIMITED, Elliot Lake, Ontario, Canada.

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[11] MURRAY, D.R., WEBBER, R. & LAROCQUE, E., Reclamation of the Lower Williams Lake tailings area of Denison Mines Limited. CIM Bulletin, 3 (1979) 135.

[12] KALIN, M, "A Preliminary Assessment of the Environmental Conditions of Two Abandoned Uranium Mill Tailings Sites in Saskatchewan." EPS (Saskatchewan) Report; EPS-5-WNR-81-1, May 1981.

[13] KALIN, M (ed.), "An Investigation into Selected Ecological Aspects of the Aquatic and Terrestrial Environment of an Abandoned Uranium Mill Tailings Pond, Bancroft, Ontario (Canada)." University of Toronto, Institute for Environmental Studies, Toronto, Canada, Pub. No. EE-15 (1980) 106 p.

[14] GLEASON, H.A. & CRONQUIST, A., "Manual of Vascular Plants." D. Van Nostrand Company, Toronto, Canada (1963) 810 p.

[15] SCOGGAN, H.J., "The Flora of Canada, Part 1-4." National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada. Pub. No. 7(3)/(1978) 1711 p.

[16] PORSILD, A.E. & CODY, W.J., "Vascular Plants of the Continental Northwest Territories, Canada." National Museum of Nat. Sciences, National Museums of Canada. Cat. No. MN92-71/Q979) 667 p.

[17] VOSS, E.G., "Michigan Flora. Part I: Gymnosperms and Monocots." Cranbrook Institute of Science, Michigan, USA (1972) 488 p.

[18] HUTTEN, E., "The Circumpolar Plants HI." Almquist & Wiksell, Stockholm, Sweden (1962) 738 p.

[19] DORE, W.G. & McNEILL, J., "Grasses of Ontario." Agriculture Canada, Sup­ply & Services Canada, Quebec, Canada. Monograph 26 (1980) 566 p.

[20] RAUP, H.M., "Phytogeographic studies on the Athabasca-Great Slave Lake region. J. of Arnold Arboretum, 17 (1936) 180.

[21] BRUMELIS, G., "Bryophyte Colonization of Abandoned Uranium Tailings Sites." Fourth year Thesis, Department of Botany, University of Toronto, Toronto, Ontario, Canada (1982) 31p.

[22] BRADSHAW, A.D. & CHADWICK, M.J., "The Restoration of Land: The Ecology and Reclamation of Derelict and Degraded Land." Blackwell Scientific Publications, Los Angeles, CA (1980) 317 p.

[23] KIMMERER, R.W., "Natural revegetation of abandoned lead and zinc mines (Wisconsin)." Restoration and Management Notes, I I (1981) 20.

[24] SHAFT, M.I. & YARRANTON, G.A., Diversity, fioristic richness, and species evenness during a secondary (post-fire) succession. Ecology, 54 (1973) 897.

[25] BAUER, H.J., "Ten years' studies of biocenological succession in the excavated mines of the Colonge Lignite District." Ecology and Reclamation of Devastated Lands, Vol. 1. Hutnik, R.J. & G. Davis (eds.). Gordon & Breach, Science Publications, New York, N.Y. (1973) 271.

[26] ARCHIBOLD, O.W., "Seed input into a postfire forest site in northern Saskatchewan." Can. J. For. Res. 10 (1980) 129.

[27] KIMMERER, R.W., "A quantitative study of the flora of abandoned lead and zinc mines in south-western Wisconsin." Michigan Botanist (1982). In press.

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[28] GRIME, J.P., "Plant Strategies and Vegetation Processes." John Wiley and Sons Ltd., Toronto, Canada (1979) 222 p.

[29] BRYNES, W.R. & MILLER, J.H., "Natural revegetation and cast overburden properties of surface-mined coal lands in southern Indiana," Ecology and Recla­mation of Devastated Lands, Vol. 1. Hutnik, R.J. and G. Davis (eds.). Gordon & Breach, Science Publications, New York, N.Y. (1973) 285.

[30] MORRISON, R.A. & G.A. YARRANTON. "Diversity, richness and evenness during a primary sand dune succession at Grand Bend, Ontario." Can. J. Bot., 51 (1973) 2401.

[31] EINARSSON, E., "Invasion of terrestrial plants on the new volcanic island Surt-sey," Ecology and Reclamation of Devastated Lands, Vol. 2. Hutnik, R.J. and G. Davis (eds.). Gordon & Breach, Science Publications, New York, N.Y. (1973) 253.

[32] SKUTCH, A.F., "Early stages of plant succession following forest fires." Ecol­ogy, 10 (1929) 177.

[33] VOGEL, W.G. & BERG, W.A., "Fertilizer and herbaceous cover influence establishment of direct-seeded Black Locust on coal-mine spoils." Ecology and Reclamation of Devastated Lands, Vol. I. Hutnik, R.J. and G. Davis (eds.). Gordon & Breach, Science Publications, New York, N.Y. (1973) 189.

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THE TECHNOLOGY DEVELOPMENT EFFORT OF THE URANIUM MILL TAILINGS REMEDIAL ACTIONS PROJECT

M.L. MATTHEWS United States Department

of Energy, Uranium Mill Tailings Project Office, Albuquerque, New Mexico, United States of America

Abstract

THE TECHNOLOGY DEVELOPMENT EFFORT OF THE URANIUM MILL TAILINGS REMEDIAL ACTIONS PROJECT.

A multi-facet technology development programme was initiated by the Uranium Mill Tailings Remedial Actions (UMTRA) Project Office of the United States Department of Energy (DOE) in order to develop better techniques, designs and systems for the stabilization of uranium mill tailings piles. In 1978 the United States Congress passed a law which authorized the DOE to perform remedial actions at 24 inactive uranium mill tailings piles. It was determined that a major research and development programme needed to be initiated in order to achieve a high degree of assurance that compliance with strict remedial action standards could be met. The purpose of the technology development programme is to aggressively expand the state of the art in the area of stabilization systems. Therefore, an applied research effort was undertaken to determine the characteristics, phenomena, and dynamics of the inactive tailings piles. In addition, a development effort commenced that consisted of testing advanced cover and liner systems as well as evaluating schemes to recondition the tailings.

Background

In 1978, in view of the results of radiological surveys and engineering assessments of inactive uranium mill sites located in eight western states, the Department of Energy (DOE) submitted proposed legislation to the U.S. Congress that would authorize the stabilization and control of the tailings in a safe and environ­mentally acceptable manner. As a consequence of Congressional hearings on the proposed legislation, Public Law 95-604, the "Uranium Mill Tailings Radiation Control Act of 1978," was enacted on November 8, 1978 (Figure 1). The Act authorizes the DOE to enter into cooperative agreements with the affected states and Indian tribes in order to establish assessment and remedial action programs at inactive uranium mill tailings sites.

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o DOE to enter in t o cooperat ive agreements with a f f e c t ed s ta t es and Indian t r i b e s to accomplish remedial a c t i on .

o Expressions o f i n t e r e s t t o be obtained f o r reprocessing o f t a i l i n g s .

o DOE to meet EPA standards, NRC l i cens ing cond i t i ons .

o 90/10 cost sharing between Federal Government/states, except on Indian t r i b a l lands where 100% o f costs borne by Federal Government.

o P r o j e c t has seven-year l i f e .

FIG.l. Public Law 95-604, Uranium Mill Tailings Radiation Control Act of 1978.

The Act provides for DOE solicitation of expressions of interest for reprocessing of the mill tailings to recover valuable minerals, with reprocessing to be accomplished only when it is determined to be economically feasible and consistent with remedial action. Title I of the Act further stipulates that DOE will perform the remedial actions in accordance with standards promulgated by the Environmental Protection Agency (EPA) and the licensing requirements of the Nuclear Regulatory Commission (NRC). DOE is to finance up to 90 percent of the remedial action costs, with the affected states to pay the remaining costs. In those instances where remedial actions are to be accomplished at sites on Indian tribal lands, 100 percent of the costs will be borne by the Federal Government. The Act includes a provision that DOE is to accomplish the total remedial action program within seven years of the issuance of EPA standards.

To fulfil the Congressional mandate of P.L. 95-604, the Uranium Mill Tailings Remedial Actions Project Office (UMTRA-PO) was established in October 1979 at the DOE Operations Office in Albuquerque, New Mexico. The Project Office is responsible for negotiating agreements with the states and Indian tribes, carrying out research and development programs, preparing environmental impact documentation and remedial action plans, accomplishing engineering designs, and implementing remedial actions at the sites. Sandia Laboratory has been assisting the Project Office on an interim basis until the permanent Technical Assistance Contractor (TAC) was selected through the competitive bid process. Jacobs Engineering was selected as the TAC and will be taking over all of Sandia's activities, except for the preparation of environmental documents.

The DOE has designated 24 uranium mill tailings sites in ten states as eligible for remedial actions under Public Law 95-604 (Table 1 ) . Also, as noted in Table 1, the sites were classified as being in a high, medium or low priority category,

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TABLE 1 ,'PROCESSING SITES AND PRIORITIES

State Location Processing Site Priority

Arizona Monument Valley Tuba City

•Monument Valley •Tuba City

Low Medium

Colorado Durango Grand Junction Gunnison Maybe11 Naturita Rifle Rifle Slick Rock Slick Rock

Durango Grand Junction Gunnison Maybe11 Naturita New Rifle Old Rifle Slick Rock Slick Rock

High High High Low Medium High High Low Low

Idaho Lowman Lowman Low

New Mexico Ambrosia Lake Shiprock

Ambrosia Lake •Shiprock

Medium High

North Dakota Belfield Bowman

Belfield Bowman

Low Low

Oregon Lakeview Lakeview Medium

Pennsylvania Canonsburg Canonsburg High

Texas Falls City Falls City Medium

Utah Green River Mexican Hat Salt Lake City

Green River •Mexican Hat Salt Lake City

Low Medium High

Wyoming Converse Riverton

Converse County Riverton

Low High

•Processing site on tribal lands owned by the Navajo Nation.

depending on the potential health effects of the tailings piles on the surrounding populations. Remedial actions will first commence at the high priority sites, although completion of remedial action is not required at these sites prior to initiation of remedial action at medium and low priority sites.

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Condition of the Sites

With the exception of the site at Canonsburg, Pennsylvania, all of the inactive uranium mill tailings sites that are included in the remedial action program are in the western United States. Most of the sites are located in basically dry or semi-arid environments. Thus, with the evapotranspiration conditions that exist at many of the sites, downward migration and leaking of contaminants into the underlying soil is not normally a major concern. There are instances, however, such as at Salt Lake City, where an aquifer or the water table intersects the tailings pile or is near the interface between the tailings and underlying soil. In these few cases, possible contamination of the ground water is an important consideration. Furthermore, while some of the sites are close to a river or stream with the possibility of water contamination, other sites are far from a surface water source with the result being that there is little likelihood of water contamination.

The tailings sites range from being largely uncovered and subject to continuing wind and water erosion to having vegetation well established all over the site. Some of the sites, such as Spook, Wyoming, are in very remote locations, while others, such as Salt Lake City, are in highly populated areas. In addition, tailings have been removed from many of the sites for private use, such as for construction fill for homes and businesses. The remedial action program is also responsible for the cleanup of these off-site contaminated properties.

EPA and NRC Requirements

As noted earlier, the EPA is responsible for issuing standards for the remedial action program, and the NRC will license the final disposal sites.

Under Public Law 95-604, no remedial action may begin until final cleanup standards have been promulgated. The final standards have not yet been issued. However, in order to permit remedial action to begin at contaminated off-site or vicinity properties, the EPA has issued interim standards for open lands and structures in which elevated radiation levels occur because of the presence of residual radioactive materials from a designated inactive processing site. The numerical criteria are outlined in Table 2.

The EPA has also proposed standards governing the disposal of residual radioactive materials from inactive uranium pro­cessing sites. These standards (Table 3) place limits on the amounts of certain elements and substances that may be released

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TABLE 2. EPA INTERIM STANDARDS FOR REMEDIAL ACTION CLEANUP OF OPEN LANDS AND STRUCTURES

Type of Radiation

External gamma radiation (EGR) in dwellings

Radon Daughter concentration (RDC) in dwellings (annual average)

Ra-226 concentration on open lands

Remedial Action fRAl Standard

RA required if EGR greater than 0.02 mR/h above background

RA required if RDC greater than 0.015 WL including background

RA required if Ra-226 greater than 5pCi/g

Legend

mR/h = milliroentgen per hour WL = working level, or RDC per liter of air that results

in eventual emission of 1.3 x 10^ MeV of alpha energy

pCi/g = picocuries per gram

from the final disposal site. In addition, the disposal of the radioactive material must be done in such a manner that there is a reasonable expectation that the limits in the proposed standards will be maintained for at least 1000 years. The standards impose the following limits:

1. The average annual flux of radon-222 from the surface of the site is limited to values less than 2 picocuries/meter^-second.

2. Concentrations of the elements listed in Table 3 in sources of underground drinking water are limited. Material released from a disposal site is neither to cause the concentrations of the specified elements in the drinking water to exceed the levels in Table 3 nor to result in any increase in their concentrations in water that exceeded those levels before the remedial actions. These limitations apply to underground drinking water beyond 1.0 kilometer from a disposal site that was a processing site and beyond 0.1 kilometer from a new disposal site.

3. Materials released from disposal sites should not cause an increase in the concentration of any toxic substance in any

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Element Concentration in Sources of Underground Drinking Water

Maximum permissible concentration

Element in ground water

Arsenic 0. .05 milligram/liter Barium 1. ,0 milligram/liter Cadmium 0. .01 milligram/liter Chromium 0. ,05 milligram/liter Lead 0. ,05 milligram/liter Mercury 0. ,002 milligram/liter Molybdenum 0.05 milligram/liter Nitrate nitrogen 10. ,0 milligram/liter Selenium 0. .01 milligram/liter Silver 0. ,05 milligram/liter Combined radium-226 § radium-228 5. ,0 pCi/liter Gross alpha particle activity

including radium-226 (but excluding radon and uranium) 15. ,0 pCi/liter

Uranium 10. .0 pCi/liter

Radon Flux Limit From Disposal Site

Maximum permissible radon flux emitted from residual radioactive ^ materials at the disposal site 2.0 pCi/m -second

(annual average)

Legend

pCi = picocuries m^ = square meter

surface waters. In general, "surface waters" means any bodies of water on the earth's surface that the public may traverse or enter, or from which food may be taken.

The NRC is also involved in establishing requirements for remedial actions. The NRC does not intend to issue regulations that specifically address the cleanup and disposal of residual radioactive materials at inactive uranium processing sites. Instead, certain of the rules and criteria that apply to the

TABLE 3. EPA DRAFT STANDARDS FOR TAILINGS DISPOSAL

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licensing of active uranium mills will be used by the NRC staff to the maximum extent practicable, both in deciding whether they concur with UMTRA remedial actions and in deciding whether to license an UMTRA disposal site. The following is a summary of the NRC criteria that are most applicable to the disposal of tailings and other contaminated materials from designated inactive processing sites.

1. The disposal site should be as remote from populated areas as possible.

2. Proliferation of small disposal sites should be avoided.

3. Hydrogeologic and related environmental conditions at a site should favor the isolation of contaminants from humans and the environment for thousands of years; there should be no need to rely on ongoing, active maintenance to achieve isolation.

4. The prime option for tailings disposal is placement below grade.

5 . Methods such as liners or dewatering should be employed where necessary to reduce the seepage of toxic materials into ground waters.

6. Sufficient earth cover, but not less than 3 meters, should be placed over the tailings or radioactive residues to reduce the calculated radon-222 exhalation from the tailings or wastes to not more than 2 picocuries/meter^-second.

7. A full self-sustaining vegetative cover or a rock cover should be established on the earth cover to reduce the potential for significant wind and water erosion of the earth cover. A rock cover is mandatory in arid and semi-arid regions where it is unlikely that vegetation will be fully self-sustaining.

Technology Development Program

In order to provide us with a high degree of assurance that compliance with the strict standards can be achieved, a major research and development program was initiated. The objective of this intensive research and development program is to provide concepts and techniques that are at the cutting edge of technology development. In this way, it is hoped that an advanced and improved stabilization system can be designed and constructed for the tailings. A discussion of the specific technology projects follows.

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COVERINGS TECHNOLOGY

Asphalt Emulsion S ing le Covers

Composite Covers B iobar r i e rs

Revegetat ion/Riprap

LINERS TECHNOLOGY

Liner Systems: Asphalt Clay Others

MEASUREMENTS/MONITORING

Rad io log i ca l Data Instrumentation

TAILINGS CONDITIONING/ MINERAL RECOVERY

Assay/Reprocessing Recondit ioning

GENERAL SCIENTIFIC STUDIES

Hydrology Geochemical Study

Geotechnical Study Contaminant Transport

FIG.2. Technology development programme.

As noted in Figure 2, one major part of the technology program is concerned with developing a cover system, which has the purpose of limiting the radon emanation rates while not being degraded by plant or animal intrusion or erosion. There are several activities being pursued in the covers area. An asphalt emulsion sealant of approximately 80 millimeters thickness is being studied by Battelle Pacific Northwest Laboratory (PNL) as a radon barrier. After the asphalt emulsion is applied and compacted on top of the tailings, a 0.6 - 1.0 meter layer of overburden is applied to protect the seal from ultraviolet degradation. Soil is then placed on top of the overburden. By using an admix seal of cationic asphalt emulsion and a fine aggregate such as concrete sand, an electrostatic bond is established forming a continuous membrane. The major concern regarding the use of an asphalt emulsion is its long-term stability in the light of possible subsidence, oxidation, microbial attack and freeze-thaw cycles. There have been three years of laboratory and field tests that have indicated that the asphalt emulsion can probably be an effective radon diffusion barrier. An extensive and large-scale field experiment was initiated in 1981 at the Grand Junction tailings pile to provide better answers to the questions regarding the feasibility of an asphalt emulsion cover. Different application techniques have also been tested, and the cold mix paver sealant seems to result in the best seal.

A multilayer cover system that would reduce the overall cover thickness requirement is being investigated by PNL and Rogers £ Associates. The layering sequence for this system

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consists of a coarse layer of cover material placed on top of the tailings, a wet clay layer emplaced on the coarse material, another coarse layer applied on top of the clay, and fill and topsoil emplaced onto the top coarse layer. The clay layer remains saturated due to the hydraulic barrier that is established, and the top coarse layer acts as the capillary barrier. This barrier is a layer of clean, washed rock that isolates the wet clay from the topsoil. In addition to keeping the clay layer wet, the barrier limits the upward migration of contaminants from the tailings. The moist clay acts as a radon seal and less cover thickness is required to meet the EPA radon exhalation standards. The total thickness of the cover system is approximately 1% meters as compared to the referenced three meters for an earthen cover. In addition to tests conducted in 1980, the large-scale field test at the Grand Junction tailings pile, which was mentioned earlier, includes a multilayer cover system with wet clay mixtures. Three meters of earthen cover are also being tested at the large-scale experiment with the result being that an excellent side-by-side experiment of asphalt emulsion, multilayer, and earthen covers is being performed. The earthen covers test consists of four systems that will reveal the effects of compaction, thickness and moisture content on radon exhalation. Data from this test effort will provide input into the design of radon-control cover systems.

Also, as part of the covers technology development, efforts are underway by PNL in the areas of revegetation/riprap and biobarriers. The revegetation task is concerned with schemes to revegetate the topsoil of the tailings impoundment system. The types of species, nutrient requirements, how and when to plant, the root depth, erosion potential, and long-term stability of the plants are being investigated. The riprap task is examining different possible rock covers and the interaction between plants and rocks. A modeling and optimization effort is also being pursued in this area. This work is quite important since the prevention of wind and water erosion is a critical part of any cover system. The methodology being developed will determine whether riprap or vegetation, or a combination of both, is preferred for a specific disposal site. The cost for vegeta­tion and rock cover systems will also be determined. In addition, the effect of surface stabilization treatments on moisture retention in the covered piles is being examined. While vegetation can result in a stable moisture content, the evapotranspiration from rock cover systems can cause drainage due to an evaporation reduction and an increase in moisture content. This can, in turn, result in a ground water pollution problem.

As part of the biobarriers task, the control of animal intrusion and root growth is being studied. A coarse rock layer

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would be used as an animal and possibly a plant root barrier, and a chemical in the form of pellets would prevent root intrusion into the seal. While a pellet system lasting 100 years is attainable, a 1000 year pellet system seems to be beyond our reach at this time. Thus, gravel barriers are currently being emphasized in the program. There appears to be a direct relationship between the rock size in the layers of loose rocks that are placed below the soil surface, and the size of the animals which are deterred from penetrating the radon seals.

The investigation of different liner materials is also a major element in the technology development program. This effort by PNL and Oak Ridge National Laboratory consists of evaluating the need for and effectiveness of liners and developing emplacement techniques. Accelerated aging tests of different materials have been performed, and field tests of suitable liners are underway at the Grand Junction pile. The most suitable liner materials have been determined to be natural soil, clays, and asphalt. Of the eight liner materials „iat have been tested, catalytic airblown asphalt and soil amended with 10% sodium bentonite were revealed to have superior liner characteristics. In addition, the criteria are being developed that will determine the necessity of a liner on a site-by-site basis, and the liner design parameters will also be defined.

Another significant area that is being investigated is the reprocessing/reconditioning effort. Through fiscal year 1981, ORNL had been looking at actinide separation of the tailings by nitric acid leaching. This effort was discontinued due to several problems or concerns regarding this process; i.e., it is not a heap leach process since it must be performed at high temperatures, special equipment is required, and nitrates which can cause water contamination are produced. Los Alamos National Laboratory (LANL) is investigating the immobilization or removal of the contaminants through two main activities. The main concept being studied is thermal stabilization, whereby the tailings are heated to 1200°C to radically alter the tailings structure. This sintering process forms a slag, thereby reducing the radon emanation. Mineral transformations take place, and radon reduction of up to 99% can be achieved. The slimes are turned into glass and the sands are turned into aggregate crystals. A coal-fired rotary cement kiln could be used to sinter the tailings. An economic analysis of this concept has indicated that it can be competitive at certain tailings sites where the other remedial action options consist of transporting the tailings to a new disposal site. The other LANL activity deals with sulfuric acid leaching which can remove the radionuclides and residual minerals. Substantial mineral

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recovery requires strong acids, and concentrated sulfuric acid can extract significant percentages of radium-226, barium, thorium-230, uranium, molybdenum, cobalt and vanadium.

An assay/reprocessing program is also being conducted as part of the reprocessing/reconditioning effort. The feasibility of reprocessing the tailings at 13 of the 24 sites is being investigated by means of assays, tests and economic evaluations. EPA listed elements are being identified in the tailings, and the radium concentrations beneath the piles and in the storage pond areas are being determined. Furthermore, as an adjunct of the assay test program, additional data is being gathered in support of other sections of the technology development program that will be further described below. For example, the engineer­ing properties are being determined and piezometers are being emplaced to evaluate the release mechanisms and transport phenomena of the contaminants. Sandia Laboratories, Mountain States Mineral Enterprises, Sergent Hauskins and Beckwith, and Colorado State University (CSU) are involved in these activities.

In addition, an area called general scientific studies is included as part of the technology development program. A hydrology effort has been initiated by Lawrence Berkeley Labora­tory (LBL), with assistance from CSU, to look at radionuclide release mechanisms and water table contamination. Two sites (Riverton and Maybell) will be looked at in detail, although some data will be gathered at all of the 13 sites being studied by the assay program. A hydrology model that will address contaminant mobilization mechanisms and transport rates will be developed by LBL that can be applied at all of the sites. Also, a geochemistry program is being pursued at Geochemistry and Environmental Chemistry Research, Inc. (GECR). This program is developing site specific characterization of the geochemical nature of the tailings and the site specific extent of the contamination. The program assesses the magnitude and extent of contamination at the sites, examines the mobility of contami­nants, and assesses the significance of chemical conditions and reactions which may affect the stabilization systems. The initial conclusions by GECR are that contamination is mainly upward and toward the surface for tailings piles in dry environ­ments. Thus, according to GECR, there is little need for liners at most sites, and chemical processes must be examined in order to locate suitable disposal sites. Also, as part of the general scientific studies that are being supported, a tailings stability program is underway by CSU. CSU will issue site reports that will describe the engineering properties, such as moisture, density, grain size distribution, compaction and permeability, of the tailings at all sites.

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UMTRAP Technology Steer ing Committee

Mark L. Matthews (DOE) - Chairman Paul O'Brien (SNLA) - V i ce Chairman Tom Shepherd (CSU) Vern Rogers (RAEC) Jim Hart ley (PNL) TAC Member (JE)

Task Group on Geotechnical Studies

Task Group on Containment Systems

John Nelson (CSU) - Chairman Kathy Bush (GECR) Don Diego Gonzalez (SNLA) Art White (LBL)

Jim Buelt (PNL) - Chairman Glendon Gee (PNL) - V. Chairman Peter Beedlow (PNL) Jack Cl ine (PNL) Gergely Markos (GECR)

Task Group on Spec ia l Studies O f f i c i a l Observers

Dave Dreesen (LANL) - Chairman Don Groelsema (DOE) Lew Hanchey (SNLA) George Birchard (NRC) Ed Thode (NMSU) Wi l l iam Shaf fer (NRC)

FIG.3. Technology group structure.

Finally, a measurements/monitoring effort is included in the research and development program. This work has included obtaining and evaluating data describing radiation and radio­activity levels at the sites, implementing radiological surveillance programs to provide required data before and after remedial action at all the sites, and developing models that predict radiological impacts from the storage and transpor­tation of uranium mill tailings. Also, an effort to coordinate radon and radon daughter instrumentation and measuring techniques will be vigorously pursued starting this year. While Argonne National Laboratory has been extensively involved in this program, Bendix has been designated as the measurements center and will coordinate this particular effort.

In order to better coordinate and direct the technology development program, a steering committee and task group structure have been established (see Figure 3 ) .

The Task Group on Geotechnical Studies reviews the hydrology, geochemical, mechanical stability, and contaminant migration programs. The Task Group on Special Studies covers the reprocessing and reconditioning programs. The Task Group on Containment Systems assesses the cover and liner programs.

The Task Groups on Geotechnical and Special Studies will examine and evaluate the phenomena and the dynamics that are

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present at each tailings pile. This information will be supplied to the Task Group on Containment Systems, which will determine the requirements and the possible types of cover and liner systems for each tailings site. This information will, in turn, be assessed by the Steering Committee. The committee will provide recommendations to the UMTRA Project Office regarding the preferred types of covers and/or liners for each tailings site. The Project Office will review those recommendations and provide the necessary guidance to the TAC for the TAC to develop the conceptual designs for each site. The Remedial Actions Contractor (RAC) will then use the conceptual designs to prepare preliminary and final designs for remedial action at the various tailings sites.

In this way, an effective vehicle is established for the transfer of information from the technology program to the TAC and RAC.

Summary

In order to carry out the mandate of the U.S. Congress, a remedial action project has been established. A broad-based research and development effort was initiated to develop concepts for remedial actions, and a task group structure was developed to assist the DOE in the transfer of the new technology to the performance of the remedial actions.

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THICKENED TAILINGS EXPERIMENT FOR CLOSE-OUT OF URANIUM MILL TAILINGS AT DENISON MINES LIMITED

J.L. CHAKRAVATT I , E. LaROCQUE Denison Mines limited, Elliot Lake, Ontario

D.W. READES Golder Associates, Toronto, Ontario

E.I. ROBINSKY E.I. Robinsky Associates Limited, Toronto, Ontario, Canada

Abstract

THICKENED TAILINGS EXPERIMENT FOR CLOSE-OUT OF URANIUM MILL TAILINGS AT DENISON MINES LIMITED.

As a necessary prerequisite for the development of an acceptable close-out scenario, a suitable rehabilitation programme is required which will minimize the potential adverse effects on the surrounding environment and hasten the restoration of the area. One 'close-out' alternative which is being investigated in Elliot Lake by Denison Mines is the placement of a cap of thickened tailings during the final stages of tailings deposition in currently active tailings management areas. Laboratory experiments have shown that, by discharging tailings at relatively high solids concentrations, the slope of the deposited tailings can be increased to about 5%, thereby increasing surface run-off, minimizing infiltration and providing good surface drainage for future vegetation. A programme of research with a 10 000 tonne 'mini' pile of thickened tailings to investigate the feasibility of in-situ coning and the effects of run-off, seepage flow, pyrite oxidation and evapotranspiration has been initiated, to be followed by the close-out of a tailings management area. This paper discusses the results of the laboratory testing and the geotechnical monitoring of this 'mini' pile.

1. INTRODUCTION Environmental Assessment into the Expansion

of the Elliot Lake Uranium Mines in Ontario, Canada [1] identified two concerns associated with the long-term effects of Elliot Lake tailings following their close-out: 1. Potential acid generation from the oxidation

of pyrite contained in the tailings.

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2. Possible release and migration of heavy metals and radionuclides from these tailings to the water and the air environments.

It is believed that these long-term concerns can be effectively mitigated and it is to this end that the current research is being direct­ed. One "close-out" alternative which is being investigated by Denison Mines Limited in Elliot Lake is the placement of a cap of thickened tailings [2,3] during the final stages of the placement of tai­lings in currently active tailings management areas. It might also be a viable means for closing out some of the existing inactive tailings areas.

Denison Mines' mining and milling facilities in Elliot Lake have been in continuous operation since 1957, and the capacity of the hydrometallur-gical plant is currently being increased from 6 600 tonnes per day to 13 500 tonnes per day.

Uranium is leached from the ore at elevated temperatures and high sulphuric acid concentrations [4]. Liquid solid separation combining acid wash thickening with rotary vacuum drum filtration is followed by clarification of the uranium bearing pregnant solution, purification and concentration by strong base ion exchange and final precipitation with ammonia to produce an acceptable "yellowcake" for further refining. The barren solids and ion exchange barren solution are neutralized with lime and pumped to the tailings area.

Since 1959, over 35 million tonnes of tai­lings have been discharged to the major tailings impoundment, the Denison Mines Tailings Management Area, which is approximately 2.8 km long by 1 km wide. The tailings from the mill are presently discharged as a slurry containing 35 percent solids which settle at slopes varying from about 1 percent near the point of discharge to as little as 0.3 percent near the headpond.. The tailings segregate markedly upon discharge; the coarser sand fraction being deposited nearer to the point of discharge and the finer silt-sized fraction settling out in the pond region.

Hydrogeochemical investigations [5] at opera­tionally inactive tailings sites in the area indi­cate that the chemical composition of the porewater has been substantially altered by the oxidation of pyrite in the tailings. Although the oxidation of pyrite is a complex process consisting of several

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bacterially mediated reactions, the overall result of the process in the tailings can be represented by the following expression:

2FeS 2 + 70 2 + 2H 20 = 2Fe 2 + + 4 S 0 2 ~ + 4 H +

These investigations have also revealed that the penetration of oxygen from the atmosphere into the tailings and the infiltration of precipitation and surface water is greater in the coarser frac­tion deposited close to the discharge line and that the effects of pyrite oxidation are more evident in such an area.

As a necessary pre-requisite for the deve­lopment of an "Acceptable Close-Out Scenario", a suitable rehabilitation program is required which will minimize the potential adverse effects on the surrounding environment and hasten the restoration of the area. Criteria for such a rehabilitation program include:

a) Confining the tailings solids against movement due to water or wind forces.

b) Minimizing the quantity and/or improving the water quality of seepage exiting from the area.

A two part study was proposed to assess the viability of thickened tailings as a close-out alternative at Denison Mines. The first part invol­ved laboratory tests to determine the relationship between the solids content and slope of the deposi­ted tailings. The second part consists of a 10 000 tonne "mini" tailings pile to investigate the via­bility of handling thickened tailings and to deter­mine the effects of thickening on run-off, seepage flow, pyrite oxidation and evapotranspiration. If these two stages are successful, they will be fol­lowed by close-out of a tailings management area.

2. PRINCIPLES OF THICKENED TAILINGS DISPOSAL

Thickened tailings disposal consists of dis­charging tailings with a relatively thick consis­tency such that the tailings form a cone. When tailings are thickened, segregation (in which the coarser fraction settles out near the discharge point) does not occur; instead the heavy slurry

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flows down the outside of the cone without effec­tive sorting until it stops.

Some of the possible advantages of the thic­kened tailings system in relation to the close-out of uranium tailings areas have been summarized as follows [6]:

1. Increased slopes will enhance run-off and reduce infiltration into the tailings;

2. The segregation of coarse grained and fine grained solids which occurs at lower solids contents is inhibited;

3. Dusting is minimized;

4. Erosion from run-off is reduced due to the uni­form distribution of fine particles which act as a "binder";

5. Since the thickened tailings slopes should re­main saturated due to capillary rise in the fine fraction of the tailings, both radon emana­tion and any pyrite oxidation should be reduced.

Although there are no fixed slopes for thic­kened tailings, a six percent slope has been com­monly recommended.

3. LABORATORY TESTS

The Denison Mines tailings are a relatively coarse grind with 50 percent coarser than the No. 200 sieve (Figure 1 ) . Although backfilling of selected stopes underground with the coarser sand fraction of the tailings is being contemplated, it was considered conservative to examine the feasi­bility of thickened tailings using unclassified tailings.

Laboratory deposition tests were therefore carried out in August 1978 on unclassified tailings [7] .

Initial studies confirmed that slurry behaviour (i.e. no differential settlement of the particles) predominated at concentrations above 55 to 60 per­cent solids. Deposition tests were then commenced

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with the slurry of 64.5 percent solids. As the percent solids was progressively increased above this value, the deposited slope steepened at an ever-increasing rate (Figure 2 ) . At 72 percent solids, the developed slope was 4 percent and from this point on, the slope increased very rapidly.

The laboratory results indicated that the tailings would have to be discharged at an extre­mely high percent solids (73 to 74 percent) in or­der to develop 6 percent slopes. The requirement for such a high concentration was believed prima­rily to be due to the very coarse grind of the tailings.

In addition to the laboratory tests, the dynamic strength of undisturbed samples of sand and silt sized Denison tailings was determined by cyclic triaxial undrained compression tests [8]. At 6 cycles of loading (corresponding to the design earthquake) the dynamic strength of the silt and sand tailings were similar. The dynamic strength of the tailings when thickened would be expected to be greater since the material settles at an increased density and is more consolidated at depth.

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_i <n 0 i 1 1 1 1

40 50 6 0 70 8 0 PERCENT SOLIDS BY WEIGHT

FIG.2. Laboratory deposition tests.

4. FIELD TRIALS

4.1 Design

Work on the 10 000 tonne "mini" pile commenced in 1979. The trial cone was constructed to:

1. Investigate and determine what problems might arise when attempting to implement a thickened tailings cone system in existing tailings management areas.

2. Examine the drainage, run-off and coning charac­teristics of a thickened tailings cone.

A site for construction of the trial cone was found on an operationally inactive' tailings area, some 500 m south of the Denison Hydrometallurgical Mill.

Although the laboratory tests indicated that an extremely high percent solids was required, the uranium tailings come off the secondary drum filters within the Denison mill at about 80 percent solids. Modifications were therefore carried out within the mill to isolate the tailings off one secondary drum filter. These unclassified thic­kened tailings were then pumped to the site through a 7.5 cm diameter plastic pipe.

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PLAN - CONE'B'

HO

- 0

i— D I S C H A R G E • D I S C H A R G E PIPE - T R E S T L E

C_0ONE "b" GRANULAR F I L L E M B A N K M E N T

- G R O U N D SURFACE

TT 10 mm. P.V.C. MEMBRANE SECTION X-X

FIG.3. Plan and section of 10 000 t mini pile.

The circular embankment for the cone was con­structed in 1979. It measures 100 m in diameter and incorporates a 10 mm thick PVC impermeable membrane across the base in order to simulate the condition of pouring the thickened tailings onto slimes (i.e. condition of no downward drainage).

The site was instrumented with a total of 9 twin lead piezometers along two axes of the cone and four standpipes installed at positions removed from the pour point, as shown on Figure 3.

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Following preparation of the site and adap­tations to the mill in 1979, thickened tailings were discharged to the site during three periods:

December/79 to January/80 - 2 400 dry tonnes

The experiment was restarted briefly in Novem­ber, 1981, during which part of the final cover of thickened tailings incorporating limestone and grass seed was added. However, freezing conditions prevented completion of the final cover.

Deposition of tailings has been intermittent due to mechanical breakdowns and operational prob­lems and the thickened tails field trial has not yet been completed. It is hoped that it will be possible to complete the field trial during 1982. The practical experience in handling tailings of such high solids densities has been costly but valuable. The main technical conclusions are summarized below.

Solids Density: It was intended that the tailings should be discharged to the "mini-piles" at a solids density of 70 to 75 percent. From both visual observation and gradational analyses, the thickened tailings placed during 1980 and the earlier part of 1981, were found to be segregating markedly. A more detailed examination during June, 1981 revealed that although thickened tai­lings were being discharged from the agitator over­flow at about 1 800 to 1 900 g/h (70 to 75 percent solids) they were reaching the outfall at about 1650 g/h (63 percent solids). Following modifi­cations to the pump on June 24, 1981, to minimize dilution from gland water, the solids content of the tailings discharge to the cone increased to about 1800 g/L (70 percent solids).

This increase in density was accompanied by a marked change in the visual behaviour of the tailings deposited in the cone, such that the tailings deposited near the centre of the cone appeared to be similar to the tailings deposited near the periphery.

Gradation Analyses: Representative samples have been obtained at intervals during the thic­kened tailings experiment for laboratory gradation

May/80 to June/80 June/81 to July/81

- 2 400 dry tonnes - 6 000 dry tonnes

4.2 Construction of "Mini" Pile

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6" 3" lltf V4" f

100 10 1.0 0.1 GRAIN SIZE , M M

0.01 0.001 0.0001

C O M L E SIZE

<Q0R9E|MED. 1 FINE COARSE | MED. | FINE S I T SIZE ( CLAY S U E C O M L E SIZE GRAVEL SIZE SAND SIZE FINE GRAIN EO

a) JUNE 1981 - 6 3 PERCENT SOLIDS TAILINGS SEGREGATING

3/«" 4"

10 1.0 0.1

GRAIN SIZE , M M

0.001 0.0001

COBBLE COARSE| MEO.| f lWE COARSE| MED. | FINE SILT S I Z E S I Z E GRAVEL S E E SAND S I Z E FINE GRAINED

b ) AUGUST 1981 - 70 PERCENT SOLIDS UNIFORM TAILINGS

FIG.4. Gradation analyses at varying distances from centre of cone.

analyses. These confirmed the change in deposition behaviour which occurred after June 24, 1981. Gradations along a typical radial line prior to and after June 24, 1981 are shown on Figure 4. These confirmed that increasing the solids content at the outfall to about 70 percent led to essen­tially uniform deposition within the cone.

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Slope P r o f i l e s ; Slope p r o f i l e s w e r e a l s o s u r ­v e y e d at i n t e r v a l s d u r i n g c o n s t r u c t i o n of the c o n e . D u r i n g the summer of 1 9 8 1 , the c o n e w a s s u r v e y e d w h i l e d e p o s i t i o n w a s o c c u r r i n g at a s o l i d s c o n t e n t of 65 p e r c e n t and t h e t a i l i n g s w e r e still s e g r e ­g a t i n g ; at that t i m e t h e a v e r a g e slope w a s 3 .0 p e r c e n t . A n o t h e r s u r v e y on A u g u s t 5, 1981 a f t e r a t h i n l a y e r of m o r e u n i f o r m t a i l i n g s had b e e n d e p o s i t e d o v e r t h e s e g r e g a t e d t a i l i n g s i n d i c a t e d that the a v e r a g e slope had s l i g h t l y i n c r e a s e d to about 3 . 4 percent..

P i e z o m e t r i c L e v e l s : T h e p i e z o m e t e r s and s t a n d -p i p e s i n s t a l l e d in t h e t a i l i n g s cone h a v e b e e n m o n i t o r e d r e g u l a r l y . The i n t e r m i t t e n t d e p o s i t i o n of t a i l i n g s in the cone c o m b i n e d w i t h the s e g r e ­g a t i o n w h i c h o c c u r r e d e a r l i e r on led to the f o r ­m a t i o n of a b l a n k e t of sand t a i l i n g s b e n e a t h the t h i n skin of m o r e u n i f o r m t a i l i n g s . T h i s has e f f e c t i v e l y a c t e d as an u n d e r d r a i n and the p i e z o ­m e t e r s and s t a n d p i p e s are a l w a y s d r y a f e w h o u r s after t h e c e s s a t i o n of p o u r i n g w h e n a c c e s s to the p i e z o m e t e r s can be g a i n e d a c r o s s the s u r f a c e of t h e t a i l i n g s .

C l o s e - O u t L a y e r : D u r i n g the l a t t e r p a r t of N o v e m b e r , 1 9 8 1 , a t t e m p t s w e r e m a d e to add a f i n a l layer of t h i c k e n e d t a i l i n g s c o n t a i n i n g 0 . 2 k g / t o n n e of g r a s s seed and 9 k g / t o n n e of l i m e s t o n e to o n e s e c t o r of the c o n e . H o w e v e r , t h i c k e n e d t a i l i n g s p r o d u c t i o n in the v e r y c o l d w e a t h e r w a s s u b j e c t to a large n u m b e r of b r e a k d o w n s and o n l y a few h o u r s of p r o d u c t i o n w e r e a c h i e v e d . F r o m t h e s e l i m i t e d r e s u l t s , it a p p e a r e d that m u c h of t h e l i m e s t o n e w a s w a s h e d d o w n t h e o u t s i d e of the cone w h i l e the d i s t r i b u t i o n of g r a s s seed w a s m o r e u n i f o r m .

R u n - o f f : M e a s u r e m e n t s of t h e r u n - o f f c h a r a c ­t e r i s t i c s a l o n g the s u r f a c e of t h e c o n e w i l l be m a d e t o a s s e s s the q u a n t i t y and q u a l i t y of t h e r u n - o f f . The c o n e site h a s a spillway/weir b u i l t into t h e c i r c u l a r e m b a n k m e n t e n c l o s i n g it so that m e a s u r e m e n t s of the q u a n t i t y and q u a l i t y of the o v e r a l l d r a i n a g e can be m a d e . In a d d i t i o n , an i m p e r v i o u s m e m b r a n e w i l l be i n c l u d e d at the e d g e of t h e c o n e to s e p a r a t e s u r f a c e r u n - o f f from s e e p a g e p a s s i n g into t h e c o n e .

M o n i t o r i n g of the site w i l l c o n t i n u e for a b o u t a y e a r a f t e r c o m p l e t i o n of p o u r i n g so that any c h a n g e s in the a b o v e m e a s u r e m e n t s w i t h t i m e can be n o t e d .

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5. CONCLUSIONS

A 10 000 tonne "mini" pile of thickened tailings has almost reached completion in Elliot Lake, Ontario. The field trial has supplemented the results of laboratory deposition tests and confirmed that unclassified uranium tailings from Denison Mines would have to be discharged at solids contents of about 70 percent to ensure uniform deposition in a cone over a tailings management area.

Radiological and geotechnical monitoring will continue for about a year when the first cone is completed with the addition of a final layer of thickened tailings containing grass seed and lime­stone .

The "mini" pile represents the first attempt to construct a cone of thickened uranium tailings. Further analysis will be required to assess whether thickened tailings are feasible in the close-out of uranium tailings management areas.

R E F E R E N C E S

[1] M A C L A R E N L I M I T E D , J.F., " E n v i r o n m e n t a l A s s e s s m e n t of t h e P r o p o s e d E l l i o t L a k e U r a n i u m M i n e s E x p a n s i o n " R e p o r t , V o l . 4, (1978) 1 0 - 1 t o 1 0 - 1 0 .

[2] R O B I N S K Y , E . I . , T h i c k e n e d D i s c h a r g e - A N e w A p p r o a c h to T a i l i n g s D i s p o s a l , B u l l e t i n o f t h e C a n a d i a n I n s t i t u t e of M i n i n g and M e t a l l u r g y , D e c e m b e r ( 1 9 7 5 ) .

[3] R O B I N S K Y , E . I . , " T a i l i n g s D i s p o s a l b y the T h i c k e n e d D i s c h a r g e M e t h o d for I m p r o v e d E c o n o m y a n d E n v i r o n m e n t a l C o n t r o l " , (Proc. 2nd Int. T a i l i n g s Symposium, C o l o r a d o , M i l l e r F r e e m a n P u b l i c a t i o n s I n c . , San F r a n c i s c o , 1 9 7 9 ) .

[4] L a R O C Q U E , E . , W E B B E R , R., W a s t e M a n a g e m e n t at D e n i s o n M i n e s (Proc. N E A S e m i n a r o n M a n a g e m e n t , S t a b i l i z a t i o n and E n v i r o n m e n t a l I m p a c t of U r a n i u m M i l l T a i l i n g s , A l b u q u e r q u e ; O E C D P u b l i c a t i o n s , P a r i s , 1 9 7 8 ) .

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[5] F E E N S T R A , S., B L A I R , R . D . , C H E R R Y , J.A., C H A K R A V A T T I , J.L., L a R O C Q U E , E . , I n v e s t ­i g a t i o n s of T w o I n a c t i v e T a i l i n g s A r e a s in t h e E l l i o t L a k e U r a n i u m D i s t r i c t , O n t a r i o , C a n a d a (Proc. F o u r t h S y m p o s i u m o n U r a n i u m M i l l T a i l i n g s M a n a g e m e n t , C o l o r a d o State U n i v e r s i t y P u b l i c a t i o n s , F o r t C o l l i n s , C o l o r a d o 1 9 8 1 ) .

[6] R O B I N S K Y , E . I . , "Uranium T a i l i n g s D i s p o s a l b y t h e T h i c k e n e d D i s c h a r g e S y s t e m " , N E A W o r k s h o p s o n U r a n i u m M i l l T a i l i n g s M a n a g e m e n t F o r t C o l l i n s ( 1 9 8 1 ) ; O E C D P u b l i c a t i o n s , P a r i s , 1 9 8 2 .

[7] R O B I N S K Y A S S O C I A T E S , " T h i c k e n e d T a i l i n g s D i s ­p o s a l , L a b o r a t o r y D e p o s i t i o n T e s t s , D e n i s o n M i n e s L t d . " , R e p o r t 7 8 - 4 2 5 ( 1 9 7 8 ) .

[8] S I L V E R , M . , "Cyclic S t r e n g t h P r o p e r t i e s of U n d i s t u r b e d F i n e T a i l i n g s , D e n i s o n M i n e s L t d " R e p o r t ( 1 9 8 0 ) .

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1. INTRODUCTION

Twenty-five inactive uranium mill t a i l i n g s s i tes in the United States have been designated for remedial action under the direct ion of the U.S. Department of Energy (DOE). How­ever, str ingent health and environmental standards [ 1 ] , p ro ­posed by the U.S. Environmental Protection Agency (EPA), must be met before any disposal method can be put into e f f ec t . In

* Work supported by the United States Department of Energy under Contract DE-AC06-76RL0 1830.

URANIUM MILL TAILINGS REMEDIAL ACTION PROJECT (UMTRAP) - COVER AND LINER TECHNOLOGY DEVELOPMENT PROJECT*

J.N. HARTLEY, G.W. GEE, H.D. FREEMAN,

J.F. CLINE, P.A. BEEDLOW, J.L. BUELT,

J.R. RELYEA

Battelle Pacific Northwest Laboratories,

Richland, Washington

T. TAMURA

Oak Ridge National Laboratory,

Oak Ridge, Tennessee,

United States of America

Abstract

URANIUM MILL TAILINGS REMEDIAL ACTION PROJECT (UMTRAP) - COVER AND LINER TECHNOLOGY DEVELOPMENT PROJECT.

Cover and liner systems for uranium mill tailings in the United States of America must satisfy stringent requirements regarding long-term stability, radon control, and radionuclide and hazardous chemical migration. The cover placed over a tailings pile serves three basic purposes: (1) to reduce the release of radon, (2) to prevent the intrusion of plant roots and burrowing animals into the tailings, and (3) to limit surface erosion. The liner placed under a tailings pile prevents the migration of radionuclides and hazardous chemicals to groundwater. Battelle Pacific Northwest Laboratories is developing and evaluating cover and liner systems that meet these objectives and conform to federal standards. The cover and liner technology discussed in this paper involves: (1) single and multilayer earthen cover systems, (2) asphalt emulsion radon barrier systems, (3) biobarrier systems, (4) revegetation and rock covers, and (5) asphalt, clay, and synthetic liner systems. These systems have been tested at the Grand Junction, Colorado, tailings pile, where they have been shown to effectively reduce radon releases and radionuclide and chemical migration.

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compliance, DOE's Uranium Mill Ta i l ings Remedial Action Project (UMTRAP) is developing the technology to i so la te the t a i l i n g s from the environment in the most pract ica l and economical way for each s i t e .

The UMTRAP technology includes covers and l ine r s , which must meet s t r i c t speci f icat ions on long-term s t a b i l i t y , radon exhalation (2 pCi «m -2 • s - 1 ) , and maximum permissible concentra­tions in groundwater for individual radionuclides and heavy metals. Under UMTRAP, Paci f ic Northwest Laboratory (PNL) is developing cover and l iner systems that comply with these c r i ­t e r i a . Laboratory and f i e l d tests have been conducted since 1979 to determine the ef fectiveness of:

• s ing le and multi layer earthen covers • asphalt emulsion admix seals • b iobar r ie rs • revegetation and rock covers • asphalt , c lay , and synthetic l i n e r s .

The mill t a i l i n g s p i l e at Grand Junction, Colorado, is the s i te of the f i e l d tes t ing .

In 1981, a " jo int f i e l d tes t " was conducted at Grand Junction to evaluate a l l systems simultaneously and under s imilar conditions. This paper discusses each system and sum­marizes the resu l ts of the 1981 t e s t s , a culmination of the technology developed to date.

2. COVER TECHNOLOGY STUDIES

The laboratory and f i e l d studies on the cover systems have shown that each method is e f f ec t ive in reducing radon re leases to near-background level and maintaining long- last ing s t a b i l ­i t y . The data from the jo int f i e l d test are now being used for comparative evaluations and for developing engineering s p e c i f i ­cations for remedial actions.

2.1 Earthen cover systems

The materials selected for the earthen cover systems were subsoil materials native to the Grand Junction area: Adobe c l ay , Mancos shale , and Bentonite c lay . These mater ia ls , which were selected because of their potential for reducing radon re l ease , have radon di f fusion coe f f ic ients of about 0.01 crn^/s1 at ambient moisture. Selected physical properties of these materials are l i s ted in Table I .

The four earthen covers systems (F ig . 1) consisted of: 1) 1.2 m compacted Mancos shale plus 1.8 m Adobe c lay ; 2) 1.2 m compacted Bentonite plus 1.8 m Adobe c lay; 3) 1.2 m compacted Adobe clay plus 1.8 m Adobe c lay; and 4) 3 m Adobe clay dumped

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IAEA-SM-262/39 431

TABLE I . Earthen Cover Material C h a r a c t e r i s t i c s ^ )

Sieve Maximum Dry Optimum Analysis Density(b) Mo i s tu r e^ ) Speci f ic °l° Passing

Material g/cm3 wt% Gravity 200 Mesh

Adobe Clay 1.87 13.9 2.63 85.0

Mancos Shale 1.89 12.8 — 18.7

Bentonite Clay 1.58 22.3 2.41 87.6

( a ) Data from f i e l d samples taken during cover appl icat ion. (b ) This Proctor was completed in accordance with ASTM D-698,

Proctor Moisture-Density Relationship of So i l .

T A I L I N G S

FIG. 1. Pro file of earthen co ver test plo t.

and spread. The plot area for each earthen cover test covered 580 m (30.5 m x 19.0 m).

The procedure for applying the earthen covers to the t a i l i n g s involved: (1 ) dumping the overburden and spreading i t out with a

tractor to form a 0.15 to 0.20 m l i f t (2 ) watering the cover with a d i s t r ibut ion water truck (3) compacting the l i f t with a vibratory "sheep's foot"

compactor (4 ) measuring the density and water content of the com­

pacted l i f t with a nuclear density-moisture meter. The character i s t ics of the 1.2 m of compacted materials

a f ter appl ication are summarized in Table I I . Only 80 to 93% of the maximum (Proctor ) density was achieved using 0.10 to

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Maximum Average (b)

Dry( a) Dry Optimum^ 3) Actual Average'b) Density, Density, Moisture, Moisture, % Maximum

Material g/cnr g/cnr wt% wt% Proctor Adobe Clay

(compacted) 1.87 1.50 13.9 11.9 80

(uncompacted) 1.89 1.40 13.9 6.5 75

Mancos Shale 1.89 1.75 12.8 15.8 93

Bentonite Clay 1.58 1.38 22.3 20.2 87

(a) These Proctors were completed in accordance with ASTM D-698 (Standard Proctor Test).

(b) These values were obtained with a nuclear density-moisture during cover application.

0.15 m l i f t s and 6 to 8 passes of compaction at soi l water con­tents near the optimal (Proctor ) moisture. Improving this com­paction would increase costs since smaller l i f t s would have to be applied and more compaction would be necessary.

The top 1.8 m layer of the earthen covers was applied by dumping and spreading the overburden again in 0.15 to 0.20 m l i f t s . The ambient moisture ranged from 4 to 8 wt%. No com­paction was applied other than by 23-m3 dump trucks driving over the l i f t s ; however, a r e l a t i v e l y good compaction was achieved by this method.

The data given in Table I I I indicate that thick compacted clay materials give varying resu l ts in radon reduction. Com­paction and moisture conditioning are seen to be c r i t i c a l parameters in determining the radon control by these systems. The long-term equil ibrium moisture of these conditioned clays wi l l l i k e l y decrease with time giving r i s e to increased radon f lux values. Radon f lux measurements have been made on a l l test s i tes and w i l l continue pe r iod ica l l y throughout the next 2 years .

To reduce the quantity of material used in the earthen covers, the multi layer cover system (F ig . 2) was devised to optimize the radon control properties (moisture content and compaction density) of soi l materials while minimizing the cover thickness required to achieve a predetermined, low radon f lux . The multi layer cover is a t i gh t l y compacted clay/gravel layer that is hydraul ica l ly isolated from the surface soi l by a " c ap i l l a r y ba r r i e r " composed of a 0.24-m thick l i f t of 0.03-m diameter, clean, washed rock. Typical thicknesses for the

TABLE I I . Character ist ics of Compacted Earthen Covers

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TABLE III. Radon Flux Measurements from Earthen Cover Plots Before (November 1981) and After (February 1982) Cover Placement

Average Radon Flux

Earthen Cover (pCi-m -2

Before After % Reduction

1.8 m Adobe/1.2 m Mancos Shale 605 1.7 99.8

1.8 m Adobe/1.2 m Bentonite Clay 570 13.2 97.7

1.8 m Adobe/1.2 m Compacted Adobe 371 6.2 98.3

3.0 m Adobe 209 24.7 88.2

clay/gravel layers tested at the Grand Junction field site have ranged from 0.15 to 0.36 m. The soil cover is a 1-m lift of local soil material (Adobe clay).

FIG.2. Multilayer cover system for uranium mill tailings.

Laboratory tests and diffusion modeling have shown that this system can reduce radon fluxes by as much as 99.9% if the water content in the clay layer is near saturation. When the clay layer is virtually saturated, the measured radon diffusion coefficient is near 10~6 cm 2/s [2,3].

The effectiveness of the multilayer system was evaluated in a field test that began in August 1980. A large area (1.4 x lO 3 m^) was covered by a multilayer cover system similar to that shown in Fig. 2. The average thickness of the wet clay/ gravel layer was 0.18 m. The initial radon flux from exposed tailings at this site was 618 pC i • m - 2 • s"1. After cover place­ment, the test area was monitored for surface radon flux, and water content was monitored in the soil cover material. During the first year after placement, radon flux measurements on the covered plot ranged from <0.1 to 260 pCi - i r r 2 • s"1, suggesting that an effective radon seal was not achieved at all points on the test area. Average flux reductions ranged from 93 to 99%.

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URANIUM TAILINGS

FIG.3. Asphalt emulsion radon barrier system.

In October 1981, one-half of the surface was covered with a 0.15-m thick layer of washed rock (~0.03 m d i a . ) to assess the impact of rock cover on soi l water storage. In February 1982, 4 months after placement of the rock cover, the radon f lux averaged 0.4 pCi•rrr? • s"1 on the rock covered area compared with 18.9 pCi-nr^.-s" 1 for the rest of the test area. The low f lux from the rock cover is attr ibuted to increased moisture accumulation in the soi l cover (F ig . 2 ) .

A second area (3.2 x 10 3 m^) was covered in July 1981 with four selected multi layer covers with the clay/gravel layer ranging in thickness from 0.15 to 0.40 m. The average surface radon f lux before cover application was 263 pC i •m~2• s

_ 1 . One month after cover placement the average f lux was 6.4 pC i -m-2 - s - 1 . After 6 months, the average radon f lux had increased to 23 pCi-nr^ • s" 1, suggesting that some moisture migration had occurred from the clay/gravel layer and thereby reducing the ef fectiveness of the system. Monitoring of these test s i t e s is planned to continue for the next 2 years to f o l ­low moisture migration and radon f l ux .

2.2 Asphalt emulsion radon bar r i e r system

The asphalt emulsion system (F i g . 3) consists of an 8-cm thick asphalt emulsion/aggregate admix seal that is covered with ~0.6 m of overburden. The admix sea l , which forms the radon-impermeable di f fusion ba r r i e r , is a mixture of cat ionic asphalt emulsion and an aggregate such as concrete sand. When cured, i t contains ~22 wt% asphalt and less than 1 wt% water. The overburden s t ab i l i z e s the admix seal and protects i t from UV exposure, ra in , extreme temperatures, and sudden temperature changes.

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TABLE IV. Effective Diffusion Coef f ic ients for Radon Through Asphalt Seals

Seal Description D e f f ^ 1 0 c m / s )

Asphalt Cement 0.44 to 1.5

Rubberized Asphalt 0.12 to 0.15

Laboratory Prepared Asphalt 1.6 to 31

Emulsion Admix Seals

Grand Junction Field Test 2.2 to 10

Asphalt Emulsion Admix

Seal Core Samples

Typical Earthen Cover 10 000 to 20 000

The asphalt admix seals were formulated and tested in the laboratory , where e f f ec t ive di f fusion coe f f ic ients for radon through various seal configurations were determined. Typi­c a l l y , the di f fus ion coef f ic ient was ~10 _6 cm 2/s, which showed that the seals were extremely impermeable to radon. Results of some of the tests are given in Table IV.

In addition to ongoing radon di f fusion measurements, chem­ical and physical s t a b i l i t y tests are continuing, including aqueous leaching, oxidation, and structural s t a b i l i t y t e s t s . Aqueous leaching or oxidation is not expected to degrade the seal during i t s expected l i f e (>1000 a ) . The mechanical prop­e r t i e s of the asphalt seal are more important for assessing the long-term s t a b i l i t y of the radon sea l . The seal must be able to withstand the loading and deformation that is l i ke ly to resu l t from d i f f e rent i a l s e t t l ing of the underlying t a i l i n g s . The amount of deformation wi l l depend on spec i f ic conditions and vary considerably from s i te to s i t e , but approximations can be made based on exist ing knowledge about several t a i l i n g s areas. Material characterization tests that have been con­ducted to date indicate that the mechanical properties of the admix seal are su i tab le for most conditions expected at a t a i l ­ings p i l e . However, additional f i e l d data are needed before a f ina l evaluation can be made. These data are currently being obtained from the 1980 and 1981 f i e l d tes t s .

Three years of laboratory and f i e l d test ing have demon­strated that asphalt emulsion seals are e f fect ive radon d i f ­fusion ba r r i e r s [4-6], Spec i f i c a l l y , tests using the PNL-developed radon measurement system [7] have shown that an asphalt emulsion seal can reduce radon f luxes by greater than 99.9% (<2 pCi -m-2 -s - 1 ) (Table V ) .

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TABLE V. Effectiveness of Asphalt Emulsion Radon Barrier Systems

System Description

Average Radon Flux

Bare Tailings, Above Seal, Reduction, Average Average %

Radon Flux, pCi-m c-s

1979 In-situ Asphalt Emulsion-Tailings Seal

270 47 75.5

1980 In-situ Asphalt Emulsion-Tailings Seal

410 30 96.5

1980 Asphalt Emulsion-Aggregate Admix Seal applied with Cold-mix Paver

410 1.0 99.9

1980 Hot Rubberized Asphalt Seal applied with Distribution Truck

410 6.0 99.3

1981 Asphalt Emulsion-Aggregate Admix Seal applied with Cold-mix Paver

400 7.1 99.1

The field tests have included site characterization (radon flux, radium content, density, moisture, emanation and chemical composition); site preparation (contouring, compaction); seal application and compaction; and post seal measurements. The most successful technique for applying an admix seal was a cold-mix paver, which was used exclusively during the 1981 field test. It applied an admix that contained ~22 wt% resid­ual asphalt over 0.4 ha (0.9 acres). The +73 mV cationic, medium set (CMS) asphalt emulsion, containing 63 wt% asphalt, was mixed with concrete sand to form the admix. Six weeks after the admix was applied, the seal was compacted with a vibratory roller to a thickness of ~7.6 cm.

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IAEA-SM-262/39 437

TABLE VI. Grand Junction Field Test Costs

Earthen Covers

Asphalt Cover

Multilayer Covers

Site Preparation and Maintenance, $lm^

2.50 3.20 2.50

Cover Application, 7.70 7.20 22.30

Materials, 2/m 2 16.70 16.80 32.30

Total, $/m 2

(Range) 26.90

(25.5 - 32.8) 27.20 57.10

(42.8 - 64.8)

Area Covered, m 2 2500 4900 3250

Total Cost, $ 67 200 133 200 185 600

2.3 Grand Junction field test costs

The actual costs incurred during the 1981 Grand Junction field test were compiled for all three types of cover systems (Table VI). These costs include all subcontractor costs and PNL labor costs incurred at the site. PNL costs associated with engineering and planning the field test are not included. The costs for the earthen and multilayer systems are an aver­age of the four different systems tested. The range of the costs for the different systems is also shown. The Mancos shale and Adobe clay were the least expensive earthen covers. The 15-cm gel system was the least expensive multilayer cover.

2.4 Biobarrier systems

Plant root penetration and burrowing animals can affect the stability of radon barrier systems. Consequently, the work at Grand Junction included development of biobarriers that suc­cessfully prevented plant and animal intrusions.

Although root growth can be controlled for a short term (1 to 4 years) by incorporating herbicides into or over the sealant, chemical and microbial degradation of the herbicide rapidly dilute its phytotoxicity. To overcome the problem of degradation, a polymeric/carrier phytotoxin delivery (PCD) sys­tem was developed in which polymeric pellets continuously release specified levels of an herbicide for long time periods (i.e., 100 years). The herbicide used in the PCD system is

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N O T R E A T M E N T T R E A T M E N T

FIG.4. Preventative trifluralin-treated PCD system relative to a non-treated system.

t r i f l u r a l i n which prevents root t ip ce l l d iv is ion but preserves normal plant growth above ground (F i g . 4 ) . The PCD system development and manufacture is described by Burton [ 8 , 9 ] and Cline [ 1 0 ] . The pe l l e t s were placed over a part of the asphalt and multi layer test plots at Grand Junction and are being moni­tored for long-term e f f ic iency .

The small-mammal bar r ie r was based on previous studies which showed that layers of various sized stones can prevent animal intrusions [ 1 1 ] . Spec i f i c a l l y , these studies involved a ba r r i e r made of crushed rock 2.5 to 4.0 cm in diameter, which deterred townsend ground squirrel excavations. Consequently, rocks of this diameter range were placed 0.3 to 0.6 m below the surface soi l at Grand Junction. Figure 5 i l l u s t r a t e s the design of the study p lo t . P ra i r i e dogs, which are larger than ground squ i r r e l s , were able to tunnel 15 to 18 cm into the rock b a r r i e r , suggesting a d irect re lat ionship between rock s ize and animal s ize . Larger rocks appear to be a more s u i t ­able bar r ie r for p ra i r i e dogs; however, further studies are needed to ver i fy this conclusion.

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FIG,5. Animal barrier test facility.

2.5 Revegetation and rock covers

Soil placed over a ba r r i e r provides a protective mantle i f i t i s not affected by erosion. Vegetation is an a t t rac t ive choice for control l ing erosion because i t can provide an eco­nomic sel f -renewing cover that reduces erosion by both wind and water. However, in extremely arid areas vegetation alone may not adequately s t a b i l i z e the surface. In those areas, a properly designed surface treatment of rock cover, perhaps in conjunction with vegetation, may be necessary to s t a b i l i z e the t a i l i n g s surface.

To minimize re lease of toxic mater ia ls , surface treatments must be compatible with the other components of the impoundment system. Test p lots have been establ ished to evaluate: 1) the interaction between vegetation and sea lant/bar r ie rs ; 2) the e f fects of rock covers on vegetation; 3) the ef fects of rock and vegetation on soi l moisture; and 4) the appropriateness of plant types and planting methods for various surface t r e a t ­ments. Differences in so i l s and climates in the various d i s ­posal areas require that the covers be studied under a wide range of environmental conditions. Regional evaluations of c l imate, s o i l s , and vegetation w i l l provide a means to deter ­mine whether vegetation alone is l i k e l y to s t a b i l i z e the sur ­face in view of expected erosion events or i f rock covers w i l l be needed.

Simulations of soi l moisture in the multi layer earthen cover system demonstrated that surface treatments of rock and vegetation lead to di f ferent degrees of moisture retention in the covered t a i l i n g s p i l e . For example, the evapotranspiration

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from vegetation can resu l t in a r e l a t i vey stab le moisture con­tent ( F i g . 6 ) , whereas rock covers can lead to increased mois­ture throughout the system (F ig . 7 ) . This var iat ion may improve the radon control a b i l i t y of the cover system, but i t a lso may adversely af fect the long-term s t a b i l i t y of the sys ­tem. Therefore, surface s t ab i l i z a t i on treatments must be com­pat ib l e with s i t e - s pec i f i c s o i l , vegetation, and climate conditions to control erosion while enhancing the empoundment c apab i l i t i e s of the bar r ie r systems.

3. LINER TECHNOLOGY STUDIES

One of the primary concerns for the f inal disposal of uranium mill t a i l i ng s is preventing hazardous chemicals and radioactive elements from migrating into the groundwater. Pro­posed EPA c r i t e r i a state that maximum permissible concentra­t ions of these components may not be exceeded within 100 m of newly relocated disposal s i tes for 1000 years [ 1 ] . For e x i s t ­ing t a i l i n g s p i l e s that are not to be re located, the c r i te r ion is extended to 1000 m. Paci f ic Northwest Laboratory (PNL) and Oak Ridge National Laboratory (ORNL) are developing the tech­nology to determine the need and type of l i ne r , i f required, to conform with the proposed c r i t e r i a .

As part of the l iner technology development, PNL is deve l ­oping a decision tree to be u t i l i zed by the designer of the t a i l i n g s containment system. The decision tree w i l l r e l a te the l iner and soi l evaluations being performed by PNL and ORNL with the proposed c r i t e r i a . The l iner and so i l evaluations include:

• c lay l iner and soi l interaction studies with t a i l i n g s leachates to predict their long-term moisture ba r r i e r and chemical f i l t e r i n g potential

• accelerated aging tests of asphalt and synthetic l iners to predict their moisture ba r r i e r performance over the long term

• an assessment of adapting in - s i tu grouting methods for creating a long-term moisture bar r ie r without relocating the t a i l i ng s p i l e .

3.1 Decision tree

The decision t ree , as shown in Fig. 8, is a step-by-step guide developed to aid in deciding whether or not a l iner is required below the t a i l i ng s p i l e at a par t icu la r s i t e . The f i r s t step is to characterize the hydrology and soi l around and under the proposed disposal s i t e . This step provides data needed to set up and run a computer model that predicts ground­water and contaminant movement at the s i t e . Next, the computer

Page 455: Management of Wastes from Uranium Mining and

0 0.10 0.20 0.30 0.40

VOLUMETRIC MOISTURE CONTENT

FIG.6. Volumetric moisture content without rock cover.

0 0.10 0.20 0.30 0.40

VOLUMETRIC MO ISTURE CONTENT

FIG. 7. Volumetric moisture content with rock cover.

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I HAS THE SITE

BEEN CHARAC­TERIZED

NO ^ CHARACTERIZE HAS THE SITE BEEN CHARAC­

TERIZED W THE SITE

YES 1

IS THE WATER TABLE BELOW NO

THE PIT BOTTOM

YES

DOES WATER FROM PIT STAY

WITHIN THE SITE BOUNDARY

ARE RETARDED CONTAMINANT

CONCENTRATIONS BELOW THE EPA

CRITERIA

DOES WATER FROM A LINED

PIT STAY WITHIN THE

SITE BOUNDARY

NO ARE RETARDED CONTAMINANT

CONCENTRATIONS FROM A LINED PIT BELOW EPA

CRITERIA

NO REDESIGN OR CONSIDER AN ALTERNATE

SITE

YES YES

USE AN UNLINED PIT

YES YES

USE A LINER IN THE DISPOSAL

PIT

FIGS. Liner decision tree.

Page 457: Management of Wastes from Uranium Mining and

model is used to predict the movement of water from the t a i l ­ings p i l e without a l i ne r . If water does not move as far as the 100-m s i t e boundary, contaminants from the t a i l i ng s would have no mechanism for transport outside the boundary, and the disposal s i t e would meet the c r i t e r i a without a l i ne r .

Step 3 of the decision tree is required only i f leachate from the t a i l i n g s is found to travel beyond the s i t e boundary. In this case, chemical interactions within the underlying and surrounding s o i l , determined by the so i l/ leachate interaction studies , are considered while predicting contaminant concentra­tions in water that leaves the s i t e boundary. If predicted contaminant concentrations at the s i te boundary are below the maximum permissible concentrations for the time period defined by the EPA c r i t e r i a , the s i t e s a t i s f i e s the requirements and a l iner is not required.

I f the s i t e f a i l s to meet the contaminant c r i t e r i a even when interactions with surrounding s o i l s have been considered, the evaluation must proceed to include the character i s t ics of l iner mater ia ls . In Step 4, a l iner material and l iner design are se lected. The hydrologic model is then altered to include the long-term permeabil ity of the proposed l iner determined in the l i ne r evaluation studies in addition to the hydraulic prop­e r t i e s and chemical interactions with the surrounding s o i l s . The a ltered hydrologic model is used to predict water and con­taminant movement as in Step 3, and a decision can be made as to whether or not the l ined s i t e s a t i s f i e s the EPA spec i f i c a ­t ions . This step may be repeated several times for comparison of the ef fect iveness of d i f fe rent l iner materials and/or l iner designs.

If the s i t e s t i l l f a i l s to meet the standards, the contam­inant retarding c apab i l i t i e s of various l i n e r s , a lso determined in the l ine r studies , must be added to the computer model in Step 5 of the decision t ree . This procedure ensures that the most technolog ica l ly acceptable and economical containment sys ­tem design w i l l be incorporated at the disposal s i t e .

3.2 Clay l iner and soi l interaction studies

The so i l /c l ay l iner evaluation studies at PNL include character izat ion of t a i l i n g s , s o i l s , and l iner mater ia ls . The interactions between t a i l i n g s leachate and s o i l s or c lay l iner materials are a lso beinq ident i f i ed .

Characterization of typical types of t a i l i n g s (two acidic samples and one a lka l ine sample) has shown that most of the contamination from uranium mill t a i l i n g s is released in a r e l a ­t i v e l y small amount of water (the f i r s t one or two pore volumes of l eachate ) . Precip itat ion reactions of leachate with s ed i ­ments appear to dominate the chemistry of the leachate-sediment interactions as leachate seeps from the t a i l i n g s .

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TABLE V I I . Comparative Evaluation of Asphalt and Synthetic Liners

S t ab i l i t y Measured by Ratio Moisture Barr ier of Final Effectiveness

and In i t i a l (Permeabi l ity Relative , Permeability Thickness, s ) Cost, g/m'

Catalyt ic Airblown Asphalt Membrane

1 8 x 10-9 4.30

Vulcanized Asphalt -Rubber Membrane

60 5 x 10-6 4.40

Hydraulic Asphalt Concrete

9 7 x 10-9 9.60

Chlorosulfanated Polyethylene

7 2 x 10-9 7.80

For acid t a i l i n g s , c lay 1iner material is containment capab i l i ty .

the buffering capacity of a a key parameter in assessing

Buffer capacity is defined

soi l or the l iner as the

quantity of acidic t a i l i n g s leachate that can be neutral ized by each gram of soi l or l iner mater ia l . As an example, soi l mate­r i a l s from a proposed t a i l i ng s disposal s i t e near, C l ive , Utah were used in batch type interaction tests with synthetic t a i l ­ings leachate. For two local clay s o i l s tested, about 100 g of soi l were found to neutra l ize 500 ml of acidic leachate to pH values between 6 and 7. In this pH range, most of the contami­nants from the leachate w i l l prec ip i tate as immobile so l id com­pounds; hence, these so i l s would appear to make excel lent l iner materials for acidic t a i l i n g s .

In further tes ts , the buffering capacity derived from batch tests w i l l be used to predict the e f f luent volume needed to exhaust the neutral izing a b i l i t y of the so i l s and l iner mater ia l . This prediction can be compared with experimental resu l ts from column studies for ve r i f i c a t i on .

A ser ies of screening tests have been completed with various types of asphalt and synthetic l iner materia ls . Four l i n e r s , l i s t ed in Table V I I , were subjected to accelerated aging conditions in 0.6-m diameter exposure columns. These four materials were selected for test ing on the basis of ava i l ab le performance data published in the l i t e ra tu re [ 1 2 ] . The four materials were then evaluated by three c r i t e r i a :

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• material stability as measured by the change of per­meability with time

• moisture barrier effectiveness as measured by the final ratio of material permeability and liner thickness

• relative cost. Table VII gives a synopsis of the results of the compara­

tive evaluation. The catalytic airblown asphalt exhibited the best of the combined characteristics. Aside from having the most stability and least cost, it was among the materials with the greatest effectiveness as a moisture barrier. Catalytic airblown asphalt is currently undergoing exposure to a variety of conditions to quantify its expected lifetime when exposed to tailings leachate.

3.3 In-situ liner technology

Because of their size, location, and condition, tailings piles may be uneconomic to move and stabilize. In such situa­tions, in-situ stabilization is likely to be the best alterna­tive for effective remedial action. In some topographic settings, liners on the bottom and sides of the piles will be needed in addition to covers to stop leaching caused by lateral groundwater flow through the pile.

In-situ stabilization requires that a grout be injected at the contact of the soil material and the tailings. The grout could be a slurry containing particles such as cement and/or clay or could be a solution containing dissolved materials which either polymerize or interact with the substrate parti­cles and seal the pores. Considering that uranium mill tail­ings piles are mostly composed of sand sized materials, injection of slurries would be less predictable in terms of intergranular pore coverage. In soil-like material with a hydraulic conductivity of less than 0.1 cm/s, chemical (solu­ble) grouts are recommended [ 1 3 ] . Engineering grouting tech­nology is a process commonly used in similar environmental situations such as dam seepage shutoff, earth stabilization for water control and construction stabilization, and sanitary landfill leaching and stabilization [ 1 4 ] .

As part of the evaluation of in-situ grouting, several grouting materials were investigated under laboratory condi­tions. Data on the hydraulic conductivity of treated tailings material are given in Table VIII. The tailings material exhibited hydraulic conductivity of 6 x 10~3 cm/si. The mate­rial contained 81% sand, 10% silt, and 9% clay size particles; the pH in a water suspension was 3.7. Note that the particu­late 5% bentonite slurry did not penetrate the pores of the material under the test conditions and thus did not reduce the conductivity.

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TABLE V I I I . Grouting Results Using a Shiprock Ta i l ings Sample as an Example

Grout Hydraulic Conductivity Problems

10% Aery1 amide <2.6 x 10-7 c m / 5

5% Bentonite Refused

10% Resorcinol + Formaldehyde <2.6 x 10-7 c m / s

20% Urea + Formaldehyde 3.5 x 10-3 c m / s Poor set

40% Sodium S i l i c a t e 4 x 10-6 c m / s

Both the 10% acrylamide and the resorcinol/formaldehyde formulations reduced conductivity to less than 2.6 x 10~7 cm/s,, which was the l imit of accuracy in measure­ment. The urea/formaldehyde solution did not substant ia l ly reduce the permeabil ity; the acidic nature of the Shiprock sample is suspected to be the cause of the poor set . These results are preliminary, however, and do not represent exten­sive test ing of d i f ferent formulations. It should be noted that production of acrylamide has been stopped in the United States because of the toxic nature of the acrylamide monomer; however, new re lated products with less toxic properties have been produced [15, 16 ] .

Before in - s i tu grouting can be implemented, investigations of the p i l e , including leaching and groundwater, conditions must be conducted. Field tests should be conducted in selected areas of the p i l e preferably with concurrent cover studies . F ina l l y , cost estimates comparing in - s i tu s t ab i l i z a t i on versus movement and new disposal f a c i l i t y should be performed so that a cos t - e f f ec t ive solution can be implemented.

4. CONCLUSIONS

The resu l ts of the cover and l ine r studies are summarized below.

4.1 Covers

• Earthen covers, multi layer covers, and asphalt emulsion radon bar r i e r s have been shown to be e f f ec t ive in reducing radon re lease from uranium mill t a i l i n g s . The most e f fect ive

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radon bar r ie r is the asphalt emulsion system which consistent ly reduced radon re lease by greater than 99% to near background (2 pCi -nr 2 • s - 1 ) .

• The use of a spec i f ic cover system w i l l depend on the requirements at each s i t e , such as a v a i l a b i l i t y of mate­r i a l s (cover s o i l , asphalt , e t c . ) and cost . A l so , the s t a b i l i t y of the p i l e before cover application w i l l have an influence on cover se lect ion . Al l of the cover systems are cost competitive depending on s i t e - s pec i f i c requirements.

• To enhance cover s t a b i l i t y , b iobar r i e r s have been deve l ­oped that can prevent plant root intrusion for up to ~100 years and animal intrusion for a very long period of time.

• Revegetation or rock cover w i l l also improve the long-term s t a b i l i t y of the cover system by reducing water and wind erosion, but the e f fects of increased water holding capac­i ty of the system where a rock cover is added must be ca re fu l l y considered.

4.2 Liners

• A decision tree process, which incorporates newly deve l ­oped l iner technology, can be used for decisions on l iner requirements at individual t a i l i n g s disposal s i t e s .

• For ex ist ing t a i l i ng s p i l e s where groundwater movement through the p i l e may occur, chemically so luble grouts have been successful in laboratory tests in reducing the hydraulic conductivity of t a i l i n g s materia l .

• Where a moisture or leachate ba r r i e r is required for a relocated t a i l i n g s p i l e , the ca ta ly t i c airblown asphalt membrane was determined to be the most acceptable l iner material on the basis of s t a b i l i t y , moisture bar r ie r e f fect iveness , and cost .

• Soil materials at a proposed s i t e for t a i l i ng s disposal at C l ive , Utah, exhibited a buffering capacity of ~5 ml/g when acidic t a i l i n g s leachates were neutral ized to pH values between 6 and 7. The neutra l izat ion was accom­panied by prec ip i tat ion of major cations in the leachate and coprecipitat ion of trace contaminants.

REFERENCES

[ 1 ] ENVIRONMENTAL PROTECTION AGENCY (EPA), Proposed disposal standards for inactive uranium processing s i t e s , 40 CFR Part 192, Federal Register, 46 6 (1981)

[ 2 ] NELSON, R. W., GEE, G. W., and OSTER, C. A. , "Radon control by multi layer earth ba r r i e r s . 1. Modeling of moisture and density e f fects on radon di f fusion from uranium mill t a i l i n g s , " (Third Symposium on Uranium Mill Ta i l ings Management, 1980, Ft. Co l l in s , Colorado) .

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[ 3 ] GEE, G. W., et a l . , "Radon control by multi layer earth b a r r i e r s , " (Fourth Symposium on Uranium Mill Ta i l ings Management, October 26-27, 1981, Fort Co l l ins , Colorado) .

[ 4 ] HARTLEY, J. N., et a l . , Asphalt Emulsion Sealing of Uranium Ta i l i ngs , 1980 Annual Report, Paci f ic Northwest Laboratory, Richland, Washington DOE/UMT-0201, PNL-3753 (1981).

[ 5 ] HARTLEY, J. N., et a l . , Asphalt Emulsion Sealing of Uranium Ta i l i ng s , 1979 Annual Report, Paci f ic Northwest Laboratory, Richland, Washington PNL-3290 (1980).

[ 6 ] HARTLEY, J. N., et a l . , "F ie ld test ing of asphalt emulsion radon bar r ie r systems," (Fourth Symposium on Uranium Mill Ta i l ings Management, October 26-27, 1981, Fort Co l l ins , Colorado) .

[ 7 ] FREEMAN, H. D., "An improved radon f lux measurement system for uranium t a i l i n g s p i l e measurement," (Radiation Hazards in Mining: Control, Measurement, and Medical Aspects October 4-9, 1981, Golden Colorado) .

[ 8 ] BURTON, F. G., et a l . , "Application of control led re lease technology to uranium mill t a i l i n g s s t a b i l i z a t i o n , " The State of Waste Iso lat ion in the U.S. and Elsewhere. Advocacy Programs and Public Communications, Post R.G. ( e d . ) Vol. 2 (1981) 1009-1021. (Proceedings of the Symposium on Waste Management, Tucson, Arizona, February 23-26, 1981) Waste Management 1981, ANS topical meeting, The University of Arizona (1981).

[ 9 ] BURTON, F. G., et a l . , "The use of control led re lease herbicides in waste burial s i t e s , " (8th International Controlled Release Symposium, July 26-29, 1981, Ft. Lauderdale, Flor ida) ( in p r e s s ) .

[10 ] CLINE, J. F., et a l . , 1981. Biobarr iers used in shallow burial ground s t ab i l i z a t i on , Journ. of Nuclear Tech. ( in p r e s s ) .

[ 11 ] CLINE, J. F., GANO, K. A. , and ROGERS, L. E., Loose rock as b iobar r ie rs in shallow land bu r i a l , Health Physics 39. (1980) 497-504.

[12 ] BUELT, J. L., et a l . , An Evaluation of Liners for a Uranium Mill Ta i l ings Disposal S ite - A Status Report, Pac i f i c Northwest Laboratory, Richland, Washington D0E/UMT-0200 PNL-3679, (1981).

[13 ] CARON, C , The state of grouting in the 1980's, Grouting in Geotechnical Engineering (1982) 346-358.

[14 ] BAKER, W. H. ( e d ) , Grouting in Geotechnical Engineering. American Society of Civi l Engineers, New York (1982).

[15 ] BERRY, R. M., In ject i te -80 polyacrylamide grout, Grouting in Geotechnical Engineering (1982) 394-402.

[16 ] CLARKE, W. J . , Performance character i s t ics of acrylate polymer grout, Grouting in Geotechnical Engineering (1982) 418-432.

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URANIUM MILL TAILINGS STABILIZATION WITH ADDITIVES

D. MARCUS Gulf Research and Development Company, Pittsburgh, Pennsylvania

D.A. SANGREY Department of Civil Engineering, Carnegie-Mellon University, Pittsburgh, Pennsylvania, United States of America

Abstract

URANIUM MILL TAILINGS STABILIZATION WITH ADDITIVES. Subsurface trench disposal of uranium mill tailings is one of the new techniques developed

to meet safety and environmental constraints. The stabilized tailings in trenches have to develop sufficient strength to support a layer of fill placed as cover over the trenches. The use of chemical additives to achieve the stabilization of mill tailings is discussed in this paper. Special emphasis was placed on using stabilization additives which were waste products from other industries. For the acidic mill tailings, the most suitable additives are the alkaline ones: fly ashes and kiln dust. The neutralization of tailings acidity is completed by precipitation of hydroxides and formation of silicates so that the various metals become insoluble. The strengthening processes take place due to the bridging of the solid particles by the growing crystals of the reaction products, while the water is dissipated by chemical means. The required engineering properties for stabilized fine uranium mill tailings depend upon the specific disposal method. For one system of trench disposal, a shearing resistance of 8 lbf/in2 was a minimum requirement for ultimate bearing capacity to support cover material. This value of 8 lbf/in2 was used as a design objective for the testing programme. Other engineering properties and characterization values were defined for those materials which could meet the strength requirements. These are reported and discussed in the paper. The paper concludes with both specific and general recommendations. The specific recommendations pertain to the particular fine uranium mill tailings and additives used in this research programme. The general conclusions describe the design of an experimental programme to stabilize fine tailings from any source.

1. Introduction

In the recent past, there has been a tendency to develop new techniques for uranium mill tailings disposal. The use of large dams is no longer an "agreeable technique" for some regulatory agencies due to hazardous situations created in case of a dam failure. This project was based on a request to develop a technical solution for subsurface storage of tailings. This eliminated the thickened discharge method developed by Robinsky, (1,2) which was the first alternative to the dam disposal, because it was considered to be an "on the surface disposal." Trench burial was recommended (3,4) as the most effective use of a limited disposal area

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SPOIL RIDGE

100% ROCK

TAILING CELL BARRIER PILLAR

FIG.l. Typical trench burial section.

The total volume of tailings to be disposed is directly related to the mill capacity and planned lifetime. To reduce the total volume of tailings, a split of mill tailings was considered: the coarse fraction to be used as mine backfill, the fines to be buried in trenches. Two objectives are met in this way: a reduced tailings volume for the disposal site and a suitable sandy material (5) of lower radioactivity for backfilling.(6)

The subject material for this research was produced as a 100 mesh split of tailings by hydrocycloning the underflow of the last thickener of the CCD system, diluted by recirculating raffinate. The hydrocyclone overflow, the "minus 100 mesh fraction" as a 30% slurry had to be pumped to the trench disposal site. The objective of research was to define the minimum conditions for trench burial of the minus 100 mesh fraction, using additives to get the necessary strength to support the overburden in a- limited period of time - 6 months. Tests on higher solids content slurry were justified if it proved to be infeasible to get the necessary shearing resistance of the tailings in a 30% slurry, in this period of time. In this case, a dewatering step would take place before adding stabilizers.

The study had to be focused on a technical solution for the worst case, defined as a "no evaporation, no drainage condition". This condition may be comparable to the stabilization of an element located in the center of a large volume of tailings. From these tailings the liquid phase is neither lost by evaporation nor squeezed out

Certain minimum property requirements can be defined for trench disposal of stabilized tailings. These property requirements, especially strength requirements, are closely related to the anticipated thickness of cover material over the tailings. The illustration presented in Fig. 1 is a typical cross-section of a trench disposal plan where all of the material excavated to make the trench is used as cover. This is both the most realistic and the most economical scheme even though the resulting cover thickness of 50 ft. (15 m) is far in excess of the thickness specified by regulatory authorities. When developing a disposal area such as illustrated in Fig 1, the cover is placed as the adjacent trench is opened, thus minimizing the handling and transport of soil material.

The geometry illustrated in Fig. 1 has been used in an engineering analysis of the bearing capacity requirement of stabilized tailings to support 50 ft. (15 m) of cover The conclusion of this study indicated that a shearing resistance of 8 lbf/in 2 (55 kPa) would be required and this became the target for research on stabilization of tailings.

2. Characterization of Tailings

The tailings for this study were from western sandstones processed by usual acid leach conditions at normal pressure and 80 °C. To get the minus 100 mesh fraction for the laboratory study, the tailings were screened on a 100 mesh sieve. The use of hydrocyclones in the full scale mill will not give as sharp a cut as the sieves do. In

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The - 1 0 0 Passing, Screen Total Tails Mesh Fraction

% %

30 mesh 98.6

50 mesh 78.6

100 mesh 41.4 98.8

140 mesh 29.5 88.6

200 mesh 21.6 78.5

325 mesh 19.0 62.5

400 mesh 17.5 40.3

Table 2. Coulter Counter Analysis of the - 4 0 0 Mesh Material of Tailings

Size, ftm %

1-2 45.1

2 - 5 27.0

5 - 1 0 9.6

1 0 - 2 0 12.1

2 0 - 3 0 6.2

general, a broad particle size distribution (i.e., the fraction from hydrocycloning) is more suitable for stabilization. Consequently, the use of sieves to define the size distribution introduced another conservative factor.

2.1. Solids in Tailings

The particle size distribution of the tailings is shown in Tables 1 and 2 (mean values). The fraction considered for trench disposal in this study has more than 75% fines (minus 200 mesh) and 40% very fine particles (smaller than 37 fim). The main part of these minus 400 mesh particles are extremely fine particles — 72% are smaller than 5 microns.

Scanning Electron Microscopy (SEM) photographs and X-ray diffraction patterns were used for mineralogical characterization. The predominant mineral of the tailings is alpha quartz, as would be expected from this sandstone ore. Other minerals are albite-anorthite, K-feldspar and kaolinite. Special attention was paid to the extremely fine particles, 1-2 microns. The main components of these particles are clays, flocculated particles of kaolinite and montmorillonite, along with precipitates of amorphous silica with amorphous aluminum hydroxide. It is very likely that part of the clays were destroyed during the leaching, resulting in the amorphous components. Small calcium sulfate crystals are also the result of acidic attack on calcium minerals.

The density of solids material in the tailings is 2.43 g/cm 3 .

Table 1. Screen Analysis of Tailings

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MARCUS and SANGREY

Table 3. Chemical Analysis of Tailings Liquor*

s o 2 -

4 "= 57 900 mg/l CL" = 5 900 mg/l

F e 3 + = 3 685 mg/l F e 2 + = 1 251 mg/l

Al = 2 215 mg/l K = 184 mg/l

Si = 598 mg/l Mg = 52 mg/l

Na = 418 mg/l Ca = 3.3 mg/l

Mn = = 260 mg/l Mo = 21 mg/l

V = 107 mg/l

*The major components of the liquid phase are ^ j ' S O ^

- 13.2 g/l. A I 2 ( S 0 4 ) 3 - 13.9 g / l , H 2 S 0 4 - 5.6 g/l, FeSC>4

- 2.2 g/l.

2.2. Liquid in Tailings

The liquid phase in the tailings was a diluted solution of sulfuric acid and sulfates. The pH value is 1.24, Eh value 480, density 1.1065, total dissolved solids 95.05 g / l . The chemical analysis of the main components of the liquid phase is shown in Table 3.

3. Additives

3.1. Additives Selection

The research project objective was to minimize the cost for stabilizing additives. This led to the decision that no neutralization was to be considered prior to the treatment with additives and that the maximum amount of additives to be used be 10% of the weight of solids in slurry. Limestone, the most common additive for soils consolidation and acidity neutralization, was eliminated by these constraints because the cost of ground limestone equals that of Portland cement in the remote areas where uranium mills are usually located. For the same economic reasons, no type of cement (Portland, Slag, Puzzolanic, etc.) was considered for this study.

The following wastes from other industries were selected for uranium mill tailings stabilization: fly ash type F and fly ash type C from nearby power plants and kiln dust from a cement plant.

3.2. Additives Characteristics

The physical characteristics of selected additives for tailings stabilization are shown in Table 4. Standard specifications from ASTM C 6 1 8 - 8 0 and C 1 1 4 - 8 0 (7) were used for this purpose. The chemical characteristics are shown in Table 5. The fly ash F particles are much coarser than those of fly ash C and kiln dust (which have almost similar particle size distribution). Furthermore, the fly ash F has coarser particles than the tailings fraction used in this study while fly ash C and kiln dust have finer particles than the tailings.

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Table 5. Chemical Characteristics of Additives, %

Fly Ash F Flv Ash C Kiln Dust

SiO„ + Al 0 + Fe O 2 2 3 2 3 88.0 63.0 34.0

CaO 2.4 22.7 45.0

MgO 6.3 3.0

Alkalies as N a 2 0 1.5 1.5 2.5

so 3 5.0 3.5 1.0

Loss on Ignition 1.3 1.8 13.5

The lime saturation factor is an important characteristic for potential stabilizers. It represents the ratio between % CaO and the sum of 2.8(%SiO ) + 1.1 (%AI 0 J + 0.7(%Fe 0 ). A higher value of this factor means a higher reactivity of the product Fly ash F snows 'the lowest LSF (Lime Saturation Factor), while fly ash C has a high LSF and excess lime (pH 12.3). Kiln dust has the highest LSF 30% CaCO (very high LOI value) and excess lime (pH 12.4). Alkalies and sulfates are minor components: Fly ash F has a high F e 2 0 3 percentage, in spinel phase and a high mullite content. (8)

Table 4. Physical Characteristics of Additives

Fly Ash F Fly Ash C Kiln Dust

Bulk Density g/cm 3 o 75 0 .97 Q72

Moisture, % 2.78 1.06 1.57

pH of 10% Suspension 10.67 12.33 12.41

Particle Size Distribution

+ 100 7.0 4.6 4.3

1 0 0 - 4 0 0 15.7 2.4 2.9

1 4 0 - 2 0 0 16.1 4.1 7.8

2 0 0 - 3 2 5 26.6 8.5 17.7

3 2 5 - 4 0 0 5.2 3.9 0.5

- 4 0 0 29.2 76.2 66.6

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4. Experimental Design

4.1. Theoretical Expectations

The "no evaporation, no drainage" conditions imposed as a constraint in the project eliminated a key element of most stabilization programs. Neither evaporation nor consolidation processes could be used to reduce the volume of liquid phase in the tailings. Consequently, the only water dissipation in this case could be by chemical means, binding the water molecules in the reaction products, which must be in crystallized form.

The large volume of liquid phase also imposed severe limitations which could be expected to limit the effectiveness of any stabilization program. If a liquid phase was 70% of the system (30% solids) and maximum additive consumption could be no more than 10% of solids, the maximum additive concentration was limited to 3%. This low level would eliminate chemical binding of water because of insufficient reagent

The interparticle distance in a slurry is directly related to the solids concentration. The mean size of particles in the - 1 0 0 mesh fraction is 40 ftm Assuming all the particles are spherical, the interparticle distance would be 68 //m in a slurry of 30% solids. An increase in solids concentration in the slurry would result in a decrease of interparticle distance and for a 50% solids slurry the distance is almost half of that mentioned above. Any bonding crystals (reaction products) have to fill the interparticle distance, as the stabilization is based on the formation of bridges between particles. The quantity of additives must be sufficient to generate enough crystals to fill the void volume. As a result, for a limited amount of additives, the solids concentration in the slurry must be a crucial factor for the stabilization processes.

The chemical reactions were expected to be similar to those of cement setting in water since all of the additives are of the silicates-aluminates-carbonates type. However, in the presence of free acid in the liquid phase, fast reactions between sulfuric acid and alkalies, carbonates or silicates do take place. The remnant reacting components of additives are then available for the hydration-setting processes. A high content of liquid phase in the slurry means a large quantity of free acid and a higher additive consumption before the setting processes can occur.

The chemical analysis of tailings liquor (Table 3) and the chemical characteristics of additives (Table 5) are useful for understanding the potential processes leading to the tailings stabilization. Four different types of processes are expected to take place (9,10) in these conditions:1

4.1.1. Neutralization

Neutralization of free acidity in the initial stages:

CaO-H O + HO-SC- -> CaOSC> + 2H 0 (1) 2 2 3 3 2

CaOC0 2 + H 2 O S 0 3 -> CaOSC>3'+ H 2OCC> 2 (2)

The strong sulfuric acid will react with calcium oxide or calcium carbonate when present in additives resulting in nonsoluble calcium sulfate. As fly ash F has an insignificant amount of calcium oxide available for these reactions, these neutralization reactions would be of no importance when this additive is used. In fly ash C, the fast neutralization reactions will take place, but the second reaction is insignificant as the calcium carbonate content is minor (LOI is mainly due to organic matter in these fly ashes). However, kiln dust having free lime and calcium carbonate will show the most intensive neutralization reaction and release of C 0 2 from the system.

Notation used in cement chemistry

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The strong acid will react not only with calcium oxide and carbonate but with any calcium salt of weak acids if present. Such weak acid salts would include calcium silicates, aluminates or siiicoaluminates, and would lead to the formation of new compounds. For example.

CaOAl 0 2SiO + H O'SO + H O -> Al 0 , 2 S i O , 2 H 0 + CaOSO_ (3)

The pH value of the system also will be a significant factor in these reactions.

4.1.2. Precipitation

Precipitation reactions may take place as the pH value increases:

F e , 0 , 3 S O _ + 3[CaOH 0 ] -* 3 [CaOS0„] + Fe O 3H 0 (4)

A I 2 0 3 3 S 0 3 + 3 [ C a O H 2 0 ] -* 3 [ C a O S 0 3 ] + A I 2 0 3 3 H 2 0 (5)

F e O S 0 3 + CaOH 2 0 -» C a O S 0 3 + FeOH 2 0 (6)

As a result of these reactions, new quantities of calcium sulfate are produced while the metals precipitate as hydroxides (directly related to the pH of precipitation). At high pH values all the metal impurities are precipitated in an insoluble form (assuming that the pH does not reach the value 13 -14 when most of them redissolve).

The fixation process for heavy metals seems to be much more complex than the simple hydroxides precipitation which is dependent on pH value. The formation of new components illustrated in reaction (3) brings new elements into the fixation process. These reaction products have intensive ionic exchange properties and many metals will be bound this way. The precipitation of heavy metals by silicates or aluminosilicates is a well known procedure for fixation in the most insoluble form (11,12). A similar process would be expected in this research, even in the absence of soluble alkaline silicates (aluminosilicates) to precipitate the heavy metals due to cation exchanges. The fixation should take place as in any other process where cements are used, assuming that the quantity of cementing additive is enough for the fixation of all the heavy metals, radium included (13,14). A complete study of the fixation processes and the entrapment of heavy elements in the silicates structure is outside of the scope of this paper.

4.1.3. Hydrolysis

Hydrolysis reactions of calcium silicates and aluminosilicates are typical cement setting processes. When they take place in the presence of acid or acid salts, the resulting calcium hydroxide is expected to be used in the neutralization reactions and the equilibrium will be moved towards the right in the following reactions given as examples.

2 [3CaOSi0 2 3 + Aq 3Ca02Si0 2 (Aq) + 3CaOH 2 0 (7)

2 [ 2 C a O S i 0 2 ] + Aq -» 3Ca02Si0 2 (Aq) + C a O ^ O or (8)

2 [2CaOSi0 2 3 + Aq 2Si0 2(Aq) + 4CaOH 2 0 (9)

3CaOSi0 2 + Aq -» Si0 2(Aq) + 3CaOH 2 0 (10)

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4.1.4. Hydration-Crystal I ization

Hydration-Crystallization reactions are the most important processes in water dissipation. The following examples illustrate these processes:

CaOS0 3 +Aq -» CaOSC> 3 2H 2 0 (12)

3CaOAI 2 0 3 +Aq -> 3CaO AI 2 C> 3 6H 2 0 (13)

3Ca02Si0 2 +Aq -> 3Ca02SiC> 2 3H 2 0 (14)

4Cat>AI 0 +Aq -> 4CaC-AI 0 -19H 0 (15)

3 C a O A I 2 0 3 + 3 [ C a O S 0 3 ] + A q -> 6 C a O A I 2 0 3 3 S 0 3 ' 3 2 H 2 0 (16)

3CaOAI 2 0 3 +CaOH 2 0+Aq -> 4CaOAI 2 C> 3 12H 2 0 (17)

The first reactions (12) and (13). are fast, while the other ones are slow. The crystallization process requires a long time, and the quantity of water in the crystal constitution is very high. These reactions illustrate the chemical binding of water in a solid form.

There can be additional reactions between the reaction products, resulting in aluminosilicates, as for example:

3 C a O A I 2 0 3 6 H 2 0 + 3 C a O S i 0 2 H 2 0 -> -> 3 C a O A I 2 0 3 S i 0 2 4 H 2 0 + 3 t C a O H 2 0 3 (18)

The crystals will grow in time while water is consumed in the above reactions inducing the precipitation of hydroxides and other reaction products .The result will be the filling of void volume between the particles, and finally the bridging between solid particles. At this final stage, the material will be stabilized and may have sufficient strength and stability.

These theoretical expectations were verified in the testing program.

4.2. Testing Procedure

A series of preliminary tests was completed and indicated that no stabilization process took place in 30% solids slurry, using 10% of any additive or combination of them However, if a limited evaporation was permitted, the setting processes were visible after 10 days. Based on this, a first set of tests using 30% solids slurry and the maximum accepted quantity of additives (10% of solids content in slurry) was carried out. In addition, specimens with an extreme concentration were prepared. These specimens served two purposes; to confirm the theoretical expectations for stabilization and to provide data for calibrating an accelerated curing program in which specimens cured at 40 °C were to represent samples at 20 °C. The high additive concentration was a kiln dust (KD) to solids ratio of 1:1. This corresponds to a 2:1 ratio of liquid phase to kiln dust.

The reaction (11) takes place only when CaOH^O concentration decreases:

4 C a O A I 2 0 3 + Aq -» 3CaOAI2C>3(Aq) + CaO+^O (11)

The reagents in these examples are specific for each additive. The hydrolysed silicates or aluminates are in a reactive form suitable for hydration - . crystallization processes or for fixation reactions of heavy metals - reactions (9) and (10) illustrate the last case.

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25 -

T IME. DAYS

FIG.2. Strengthening effect of high additive consumption for 30% solids slurry. Liquid phase in slurry: additive KD ratio 2:1. Curing temperatures marked on curves.

The following procedure was adopted: the additive was added in small portions in 2 kg of slurry under stirring conditions. The glass pans (6 in. diameter) used for mixing were then sealed, covered, and set for curing in incubators. Three identical mixes were made of each additive: fly ash type C (FAC), fly ash type F (FAF) and kiln dust (KD) and combinations of two in equal parts. Each type of mix was cured at 20 °C and 40 °C. The mixes were usually checked every 3 to 7 days and the consistency or the shearing resistance, was measured using one of two cone penetrometers. As the shearing resistance increased, a laboratory vane shear device was used to measure strength. The three devices used for determining the strength (light cone penetrometer, heavy cone penetrometer, laboratory vane) had overlapping ranges which allowed for calibration among the different data.

The results of tests on the 30% solids slurry supported these conclusions:

a. No additive or combination of additives using 10% of solids gives a measurable strengthening effect after 60 days curing time.

b. A noticeable stabilization takes place when the liquid phase:additive ratio is 2:1 (see Fig. 2).

c. Tests at higher temperature could be used to evaluate the setting of specimens at 20 °C. The 40 °C curing was selected for further tests and calibration to 20 °C was established.

d. The theoretical expectations were confirmed.

Based on these test results, the testing program was extended to consider slurries with a higher solids content The limitations of "no evaporation, no drainage" and of additive content limited to 10% of the weight of solids were continued.

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MARCUS and SANGREY

Table 6. Testing Program for Fine Tailings Slurries Stabilization

Solids in Slurry 40% 50% 55%

Additive: Quantity Used, Percent of Solids in Slurry.

FAC 3,6; 10 3;6;10 3;6;10

FAF 3;6;10 3;6; 10 3;6;10

KD 3;6;10 3;6;10 3;6;10

Scheduled mixes: 27

Setting conditions for all mixes: 40 °C, in sealed glass pots.

Table 7. Calibration Tests for Mixes Stabilization at 2 0 ° C

Solids, % Additive, % Solids, % Additive, %

40 - FAC 10 50 - - -

40 - FAC 6 55 - - -

50 - FAC 6 55 - FAC 3

4.3. Testing Program

The testing program listed in Table 6 and Table 7 was developed to define:

a The setting effect of each additive.

b. The minimum quantity of additive to get a satisfactory stabilization in an acceptable period of time (3 to 6 months).

c. The calibration of accelerated tests.

Several important observations were noted during the early stages of these tests. The setting reactions were expected to be different for different additives especially in that the hydration crystallization reactions were expected to be strong for fly ash C and kiln dust, but very limited for fly ash F. The dominant phases of FAF, glass and mullite-quartz do not offer any contribution tp the chemical binding of water, but on the contrary, increase the permeability of the mixes resulting in water release from the system (FAF has coarser particles than the tailings). As expected, in tests of FAF, the liquid phase separated from the slurry and covered the surface of test specimens.

A significant quantity of gas was released during the first 12 hours when kiln dust of high calcium carbonate content was used. Carbon dioxide results from the neutralization reactions and in some cases formed bubbles which split the test specimens. When lower solids concentrations were used, CO gas was released during the stirring step.

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FOR t = CONST t s T IME

R= 4 . 1 LOO t - 1 . 2

FIG.3. Temperature effect on duration of stabilization. Slurry 55% solids. Additive KD: 3%. Temperatures marked on curves.

Strength tests using both penetrometers and the laboratory vane shear device were conducted at time intervals to evaluate shearing resistance as a measure of stabilization. To provide some perspective on the potential settlement problems when heavy loads (including the thick cover layer) were placed on stabilized tailings in trenches, a series of consolidation-compression tests were done. Conventional testing procedures were used (7). Both the concentration of solids in the tailings and the type and quantity of additive were varied in the experimental program.

Although one of the principal objectives of this research was definition of time-strength relationships for various mixtures of uranium mill tailings and additives, it was unrealistic to conduct the experimental program within an actual time scale. Six months would be a realistic maximum time for an actual trench filled with stabilized tailings to remain uncovered or lightly covered prior to deep covering when the adiacent trench was excavated. However, a six month time scale for laboratory testing was unacceptable within the scope of research. An accelerated testing program was developed to overcome these problems.

Accelerated curing was accomplished by increasing the ambient temperature to 40 °C. As illustrated in Fig. 3, this method reduced the time required to do a particular experiment, thus permitting a broad range of variables to be studied within the available time and resources. The time scaling relationship between tests run at 40 °C and the field environment (20 °C) were established by conducting a limited number of duplicate tests at both 40 °C and 20 °C. Again, as shown in Fig. 3, these test pairs could be related mathematically. The resulting calibration equations were established for the relevant test data.

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T I M E - DAYS

FIG.5. Strengthening effect of different additives on fine tailings slurry. Solids concentration: 55%. Additive: 3%. Temperature: 40°C.

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3 5

30 -

25

20

15 -/ 65%

l O

f 5 0 % / J 5 iL > ^ 0 %

*/C^r ( N O MEASURE ABLE f^^j^f^^ - — 1 3 0 % | STRENGTH)

0 9 2 0 4 0 60 8 0 100 TIME - DAYS

FIG. 6. The influence of slurry solids content on shearing resistance for low additive consumption (3% KD). Solids concentration marked on curves. Curing temperature: 40°C.

TIME - DAYS

FIG. 7. Strengthening effect dependence on additive KD consumption. Slurry solids concentration: 50%. Curing temperature: 40°C. Additive consumption marked on curves.

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25r -

160 TIME - DAYS

FIG.9. Strengthening effect of 6% additives on 40% solids slurry. The additives are marked on curves. Curing temperature: 40°C.

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"e 2 0 -

T I M E - D A Y S

FIG. 10. Strengthening effect of 10% additives on 40% solids slurry. The additives are marked on curves. Curing temperature: 40°C.

2 5 r -

T IME - DAYS

FIG.11. Strengthening effect of 6% additives on 50% solids slurry. The additives are marked on curves. Curing temperature: 40°C.

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3 5 r

SOLIDS % IN SLURRY

FIG.13. Area of applicable combinations of additive consumption and slurry concentration for fine tailings stabilization. Strengths after 42 days setting. Curing temperature: 40°C.

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5. Results of Stabilization - Strength Increase

The various effects of using additives to stabilize fine uranium mill tailings are illustrated in Figs. 4 - 1 2 . Because there were three principal variables being examined (solids content, additive type and additive concentration), it is easier to illustrate the.effects and interactions of these variables by examining them one at a time. For example, the effect of the type of additive is illustrated in Fig. 4 for a 30% solids slurry and a 10% concentration of ail additives. The trend that kiln dust (KD) was more effective than fly ash C (FAC) which was, in turn, more effective than fly ash F (FAF) is a general trend throughout all of the experiments. More typically, KD and FAC were quite similar in effect with FAF being much less effective (Fig. 5). Note that on all figures the required shearing resistance limit of 8 lbf/in 2 is shown by a dashed line.

The initial dewatering of slurry to increase the solids content had a major effect on stabilization effectiveness. For 3% KD mixtures, these effects are illustrated in Fig. 6. The slurry solids concentration was a key requirement for effective stabilization. When the solids content was 30% or lower, the only effective stabilization required uneconomical quantities of additives. Conversely, if the solids content could be increased to 55%, very small quantities of the more effective additives (FAC and KD) could be used to achieve the required strength increase.

The effect of increasing the quantity of an additive used with a particular concentration of fine tailings was as expected. As the quantity of additive increased, the strength increased and the time required for strengthening to a particular level was shortened. The effects of KD concentration in a 50% solids slurry are shown in Fig. 7.

The effects of additive type were illustrated in Fig. 4 for a 30% solids slurry. Higher concentrations of solids are more easily and economically stabilized and for various situations of solids content and additive quantity, the data shown in Figs. 8 - 12 illustrate the relative effectiveness of additives. For the same additive consumption, the increase of solids concentration in the slurry from 40% to 50% roughly reduces by half the required time duration to reach the minimum strength, 8 lbf/in 2. In contrast, for a given solids concentration, the additive consumption must be increased three times in order to reduce by half the setting duration for the minimum strength requirement The general conclusion to be drawn from these data is that the more alkaline KD and FAC are much more effective stabilizers than FAF. This general conclusion holds regardless of the solids concentration although the specific degree of effectiveness varies.

6. Conclusions

This study has a principal contribution to the new technique of trench disposal of uranium mill tailings. The feasibility of this technique has been demonstrated and a technical solution was found for the worst case defined as "no evaporation, no drainage" condition. The strengthening effect took place in a limited period of time when proper additives were used for tailing stabilization,

The additive effect on uranium tailings stabilization for trench disposal is essentially dependent on these factors:

a. The solid/liquid content in the slurry

b. The liquid phase acidity

c. The chemical composition of the additive

The minimum quantity of additive to be used is related to the chemical reactions which take place during the stabilization processes. The physical characteristics of the additive and the particle size distribution of the tailings have an important effect on the duration of stabilization processes. In the "no evaporation, no drainage" conditions, the

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reaction products should be in sufficient quantities to fill the void volume between solid particles and to dissipate the present water by chemical means.

The cost of tailings stabilization with additives is directly related to three factors when no evaporation or drainage take place:

a. Dewatering cost, if used

b. Quantity of the additive to be used and the cost of additive

c. Required time to ensure the needed strength to support the overburden

Additional factors contributing to the cost reduction of tailings stabilization in trenches are specific for local conditions: partial neutralization using local sources; extensive disposal area and limited volume of overburden; mix of mill tailings with coarser mine tailings, etc.

For the particular conditions of the research presented herein, the most effective combination for stabilization is shown in Fig. 13. In order to reach the strength requirements in the same period of time, the high solids concentration tailings need lower additive consumption than the diluted slurry. The evaporation and drainage factors should also be considered in many disposal schemes.

The methodology described in this paper should be applicable to other acidic mine and mill tailings disposal problems.

REFERENCES

1. Robinsky, E.I., Tailings disposal by the thickened discharge method, in Tailings Disposal Today, Vol. 2, 1979, pp. 7 5 - 9 1 .

2. Robinsky & Assoc., "Thickened Tailings Disposal Feasibility Study," Report to Gulf Minerals Resources Co., Denver, 1980.

3. Brawner, CO., Concept and experience for subsurface storage of tailings, in Tailings Disposal Today, Vol. 2, 1979, pp. 153 -173 .

4. Brawner, CO., Design and construction of tailings impoundments, C.S.U. Short Course, Fort Collins, CO, Jan. 1981.

5. Ford, R.A., A review of backfill mining practice, in Mining with Backfill. CIM Spec. Vol. 19, Sudbury, ONT, 1978, p. 4 -5 .

6. Momeni, M.H. and others, Radiological impact of uranium tailings and alternatives for their management, Argonne National Lab., 1979, p. 21 .

7. 1980 Annual Book of ASTM Standards, part 13, C114; part 14, C618 and part 19, D4235.

8. Hullet, L.D. and others. Chemical Species in Fly Ash from Coal-Burning Power Plants, in Science, 19, Dec. 1980, pp. 1356 -1358 .

9. Jacobson, C.A., Encyclopedia of Chemical Reactions, Vol. 2, Reinhold Pub. Corp., New York, 1948, p. 175-182 .

10. Kirk Othmer, Encyclopedia of Chemical Technology, Second Ed. Vol. 4, John Wiley, NY, 1964, pp. 4 2 4 - 4 2 5 and pp. 6 8 8 - 6 9 0 ,

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11. Conner, J.R., U.S. Patent 3,837,872, Sept. 24, 1974.

12. Hayes. J.F., U.S. Patent 4,173.546. Nov. 6. 1979.

13. Rancon, D. and Rochon, J., Retention des Radionuclides a Vie Long par Divers Materiaux Naturels, in Workshop on the Migration of the Long-Lived Radionuclides in the Geosphere, Proceedings, Brussels, 1979, pp. 3 0 2 - 3 2 2 .

14. Halcomb, W.F., An Overview of the Available Methods of Solidification for Radioactive Wastes, in Toxic and Hazardous Waste Disposal, Vol. 1, Ann Arbor Sci. Pub., Ann Arbor, 1979. pp. 23 -64 .

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RADIOLOGICAL IMPACT ASSESSMENT

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Chairman

J. SCHMITZ Federal Republic of Germany

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OPTIMIZING RADIATION PROTECTION IN THE MANAGEMENT OF URANIUM MILL TAILINGS

R.V. OSBORNE Health Sciences Division, Chalk River Nuclear Laboratories, Atomic Energy of Canada Limited

Research Company, Chalk River, Ontario, Canada

Abstract

OPTIMIZING RADIATION PROTECTION IN THE MANAGEMENT OF URANIUM MILL TAILINGS.

The Nuclear Energy Agency of OECD has organized a study of the applicability of the ICRP system of dose limitation to the management of uranium mill tailings. Reference sites in Australia, the USA and Canada have been defined, management options costed and the radiation doses from radionuclides dispersed from the tailings determined, either from existing data or by new modelling. The values of incremental cost-effectiveness between options have been estimated with reduction in collective effective dose equivalent commit­ment being the measure of effectiveness. Included in the options are erodible and non-erodible covers, vegetative covers, impermeable dams, removal of radium and thorium, and burial of waste rock. The effects on incremental cost-effectiveness of different integration times for estimating the collective dose commitment and of a dose rate cut-off for that calculation are noted.

1• General Principles

One of the main tasks in the study of uranium mine and mill tailings by a group working under the auspices of the Nuclear Energy Agency of OECD is to determine how and to what extent the system of dose limitation recommended by the ICRP [1] can be applied.

The objectives for radiation protection in this system are now well-known by the names justification, optimization and dose limitation, with the second also being commonly referred to by the acronym ALARA. The Nuclear Energy Agency of OECD has already [2] considered how gaseous effluents from some nuclear facilities might be managed to meet the optimization and dose limitation objectives. The study described here takes a similar approach.

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The resu l t of meeting the optimizing objective would be that the t a i l i ng s are managed so that the tota l ' c o s t ' - the cost of the measures used to achieve protection plus the cost of the res idual hazard - i s a minimum. With such optimum manage­ment any addit ional protection would only be attained at an addit ional cost that was greater than the perceived value of the reduction in the r i sk from rad iat ion . Meeting the dose l im i t a ­t ion object ive would ensure that no individual i s unacceptably exposed to radiat ion; this might also af fect the optimizing.

There are two fundamentally d i f fe rent ways of managing the radionuclides that accompany the uranium in the ore and which are potentia l environmental contaminants. One is to remove them from the other waste material in the m i l l . For example, radium and thorium could be handled in this way. The removed nuclides are then stored out of the biosphere. The other type of control i s to ensure that the nuclides remain in the t a i l i n g s , su i tab ly i so la ted from humans. Chemical treatments, s i t e se lect ion , engineered impoundments, l ine r s and covers are measures that can be considered, e ither s ing ly or in various combinations, as the management options.

2. The NEA Study

For this study reference s i tes have been defined, one each in Canada, Aust ra l i a and the USA, with environments (geology, hydrology, cl imate, demography) reasonably character i s t ic of a rea l region. Various typ ica l t a i l i ng s management options have a lso been defined. For Canada [3 ] a va l l ey dam impoundment is the base case with a vegetative cover, an impermeable dam and radium-thorium removal being the various options considered as in Table 1. Water transport of radionuclides and atmospheric dispersion of radon have been modelled [ 4 ] . For the USA two s i t e s are considered, an open p i l e with a small s tar ter dam and a spec ia l ly dug p i t . The various kinds and thicknesses of covers considered [5] are noted in Table 1. The dispersion of radon from t a i l i ng s that erode and fan out in time has been modelled [ 6 ] . For Aus t r a l i a , a" r ing dyke with a waste rock cover is the base case with a l te rnat ive covers being as l i s t e d in Table 1. The presence of a waste rock p i l e is also considered [ 7 ] . Water and wind-borne transport of radionuclides and radon dispersion are modelled [ 8 ] .

The f i r s t step in the analysis has been to determine ( a ) the costs of the various options that provide protection, and ( b ) the protection of individuals and the general population that is so atta ined. The next step has been to estimate the values of incremental cost -e f fect iveness for the various options; i . e . , the quotients of the dif ferences in costs ( A X ) by the di f ferences in protect ion. The quantity taken to represent the change in protection is the change in co l l ec t ive dose

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Table 1. Tailings management options considered at the reference sites in the NEA study.

CANADIAN TAILINGS OPTIONS

• l Base 2 + Vegetation

o 3 + Impermeable dam • 4 #1 and Ra, Th removed

5 #2 " " " " • 6 #3

US TAILINGS - OPTIONS

D Base O 1 Sand cover, 1 m O 2 Sand cover, 3 m O 3 Clay cover, 1 m • 4 #1 + Gravel cap • 5 #2 + Gravel cap • 6 #3 + Gravel cap • 7 Below ground

AUSTRALIAN TAILINGS OPTIONS

• 1 Waste rock cover, 2 m o 2 Soil, gravel, clay cover, 1 m o 3 Soil, rock, clay cover, 2 m o 4 •• 3 m O 5 •• •• 5 m A Waste rock pile

RESIDUAL COLLECTIVE DOSE COMMITMENT (S) mon • Sv

FIG.l. Estimating incremental cost-effectiveness between two options A and B.

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RESIDUAL IMPACT (S)

FIG.2. Cost-effectiveness in practice. The bars represent estimates of uncertainties in the X, S values.

commitment (AS), defined as in the previous study 12]. Figure 1 illustrates these quantities between two options A and B. The optimum option can then be identified as the one with the lower value of X in the pair that has the set with the largest value of (AJK/&S) that is less than some designated value. Such designation might be by a regulatory body or other national authority and would be the judged worth of saving a unit of collective dose commitment. The study group is not making that judgement itself. For determining the level of protection for individuals the maximum dose rates to the most highly exposed individuals have been estimated.

It was clear at the start of the study that there would be large uncertainties in the estimates of both costs and doses, perhaps sufficiently large that the estimates of incremental cost-effectiveness between some options would not be significant. The X-S plot for the various options might therefore appear as shown in Figure 2. The aim is to identify which options define the lowest concave-upwards envelope to the plot - as illustrated on the Figure. When differences are not significant, then the choice between such options must be on some other basis. There are, of course, many sources of uncertainty. For example, the variation in time of the effectiveness of a particular impoundment may only be predicted with an 'educated' engineering guess. Also, the modelling of the movement of the radionuclides from the tailings, particularly in the hydrosphere and over long times (thousands of years), is very uncertain. Judgements of the appropriate weighting factors for future doses, for collective doses at different average individual dose rates, and for amortizing the costs of protection are additional uncertainties. The presence

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of non-radioactive contaminants obviously will have an effect on management decisions.

In this paper I shall illustrate incremental cost-effectiveness analysis applied to uranium mill tailings with some of the preliminary results obtained [3-8] for the NEA study. The interpretations here are not necessarily those of the members of this study group and the data are selected to illustrate particular points rather than with the intent of being a complete review of the results. Non-radioactive materials are not considered.

3. Incremental Cost-Effectiveness Analysis

3.1 USA Reference Tailings

The USA reference tailings are typical of the Western States where the climate is dry and radon emanation is the main concern in assessments. The group of options considered is aimed to reduce the emanation and the erosion of the tailings. The importance of considering erosion is evident in the analysis of this set of options.

With a simple model of a tailings pile that is emanating radon and is also eroding, the collective dose commitment rate may be as shown on Figure 3. The rate is constant (mainly from radon and progeny with a minor contribution from the eroded material) until the tailings have eroded away when the rate falls in a way determined by the disappearance from the biosphere of the eroded tailings. With an erodible cover that initially attenuates the emanation the dose rate will increase with time as shown by the dashed line until the tailings are uncovered when erosion will continue as before. It is clear that if the collective dose commitment is estimated for times short compared with the time to erode, the presence of the cover will have resulted in a reduction in the dose commitment but if the integration continues beyond that time then the presence of the cover will have increased the dose commitment. The estimates in the study integrate as far as 10^ years by which time the model of erosion used predicts just about complete loss of the erodible covers, fanning of the tailings and similar emanation rates in all cases. A consequence of this is that an incremental cost-effectiveness analysis with integration to, say, 100 years would indicate the erodible but less expensive options as being preferred but with integration to 10^ years this is no longer the case. Figure 4 shows the incremental cost effectiveness analysis for 10^ years integration. Without uncertainties assigned to the values of dose commitment and cost the magnitudes of the incremental cost-effectiveness values which are shown in the boxes can only be regarded as very

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TIME

FIG.3. The effect of erodible covers on collective dose.

COLLECTIVE DOSE COMMITMENT I 0 4 man • Sv

FIG.4. The incremental cost-effectiveness values for USA tailings options when the collective dose commitment is estimated for 104 years. The key to the symbols is in Table 1.

approximate. Nevertheless, the erodible options (1-3) clearly must lie above the line joining the base case to option 4 for some integrating time with this model. The choice of erosion model clearly has a major effect on the implications of such an analysis.

For the options where erosion is considered not to occur, within the time scale to 10^ years, the values of incremental cost-effectiveness scale inversely with integrating time. For example the options with the incremental values of approximately 200 dollars per man-sievert at 10^ years would obviously have values near 2000 at 10^ years. This emphasizes the need for a way of resolving the question of how to limit the integration in time. Two comments are prompted by this example. The uncertainties in the results beyond some time may be so large that the significance of any incremental value may be zero. The cut-off would be determined by the validity of our modelling. A second possibility is that at very short times (e.g. 100 years)

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incremental values might s t i l l be below a chosen l im i t . For example i f 3 x 10 4 $/( man-Sv) were to be chosen as a l imit ing value and i f erodib le options were ignored, then option 6 would be the optimum even at 100 years integrat ion.

Although as noted e a r l i e r , there are uncertainties in the values given here, the more than two orders of magnitude in incremental cost -e f fect iveness from option 6 to option 7 (the below ground d i sposa l ) may be su f f ic ient to discriminate between the two options in this kind of ana lys i s . These data also i l l u s t r a t e the important d is t inct ion between cost -e f fect iveness and incremental cost -e f fect iveness . Options 6 and 7 d i f f e r by only about 30% in cost -e f fect iveness ( r e l a t i v e to the base case) but by more than 2 orders of magnitude in incremental cost -ef fect iveness .

3.2 Austra l ian Reference Ta i l ings

Modelling of erosion i s a lso important in the analysis for the reference Austra l ian t a i l i ng s s i te but with the addit ional complication that the doses from the eroded material for some options become major contributors to the doses. Water transport of radionuclides has to be considered as wel l as radon d ispers ion .

Waste rock, rather than t a i l i ng s can be the major source of radionuclides as shown in Figure 5. Water-borne radionuclides from waste rock are estimated to be responsible for over half the co l l ec t ive doses up to 10 4 years except where the t a i l i ng s cover erodes appreciably in that time (options 2 and 3, see Table 1 ) . Seepage from the t a i l i ng s and radon emanation from both t a i l i ng s and rock are much lower. The source term models are such that even at 10 4 years the co l l ec t ive dose commitments are increasing l i n e a r i l y .

As might be expected, removal of the excess waste rock as a source term (by burying i t in the mine) from the least expensive option (#1) i s one of the poss ib le optimum s t r a t eg i e s . This is apparent on Figure 6 which is the X-S plot for the Austra l ian options when the integrat ion is to 10 4 years . The t r iang les indicate when the waste rock p i l e is present. The next poss ib le optimum - option 5 - has an incremental cost -e f fect iveness nearly an order of magnitude greater . Note that as a result of the assumptions in the source term model the values of the incremental cost -e f fect iveness for these reference options a l so scale approximately inverse ly with integrat ing time in the time span to 10 4 years .

3.3 Canadian Reference Ta i l ings

In the analysis of the Canadian reference s i t e water-borne contaminants appear to be the major concern and their behaviour

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COLLECTIVE DOSE I 0 3 6 mairSv

EROSION, #2

WATER, WASTE ROCK EROSION, * 3

WATER, TAILINGS RADON, WASTE ROCK RADON,TAILINGS

FIG.5. Relative contributions of various source terms in the Australian reference tailings site to the collective dose commitment.

4 0

3 0

COST M$

20

2 4 6 8 10 12 14 16

COLLECTIVE DOSE COMMITMENT I 0 3 manSv

FIG.6. The incremental cost-effectiveness values for Australian tailings options when the collective dose commitment is estimated for lO* years. The key to the symbols is in Table 1.

as modelled serves to illustrate the possible role that maximum and average individual dose rates might play in determining the tailings management to be preferred. The implications of removing radium and thorium are also illustrated.

The model of the tailings behaviour allows all the leachable radionuclides to be removed from the tailings and to pass through (or sediment in) the local and regional waterways and be mixed in the North Atlantic. Figure 7 shows, for example, the variations in time of the concentration of radium-226 in a local lake for the reference base case with a

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LAKE

WATER 1

CONCENTRATION BASE___J

kBq-m3

O.I IMPERMEABLE DAM

0.01- i / i ., I 10 100 103 I 0 4

TIME - a

FIG. 7. The variations with time of the relative concentration of radium-226 in a lake below the Canadian reference tailings site for two options, the base case (1) and with an impermeable dam (3).

I 0 2 I 0 3 I 0 4

TIME -a

FIG.8. The increases of collective dose commitments with integrating time for two Canadian options (1, 3) by the aquatic pathway and for the base case (1) by the terrestrial pathway.

particular leaching model and also for the option in which the dam is assumed to be impermeable. This pattern of dispersion repeated through the hydrosphere allows the integration of collective dose commitment to be complete and, as expected, the integrals reach steady values as shown in Figure 8. The relatively small contribution of radon to the collective dose is also shown. However, the dose rate to individuals by the lake water pathway will depend on the release rate of the radionuclides. Whether this becomes a limiting criterion will depend on how well the release rates can be predicted for any of the options and what the actual values are.

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l$/mon-Svj

6(-Ra only)

2

o 3

0 500 1000 1500 2000 2500

COLLECTIVE DOSE COMMITMENT man-Sv

FIG.9. The incremental cost-effectiveness values for Canadian tailings options when the collective dose commitment is estimated for 10* years.

The cost-effectiveness plot for the Canadian tailings options is shown in Figure 9. The options 2 and 3 are seen to be ineffective; the retardation of loss of thorium-230 from the tailings allows ingrowth of radium-22 6 which, when it eventually leaches out, results in an increased collective dose. Removal of radium and thorium is the only option considered that appears to have a significant effect, albeit with a fairly high incremental cost-effectiveness. Figure 9 also indicates the effect of removing only radium in the mill (shown as "- Ra only"). Ingrowth of radium-226 from thorium-230 reduces the effectiveness of removal; the ingrowth in option 6 eliminates any saving of collective dose. Hence only removal of both radium and thorium is effective by this analysis so far. Not taken into account though are the problems of handling the radium and thorium and of storing or disposing of them.

The collective dose commitments calculated are delivered at individual dose rates from a few tens of microsieverts per year down many orders of magnitude. If the collective doses are only summed for the population group where the individual dose rates average more than a microsievert per year, then the values of incremental cost-effectiveness increase by an order of magnitude.

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4. Conclusions

In summary, some of the possibilities and problems of optimizing (in the radiological sense) the management of uranium mill tailings are apparent in a preliminary analysis of data generated by a group working under the auspices of the Nuclear Energy Agency of the OECD. Incremental cost-effectiveness values between some options differ by orders of magnitude. Such analyses may therefore have weight in deciding the preferred management strategy. The choice of integrating time for collective dose commitment and of dose rates down to which the collective doses are included in the summation may be important. This would be so if the predictions of the models used are shown to be sufficiently certain in actual applications for the incremental quantities needed to be significant in the time scales considered.

Acknowledgement

I have benefitted greatly from discussions with my colleagues in the working groups that are carrying out the NEA study.

References

[1] International Commission on Radiological Protection, Recommendations of the International Commission on Radiological Protection, ICRP Publication No. 26, Annals of the ICRP 1_ 3, (1977).

[2] Nuclear Energy Agency, The Radiological Significance and Management of Tritium, Carbon-14, Krypton-85 and Iodine-129 Arising from the Nuclear Fuel Cycle, OECD, Paris (1980).

[3] Joe, E.G. Pullen, P.F., Private Communication, 1982. [4] Lush, D.L., Snodgrass, W.J., Private Communication, 1982. [5] Volpe, R.L., Private Communication, 1982. [6] Overmyer, R.F., Groelsema, D.H., Martin, D., Private

Communication, 1982. [7] Burgess, P., Private Communication, 1982. [8] Davy, D., Private Communication, 1982.

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AQUATIC PATHWAY VARIABLES AFFECTING THE ESTIMATION OF DOSE COMMITMENT FROM URANIUM MILL TAILINGS

D.L. LUSH, W.J. SNODGRASS, P. McKEE

Beak Consultants Limited,

Toronto, Ontario,

Canada

Abstract

AQUATIC PATHWAY VARIABLES AFFECTING THE ESTIMATION OF DOSE COMMITMENT FROM URANIUM MILL TAILINGS.

As one of a series of studies being carried out for the Atomic Energy Control Board of Canada, the environmental variables affecting population dose commitment and critical group dose rates from aquatic pathways were investigated. A model was developed to follow uranium and natural thorium decay series radionuclides through aquatic pathways leading both to long-term sediment sinks and to man. Pathways leading to man result in both a population dose commitment and a critical group dose rate. The key variables affecting population dose commitment are suspended particulate concentrations in the receiving aquatic systems, the settling velocities of these particulates and the solid-aqueous phase distribution coefficient associated with each radionuclide. Of secondary importance to population dose commitment are the rate at which radionuclides enter the receiving waters and the value of the water to food transfer coefficients that are used in the model. For the critical group dose rate, the rate at which the radionuclides leave the tailings, the water to food transfer coefficients, the rate of water and fish consumption and the dose conversion factors for 2 1 0 Pb and 2 1 0 Po are of secondary importance.

1. Introduction

The Atomic Energy Control Board is currently sponsoring a series of studies aimed at estimating how various uranium mill tailing management techniques affect long term dose commitment. In this context long term is taken to mean the time taken for the leaching of relatively mobile radionuclides from the tailing mass.

The first set of studies focused on the effect of various milling and close out practices on the behaviour of the tailing mass through time. More specifically, these studies investigated the way in which engineered and geochemical processes affect the rate of release of radioisotopes from the tailing containment dykes, the degree of revegetation and surface stabilization that occurs, and options for in-mill reduction of radium-226 and thorium-230 to lower the specific

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activity of the tailings. More detail on these source term studies and the composite tailing area from which they derive may be found in the paper by Dr. William Snodgrass in this same volume. (1)

Other related studies have investigated natural variations on engineering containment structures such as the placement of tailings in deep lake basins where they are covered by several tens of meters of overlying water. (2)

The second set of studies in this series concentrated on defining those environmental transport pathways which are found in aquatic and terrestrial systems. These pathways were defined and the processes operational within them were quantified. The pathways were held constant through time except where they are affected by tailing discharge. The variable source term from the tailing mass, as defined by the first set of studies, was then fed into these pathways. The fate of uranium and natural thorium decay series radionuclides were traced through the various pathways to either natural long term environmental sinks where they were lost from the pathway or to man where they contributed to a critical group dose rate or population dose commitment. The calculations done as part of this study were managed by a modular computer program designed specifically for this task.

This paper presents the aquatic pathways which culminate in long term sediment sinks or man. It is broken up into a series of parts including sections on Environmental Transport, Food Chain and External Exposure Pathways Dosimetry and System Sensitivity. Possible critical group dose rates and population dose commitment patterns that may be associated with generic containment practices are also suggested.

2 . Aquatic Environmental Transport

Although this study was generic in nature, it focused on the Elliot Lake mining area of northern Ontario, Canada. The composite hypothetical tailings area which supplies the radionuclides to the aquatic system is located on the shores of a large lake. This lake is one of the headwater lakes of the Serpent River system which drains into the North Channel of Lake Huron. Lake Huron then drains into Lake Erie, Lake Ontario and eventually to the North Atlantic Ocean.

An aquatic transport model was developed to keep track of the radionuclides released and to follow their progress through the aquatic system. The model "partitions' radionuclides within any given lake into a series of 'compartments'. The principal compartments evaluated are water, particulates in the water column and lake sediments (Figure 1). The following provides a brief summary of the

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r-INGROwING PARTICLE 1

BURYING

FIG.l. Major mechanisms in lake model

processes responsible for determining the transport and fate of radionuclides in the lake and ocean systems.

It has been assumed that present water quality and biological processes operating within the lake and ocean systems are constant through time except as a f f ec ted by tailings discharges.

The first major body of water receiving the tailings source term is a local lake. As the tailings stream enters the lake it is instantaneously mixed with and assumes the general qualities of present day lake water. During the initial leaching process, the pH of the tailing stream wi l l be depressed from its present value o f 7-8 to a value of 6-7. This wi l l result in l i t t le change in the gross chemistry of the lake system. When mixing has occurred, adsorption of radionuclides on to particulates in the water column and uptake by fish and aquatic macrophytes wi l l commence. Adsorption for each of these components or their equivalent in each of the three systems are

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shown in Table I and JJ. Thus, for each time step as the input loading changes, the concentrations of various radionuclides in water, water column particulates, fish and aquatic plants also change.

The receiving lake for this study has been assumed to have a mean depth of 37 m and a naturally occurring mean annual suspended particle concentration of 0.1 mg/L in the water column. Each particle is assumed to have a settling velocity of 25 m/a. This settling velocity, coupled with the mean depth and particle sedimentation characteristics in the lake results in some of the radionuclides being incorporated into deep lake sediments and others into shoreline beach sediments which are potential contributors to external radiation dose from shoreline exposure. The major portion of the sediment accumulates in the deep depositional zones of the lake where it is continually being buried by new sediment. The net result is that the fresh surficial sediments will have a specific activity proportional to the activity of the particulates in the overlying water column and the deeper sediments will have an activity, corrected for decay corresponding to water concentrations during the time they were deposited. The sediments themselves, for modelling purposes, have been artificially split into three boxes. The surficial compartment 4 cm in the first lake, which varies in depth depending upon the lake and degree of mixing by invertebrates, is oxidizing in nature. The pore water concentration of radionuclides in these oxidized sediments is controlled by the burying rate and the adsorption processes typical of an oxidizing environment.

Below the oxidizing layer is a reduced layer where solid liquid adsorption processes reflect the change in oxidation-reduction potential. In the receiving lake this layer is 10 cm in depth. Radionuclides within these two compartments diffuse back into the overlying lake water.

Below the 14 cm depth is the third compartment and below this depth the transport back into the overlying water becomes insignificant. Accordingly, once they are buried in the third box they are assumed to be lost from the system.

As the characteristics of the tailing stream entering the receiving lake change with time from a high pH input (7-8) to a low pH input (2-3), the pH of the receiving lake is calculated to change from 6-7 to 4-5. Resultant chemical precipitation and dissolution processes become important in the case of thorium. At a low pH (4-5), thorium is very soluble as a thorium sulphate complex, but at pH 7-8, is very insoluble as thorium hydroxide.

When the tailings pore water goes acidic, available thorium dissolves and migrates out to the receiving lake as a pulse. Because of the near neutral pH in the receiving lake, much of the thorium

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TABLE I. ADSORPTION COEFFICIENTS, KD, USED IN THE MODEL (mL/g)

Sediments* Sediments* Radionuclide Shield Lake Gre,at Lakes/Ocean

U-238, U-234 10 000 500

Th-228, Th-230, Th-232 5 000 50 000

Ra-226, Ra-228 500 200

Po-210 1 000 1 000

Pb-210 1 000 1 000

* Coefficients in water column are lOOx greater

TABLE II. SUMMARY OF FOOD CHAIN TRANSFER COEFFICIENTS (pCi/L)/(pCi/kg)

Isotope Environmental Compartment Boney Fish

water macrophyte fresh marine marine moose (wild rice) water shellfish

U-238 1 20 10 10 10 1.74

U-234 1 20 10 10 10 1.74

Th-230 1 30 30 10 000 2 000 1.53

Ra-226 1 50 50 50 100 4.85

Pb-210 1 4 300 300 170 .329 Po-210 1 40 50 3 000 1 600 2.79

Th-232 1 30 30 10 000 2 000 1.53

Ra-228 1 50 50 50 100 4.85

Th-228 1 30 30 10 000 2 000 1.53

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reprecipitates to the lake sediments. The remainder of the thorium undergoes normal lake processes of adsorption, settl ing and transport downstream. Upon complete oxidation of pyrite within the tailings, the tailings pH and that of the receiving lake return to near neutraL

During and after release of the radionuclides' from the tailings, natural lake and sediment processes continue. On the bottom of the lake, sediment accumulation wi l l eventually bury contaminated sediments, eliminating transfer of radionuclides back into the overlying water column by diffusion. Similarly, shoreline erosion wi l l continue and shore deposited radionuclides wi l l slowly work their way into deeper lake sediments. These sediments wi l l eventually become buried and the radionuclides they contain wi l l be lost from the system.

As water and its soluble radionuclides move out of the receiving lake, they pass through a series of downstream lakes. In each lake the same processes occur. Soluble radionuclides adsorb onto particulates in the water column and sett le to the lake sediments or contribute to beach sediment act iv i ty. Those radionuclides which do not adsorb to particulates are taken up by fish and macrophytes, or are washed downstream to the next lake. With each lake the adsorption coef f ic ients, which influence the partitioning between soluble and particulate phases, hydraulic inflows and outflows, sedimentation rates, fish and macrophyte production, water consumption, etc . change according to the environmental conditions in each lake.

In the North Atlantic Ocean, the treatment of radionuclides is somewhat di f ferent. They first enter a surface water circulation system where transfer to human exposure pathways (fish, shellfish, beach sediments) and sedimenting particulates occurs. Once a radionuclide atom has sett led out of the surface layers (top 75 m), it enters the deeper waters. From the deep waters, it can sett le to the deep sediments and be lost to the surface water circulation or be carried back to surface waters by upwelling. This is shown schematically in Figure 2.

3. Food Chain and External Exposure Pathways

Foodchain and external exposure pathways are mediated, with the exception of direct water intake, by a transfer of radionuclides from the solution phase to the solid phase. This transfer may be abiotic in nature such as the adsorption onto clay or silt particles suspended in the water column or biotic in the case o f uptake by algae, fish, shellfish and aquatic macrophytes. Uptake by sedimenting particulates contributes to beach material act iv i ty and thus to external dose. As a result of uptake by biological systems

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SURFACE WATER

PROFUNDAL WATERS

PROFUNDAL SEDIMENTS

FIG.2. Major mechanisms in ocean model.

from the aqueous phase, the potential for transfer to man and a resultant internal radiation dose exist.

In evaluating this latter route, a cr i t ical pathway approach has been employed. This involves the identif ication from the l iterature of the most important aquatic food chains leading direct ly or indirectly into man. Coupled with this is the selection, again based upon literature values (3), of transfer coef f ic ients for the radionulcides of the U-238 and Th-232 decay series in freshwater and marine systems. The values chosen for the most important radionuclides are summarized in Table II.

The use of these transfer coef f ic ients allows the direct calculation of body burdens of radioisotopes in organisms such as fish, shellfish and aquatic plants which may feed direct ly into the diet of man. In addition to internal exposure through consumption of food and water, the cr i t ica l group and regional population wi l l rece ive a certain dose component from external exposure. This wi l l occur through immersion in water and walking or lying on beach sediments which contain radioact ive materials derived from upstream uranium tailings material. A brief discussion of the food chains and exposure pathways considered to be most important to the cr i t ica l group and in the various regional systems fol lows:

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vo o

TABLE III. CONSUMPTION PATTERNS AND LIFESTYLE HABITS OF THE FOOD CHAIN MODEL (CRITICAL GROUP)

Consumption Pattern Lifestyle Habits

Adult Infant Adult Infant

Water Consumption 730 L/a 3 30 L/a % of time water immersion 1.3% 1.3%

Wild Rice Consumption 15.6 k g / a nil % of time walking on contaminated beach

.68% .68%

Fish Consumption 20.1 kg/a 2.2 kg/a % of time lying on beach .37% .37%

Moose Consumption 35 kg/a nil

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3.1 Critical Group

For the purpose of this study, a synthetic critical group was defined as living year round on the shores of the receiving lake. This group consists of both infants and adults and has consumption patterns and living habits which would result in a maximum reasonable exposure to radionuclides released from the synthetic tailings site located on the shores of the lake.

These consumption habits assume that all drinking, bathing and wash water come directly from the surface waters of the receiving lake.

For food consumption it is assumed that wild rice could be grown in the lake. It is also assumed that all fish consumed by the critical group are derived from the receiving lake to its limit of production. The moose consumed by the critical group are assumed to derive all of their drinking water and the aquatic macrophyte component of their diet from the lake.

The critical group's external exposure comes from immersion (swimming or bathing) in the receiving lake water and walking on contaminated shoreline sediments. The degree of sediment contamination is calculated by taking the specific activity of the general lake sediments and correcting them for a shoreline winnowing effect. The resultant external exposure is based upon a specified contaminated sediment depth, a shoreline width factor and an exposure factor. Food consumption and lifestyle assumption affecting dose to the critical group are shown in Table TU.

3.2 Local Group

This local group comprises a population of about 15 000 individuals, the majority of which live in a nearby town. In evaluating the dose to this group, several approaches were taken.

In the case of water consumption, water immersion and external exposure to contaminated sediments, the population that is presently located on or immediately adjacent to the local river system was assumed to derive all of its drinking, washing and bathing water from the system downstream of the tailing area. Consumption of fish from the local river system was assumed to be 33% of the maximum sustainable yield based upon present water quality and calculated using the Morpho-edapic index (4). No corrections for yields changing with future changes in lake water chemistry related to acid release were made.

The quantity of moose consumed for each lake drainage basin in the system was related to the number of moose killed in the local

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area, the average moose population density and the drainage area for each lake. The radioisotope concentration in moose meat was related to the lake concentration by a bio accumulation factor calculated by this study and shown in Table II. This bioaccumulation factor is based upon bioaccumulation factors between macrophytes and water and on moose macrophyte and water consumption habits. The quantity of moose consumed was then assumed to be spread throughout the local population when calculating the local population dose.

3.3 Great Lakes (Regional) Group

This regional group consists of 38.8 million individuals living around three Great Lakes (Huron, Erie and Ontario), who derive their drinking and washing water from these lakes. The amount of t ime they spend bathing, washing and swimming, estimated at 0.3% of the t ime, is similar to that of the Local Group.

In estimating the dose to the Great Lakes regional population, the commercia l fish catch for each of the three Great Lakes downstream of the local r iver system was estimated based upon commercia l catch data from the 1970s. Concentrations of radionuclides in fish from each of these lakes was calculated based upon the concentration factors in Table II. The catch was assumed to be consumed by the Great Lakes group to calculate the fish contribution to the regional dose, even though a high percentage of the commercia l fish catch is exported out of the Great Lakes basin.

Within the Great Lakes basin, there are no significant contributions to the regional dose from aquatic plans such as wild r ice and/or from mammals such as moose.

3.4 North Atlantic Regional Group

The waters draining the synthetic tailings area, after passing through the Great Lakes, eventually discharge to the North Atlantic to mix with the oceanic surface waters. In the evaluation of the North Atlantic regional dose, a population of 38 5 x 106 persons was assumed to have access to the coastline for recreational use. External dose to this group was from swimming, walking on the beach and sunning on the beach. No dose occurred to this group from drinking water from the North Atlantic, as seawater is not consumed.

The hydraulic model for the North Atlantic allows for the separation of surface and deep waters and the calculations of radioisotope concentrations in each of these dif ferent water masses. Surface water concentrations were used to determine the concentration of the radioisotopes in the commercia l fish and

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shellfish from the North Atlantic. The concentration factors used are shown in Table U. Fish and shellfish consumption was the major contributor to internal dose.

4 . Dosimetry

Radioactive materials released to surface water will lead to human exposure through ingestion of water and foods and from direct exposure to contaminated shoreline and water immersion. The more important exposure pathways and a general outline of dose calcula­tions for the individual are shown in Figure 3.

The effective dose equivalent for individuals, H E , is defined as:

H E = E W l H T + 0 . 0 1 H s k i n ( 0 1 )

where: = dose equivalent in tissue T;

= weighting factor for each tissue, representing the ratio of the stochastic risk from irradiation of the tissue, T, to that for the whole body when uniformly irradiated;

H . . = the skin dose. skin

The weighting factorsw-p, have been defined for all body organs and tissues, except for skin, plus hereditary effects for the first two generations.

The collective effective dose equivalent^ , is given by:

SE = A N ( H E ' D HE ( 0 - 2 )

o where: N(Hg) is the number of individuals receiving an effective equivalent in the range H £ to Hg+dHg.

The collective effective dose equivalent commitment, Sg, is obtained by integrating the collective effective dose equivalent rate (say, rem/year) over all time, i.e.:

C r 0 0

S E = J S E ( t ) d t ( 0 - 3 )

o If integration is limited in time, the resulting integral is called

the truncated or incomplete collective effective dose equivalent commitment.

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SOURCE PATHWAY

CONCENTRATION FACTOR

pciAg pCi/day

A

CONCENTRATION IN LAND ANIMALS

(pciAg)

ANIMAL INTAKE OF WATER AND AQUATIC FOODS (kg/day)

CONCENTRATION CONCENTRATICN FACTOR IN IN FISH OR

AQUATIC BIOTA AQUATIC PLANTS pciAg (pciAg) pCi/ l i t re

CONCENTRATION FACTOR IN SHORELINE SEDIMENT pciAg

pCi/ l i t re

CONCENTRATION IN SHORELINE

SEDIMENT (pciAg)

DIET

CONSUMPTION RATE

(kg/year)

CONSUMPTION RATE

(kg/year)

WATER INTAKE RATE

( l i tres/year )

HABIT DOSE CONVERSION FACTOR

SWIMMING (Fraction of time)

EXPOSURE FACTOR

(Fraction of time)

Reny/pCi

Rem/pCi

Renv/pCi

Reny/Year pCi/ l i t re

Reny/Year pCi/kg

DOSE

INTERNAL DOSfl

(Rem/year)

INTERNAL DOSE

(Rem/year)

INTERNAL DOSE

(Reny/year)

EXTERNAL DOSE*

(Rem/year)

EXTERNAL DOSE

(Rem/year)

FIG.3. Exposure pathways and individual dose calculations for radionuclide releases to surface water.

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For internal exposures, S £ is more conveniently represented as:

= H,, I.C. (t) dt ( 0 . 4 ) E bj , o

where: I = tota l intake rate of food, water or air by the population (kg/a or m^/a);

C(t) = concentration of radionuclide in food, water or air (pCi/kg or pC i/m 3 ) ;

Hg = population averaged e f f ec t i ve dose equivalent per unit of radioactiv ity intake (rem/pCi).

The quantity LC. ( t ) is the co l lec t ive intake rate (pCi/a). H E for the population is approximated by the 50-year integrated commit ted e f f e c t i v e dose equivalent for adults, H50E) which is commonly tabulated for occupational exposures.

The incomplete co l l ec t ive e f f e c t i ve dose equivalent commitment, which is the quantity evaluated in this study, is the sum of the e f f e c t i ve dose equivalent commitments ( integrated to a finite t ime T ) , rece ived by al l populations in all identif ied regions for all radionuclides and through all exposure pathways. To account for the risks from hereditary e f f ec ts to populations beyond the first two generations as wel l as from fatal skin cancer, the total incomplete co l l ec t ive e f f ec t i ve dose equivalent commitment, Sy, is calculated as:

S v = s£ + 0.25 S C , + 0.01 S C . . , n K , Y E gonads skin ( 0 . 5 )

Dose conversion factors used in this study for external and internal exposure for each parent plus daughters in equilibrium are summarized in Table IV.

Selection of isotopes considered the fact that the daughters of the various isotopes listed have half- l ives which are short compared to the study period of the order of many centuries. The dose factors for external exposure to contaminated shoreline sediment is labeled Individual-External-Beach for the Control Group and Co l l ec t i ve -External-Beach for the di f ferent population groups (units: rem/a per pCi/kg ) . They consider that exposed shoreline sediment is uniformly contaminated to some depth and include corrections for shore width. These factors are based upon the air gamma dose at 1 m above sediment and are corrected to e f f ec t i ve dose equivalent. The skin dose is based upon the sum of photon and electron doses at 70 j*m below the body surface corrected to e f f ec t i ve dose equivalent.

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TABLE IV. SUMMARY OF D O S E CONVERSION F A C T O R S F O R D O S I M E T R Y M O D E L

Dose Conversion F a c t o r s 3

Collective Individual-External Individual-External -Internal Collective-External

1 year Adult Swim Beach Adult Swim Beach

U-238 .410E- 06 .240E- 06 .370E- 06 .600E- 07 .240E- 06 .483E- 06 .210E- 07 U-234 .480E- 06 .280E- 06 .230E- 07 .450E- 09 .280E- 06 .290E- 06 .560E- 09 Th-230 .130E- 05 .560E- 06 .222E- 07 .480E- 09 .500E- 06 .276E- 07 .600E- 09 Ra-226 .264E- 05 .107E- 05 .262E- 04 .180E- 05 .810E- 06 .450E- 04 .220E- 05 Pb-210 .130E- 04 .310E- 05 .980E- 07 .180E- 08 .310E- 05 .115E- 06 .220E- 08 Po-210 .500E- 05 .170E- 05 .132E- 09 .900E- 11 .170E- 05 .158E- 09 .110E- 10 Th-232 .730E- 05 .270E- 05 .185E- 07 .380E- 09 .270E- 05 .229E- 09 .470E- 09 Ra-228 .370E- 05 .850E- 06 .142E- 04 .900E- 06 .850E- 06 .175E- 04 •116E- 05 Th-228 .260E- 05 .440E- 06 .240E- 04 .140E- 05 .440E- 06 .293E- 04 .172E- 05

Read .410E-06 as 0.410 X 10"6, etc.

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For internal exposure to radionuclides, the Committed Effective Dose Equivalent conversion factors are given for Individual-Internal for 1-year-olds and adults of the Critical Group and for Collective-Internal-Adult for the population groups. These factors are those calculated for intake by adults, integrated over a period of 50 years after uptake. Gonodal dose factors, available only for Ra-226 and Ra-228. They are used in collective effective dose equivalent commitment calculations as shown in equation 0.5.

Use of these dose conversion factors together with the consumption rate of foods (internal exposure) and the exposure rate to contaminated sediment and water (external exposure) given previously, permit calculation of the internal and external dose rates (e.g., rem/a) for the Critical Group and the different population groups (local, regional, oceanic). Interpretation of the effective dose equivalent commitment rate from all radionuclides through all exposure pathways to the time T gives the incomplete collective effective dose commitment for that population. This quantity is hereafter abbreviated and called the cumulative population dose, the population dose or the population dose to time T.

4.1 Population Dose Commitment and Critical Group Dose Rate

The time trend of the cumulative population dose for the three subgroups (local group, Great Lakes, North Atlantic) and the global dose are shown in Figure 4 for the base case reflecting a relatively rapid dispersion of radionuclides. Two distinct inflections and one less distinct inflection are observed at 160 years, 186 years and after 380 years. For the North Atlantic and the global population dose, the inflections are somewhat after these points in time due to the travel time from the tailings to the North Atlantic (38 a). These points in time correspond to changes in the source term.

The local population has the lowest total dose, with the regional group being between the local and oceanic population groups. The oceanic, regional and local groups account for 56%, 3 3 % and 11% respectively of the global dose (Figure 4).

The contribution of Ra-226, Pb-210 and Po-210 through the water consumption and fish pathways constitute almost all of the population dose. Other pathways associated mainly with Ra-226 and daughters give minor contributions.

For the other management options, there is no significant difference in the time trend and only the time scale is different. For a vegetated tailings and engineered isotope removal (option), the time scale is approximately the same. For the option involving an impermeable dam, the time scale runs to 10 000 a and the rate of increase is approximately linear.

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FIG.4. Cumulative population dose commitment trend (leaky containment structure).

The population doses from all other isotopes (U-238, U-234, Th-230, Th-232, Ra-228, Th-228) is either small or insignificant compared to Ra-226, Pb-210 and Po-210 as discussed above. External exposure due to swimming, bathing, beach-walking and sunning is at least an order of magnitude and typically several orders of magnitude lower than internal pathways. Hence the principal routes o f concern through aquatic pathways for dose commitment calculations are ingestion of food (mainly water and fish), containing Ra-226 and daughters.

The calculated radiation dose for the various population groups is given in Table V for di f ferent management and eningeering alternates. Calculations as a function of t ime provide some evidence for benefits derived due to delaying the t ime of release from the tailings of the radioisotopes. There is a small decrease in population doses due to vegetat ing the tailings during the initial 100 years. This results from a lower rate of release of radioisotopes caused partly by the lower hydraulic flow rate through the tailings (10%). It also results from larger quantity of calcium and sulphate from acid formation and consumption reactions (30%) in the tailings. However, for total population dose, there is essentially no di f ference between the vegeta ted and unvegetated options. There is a significant t ime di f ference in radionuclide release between the impermeable dam option and the first two cases, due to the hydraulic flow rate being an order of magnitude lower. There is only a small d i f ference between the total population doses. The total dose in the instance where the tailings are retained longer is larger than where the radionuclides are

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T A B L E V . C U M U L A T I V E P O P U L A T I O N D O S E F O R D I F F E R E N T M A N A G E M E N T O P T I O N S

CUMTLATIVE DOSE (REM) Time Serpent Great North

CASE DESCRIPTION OF OPTION l (a) River Lakes Atlantic Global

1 Permeable dam 100 3 600 9 600 9 700 23 000 1 000 22 000 68 000 120 000 210 000 10 000 - - - -

2 Permeable dam; 100 2 200 6 000 6 100 14 000 vegetated cover 1 000 22 000 66 000 110 000 200 000

10 000 - - - -3 Impermeable dam 100 290 890 140 1 300

1 000 2 800 8 900 15 000 26 000 10 000 25 000 79 000 150 000 250 000

4 Permeable dam; 90% 100 1 500 3 100 2 500 7 000 removal of mobilized 1 000 3 400 8 900 13 000 24 000 Radium and Thorium 10 000 - - - -

5 Permeable dam; 100 930 2 000 1 800 4 700 vegetated 90% removal 1 000 2 900 8 100 13 000 24 000 of mobilized Radium 10 000 - - - -and Thorium

6 Impermeable dam; 90% 100 100 300 500 900 removal of mobilized 1 000 450 1 400 2 300 4 100 Radium and Thorium 10 000 2 700 8 400 15 000 27 000

assumed to migrate out at a faster rate . This is because radium ingrowing from Th-230 in the tailings becomes significant over a t ime frame of 1 000 years. Approximately 60% of Ra-226 and 95% of Th-230 is chemical ly leached in the mill and leaves the tailings during this t ime in the case we investigated with a leaky retaining dam.

Where engineered removal o f 90% of thorium and radium mobil ized from ore by acid leach has been postulated, the calculated population dose is approximately 10% of the corresponding values for cases with no engineered removal of thorium or radium. The decrease re f lects the amount of engineered removal of isotopes; the decrease is not exact ly 10% because of assumptions relating to the value of the initial concentration of radioisotopes in the tailings pore water.

These data show that there is no significant di f ference in management options upon the tota l population dose (the co l l ec t i ve e f f e c t i v e dose equivalent commitment) , unless engineering removal

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T h - 2 3 0 R a - 2 2 6 P b - 2 1 0 P o - 2 1 0

o 100 200 300 400 500 600 700 800 9O0 1000

TIME (YEARS)

FIG.5. Water column concentration of radioisotopes in receiving lake (leaky containment

of isotopes is used. If one can view the saving of a population of people from exposure for a certain t ime period (e.g. 1 000 years) as a significant benefit , then management options which minimize the hydraulic flow rate through tailings provide a significant benef it .

The calculated concentration trend of radioisotopes in the receiving waters is shown in Figure 5. These changes re f lec t geochemical and biological processes occurring within the tailings mass itself and relate to :

i) t ime to completely use up acid neutralizing capacity, ii) t ime of acidic conditions iii) post-acidic conditions when gypsum is being dissolved, and iv) post-gypsum phase, when no more gypsum is available to be

dissolved.

These changes are discussed in the paper by Dr. W.J. Snodgrass in this same volume. The calculated cr i t ica l group dose rate trend is shown in Figure 6 for these water concentrations. It shows 4 di f ferent patterns (t ime 0-175 a, 175-186 a, 186-380 a, and 380 a ) , three of them corresponding to geochemical changes occurring in the tailings themselves and one relating to a change in the biology of the receiv ing waters and hence in cr i t ical group diet.

The peak dose rate occurs during the third t ime period. During the second t ime period, Ra-226, Pb-210 and Po-210 concentations in the receiving lake increase dramatically due to a release of Ra-226

structure).

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TOTAL WATER FISH

under acidic conditions associated with the breakdown of geothite derived from jarosite. This causes an initial increase in the dose rate . However, this period is closely fol lowed by the receiv ing lake becoming acidic, reducing the fish population dramatically and inducing a shift of wild r ice to other species of macrophytes. Accordingly, during the period, it is assumed fish and macrophytes are unavailable and that water and moose consumption are the only two food pathways to the cr i t ical group.

Following this period, the lake pH re-adjusts and fish and wild r ice re-appear in the diet of the cr i t ical group. An analysis of the data shows that management of the tailings design is as important as the engineered removal of radioisotopes. The e f f ec t of tailings design is to change the flow rate through the tailings by up to an order of magnitude, causing a commensurate decrease in the dose rate. Decreasing the flow rate by an order of magnitude causes the same decrease in cr i t ical group dose rate as does engineered removal of thorium and radium. Combining the two options causes a two order of magnitude diminuation in dose rate to the cr i t ical group.

4.2 Sensitivity Analysis

A sensitivity analysis was conducted to determine the sensitivity o f dosimetry calculations to errors in di f ferent parameters in the model and to estimate the numerical di f ference between population doses required in order that this di f ference be considered

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significant. The analysis was l imited to components of the loading model, the lake model, the food-chain model and the dosimetry model associated with Ra-226, Pb-210 and Po-210 because these isotopes cause almost all of the cr i t ica l group dose rate and the cumulative population dose.

The population dosimetry calculations are most sensitive to the water column concentration of particles, their settl ing ve loc i ty and their adsorption coef f ic ient in the Great Lakes. Of secondary significance is the oceanic part ic le concentration, the adsorption coef f ic ient and settling ve loc i ty of particulates. The prime cause of aquatic properties in the Great Lakes being so important is because it determines the amount of Ra-226 discharged from the Great Lakes to the oceans. The ocean constitutes approximately 60% of the global dose. Approximately 2 1 % of Ra-226 discharged from the tailings reaches the oceans. Since Po-210 incorporated in fish is the main source of population dose commitment from the oceans and since there is adequate t ime for ingrowing from Ra-226, processes which control the amount of Ra-226 gett ing into the ocean are most important. Also since the Great Lakes constitute in excess o f 30% of the global dose, processes which cause Ra-226 and Pb-210 removal to the Great Lake sediments are also quite influential upon the Great Lakes regional population dose commitment.

A t the next leve l of model sensitivity (a level substantially lower than that of the first level) are factors describing the rate at which radionuclides leave the tailings and the value of food-water transfer coef f ic ients. Irreversible adsorption of Ra-226 in the tailings, the Pb-210 and Po-210 water- food transfer coef f ic ients, the Po-210 dose conversion factor and the quantity of oceanic fish consumed are the most important factors. Irreversible adsorption prevents Ra-226 solubilized with gypsum from leaving the tailings while the water- food transfer coef f ic ients determine the quantity of radionuclides associated with ingested food.

The tota l population dose commitment is re lat ive ly insensitive to such tailing processes as the hydraulic flow rate, the gypsum solubility product or the tailings adsorption coef f ic ient and to such cultural habits as where the fish in the receiving system are consumed.

For the cr i t ical group dose rate, the model is sensitive to the hydraulic flow rate through the tailings, the gypsum solubility product, the tailings adsorption coef f ic ient and the degree o f irreversible adsorption of Ra-226 in the tailings. It is also equally sensitive to the consumption rate of water and fish, to the food-water transfer coef f ic ients and to the dose conversion factors for P b -210 and Po-210, It is re lat ive ly insensitive to other factors.

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References

1) Snodgrass, W.J., D. Lush, 1982. Implications of A l ternat ive Geochemical Controls on the Temperal Behaviour of Elliot Lake Tailings. Published in International Symposium, Albuquerque, NM. 10-14 May 1982, these Proceedings (Paper IAEA-SM-262/54).

2) A tomic Energy Control Board (Canada) contract no. 34-5-2-15. (1982) A qualitative evaluation of long term behaviour of uranium mill tailings placed in deep lakes. Prepared by - Beak Consultants L imited.

3) Thompson, S.E., C.A. Burton, D.J. Quinn and Y .C . Ng. 1972. Concentration factors o f chemical elements in edible aquatic organisms. Rev . 1, Lawrence Radiat. Lab., USAEC Rep. U C R L -50564.

4) Ryder, R .A . 1965. A method for estimating the potential fish production of north-temperate lakes. Trans. Amer . Fish. Soc. 94(3):214-218.

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COMPARATIVE ASSESSMENT OF RADIOLOGICAL IMPACT FROM URANIUM AND THORIUM MILLING

Y.C. Y U A N , C.J. ROBERTS Argonne National Laboratory, Division of Environmental

Impact Studies, Argonne, Illinois, United States of America

Abstract

COMPARATIVE ASSESSMENT OF RADIOLOGICAL IMPACT FROM URANIUM AND THORIUM MILLING.

Sources and exposure pathways associated with transport of radon and thoron gases and particulate materials containing uranium and thorium and their decay products from a reference uranium mill and a thorium mill are described. Potential radiological impacts resulting from operation of the mills are summarized and compared. Individual exposures are evaluated relative to the limit of 25 mrem per year imposed by the USEPA uranium fuel cycle standard, 40 CFR 190. Calculations indicate that this limit might not be met within about 3 km downwind from either the model uranium or thorium mill. The results of this assessment also indicate that radiation protection standards that limit individual doses from radon and thoron should be established.

1. INTRODUCTION

The nuclear power reactors currently in operation were designed in a time when supplies of uranium were assured and inexpensive, and when nuclear arms p ro l i f e r a t i on was of less concern than i t is today. In order to conserve valuable uranium resources and deter nuclear p r o l i f e r a t i on , r e v a l ­uation of various concepts and fue l - cyc le options as a l t e r ­natives to the current ones (LWR-Recycle-LMFBR) may be neces­sary. A balanced evaluation of various fue l - cyc le a l t e rna ­t ives should include the fol lowing issues: ( 1 ) economic and technological f e a s i b i l i t i e s , ( 2 ) uranium resource u t i l i z a t i on and long-term energy supply, ( 3 ) safeguards against p r o l i f e r ­a t ion , and ( 4 ) environmental impacts. The scope of this paper is l imited to the l a s t of these issues and to only the f ront -end of the fuel cycles . The object ive is to provide a consis ­tent , quantitat ive evaluation of the r e l a t i ve rad io log ica l impacts from uranium and thorium mi l l ing operations and to compare the predicted dose consequences with current U.S. regulatory standards.

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2. MODEL MILLS AND THEIR ENVIRONMENT

In order to perform a comparative assessment of uranium and thorium mi l l s , i t was assumed that the character i s t ics of the thorium mill and i t s environs were s imi lar to those of the hypothetical "model" uranium mill developed by the U.S. Nuclear Regulatory Commission [ 1 ] . Most of the character i s t ics of th i s model uranium mill were derived from typical mi l l s currently in operation in the United States. At present, no thorium mill i s operating in the United States ; however, the character­i s t i c s , processes, operating procedures, and e f f luents of a thorium mill are not expected to be s i gn i f i c an t l y d i f f e rent from those of uranium mi l l s .

Each model mill is assumed to have an ore-processing capacity of 1800 t per day, which was the average uranium-mi l l ing rate of the 16 conventional mi l l s in operation in the United States in 1976. The average ore ac t i v i t y for U-238 and Th-232 is assumed to be 280 pCi/g, corresponding to ore grades of 0.1% U 3 0 8 and 0.3% Th0 2 , respect ive ly . The ore is t rans ­ported from the mine to the mill and stored on pads to await processing. With a recovery e f f ic iency of 93%, the average annual production is equivalent to about 520 t of U 3 P 3 or 1560 t of Th0 2 . The pr incipal operating character i s t ics of the model mi l l s are summarized in Table I .

Table I . Summary of Principal Operating Character ist ics of the Model Mi l l s

Character ist ic

Ore process rate

Average ore grades

Ore a c t i v i t y , U-238 or Th-232 (each with progeny in secular equi l ibr ium)

Ore storage time

Operating days per year

Extraction e f f ic iency

Average annual production

Area of t a i l i n g s impoundment

Total area control led by mi l l ing operation

Value

1800 t per day

0.10% ( U 3 0 8 ) ; 0.3% (Th0 2 )

280 pCi/g

12 days

310

93%

520 t U 3 0 8 ; 1560 t Th0 2

equivalent

100 ha (50% dry beach a rea )

300 ha

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For the purpose of comparative impact evaluat ion, each model mill i s postulated to be at the center of a hypothetical geographic region with a radius of 80 km. Because most thorium resources are located in the western portion of the United States , the character i s t ics assumed for the region surrounding the model uranium mill are a lso considered to be app l icab le to the hypothetical environs of the thorium mi l l . For the model uranium mi l l , these character i s t ics were based on weighted average values for the physiographic uranium-production regions of the United States [ 1 ] . The population in this model region is assumed to be 57,300 persons, corresponding to a density of 2.85 persons per km2, character i s t ic of a sparsely populated region in the western United States.

3. ASSESSMENT METHODOLOGY

To assess the rad io log ica l impact of uranium and thorium mi l l ing operations, i t is necessary to give careful consider­ation to the sources and exposure pathways associated with transport of radon and thoron gases and par t i cu la te material containing uranium and thorium and the i r decay products. The potentia l sources of r ad ioact iv i ty of su f f i c i en t magnitude to warrant consideration are : ( 1 ) the i n i t i a l stages of mi l l ing , including ore storage , feed, crushing and leaching; ( 2 ) the f ina l stage of product preparation, including drying and packaging, and ( 3 ) the mill t a i l i n g s or waste residue from the operations. The radioact ive emissions generated by the model mi l l s are summarized in Table I I . The pr incipal pathways through which released rad ioact iv i ty may reach people are : ( 1 ) d i r ec t , external exposure to gamma rays from radionuclides in the a i r or on the ground; ( 2 ) inhalation of rad ioact iv i ty into the lungs, poss ib ly fol lowed by red i s t r ibut ion to other organs of the body; and ( 3 ) ingestion of r ad ioact iv i ty in foodstuf fs . These sources and pathways are i l l u s t r a t ed diagrammatically in Fig. 1.

To evaluate rad io log ica l impacts from the thorium m i l l s , the Uranium Dispersion and Dosimetry (UDAD) computer code [ 2 ] developed to provide estimates of potential radiat ion exposure to indiv iduals and to the general population in the region of uranium mi l l s was modified to include thorium-232 ser ies radionuclides (THODAD). In these models, the re lease of t a i l i n g s pa r t i c l e s by wind action is estimated from theoret ­ical and empirical wind-erosion equations based on the wind speed, p a r t i c l e s ize d i s t r i bu t ion , and surface roughness. Atmospheric concentrations of rad ioact iv i ty from a l l sources are calculated using a dispersion-deposit ion-resuspension model. Source depletion as a resu l t of deposition and rad io ­act ive decay and ingrowth of radon progeny is included in a

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Table I I . Radioactive Emissions Generated by the Model Mi l l s

Thorium Milling Operations Uranium Milling Operations Particulates, mCi/a Particulates, mCi/a

Emission Source Thorium3 0thersb

Rn-220, Ci/a Uranium0 T, . d Thorium 0thers e

Rn-222, Ci/a

Ore storage, crushing and leaching 1.5 1.5 20 000 1.5 1.5 1.5 70

Product drying and packaging

150 0.15 - 150 0.73 0.15 -

Tailings pile 8.7 120 300 000 8.7 120 120 4400 Dispersed ore &

tailings - 140 000 - 24

aTh-232, Th-228 bRa-228, Ra-224, Pb-212, Bi-212 cU-238, U-234 dTh-230 eRa-226, Pb-210, Po-210

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Table I I I . Dose Conversion Factors for Radon-222 and -220 Progeny ((mrem/a)/(pCi/m3))

Organ or tissue

Radon-222 Radon-220

Organ or tissue Po-•218 Pb-214 Bi-•214 Po-216 Pb-212 Bi-•212

Tracheobronchial 0. 36 0.77 0. 51 0.001 0.30 0. 78

Pulmonary 0. 07 0.57 0. 23 0.0001 3.8 0. 67

Kidney 0. 002 0.045 0. 033 <0.0001 2.0 0. 17

standard sector-averaged Gaussian plume model. The average a i r concentration at any given location is assumed to be constant during each annual re lease per iod, but to increase from year to year because of resuspension. Surface contamina­tion is calculated by including buildup from deposit ion, ingrowth of radioact ive progeny, and removal by radioact ive decay and weathering processes. The estimation of p a r t i c l e deposition and se t t l i ng ve loc i t i e s is based on pa r t i c l e s i z e , density, and certain physical and chemical processes that influence the behavior of smaller p a r t i c l e s . The ca lcu lat ion of resuspension includes a factor that decreases as a function of time to account for the reduced a v a i l a b i l i t y of previously deposited pa r t i c l e s as a resu l t of natural processes.

Prediction of the inhalation dose to an individual is based on the ICRP Task Group Lung Model (TGLM)[3] . Following th is model, the f ract ion of inhaled ac t i v i ty deposited in the lung compartments is determined by the aerodynamic propert ies of the pa r t i c l e s . The rates of clearance from the lung are dependent on the s o l u b i l i t y of the deposited materia ls . The concentration of radon or thoron progeny in the a i r at a given location is dependent on the t r ans i t time from the source. Calculation of the concentration is based on the distance travel led and the wind speed. After the i r formation, radon and thoron decay products are rapid ly attached to dust pa r t i c l e s in the a i r , and most of the inhaled ac t i v i t y is carr ied by such pa r t i c l e s . The f ract ion of radon and thoron progeny deposited in the lung is estimated using the model developed by Jacobi [ 4 ] as a function of the free-atom fract ion in the inhaled a i r . The free-atom fract ion is dependent on the decay h a l f - l i f e and the aerosol concentration. In this paper, the f ract ion of uncombined atoms is assumed, as suggested by Jacobi , to be 25% for Po-218, 100% for Po-216 and 1% for the subsequent radionuclides in the radon and thoron decay chains. The f ract ions of radon and thoron decay products deposited in the lung, again fol lowing the model developed by Jacobi [ 4 ] , are 8% and 40% for the tracheobronchial region and the pulmonary

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ORE FROM MINES

FIG.l. Sources of radioactive effluents from the model mill and exposure pathways to man.

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Table IV. Maximum Individual Dose Commitments at Hypothetical Locations Resulting from the Final Year of Uranium Mill Operations

Doses (mrem/a)

Location Exposure Pathway

Bone Lung (P/TB) a Kidney Location

Exposure Pathway Part.b Rn c Part. Rn Part. Rn

Site boundary External (ground) 2.1 63 1.0 52 1.2 55 0.64 km External (cloud) - 1.1 - 0.9 - 0.9

Inhalation 100 1 120/3 190/330 28 13

Ranch External (ground) 0.2 4.8 0.1 3.9 0.1 4.2 2.0 km External (cloud) - 1 - 0.8 - 0.8

Inhalation 10 0.8 13/0.3 130/210 2.6 13 Ingestion (veg.) 30 - 2.5 - 7.6 -Ingestion (meat) 4.8 - 0.5 - 5.6 -

aP/TB = Pulmonary/Tracheobronchial. bPart. = Particulates. cRn = Radon-222 plus decay products.

region, respect ive ly , for a 1% free-atom f ract ion. These f ract ions are found to correspond to the values derived from the TGLM for an aerosol with a median aerodynamic diameter of 0.3 urn. The s o l u b i l i t y of the deposited decay products is assumed to be c lass D, as suggested by animal experiments and retention studies in humans [ 4 ] .

The doseiconversion factors (mrem per year per pCi of radon progeny per cubic meter of a i r ) based on the TGLM are given in Table I I I . As indicated, the tracheobronchial region and the pulmonary region are , respect ive ly , the c r i t i c a l compartments when estimating the dose equivalents from inhalation of radon and thoron decay products.

4. RADIOLOGICAL IMPACTS

The resu l ts of the radio log ica l analyses of the model uranium and thorium mi l l s are presented in the fol lowing sect ions. The ca lculated dose equivalents are the 50-year dose commitments, i . e . , the values represent the integrated radiat ion dose received over a period of 50 years fol lowing intake e i ther by inhalation or ingestion.

4 .1 . Maximum individual doses

To evaluate the maximum radiat ion r i sk to an exposed individual and compliance with appl icab le exposure l im i t s , two spec i f i c reference locations were selected: ( 1 ) the s i t e

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Table V. Maximum Individual Dose Commitments at Hypothetical Locations from the Final Year of Thorium Mill Operations

Doses (mrem/a)

Location Exposure Pathway

Bone Part.b Rn c

Lung (P/TB)C Kidney Part. Rn Part. Rn

Site boundary External (ground) 23 38 18 31 20 33 0.64 km External (cloud) - 4. 2 - 2.8 - 3.2

Inhalation 450 59 340/13 1300/150 89 700

Ranch External (ground) 2.0 3. 4 1.6 2.8 1.7 3.0 2.0 km External (cloud) - 0. 5 - 0.4 - 0.4

Inhalation 51 4. 9 38/1.5 120/18 10 59 Ingestion (veg.) 20 - 2.3 - 0.3 -Ingestion (meat) 2.4 - 0.3 - .03 -

P/TB = Pulmonary/Tracheobronchial. 3Part. = Particulates. "Rn = radon-220 or thoron plus decay products.

boundary in the downwind d i rect ion , 0.64 km from the center of the t a i l i n g s pond; and ( 2 ) a ranch 2 km downwind from the m i l l , where vegetables and beef ca t t l e are grown. The assumed rates of ingestion of l o ca l l y grown vegetables and meat by indiv iduals at the ranch were taken from Reference [ 1 ] and represent averages for typical rural farm households in the United States. Maximum individual doses at these two locations during the 15th ( f i n a l ) year of mill operation are presented in Table IV for the model uranium mill and in Table V for the model thorium mi l l . As indicated in the t ab l e s , the dose to the maximally exposed individual at the s i t e boundary is much l a r ge r from mi l l ing of thorium than uranium, espec ia l l y the dose from inhalation of the progeny of thoron as compared with those of radon. However, the dose from thoron progeny decreases rap id ly with distance from the mi l l . At the hypothetical ranch locat ion, doses from the model thorium mill have de­creased to values comparable to those from the model uranium mi l l .

The values of inhalation dose commitments to the c r i t i c a l organs as a function of distance from the source in the p r e v a i l ­ing downwind direct ion are shown graphica l ly in Fig. 2. I t i s c l ea r from this f i gure that radon and thoron are the dominant potentia l sources of rad io log ica l impacts to the general publ ic in the v i c in i ty of a uranium or thorium mi l l .

The U.S. Environmental Protection Agency regulat ion 40 CFR Part 190, which became e f f ec t ive for uranium mi l l s on

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DISTANCE, KM FIG.2. Inhalation dose commitments from the final year of model mill operations.

December 1, 1980, imposes an annual dose l imit of 25 mrem to the whole body and to any organ (except the thyroid ) of any member of the publ ic from nuclear power operations via a l l environmental exposure pathways. However, i t s p ec i f i c a l l y excludes dose commitments from releases of radon and i t s progeny. As indicated in Fig. 2 and Tables IV and V, i t appears that the 40 CFR 190 l imit could not be met at r e s i ­dences within about 3 km of e i ther the model uranium mill or thorium m i l l , depending upon individual food production and consumption patterns. I t is a lso indicated in Fig. 2 that at the same distance from the m i l l , doses to the lung from in ­halation of radon and thoron progeny are much greater than those resu l t ing from exposure to par t icu la te materia ls . With regard to 40 CFR Part 190 compliance, bone doses from inhala ­t ion of l ong - l i ved part icu lates and from ingestion become contro l l ing rather than lung doses because the major contr ib ­utors to the lung doses have been excluded from consideration

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i i — i — 1 1 1 1 • i i i i i i

DISTANCE, KM

FIG.3. Inhalation dose commitments from radon and thoron emanated from surrounding land contaminated by 15 years of model mill operation.

by the regulations ( but , unfortunately, not by the biophysical r e a l i t i e s ) . However, i f the rad io log ica l r i sk to an individual is of primary concern, the dose to the tracheobronchial region from inhalation of radon progeny and to the pulmonary region from inhalation of thoron progeny are c r i t i c a l . Based on the cancer r i sk factors used by the U.S. Nuclear Regulatory Com­mission [ 1 ] , the chance that an individual would die prema­ture ly from lung cancer is 55 times higher than the chance of dying from bone cancer as a resu l t of l i v ing at 2 km from the model uranium mi l l , and 20 times greater in the case of the thorium mi l l . The health r i sk from inhalation of radon and thoron progeny, therefore , is s i gn i f i c an t l y greater than the r i sk associated with inhalation of l ong - l i ved par t icu la te materia ls .

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In order to estimate the re lease of radon and thoron from windblown and mechanically dispersed materials that have contami­nated the area surrounding the mi l l , i t was assumed that 20% of the radon and thoron escapes to the atmosphere. The concen­trat ions of radon and thoron progeny in the ambient a i r from these re leases were assumed to occur in the fol lowing rat ios r e l a t i v e to the gas f lux from the contaminated s o i l :

• Radon decay products:

Po-218 : Pb-214 : Bi-214 : Rn-222 f lux = 300 pCi/m3 : 200 pCi/m3 : 200 pCi/m3 : 1 p C i - m - 2 ^ - 1

• Thoron decay products:

Po-216 : Pb-212 : Bi-212 : Rn-220 f lux = 4 pCi/m3 : 0.06 pCi/m3 : 0.06 pCi/m3 : 1 p C i ' m - 2 ^ - 1

These re lat ionships were estimated [ 5 ] on the basis of average ambient concentrations in the atmosphere and the f lux from the natural s o i l .

Inhalation doses to the c r i t i c a l lung compartments from o f f - s i t e contamination accumulated during 15 years of mill operation have been calculated on the basis of these assump­tions and are shown in Fig. 3 as a function of distance in the downwind direct ion from the mi l l s . Thoron emanating from the contaminated ground may make a substantial contribution to the background radiat ion dose in the v i c in i ty of a thorium mi l l . The annual pulmonary lung dose commitment ranges from 220 mrem at 0.1 km to about 1 mrem at 10 km. The lung doses from radon released from contamination near the model uranium mill are a factor of four less than those from the thorium mi l l .

4.2. Population doses

Population dose commitments are calculated by summing doses to a l l individuals within the model region out to a distance of 80 km from the mi l l . At this distance, most of the par t i cu la te material and thoron gas released from the mill s i t e would have been depleted by deposition and radioact ive decay, respect ive ly . However, because of i t s longer h a l f - l i f e (3 .8 days) and gaseous form, the released radon would not have been depleted, and would produce an immeasurable radiat ion exposure to the population beyond the 80 km distance. An estimate of this dose to the f a r - f i e l d population has been made in References [ 1 ] and [ 6 ] , and is not repeated here.

The calculated annual population dose commitments ( c o l l e c ­t ive dose equiva lents ) and the 100-year environmental dose

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Table VI. Co l lect ive Dose Commitments Resulting from Operation of a Model Mill

Annual Population Dose Commitments, person- or organ-rem/a

Thorium Mi l l ing Operations Uranium Mi l l ing Operations

Lung Lung Whole Pulmonary/ Whole Pulmonary/

Exposure Pathway Body Bone T-Bronchial Kidney Body Bone T-Bronchial Kidney

External (ground) 0.3 0.3 0.2 0.3 0.2 0.2 0.2 0.2 External (c loud) 0.2 0.2 0.1 0.2 1.3 1.4 1.2 1.3 Inha la t ion 3 0.5 4.8 29/6.5 14 0.4 10 80/140 7.3 Ingestion 1.2 10 1.3 0.1 2.0 24 2.0 25

TOTALS 2.2 15 31/8.1 15 3.9 36 83/143 34

100-Year Integrated Environmental Dose Commitments, person- or organ-rem

Thorium Mi l l ing Operations Uranium Mi l l ing Operations

Lung Lung Whole Pulmonary/ Whole Pulmonary/

Exposure Pathway Body Bone T-Bronchial Kidney Body Bone T-Bronchial Kidney

External (ground) 16 19 15 16 11 13 10 11 External (c loud) 2.5 2.7 2.3 2.5 19 21 18 19 Inha la t ion 3 8 73 470/110 220 0.6 140 1200/2000 110 Ingestion 29 240 29 2.7 49 540 49 640

TOTALS 56 335 516/156 241 84 714 1277/2077 780

Doses presented are those result ing from inhalation of shor t - l i ved radon progeny and other part icu lates .

'Dose commitments resu l t ing from 15 years of mill operations.

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commitments resu l t ing from 15 years of mill operation are presented in Table VI. The annual population dose commitments are based on a one-year period of exposure to concentrations in environmental media during the 15th year of continuous operation of the model mi l l s . These dose commitments represent the highest values that could be predicted from any s ing le one-year exposure period. The 100-year environmental dose' commitments represent the total integrated population doses from a l l re leases during the ent i re 15 years of model mill operation and extending over the 100-year period that the re leased rad ioact iv i ty may pe r s i s t in the environment. A deta i led description of the methodology used to compute these doses is given in Reference [ 2 ] .

From Table VI , i t i s apparent that most of the population doses from uranium and thorium mi l l s a r i se from inhalation and ingestion pathways. The shor t - l i ved progeny of radon and thoron are responsible for most of the inhalation doses to the lungs. However, as was the case for individual exposures, the c r i t i c a l lung compartments are d i f f e rent . For exposure to thoron, the pulmonary dose is four times greater than the tracheobronchial dose; while for radon, the tracheobronchial dose is about twice that of the pulmonary lung dose. The resu l ts indicate that thoron decay products are responsible for more than 90% of the inhalation dose to the kidney.

For the population ingestion dose ca lcu la t ions , a l l of the meat and vegetables consumed by the regional population were conservatively assumed to be produced in the region. Of the ingestion doses shown in Table VI , e s sent i a l l y a l l organ doses from thorium mi l l ing a r i se from long - l i ved rad ioact iv i ty present in released par t icu la te materia ls . For the model uranium mi l l , however, about 80% of the ingestion doses a r i se from long - l ived ac t i v i t y released in par t icu la te form, whereas the rest of the organ doses are contributed by Pb-210 and Po-210 produced by decay of radon gas a f te r i t s re lease from the mill s i t e .

As shown in Table VI , the total integrated population doses resu l t ing from 15 years of model mill operation are predicted to be approximately 84 whole body person-rem, 710 bone-rem, 1300 pulmonary lung-rem, 2100 tracheobronchial lung-rem, and 780 kidney-rem from uranium mi l l ing and 56, 340, 520, 160, and 240 person or organ-rem to the whole body, bone, pulmonary lung, tracheobronchial lung, and kidney, respect ive ly , from thorium mi l l ing . Thus the total rad io log ica l impacts (assumming the same ore a c t i v i t y ) would be about two to four times greater from uranium mi l l ing than from thorium mi l l ing .

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5. CONCLUSIONS

Comparison of the predicted rad io log ica l impacts from uranium mi l l ing to those from thorium mi l l ing (assuming the same ore a c t i v i t y ) indicates that the individual exposure l imit of 25 mrem per year imposed by the EPA uranium fuel cycle standard, 40 CFR 190, might not be met within 3 km downwind from either model mi l l . Total exposure estimates, which include thoron and i t s progeny, indicate that thoron, l ike radon from the uranium mi l l , is the greatest s ing le contributor to individual r i sk , e spec ia l l y for persons at locations in the immediate v i c in i ty of a thorium mi l l . This r i sk to an individual at the s i t e boundary of a thorium mill i s greater by a factor of four than the r i sk from radon at an equivalent uranium mi l l . However, radiat ion r i sk from released thoron decreases rapid ly as the distance from the mill increases. The total population doses within 80 km of the model thorium mill are estimated to be about two to four times less than those from the model uranium mi l l . This analysis indicates that a f te r operation of a thorium mill is terminated and the mill is decommissioned, the thoron emanating from windblown or mechanically dispersed contamination on nearby land might make a substantial contribution to the background radiat ion dose. The radiat ion dose from radon released from contaminated land surrounding the model uranium mill i s less than the comparable thoron dose by a factor of about four.

This analysis a lso suggests that i t i s important for regulatory standards to include l imits for the lung doses from radon, thoron, and the i r progeny i f the total individual r i sk from uranium and thorium mi l l ing operations is to be adequately control led.

REFERENCES

[ 1 ] U.S. NUCLEAR REGULATORY COMMISSION, Final Generic Environ­mental Impact Statement on Uranium Mi l l i ng , Rep. NUREG-0706 (1980).

[ 2 ] MOMENI, M.H., YUAN, Y .C . , ZIELEN, A . J . , The Uranium Dis ­persion and Dosimetry (UDAD) Code, Argonne National Laboratory Rep. NUREG/CR-0553 (1979).

[ 3 ] ICRP TASK GROUP ON LUNG DYNAMICS, "Deposition and reten­t ion models for internal dosimetry of the human re sp i ­ratory t r a c t " , Health Phys. 12 (1960) 173-207.

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[ 4 ] JACOBI, W., "Relation between inhaled potential a-energy of 2 2 2 R n and 2 2 0 Rn-daughte rs and absorbed a-energy in the bronchial and pulmonary reg ion" , Health Phys. 23 (1972) 3-11.

[ 5 ] JACOBI, W., ANDRE, K., "The vert ica l d i s t r ibut ion of radon 222, radon 220 and the i r decay products in the atmosphere", J. of Geophys. Res. 68 13 (1963) 3799-3814.

[ 6 ] C.C. TRAVIS et a l . , Radiological Assessment of Radon-222 Released from Uranium Mi l l s and Other Natural and Techno­l o g i c a l l y Enhanced Sources, Oak Ridge National Laboratory Rep. NUREG/CR-05-73 (1979).

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ENVIRONMENTAL SURVEILLANCE AND MONITORING

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Chairman

J. SCHMITZ Federal Republic of Germany

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L'APPORT DES MESURES HYDROBIOLOGIQUES DANS L'ETUDE RADIOECOLOGIQUE D'UN SITE FRANf AIS D'EXTRACTION ET DE TRAITEMENT D'URANIUM

B. DESCAMPS, L. FOULQUIER, Y . CARTIER, Y . BAUDIN-JAULENT Service d'etudes et de recherches sur renvironnement, Departement de protection, CEA, Institut de protection et de surete

nucleaire, Centre d'etudes nucleaires de Cadarache, Saint-Paul-lez-Durance, France

Abstract-Resumi

CONTRIBUTION OF HYDROBIOLOGICAL MEASUREMENTS TO THE RADIO-ECOLOGICAL MONITORING OF A URANIUM MINING AND MILLING SITE IN FRANCE.

The first results are given of a hydrobiological study, carried out under a CE A/EEC contract, of the Lodeve uranium mining and milling site in southern France. Water, sediment, plant and fish samples were taken in May 1981 and will again be taken in 1982. At a distance of some three kilometres downstream from the mine, these reveal some increase in the radium and uranium content of the three compartments. The uranium and radium in the water are found mainly in the dissolved part, and the uranium content is much higher. In the case of the sediment, however, the radium content is higher, which seems to indicate radium's strong preference for "fixing" itself to sediments. Fine particle size encourages the fixation of these two radionuclides. In the case of semi-aquatic plants, the increases observed are larger for uranium than for radium and are greater in the parts below ground than in those above it. Specific laboratory experiments are planned for the purpose of determining, among other things, the effect of the chemistry of the host environment and of the release on the fate of the radium and uranium and the proportions transported by the two pathways (from water and sediment) to the plant.

L'APPORT DES MESURES HYDROBIOLOGIQUES DANS L'ETUDE RADIOECOLOGIQUE D'UN SITE FRANCAIS D'EXTRACTION ET DE TRAITEMENT D'URANIUM.

Dans le cadre d'un contrat CEA-CEE, on presente ici les premiers resultats d'une etude hydrobiologique du site d'extraction et de traitement d'uranium de Lodeve dans le sud de la France. Les prelevements effectuSs en mai 1981 et a effectuer en 1982 sont relatifs a l'eau, aux sediments, aux vegetaux et aux poissons. lis montrent, a une distance d'environ trois kilometres en aval de la mine, une certaine augmentation des teneurs en radium et en uranium dans les trois compartiments. Dans l'eau, l'uranium et le radium se retrouvent essentiellement dans la fraction dissoute, les teneurs en uranium etant beaucoup plus grandes. Les teneurs en radium du sediment sont par contre plus importantes, ce qui semble indiquer une aptitude

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particuliere du radium a se «fixer> sur les sediments. Une granulometrie fine favorise la fixation de ces deux radionuclides. Pour les vegetaux semi-aquatiques, les augmentations constatees sont plus fortes pour 1'uranium que pour le radium et plus importantes pour les parties souterraines que pour les parties aeriennes. Des experiences de laboratoire specifiques sont envisagees afin de preciser, en particulier, l'influence de la chimie du milieu recepteur et du rejet sur le devenir du radium et de l'uranium ainsi que les parts prises par les deux transferts (a partir de l'eau et a partir du sediment) vers le vegetal.

1. OBJECTIFS

Le Commissariat a l 'Energ ie Atomique et les Communautes Economiques Europeennes, dans l e cadre d'un contrat de deux ans ( 1 9 8 1 - 1 9 8 2 ) , ont mis sur pied une etude radioecologique du s i te d 1 extract ion et de traitement d'uranium de Lodeve dans le Sud de la France. Ce t r ava i l a demarre en meme temps que le debut de 1 'exploitat ion de la mine. En ce qui nous concerne, nous nous sommes interesses a 1'aspect hydrobiologique, c ' e s t - a -dire a l ' e au , aux sediments, aux vegetaux et aux poissons.

L'ensemble des mesures sur les prelevements r ea l i s e s et a r e a -l i s e r devraient permettre de : - prec iser les comportements du radium et de l 'uranium apres

re jet dans 1'environnement en s 'attachant, en pa r t i cu l i e r , a noter les di f ferences entre ces deux r a d i o n u c l i d e s ;

- ca lcu ler les facteurs de transfert " in s i tu " (eau->-poissons, eau+vegetaux, eau->sediment et sediment-^vegetaux) ;

- degager des axes de recherches experimentales v isant a i n ­terpreter les mecanismes en jeu , en pa r t i cu l i e r l ' i n f luence des caracter i s t iques chimiques de l ' e au et du radionucleide sur les voies de t rans fe r t .

2. LE SITE DE LODEVE ET LES STATIONS DE PRELEVEMENTS

Le s i te de Lodeve est s itue dans le departement de 1'Herault. L ' exp lo i ta t ion de la mine a commence en mars 1981 ; l e r e j e t des eaux d'exhaures s 'e f fectuant dans un gros ruisseau, le R iv iera l ; i l vient g ross i r le Rivernoux qui se j e t t e , l u i , dans l a Lergue (a f f luent r ive droite de la r i v i e r e Herau l t ) . Les re j e t s de l ' u s ine se font directement dans la Lergue, 5,5 kilometres en amont du point de confluence du Rivernoux avec la Lergue. A pa r t i r de ce point i l n'y a que 4 kilometres pour remonter au point de re je t de la mine (vo i r fig.l).

Les stations de prelevements sont au nombre de cinq. Les s t a ­tions Lergue amont et Lergue ava l , l a station R iv ie ra l (a 300 m en aval du point de re j e t de la mine) , l a station Rivernoux et la station Herault . Dans le TABLEAU I nous faisons f i gurer le programme de nos campagnes de prelevements effectuees et a e f fectuer .

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Pour l ' e au nous u t i l i s ons un apparei l de prelevement en con t i -nu assurant, a l a su i te , l a f i l t r a t i o n des matieres en suspen­sion par passage sur f i l t r e a 0,8 um puis la concentration des elements dissous sur resines echangeuses d'ions et enfin le p i e -geage de la matiere" organique sur f i l t r e charbon. Le temps de prelevement est de 24 heures et l a quantite p r e l e -vee de l ' o r d r e de 150 l i t r e s . Les sediments preleves sont representat i fs des zones concernees. Sur l ' un d'eux on a separe les t ro i s f ract ions granulometri -ques def in ies comme suit :

0 < 50 um, 50 um < 0 < 200 um, 200 um < 0 < 2 mm.

Les vegetaux preleves sont semi-aquatiques ; i l s appartiennent a deux genres, I r i s et Juncus. tres repandus dans les cours d'eau consideres. Les part ies aeriennes et souterraines sont separees.

La peche se f a i t a 1 ' e l e c t r i c i t e ; dans les pet i t s cours d'eau comme la Lergue et l e Rivernoux cette peche permet le pre leve­ment des especes les plus representatives de leur peuplement ichtyologique. Sur l es especes l es plus consommees nous sepa-rons les principaux organes : l a peau, les v i sce res , les mus­c les et le sque lette .

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TABLEAU I. DATES, STATIONS ET PRELEVEMENTS EFFECTUES ET A EFFECTUER POUR LE SUIVI DU SITE DE LODEVE

Preleve-\ v merits Eau Sediments Vegetaux Poissons

Dates

Lergue amont

Lergue amont

Lergue amont

Mai 1981 Rivernoux Rivernoux Lergue

aval Herault

Rivernoux Lergue

aval

Fevrier 1982

Lergue amont

Rivernoux Lergue

aval

Rivieral Rivieral

Lergue amont

Lergue amont

Lergue amont

Lergue amont

Rivieral Rivieral Rivieral Mai 1982 Rivernoux Rivernoux Rivernoux Rivernoux

Lergue aval

Lergue aval

Lergue aval

Lergue aval

Herault Herault

3. RESULTATS

Les resultats que nous presentons ici sont relatifs aux seuls prelevements effectues en mai 1981. lis ne peuvent, pour le moment, etre consideres que comme les premieres cons-tatations qu'il conviendra d'infirmer ou de confirmer apres les deux autres campagnes de prelevements.

A ce jour nous disposons en plus d'un certain nombre de resul­tats relatifs a deux etudes effectuees en 1978 et 1979 qui pourront servir de point de reference avant la mise en exploi-

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TABLEAU II. TENEURS EN URANIUM ET EN RADIUM DE L 'EAU AUX STATIONS LERGUE AMONT ET RIVERNOUX EN MAI 1981

Stations Fractions analysees

Urani

(Mg/l)

L u m

(pCi/1)

Radium 226 (pCi/1)

Lergue amont

Matieres en suspension - (a) - -

Lergue amont

Eau filtree 10 + 2 3,3 1 0,6 0,1510,04

Rivernoux

Matieres en suspension - - -

Rivernoux Eau filtree 910 t 180 300 t 60 1 t 0,12

(a) Resultat non significatif

tation du site 1. Elles nous donnent les niveaux d'activite, en particulier en radium 226, des sediments, des vegetaux et des poissons preleves dans la Lergue et dans certains ruis-seaux drainant les terrains ou sont desormais implantees la mine et l'usine de Lodeve. Les prelevements ont eu lieu en mars 1978 pour les sediments et les vegetaux et en octobre 1978 pour les poissons.

3.1. L'eau

Sur l'eau nous avons mesure le radium par emanation et 1'uranium par fluorimetrie. Le TABLEAU II presente les resul­tats. II montre que la quasi-totalite de l'activite de ces deux radionuclides est associee a la fraction dissoute. A la station Rivernoux,les teneurs en uranium et en radium sont plus fortes qu'a la station Lergue amont ; l'eau y a une te-neur en uranium nettement plus grande qu'en radium. Le dese-quilibre existant entre les teneurs en uranium et en radium a la station Lergue amont est accentue a l'aval du rejet de la mine, dans le Rivernoux.

Notons que ces valeurs ont ete obtenues a une epoque ou le de­bit naturel du Rivernoux ne permettait pas une grande dilution du rejet.

1 Ces deux etudes ont et6 realisees par le Service d'etudes et de recherches sur Penvironnement (SERE) a la demande du Service de protection technique (SPT). Ces deux services appartiennent au Departement de protection (DPr).

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TABLEAU III. TENEURS EN URANIUM ET EN RADIUM DES SEDIMENTS PRELEVES EN MAI 1981 AUX STATIONS LERGUE AMONT, RIVERNOUX, LERGUE A V A L ET HERAULT (Resultats en pCi/kg sec)

^^Analyses Stations^.

Uranium Radium 226 ^^Analyses Stations^. Spectrometrie Spectrometrie Emanation

Lergue amont 1130 + 300 1370 + 600 1900 + 380

Rivernoux 34700 t 3300 55000 t 8300 53000 t 8000

Lergue aval 1670 + 320 1780 ± 540 2900 + 580

Herault 1230 + 230 1170 t 660 1000 + 200

Le type de prelevements ponctuels que nous avons ef fectues (avec concentration) permet une bonne precision des mesures. A l'avenir, pour des etudes comparatives sur une longue periode, il sera utile de se referer a des mesures resultant de prele­vements continus sur toute l'annee. II conviendra d'etre parti-culierement attentif a la localisaion precise des stations de prelevements ; en effet, compte tenu de la complexite des phe-nomenes entrant en jeu, on peut penser observer des variations notables des teneurs en uranium et en radium sur de courtes distances.

3.2. Le sediment

Le TABLEAU III donne les valeurs obtenues par spectrome­trie pour le radium et l'uranium et celles par emanation pour le radium.

Alors qu'on a une situation d'equilibre entre l'uranium et le radium a 1'amont on constate, a la station Rivernoux, une aug­mentation des teneurs en uranium et en radium et un desequili-bre en faveur du radium. A la station Lergue aval on obtient des teneurs en uranium et en radium comparables a celles obte­nues a 1'amont ; 11 en est de meme a la station Herault. Dans ces deux stations il y a equilibre entre l'uranium et le ra­dium. Ces resultats indiquent une forte capacite de fixation du sediment pour le radium et pour l'uranium ; cette fixation du sediment apparait plus importante pour le radium comme le montrent les resultats de la station Rivernoux. Ceci est en accord avec ce qui a ete dit par de nombreux auteurs £l J [2] £3].

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TABLEAU IV. TENEURS EN URANIUM ET EN RADIUM DE TROIS FRACTIONS GRANULOMETRIQUES D'UN SEDIMENT PRELEVE EN MAI 1981 A L A STATION LERGUE A V A L (Resultats exprimes en pCi/kg sec (spectrometrie 7))

Fractions granulometriques analysees Uranium Radium

200 um < 0 < 2 mm 1600 + 300 2000 + 600

50 um < 0 < 200 um 800 + 200 1100 t 600

0 < 50 um 4700 + 900 3700 ± 900

Cette capacite de f i xat ion est de toute facon suffisamment im­portante v i s - a - v i s de ces deux r a d i o n u c l i d e s pour, en mai 1981, etre parfaitement v i s i b l e dans le sediment a une d i s tan ­ce de t ro i s ki lometres.

Si on met ces resu l ta ts en pa r a l l e l e avec ceux obtenus sur l ' e au on peut penser que le radium est sous une forme chimique qui f avor i se sa f ixat ion par l e sediment.

On peut se poser la question de 1 ' inf luence de la granu-lometrie sur l a f i xat ion de 1'uranium et du radium. Pour un sediment preleve a la stat ion Lergue aval nous pouvons repon-dre : l es resu l ta ts sont dans le TABLEAU IV. On constate que les teneurs les plus importantes en uranium et en radium sont c e l l e s de l a f ract ion granulometrique l a plus f ine . Si l ' on considere la granulometrie du sediment preleve dans chacune des quatre stat ions,on vo i t que le sediment l e plus f in a l ' a c t i v i -te l a plus importante. A ins i , l e sediment preleve au Rivernoux a 88 % d'elements in fer ieures a 50 um a lors que les t ro i s au-tres sediments n'en ont qu'en-viron 15 %. I I est done tres im­portant, pour suivre 1 'evolut ion dans le temps des niveaux d ' a c t i v i t e du sediment, de toujours pre lever les echanti l lons aux memes endroits .

On peut comparer ces resu l ta ts avec ceux r e l a t i f s aux pre ­levements effectues en mars 1978. l i s ont ete f a i t s a 1'amont et dans les ruisseaux (en pa r t i cu l i e r dans le R i v i e r a l ) d r a i -nant l e s i t e .

A cette epoque des travaux preparatoires etaient en cours. Ces resu l ta t s confirment ceux de 1981 : - a 1'amont,un equ i l i b r e uranium-radium avec des ac t i v i t e s de

l ' o r d r e de 1000 pCi/kg sec pour un sediment gross ier ; - dans les ruisseaux drainant le s i te ,un desequi l ibre uranium-

radium et les a c t i v i t e s les plus importantes pour les s ed i ­ments les plus f ins (de l ' o r d r e de 2600 pCi/kg sec pour

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TABLEAU V. TENEURS EN URANIUM ET EN RADIUM DES VEGETAUX PRELEVES EN MAI 1981 AUX STATIONS LERGUE AMONT, RIVERNOUX ET LERGUE A V A L (Resultats en pCi/kg sec)

Stations Genres Part ies Uranium Radium

Lergue amont I r i s

Aeriennes < 600 < 150 Lergue amont I r i s

Souterraines 130 + 40 260 ± 130

Rivernoux

I r i s Aeriennes 1320 ± 40 200 t 230

Rivernoux

I r i s Souterraines 5900 t 900 1580 t 450

Rivernoux

Jonc Aeriennes 600 ± 120 640 t 120

Rivernoux

Jonc Souterraines 7150 + 1275 5100 + 1760

Lergue aval I r i s

Aeriennes 135 ± 40 75 ± 40 Lergue aval I r i s

Souterraines 330 ± 70 230 t 110

l 'uranium et 5200 pour l e radium dans le cas d'un sediment g ross ie r , e t , respectivement, 13600 et 48800 dans l e cas d'un sediment f i n ) .

3.3. Les vegetaux

Le TABLEAU V presente les resu l tats obtenus par spectro­metrie Ge-L i . Pour les i r i s preleves dans le Rivernoux, on constate que 1 'accroissement est plus important pour l 'uranium que pour l e radium. I I est aussi plus important pour les part ies souterraines que pour les part ies aeriennes. Pour les joncs du Rivernoux,les teneurs en uranium et radium des part ies souter ­raines sont egalement superieures a ce l l e s des part ies aeriennes. Comme pour l e sediment on trouve a la station Lergue aval a peu pres les memes valeurs qu'a la station Lergue amont.

L ' e q u i l i b r e uranium-radium, constate aux stations Lergue amont et aval pour les part ies aeriennes et souterraines de l ' i r i s , est rompu a la station Rivernoux en faveur de 1'uranium. Les resu l ta ts obtenus sur des vegetaux preleves en mars 1978 dans les ruisseaux drainant le s i te et dans des zones non a f f e c -tees par les travaux preparatoires effectues a cette epoque mon-trent une legere augmentation en radium et en uranium au niveau

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TABLEAU VI . FACTEURS DE TRANSFERT DE L 'URANIUM ET DU RADIUM POUR LE VEGETAL PAR RAPPORT A L 'EAU ET PAR RAPPORT A U SEDIMENT (Situation en mai 1981)

Stations Parties Vegetal (pCi/kg.sec) Eaufiltree(pCi/l)

Vegetal (pCi/kg.sec) Sediment (pCi/kg.sec) Stations Parties

Uranium Radium Uranium Radium

Lergue amont

Aeriennes - (a) - - -Lergue

amont Souter­raines 40 1730 0,11 0,19

Rivernoux Aeriennes 4,5 200 0,04 0,004

Rivernoux Souter­raines 20 1580 0,17 0,03

(a) Les valeurs relatives aux parties aeriennes ne sont pas significatives

de ces ruisseaux. C'est ainsi que,pour des roseaux (Phragmites communis) preleves a la station Lergue amont, on a obtenu des teneurs en uranium et en radium d'environ 1000 pCi/kg.sec alors que pour des joncs preleves dans les ruisseaux on a des teneurs de l'ordre de 2600 pCi/kg.sec (il s'agit de teneurs relatives au vegetal entier).

On peut se demander si le transfert du radium et de l'uranium vers le vegetal se fait a partir de la fraction dissoute de l'eau et/ou a partir du sediment. Pour tenter de repondre a cette question,nous avons calcule, pour les iris preleves a la station Lergue amont et a la station Rivernoux, les facteurs de transfert du radium et de l'uranium dans le cas d'un trans­fert total et exclusif par l'eau d'une part et par le sediment d'autre part (TABLEAU VI).

Dans la premiere hypothese (transfert a partir de l'eau) on arrive a trois constatations :

- les facteurs de transfert du radium sont beaucoup plus impor-tants que les facteurs de transfert de l'uranium ;

- pour le Rivernoux les facteurs de transfert des parties sou­terraines sont plus importants que les facteurs de transfert des parties aeriennes ;

- les facteurs de transfert des parties souterraines a la station Rivernoux sont a peu pres du meme ordre de grandeur qu'a la sta­tion Lergue amont.

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Cette troisieme constatation est particulierement importante car e l l e semble indiquer qu'a l ' a v a l un certa in equ i l i b re en­tre I ' eau et le vegetal s ' e s t e t ab l i apres les nouvelles con­dit ions du mi l ieu . On peut egalement dire q u ' i l est p r e v i s i b l e , s i les niveaux d ' a c t i v i t e en uranium et en radium de l ' e au (sa f ract ion dissoute) ne var ient pas dans de grandes propor­t ions, que leur teneurs en uranium et en radium des i r i s ne vont pas beaucoup evoluer.

Dans la seconde hypothese i l est surtout caracter is t ique que l e facteur de t ransfert du radium (par t ies souterraines) dans l e Rivernoux est beaucoup moins grand que dans la Lergue. Dans l e cas d'un equ i l i b re vegetal-sediment on aura i t du avoir des n i ­veaux d ' a c t i v i t e en radium plus importants a l ' a v a l . Puisque ce n ' e s t pas le cas, on peut emettre 1 ' i dee que la f i xa t ion du r a ­dium par les sediments presente des caracter is t iques d i f f e r en -tes de ce l l e s de l 'uranium. Pour ce dernier , on constate en e f fe t des facteurs de t ransfert comparables a 1'amont et a l ' a v a l ce qui p la ide en faveur d'un equ i l i b re vegetal-sediment a l ' a v a l . #

A ce niveau de notre etude i l n ' e s t pas poss ib le de d i re quel les sont les parts pr i ses par ces deux or ig ines poss ib les du t rans fert de l 'uranium et du radium. Des etudes de laborato i res devraient permettre d'y repondre.

3 . 4 . Les poissons

Nous sommes en possession des resu l tats d'une peche e f -fectuee a l a station Lefgue-aval en octobre 1978. Ces resu l ta ts concernent six especes ; nous avons obtenu des resu l ta ts s i g n i -f i c a t i f s sur quatre especes seulement : l ' a n g u i l l e (Angui l la a n g u i l l a ) , l e barbeau (Barbus ba rbus ) , l e chevssne (Leuciscus cephalus) et la vandoise (Leuciscus l euc i scus ) .

I I y a equ i l i b re entre l 'uranium et le radium et les niveaux d ' a c t i v i t e ne sont pas signif icativement d i f fe rents d'une e s -pece a l ' a u t r e . Ces niveaux d ' a c t i v i t e , in fer ieurs ou egaux a 50 pCi/kg f r a i s , sont egalement ceux que l ' on a obtenus sur des poissons preleves en 1975 et en 1977 dans le Rhone [ 4 ] . I l s sont s i g n i f i c a t i f s de zones non af fectees par des re je ts enrichis en uranium et en radium.

4 . CONCLUSION

Apres la premiere campagne de prelevements d'eau, de v e ­getaux et de sediments sur le s i t e de Lodeve nous retiendrons ces pr inc ipa les constatations.

Pour nos prelevements ponctuels d'eau le r e j e t de la mine se ma-n i f e s t e essentiellement par une augmentation en uranium et en radium au niveau de la f ract ion dissoute. E l l e est plus impor-

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tante pour 1'uranium que pour le radium. Le desequilibre consta­te a 1'amont est accentue a l'aval.

A une station situee trois kilometres en aval du point de rejet de la mine, un sediment riche en particules fines presente des teneurs en radium et en uranium significativement superieures a celles observees a 1'amont, de plus, les teneurs en radium sont plus grandes que celles en uranium.

On peut penser que le radium se trouve dans l'eau sous une forme chimique qui favorise sa fixation par le sediment ; on retrouve la une des conclusions d'une etude bibliographique consacree au radium [l] . La fixation des deux radionuclides est d'autant plus forte que la granulometrie est fine.

Pour les vegetaux nous constatons aussi une augmentation sur une courte distance ; elle est, par contre, plus importante pour 1'uranium que pour le radium. Elle est egalement plus im­portante pour les parties souterraines que pour les parties aeriennes. Dans l'hypothese ou le transfert se fait a partir de l'eau seule on voit que les facteurs de transfert du radium sont beaucoup plus importants.

Pour connaxtre 1'evolution radioecologique d'un site minier comme celui de Lodeve il est absolument necessaire d'effectuer les prelevements d'eau, de sediments et de vegetaux aux memes distances par rapport au point de rejet. Pour les sediments, et en corollaire pour les vegetaux si l'hypothese d'un transfert du sediment vers le vegetal est realiste, il est meme indis­pensable de les prelever dans un perimetre tres localise.

Les resultats des deux autres campagnes preciseront, confirme-ront ou infirmeront ces premieres constatations. Mais, d'ores et deja on envisage, pour repondre a certaines questions, la mise sur pied d'experiences de laboratoire. Nous pensons en particulier a 1'etude de 1'influence des caracteristiques chi-miques de l'eau et du rejet sur la "fixation" par le sediment et a 1'etude du transfert de l'eau vers le vegetal et du sedi­ment vers le vegetal.

REFERENCES

[1] FOULQUIER, L., «Donnees sur le radium en hydro biologies, L'impact des installations nucleaires sur l'environnement (Actes du Seminaire de Radioecologie, Cadarache, 1977), Societe Francaise de Radioprotection, Paris.

[2] MARKOSE, P.M., EAPPEN, K.P., VENKATARAMAN, S., KAMATH, P.R., Distribution of radium and chemical toxins in the environment of a uranium complex , Bhabba Atomic Research Centre, Bombay (1978).

[3] PARSONT, M.A., The distribution of 2 2 6 Ra in an aquatic environment, Thesis, Colorado State Univ., 68-7819 (1967).

[4] FOULQUIER, L., DESCAMPS, B., PALLY, M., Etude radioecologique du Rhone -Point zero radiohydrobiologique, Commissariat a l'energie atomique, Centre d'etudes nucleaires de Cadarache, St. Paul-lez-Durance (1978).

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EVALUATION DU CYCLE DU RADIUM DANS L'ENVIRONNElMENT A PARTIR D'OBSERVATIONS IN SITU DE SON IMPACT RADIOLOGIQUE

J. HUGON, J. DELMAS, J.C. CARIES Service d'Studes et de recherches sur

renvironnement, DSpartement de protection, CEA, Institut de protection et de surete nucl6aire, Centre d'etudes nucleaires de Cadarache, Saint-Paul-lez-Durance, France

Abstract-Resumd

EVALUATION OF THE RADIUM CYCLE IN THE ENVIRONMENT ON THE BASIS OF IN SITU OBSERVATIONS OF ITS RADIOLOGICAL IMPACT.

The uncertainty which surrounds the behaviour of radium in the environment and its relatively high naturally occurring value make it difficult to perform a realistic assessment-of the doses received by populations from nuclear facilities which release this radionuclide. This detailed study of radium distribution and transport at two nuclear mining sites in France attempts to concentrate as closely as possible on that part of the radium which is actually produced by such facilities. Because of the precautions taken at nuclear facilities, the quantities released by them give rise to concentrations in the environment only of the order of magnitude of the background, although the amounts of 2 2 6 Ra found in the natural environ­ment are, in fact, not negligible. The first part of the study presented here was therefore devoted to evaluating the background, which proved to originate from two sources: (1) its normal presence in the environment as a natural component of the earth's crust, with variations due to geological phenomena; (2) a local component due to releases from various plants belonging to traditional industries. The second part of the study comprised an analysis of the two main pathways by which radium is transported at the site. The transport factors from soil to cultivated plants were measured for the vine and vegetables. An estimate of the doses produced by these two pathways is compared with estimated doses at a traditional industrial site. Finally, the analysis of transport conditions in the environment shows the importance of cultivation techniques for radium behaviour.

EVALUATION DU CYCLE DU RADIUM DANS L'ENVIRONNEMENT A PARTIR D'OBSERVATIONS IN SITU DE SON IMPACT RADIOLOGIQUE.

Les incertitudes sur le comportement du radium dans l'environnement ainsi que la valeur relativement elevee de son niveau a l'etat naturel rendent difficile une evaluation realiste des doses delivrees aux populations par les installations nucleaires rejet ant ce radio­nuclide. L'6tude sp6cifique de la repartition et du transfert du radium sur deux sites nucleaires miniers frangais s'efforce de serrer au mieux la part reelle delivree par ces installations. Grace aux pr6cautions prises au niveau des installations nucldaires, les quantites rejetees entrainent dans l'environnement des concentrations de l'ordre de grandeur du bruit de fond. En effet, les quantites de 2 2 6 Ra trouvees dans l'environnement naturel ne sont pas n6gligeables.

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La premiere partie de Fetude presentee ici a done consiste a evaluer ce bruit de fond qui s'est revele provenir de deux sources: 1) sa presence normale dans 1'environnement en tant que constituant naturel de la croute terrestre avec ses variations dues a des causes geologiques; 2) une composante locale due aux rejets de certaines installations industrielles classiques. La deuxieme partie de P6tude a consiste en une analyse des deux principales voies de transfert du radium sur le site. Des facteurs de transfert du sol vers les vegetaux cultives ont 6te mesures pour la vigne et les legumes. Une estimation des doses d61ivrees par ces deux voies est donnee en comparaison de celles estimees sur un site industriel classique. Enfin, l'analyse des conditions de transfert dans 1'environnement met en evidence l'importance des techniques culturales sur le comportement du radium.

1. INTRODUCTION

Pour le radioecologiste, le radium apparait comme un sous-produit de l'extraction de 1'uranium et, a ce titre, figure dans les rejets des installations minieres.

Compte tenu de sa radiotoxicite, des precautions sont prises au niveau de ces installations, si bien que les quantites rejetees restent modestes. D'autre part, etant un radioelement naturel particulierement mobile dans certaines conditions physico-chimiques, les quantites trouv^es normalement sur les sites uraniferes sont notables; aussi est-il souvent delicat de distinguer, dans l'environnement d'un site minier, la part de nuisance due a son comportement naturel de celle due a son rejet par l'installation.

C'est precisement ce type de travail que nous avons entrepris sur le site minier de Lodeve et c'est le resultat des ces travaux qui font l'objet du present expose.

2. DESCRIPTION DE L 'ENVIRONNEMENT

Le site minier de Lodeve est situe a la limite nord du versant mediterranean des premiers contreforts du Massif Central dominant la plaine du Languedoc.

Le pay sage y est encore typiquement mSditerraneen: serie de collines profondement ravinees par de nombreux ruisseaux la plupart du temps a sec pendant l'ef e. L'altitude, qui ne depasse pas 250 metres, permet une vegetation typiquement mediterraneenne a base de chenes verts et d'oliviers. Ce paysage tres sec s'explique par un climat tres contrasts caractense' par des ecarts pluviom6triques importants et une secheresse estivale prononc6e: 1040 mm d'eau par an r6partis en 90 jours seulement.

Dans cette nature ingrate, l'homme a su s'adapter. Les ressources agricoles locales reposent essentiellement sur la vigne et l'olivier; les jardins familiaux sont rares et situSs en bordure des ruisseaux. L'elevage est pratiquement inexistant.

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Quelques chevres elevees au Mas d'Alary situe dans le perimetre d'exploitation de la mine ont maintenant disparu. La population est clairsemSe et il est bien certain que l'ouverture du chantier minier constitue une aubaine pour ce pays aux ressources bien faibles.

L'uranium est extrait d'un gisement s^dimentaire permien d'origine terrigene, un des rares exploited en France. Les mineralisations se trouvent liees a des horizons plus ou moins lenticulaires avec enrichissement le long de certains accidents.

L'exploitation est envisagee en galeries pour certaines zones mais egalement a ciel ouvert. A la mine proprement dite est adjointe une usine de traitement de minerai. C'est l'ensemble de ces installations qui, essentiellement par ses rejets liquides, introduira le radium dans l'environnement.

3. IDENTIFICATION DES VOIES DE TRANSFERT

Afin de determiner l'impact des rejets de radium sur les populations, le premier travail du radioScologiste est d'identifier les voies de transfert empruntees par le radioelement considere pour arriver jusqu'aux individus.

Apres une phase d'enquete locale, necessaire pour acquerir une bonne connaissance du site, il est apparu assez rapidement que deux voies de transfert principales devaient retenir notre attention: la vigne et les legumes. Un certain nombre de prelevements effectues dans l'environnement devaient d'ailleurs rapidement confirmer cette hypothese.

Avant de proc6der a une analyse de ces deux processus, il convient pour une meilleure comprehension de revenir sur les modalites de rejets des eaux de l'installation.

Les eaux d'exhaures de la mine sortent a un debit de 300 m3/h. Apr&s traitement au chlorure de Ba, ces eaux sont envoySes dans un bassin de decantation qui retiendra le sulfate de radium insoluble. A la sortie de ce bassin, ces eaux ont quatre destinations:

— 30 m3/h sont reinjected dans la mine; — 50 m3/h subissent des utilisations diverses (arrosage des pelouses,

humidification des steriles, etc.); — 70 m3/h sont envoyes a l'usine de traitement de minerai (nous les

retrouverons plus loin); — enfin, 150 m3/h, le trop plein, sont deverses dans un petit ruisseau, le

Rivi6ral, et constituent d'ailleurs la majorite de son debit, principalement en ete. Ce ruisseau constitue pour nous un premier point d'injection du radium dans l'environnement.

Les 70 m3/h utilises dans l'usine de traitement subissent a la sortie, apres utilisation, un traitement avant leur rejet; mais, compte tenu de leur charge

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saline, ce rejet ne se fait pas dans le Rivieral, mais dans la Lergue dont le debit moyen de 4,5 m3/s permet une dilution suffisante. II est a noter que la Lergue et le Rivieral se rejoignent quelques kilometres en aval.

Pour l'un et l'autre des rejets, les concentrations en radium restent inferieures a 10 pCi/L, norme de potabilite.1 Apres cette digression necessaire, nous pouvons maintenant revenir sur les deux voies principales de transfert que nous avons identifiees.

La vigne est cultivee en fond de vallee tan]t sur la Lergue que sur le Rivieral. Cette situation permet un proc6d6 de culture assez particulier repandu dans le Midi languedocien, la submersion.

Deux fois par an, l'eau des rivieres est def ourn6e et envoyee dans les vignes ou elle couvre le sol sur une hauteur d'ehviron 20 cm. Cette technique, d'une part, permet de constituer dans le sol une reserve d'humidite utile en periode seche, et, d'autre part, entraine un effet d'asphyxie pour differents parasites enterres vivants aux depens de la plante. Quoi qu'il en soit, une telle pratique n'est pas sans influence sur le comportement du radium.

Nous avons proc6de a deux series de mesure des concentrations en radium, dans le sol et dans le raisin sur des vignes temoins, non submergees mais contenant du radium, et des vignes submergees. Des carrotages effectues dans les deux terrains ne montrent pas une repartition tres differente du radium en profondeur, mais ces sondages n'ayant pas 6t€ poursuivis au-dela de la sole de labour, cette repartition homogene due au travail de la terre est sans signification.

II n'en est pas de meme des facteurs de transfert qui se sont reveled nette-ment superieurs sur sol irrigue. Ce facteur de transfert sur sol irrigue- est, pour le vin, de 2,2 • 10~ 3 kg/L, calcule en pCi par litre de vin pour 1 pCi par kg de sol sec. Sur sol non irrigue, ce facteur de transfert exprime dans les memes unites n'est que de 9,8 • 10" 4 kg/L.

Cette legere augmentation de la mobilite du radium est probablement due a une evolution biologique et physico-chimique de ce radioel6ment dans un sol sature en eau pendant 2 a 3 mois de l'ann6e. L'etude plus fine du mecanisme fera d'ailleurs l'objet de la suite de notre programme de recherche.

Pour determiner les quantites de radium r6ellement absorbers annuelle-ment par les populations les plus exposees du site, le radioecologiste devra tenir compte ici d'un autre facteur relatif au site.

Notre enquete in situ nous a revele qu'un seul agriculteur qui procede a la submersion a partir de l'eau du Rivieral et de la Lergue effectuait sa verification lui-meme et ne consommait done que du vin trace par les rejets de la mine. Tous les autres exploitants font partie de la cooperation vinicole du Bosc, chef-lieu de la commune, ou sont rassemblees toutes les vendanges en vue d'une vinification

1 lpCi=37mBq.

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commune. Or, toutes les vignes de la commune ne sont pas soumises a l'influence des rejets de l'installation. Le radioecologiste devra done ^valuer la dilution ainsi apportee.

Une fraction notable des plants de vigne est destined a la production de raisins de table rassembles en vue de leur commercialisation par des negotiants d'une ville voisine (Clermont-rHerault) mais qui font egalement l'objet d'une consommation locale. Malheureusement, nous n'avons pu jusqu'ici evaluer les facteurs de transfert au raisin frais.

La deuxieme voie de transfert etudiee est celle des legumes arroses par l'eau du Rivteral. Les prelevements et les analyses que nous avons effectues nous ont permis de determiner les facteurs de transfert suivants (facteur de transfert sol-plante exprime en pCi par kg de produit frais ramene" a 1 pCi par kg de sol sec):

- Salade: 2 ,4 -10 - 4 kg/kg. - Tomate: 1,4 • 10" 4 kg/kg. Outre leur interet dans la poursuite d'une evaluation d'impact, ces deux

valeurs mentent une attention particuliere dans la mesure ou elles peuvent etre revelatrices des mecanismes de transfert du radium. Bien que ces deux productions soient notoirement differentes, on peut toutefois noter que, compte tenu des techniques culturales, les salades recoivent l'eau d'irrigation essentiellement par aspersion, tandis que les tomates sont irriguees a la raie, un exces d'humidite au niveau des feuilles entrainant en effet un risque de mycose.

Malgre" toute la prudence qu'il convient d'observer, il semblerait done qu'une certaine absorption foliaire du radium serait a considerer. Ce point fera bien sur l'objet de verification dans la suite de notre programme d'etude.

4. CONCLUSION

En ne considerant, dans un premier temps, que les doses par ingestion delivrees aux populations du site a travers ces deux voies de transfert, nous sommes maintenant en mesure d'effectuer cette Evaluation. Encore convient-il d'estimer la fraction due a la presence naturelle de radium dans l'environnement.

Par comparaison des teneurs des sols exposes ou non aux rejets de l'installation, nous pouvons estimer a 200 pCi/kg dans les sols l'apport de l'mstallation.

En prenant l'hypothese pessimiste d'une consommation de 2 litres par jour pour le vin — n'oublions pas que le vin constitue la boisson normale de la population adulte — et 2 kg par jour pour les legumes, les doses annuelles delivrees a l'organe critique (l'os en l'occurence) sont respectivement de 5/100 de D M A p

pour le vin et de 0,5/1000 de D M A p pour les 16gumes.

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II est a noter que ces valeurs sont tout a fait de l'ordre de grandeur de celles evaluees pour les memes voies autour d'une installation miniere classique d'extraction de charbon associee, il est vrai, a une centrale thermique.

L'interet de la methode devaluation d'impact que nous avons appliquee pour le radium sur le site de Lodeve appelle maintenant un commentaire. Chacune des voies de transfert a ete analysee sur le site meme. Cette analyse a mis en evidence des procedes culturaux specifiques pouvant entrainer, pour le radioelement considere, un comportement particulier. Dans une deuxieme phase, l'etude plus fine de chacun de ces processus devra etre approfondie par des experiences de laboratoire. Ce sont ces experiences qui font maintenant l'objet de notre programme de recherche.

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ENVIRONMENTAL SURVEILLANCE AROUND THE URANIUM COMPLEX AT JADUGUDA*

P.M. MARKOSE, S. V E N K A T A R A M A N , K.P. EAPEN, G.K. SRIVASTAVA, M. R A G H A V A Y Y A Health Physics Unit, Health Physics Division, Bhabha Atomic Research Centre, Jaduguda, Bihar, India

Abstract

ENVIRONMENTAL SURVEILLANCE AROUND THE URANIUM COMPLEX AT JADUGUDA. Waste effluents from the uranium mine-mill complex at Jaduguda originate from two

points: the mine and the tailings pond. Both are released into a carrier stream which ultimately joins the local aquatic system. The important toxins in these streams are radium-226, uranium, manganese, chlorides and sulphates. A continuous surveillance programme has been in operation at Jaduguda to assess the pollution status of the aquatic system. The levels of toxins in the streams — mine water, tailing effluents and the public streams — have remained fairly steady and well below the appropriate permissible limits. The radioactive impact on the aquatic system owing to discharge of effluents from the uranium complex has been found to be negligible and smaller than that owing to discharge of uranium-bearing tailings from a copper plant located nearby. Occasionally, transport of solids from the tailings pond has occurred owing to temporary malfunction of the decantation system, thereby increasing the specific activity of the sediments. Bioaccumulation of radium by aquatic organisms such as spirogyra (CF = 1870) and common pond snail (CF = 30 flesh, 60 bone) has been established, but there is no evidence of any accumulation of radium or uranium by terrestrial plants. The migration of radium through subsoil has been studied and found to be insignificant; these results are confirmed by analysis of nearby well waters. Another pathway for the movement of radium, namely soil-grass-milk-man, has also been investigated. The grass species studied is the common variety, Cynadon dectylon pers. Concentration factors (CFs) range from 4 X 10"3 to 30 X 10"3, with a mean of 14.8 X 10"3. This wide variation suggests that the concentration factor depends upon several parameters which need identification and further study. The release of manganese from the tailings pond is found to depend on the pH-value of the effluent. Overall, the surveillance to date indicates that the uranium processing operation at Jaduguda has not had any adverse effect on the environment of the uranium complex.

* This study is partially supported by the International Atomic Energy Agency, Vienna, under Research Contract No.2895/RB.

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1. INTRODUCTION

The operation of the uranium mine and mill at Jaduguda, Bihar, in India, and the associated environmental surveillance programme have been in force for the last 15 years [1 ,2 ] . Long-term monitoring of the aquatic system indicated mainly two critical pollutants, radium and manganese, in addition to other less significant pollutants such as uranium, sulphate and chloride arising from mining and milling operations.

2. SOURCES AND CHARACTERISTICS OF WASTES

2.1. Mine water

A large volume of seepage water is encountered in the mining operations. A small volume of effluent, containing manganese, is contributed to this from the back-filling operations. A small fraction of uranium gets dissolved in the seepage owing to physical processes during drilling and geochemical oxidation. These effluents, after being pumped out of the mine, flow into a natural stream called Juria nala.

2.2. Tailings effluents

Uranium from the ore is recovered in the mill using the acid leaching process. The drum filter cake obtained during the filtration of the leached slurry is the solid waste and is quantitatively almost equal to the ore processed. The cake is repulped with water and the resulting slurry is pumped to a neutrali­zation facility. The barren solution from the ion-exchange process is the liquid waste. This waste, which is acidic with a pH-value of about 2, is also pumped to the neutralization plant where it is neutralized with lime. When the pH-value of the slurry reaches 10, it is mixed with drum filter slurry. The 'coarse' fraction of the waste slurry is separated using hydroclones and is sent to the mine as back-fill, while the remainder is pumped into the nearby tailings pond for impoundment.

The tailings pond has been designed to contain all the solid wastes generated. The land which covers an area of approximately 25 hectares has a natural slope from west to east. Six decantation wells have been constructed inside the pond to drain out excess liquid from the waste pile. The level of the inlet into the decantation wells can be adjusted using wooden shutters in such a way as to permit the liquid waste to remain on the tailings pile sufficiently long for the solids to settle. As the level of the waste pile rises in due course, additional shutters are used to correspondingly raise the level of the inlet. The clear liquid

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Percentage frequency

FIG.2. Concentrations of uranium and manganese in mine-water stream (composite samples).

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O.I I I I I I 1 I I I I !_

I 2 3 4 5 6 7 8 9 10 pH

FIG. 3. Concentration of manganese in tailings as a function of pH.

from all the decantation wells is channellized into Juria nala. Figure 1 shows the aquatic environment of the mine-mill complex indicating the effluent discharges.

2.3. Characteristics of the wastes

During the acid leaching process (pyrolusite, a manganese ore, is the oxidizing agent) most of the uranium gets dissolved and is subsequently recovered. Therefore, any pollution of the aquatic system from uranium may be attributed to what is discharged directly from the mine. Analyses carried out over a period of one year indicated that the average concentrations of uranium, radium and manganese in mine water were approximately 300 mg/m 3 ,1110 Bq/m3 arid 3 g/m3, respectively (Fig.2).

Approximately 0.5% of the radium gets dissolved during the acid leaching process [ 3 ,4 ] . About one-half of this dissolved radium gets fixed on the tailings

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TABLE I. TYP ICAL CONCENTRATION OF DISSOLVED POLLUTANTS IN DISCHARGES FROM THE URANIUM COMPLEX A T JADUGUDA

Type of sample Uranium Radium Manganese Sulphate Chloride (mg/m3) (Bq/m3) (g/m3) (g/m3) (g/m3)

Composite sample of 302 1110 3.03 - -mines collected by sampler

Composite sample of 2.9 5800 2.2 1892 592 tailings

during neutralization; the rest remains in solution to be released into the environ­ment along with the tailings overflow from the pile. The concentration of radium thus released amounts to about 5800 Bq/m3. Manganese also gets dis­solved during the process. Practically all the dissolved manganese precipitates during the lime treatment that follows and is held in the solid matrix of the tailings. However, manganese precipitated as hydroxide is very sensitive to changes in pH-value (Fig.3). Any reduction in pH-value of the overflowing effluent enhances the dissolution of manganese in the tailings and its subsequent escape into the environment. Consequently, wide variations in manganese concentration in the effluent and stream have been observed. Analytical data of the last few years show dissolved concentration in tailings ranging from as low as 'traces' to as high as 900 g/m3 , corresponding to a pH range of 10 to 3. Table I shows a summary of the levels of pollutants in the discharges from the mine and the tailings pile.

3. ENVIRONMENTAL SURVEILLANCE

3.1. Sampling

The mine water was collected both by random sampling and by using the continuous sampler [5 ] . It was seen that there was no significant change in the median concentration values obtained by the two methods in the long run. Tailings samples were prepared by compositing the 8-hour shift composite samples over a period of one year. Environmental samples were collected from fixed locations at regular intervals. The samples were brought to the laboratory and filtered without delay, acidified and preserved.

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O N

TABLE II. DISTRIBUTION OF CONTAMINANTS IN THE AQUATIC SYSTEM

U n a t ( m g 2 / m 3 ) 2 J 6 R a (Bq/m 3 ) Mn (mg/L) C r (mg/L ) Hardness (mg/L) S0 4 (mg/L) Location

U n a t ( m g 2 / m 3 ) Location

M M M a g M a g M o g M

Tailings pile discharge

Juria nala, 1 km downstream from tailings pile

Gara nala, 2.5 km downstream

from tailings pile

Subarnarekha river, 6 km downstream from tailings pile

Background

M = Median; a = geometric standard deviation.

100.2 2.8 1725.7 3.1 5.6 3.8

148.8 2.1 1091.5 2.5 4.2 3.5

44.1 3.8 200.5 2.8 0.8 4.3

172.1 2.6 699.5

90.0 1.8 499.9

29.8 2.7 180.3

2.1 784.9

1.7 476.6

2.0 123.8

2.4 2 >

1.9 O CO m a

3.2 2

3.2 2.2

1.3 2.2

20.0 1.9 0.03 3.0

18.5 2.5 0.02 4.1

9.1 2.5 88.7 1.4 30.4 3.0

3.8 3.2 96.4 1.4 5.6 4.4

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TABLE III. ANALYSIS OF SEDIMENTS

Location Radium (Bq/kg)

a g

Juria nala, within 1 km downstream from tailings pile

6250 1.9

Juria nala, 1.5—2 km downstream from tailings pile 8003 1.8

Juria-Gara junction, 2.5 km downstream from tailings pile 2627 1.9

Gara nala, 3.2 km downstream from tailings pile 648 1.9

Subarnarekha river, 6 km downstream from tailings pile 137 2.2

Background sample 130 1.9

3.1.1. Water

Table II summarizes the results of analyses of water samples collected over a period of one year. The median concentration values are indicated in the table. The variations depend largely on the dilution available and to some extent on the pH-value of the effluent discharge. The effluent 50 m downstream from the tailings pile contains only radium, manganese and sulphate above the derived water concentrations (DWC) [6, 7]. The discharge from the mine joins Juria nala about 200 m upstream from the second sampling location. However, there is no increase in the concentration of pollutants in the water except for uranium. This is in accordance with the concentration of uranium and radium in tailings and mine effluents. These levels decrease by the time the effluent reaches Gara nala, which is about 2.5 km downstream from the discharge point. The carrier stream is not accessible to the public from the point of discharge from the tailings pond to the point of its confluence with Gara nala. The levels of all pollutants, including radium, are within the DWC at subsequent user locations. Further downstream, at Subarnarekha, which is the main source of water for the region, the water quality is as good as natural background water available in the region.

3.1.2. Sediment

Contamination of the stream bed occasionally occurs owing to accidental release of slurry into the stream either from the tailings pile or directly from the mill. Sedimentation taking place in the stream contributes to the sediment activity.

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TABLE IV. CONCENTRATION OF RADIONUCLIDES AS A FUNCTION OF PARTICLE SIZE OF SEDIMENT

Fraction

Size (um) % Weight

Radium " (Bq/kg)

Ionium (Bq/kg)

Polonium (Bq/kg)

Uranium (mg/kg)

>130 48.0 2435 3811 4762 165

130-74 10.7 3415 48.35 5650 160

73-53 7.1 3411 8351 6934 224

52-40 10.2 6593 11 270 11 725 337

<40 24.0 8665 14 770 15 729 392

Discharge of solid waste into the streams and rivers causes the enhancement of dissolved activity in the overflowing water because of natural leaching [8] of radium from the sediment itself.

Table III shows the results of sediment analyses. Sedimentation at the downstream locations is low, as can be seen from the results of sediment analyses collected from fixed locations at various times over a period of three years. The survey indicated deposition of sediments, as may be expected, at locations where the stream is wide and flow rather slow and even. Higher sediment activity could be observed up to a distance of 3 km downstream from the point of effluent discharge. Higher sediment activity at near locations is due to the occasional escape of tailings into the streams.

Activity as a function of different size fractions of sediment was studied. Table IV shows that the activity of the sediment is inversely proportional to size and this agrees well with the characteristics of the tailings.

3.2. Movement of radium through subsoil

The movement of radium through subsoil is an important parameter to be considered, since the tailings pile holds practically the entire inventory of radium from the mine. As per conservative estimate, the total inventory of radium in the tailings pile at present is about 28 TBq, although the specific activity is low. Most of the radium present in the tailings is in the sulphate form which is sparingly soluble under normal conditions. However, a significant amount of radium can be dissolved under the influence of anions other than sulphate or organic complexing agent. Organic-bound radium, if available, can be released as a result of natural biodegradation processes. Once it is dissolved, the rate of its movement through subsoil will depend on the nature of the soil and solution characteristics.

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In order to evaluate the rate of transport of radium through subsoil, an analysis of a core sample was carried out by collecting a core sample from a place over which water with an approximate radium content of 4 kBq/m3 has been flowing for a few years. The core sample was cut into sections and analysed. The results indicated significant adsorption of radium in the first few centimetres of the top soil only. The anions like chloride and sulphate are, however, more mobile without getting adsorbed in soil and, therefore, indicate actual seepage into the groundwater. Analysis of water samples of wells situated near the tailings pile showed that there was seepage of tailings into two wells situated about 500 to 600 m away from the nearest end of the tailings pile. The con­centration of these ions in the wells increased gradually to a level equal to that of the tailings effluent over a period of about 3 to 4 years. There was only a slight increase in the level of manganese, and no increase was observed in the level of radium [9] .

3.3. Distribution of radium in soil and grass

For estimating the distribution of radium in soil and grass, the common species Cynadon dectylon was selected. Sample locations were chosen at random, within the plant premises and also from areas where the soil was known to have been contaminated with tailings effluent. Background sampling locations were chosen at a distance exceeding 10 km from the plant site. Grass was collected with the soil. The concentration of radium in soil was found to range from 98 Bq/kg to 6146 Bq/kg and that in grass from 2 Bq/kg to 101 Bq/kg. The concentration factors (CFs) for 12 sets of samples ranged from 4 X 10" 3 to 30 X 10" 3 with a mean CF of 14.8 X 10~3. Variation in the concentration factors was expected since the samples represented different regions and the uptake is dependent on many parameters. However, the data indicated that the uptake is not a function of radium concentration alone but is influenced by the physico-chemical parameters of the soil.

Analysis of milk samples from the region showed a concentration of radium in milk ranging from 0.01 Bq/L to 0.06 Bq/L, with a median concentration of 0.02 Bq/L. The concentration of radium in grass compared with that in milk cannot be directly correlated because the analysis of milk was not performed on any controlled sample. However, it may be seen that transfer of radium from grass to milk, in general, is low.

4. CONCLUSION

Environmental surveillance showed that the levels of radionuclides in the streams of public utility are below the permissible concentrations. The level of

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discharge of uranium at the discharge point itself is below the permissible limit. The decrease in the level of radium and manganese activity With distance is caused by sedimentation and dilution. The study of the activity of the sediments lays stress against any lapse in the proper maintenance of the tailings pile. Since an escape of slurry into the aquatic system does not generally take place, the radio­active impact on the aquatic system from the uranium complex is much less than that from the discharge of uranium-bearing tailings from a nearby copper plant, where concentration of uranium and radium in the tailings of the copper industry was found to be approximately 60 mg/kg and 900 Bq/kg, respectively. These tailings are discharged directly into the Subarnarekha river.

Exposure of the population to radiation from uranium mining and milling operations in India has so far been found to be negligible. Effective containment of the tailings, low level of radium in drinking water, inaccessibility of contaminated water for irrigation and other purposes and low transfer of activity from water to soil and to plants are the main reasons for this low exposure. Effective contain­ment of tailings in the pile and continued monitoring of the effluents should be ensured for protecting the environment from radioactive contamination.

ACKNOWLEDGEMENTS

The authors are grateful to Mr. S.D. Soman, Head, Health Physics Division, for constant encouragement and valuable guidance. Thanks are due to Mr. S. Somasundaram, Head, Radiation Hazards Control Section, for his guidance and to Dr. K.C. Pillai, Head, Environmental Studies Section, for his critical comments and suggestions. The provision of facilities by Mr. M.K. Batra, Chairman and Managing Director, Uranium Corporation of India Ltd., is grate­fully acknowledged. The partial support given for this study by the International Atomic Energy Agency is acknowledged with thanks.

REFERENCES

[ 1] IYENGAR, M.A.R., MARKOSE, P.M., "Monitoring of the aquatic environment in the neighbourhood of uranium mill at Jaduguda, Bihar", Natl. Symp. on Radiation Physics, Bombay (1970).

[2] IYENGAR, M.A.R., MARKOSE, P.M., "An investigation into the distribution of uranium and daughters in the environment of a uranium ore processing facility", Symp. on Radiation and Radioisotopes in Soil Studies and Plant Nutrition, Bangalore (1970).

[3] MARKOSE, P.M., Radium and the Environment, M.Sc. Thesis, University of Bombay, (1979).

[4] MISWA, H., KANAZAWA, K., MARUYAMA, M., SEGAWA, T., ASHIZAWA, T., "Solid and liquid waste at Ningyo-Toge mine", Radiological Health and Safety in Mining and Milling of Nuclear Materials (Proc. Symp. Vienna, 1963) Vol.2, IAEA, Vienna (1964)123.

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VENKATARAMAN, S., SRIVASTAVA, G.K., SAHA, S.C., KAMATH, P.R., An approach to assess the water quality around a uranium complex using a continuous effluent stream sampler, Bull. Radiat. Prot. 2 (1979). WORLD HEALTH ORGANIZATION, International Standard for Drinking Water , 2nd Edn, WHO, Geneva (1963). INTERNATIONAL ATOMIC ENERGY AGENCY, Basic Safety Standards for Radiation Protection - 1967 Edition, Safety Series No.9, IAEA, Vienna (1967) 79 pp. TSIVOGLOU, E.C., "Environmental monitoring in the vicinity of uranium mills", Radiological Health and Safety in Mining and Milling of Nuclear Materials (Proc. Symp. Vienna, 1963) Vol.2, IAEA, Vienna (1964) 231. MARKOSE, P.M., EAPPEN, K.P., VENKATARAMAN, S., KAMATH, P.R., "Distribution of radium and chemical toxins in the environment of a uranium complex", Proc. Int. Symp. on Natural Environment III, Vol.2 (1980) 1078.

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PREOPERATIONAL ENVIRONMENTAL SURVEY FOR TWO URANIUM MINE SITES IN NORTHERN ITALY

G.F. CLEMENTE, R. GRAGNANI , G.G. MASTINO, F. SCACCO, G. SCIOCCHETTI Environmental Science Division, ENEA, Casaccia, Rome

M. DALL 'AGLIO Environmental Impact of Energy

Systems Project, ENEA, Casaccia, Rome

G.P. SANTARONI National Institute for Nutrition, Rome, Italy

Presented by P. Rafferty

Abstract

PRE-OPERATIONAL ENVIRONMENTAL SURVEY FOR TWO URANIUM MINE SITES IN NORTHERN ITALY.

Both uranium mine sites considered are located in Northern Italy in mountain districts at about 1000 metres above sea level. Mining, milling and mill tailings disposal operations are yet to commence. CNEN has carried out pre-operational surveys to identify site characteristics: (i) to assess the nature and the extent of environmental impacts of uranium mining, milling and mill tailings disposal operations; (ii) to provide information necessary to define regulatory requirements for the management and disposal of mill tailings and mill decommissioning; (hi) to identify requirements for environmental monitoring needed to demonstrate compliance with regulatory requirements during both the operational phase, and the decommissioning of the mill and mill tailings disposal operations. The environment of the sites has been studied in detail by various expert groups: ENEA (formerly CNEN) and INN (National Institute for Nutrition). They have jointly carried out comprehensive studies including: (i) geological characterization of ore bodies and sites; (ii) geochemical survey of the circulation of both stable and radioactive elements of major concern through natural waters; (iii) survey of the radioactive content and of 2 2 2 Rn emanation rate of soils and rocks; (iv) survey of external gamma radiation exposure and internal exposure due to 2 2 2 Rn and its airborne daughters of the population in the area around the mine and mill sites; (v) a socio-economic survey of locally produced foodstuffs, agricultural and dairy activities, and dietary habits of the various population groups. In summary the pre-operational environmental studies indicate that: (i) for stable elements (Zn, Cu, Cd and Pb) the levels are very similar to those normally

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encountered in the region, in contrast with the geochemical enrichments of the ore bodies; (ii) for radioactive elements ( 2 1 0Pb, 2 1 0 Po, 2 2 2 Rn, 2 2 6 Ra, U nat.) the levels are higher than normal and similar to those encountered in other high background areas of Italy. Concerning the disposal of uranium mill tailings, further co-ordinated environmental and technological studies are required to select sites suited to ensure reliable management and disposal, both in the short and long term. The results of the studies are discussed on the basis of available guidelines for environmental impact assessments, and prove to be adequate with respect to a preliminary assessment of environmental impact for the planned mining and milling activities.

1. INTRODUCTION

Since the late 1950s extensive uranium exploration has been carried out in Italy to discover and ascertain resources available for the nuclear fuel cycle.

Among several radiometric anomalies encountered in the central area of the Alpine Range, commercially relevant orebodies have been identified at the sites of Novazza and Valvedello. The first site has been known and studied since the late 1950s, while the second has only recently been identified (late 1970s) and its exploration has not yet been accomplished.

Both orebodies (average concentration of approximately 1000 ppm) have been traced underground through Permian formation and will allow the recovery of 1500 and at least 3 5 0 0 1 U 3 0 8 , respectively. Orebody evaluation is still in progress and estimates of Valvedello U 3 0 8 resources may increase in the future. Although it may be considered one of the most important European uranium mining areas, the amount of recoverable mineral is rather small. The Italian nuclear power programme is relatively modest, and such U 3 0 8 resources represent for it a fuel availability of 5 to 10 years.

The exploitation of such resources was planned between the sixties and seventies when the uranium market showed very promising prospects. The original programme schedule, mostly based on the exploitation of the first site, was subsequently altered to accommodate the promising results gathered for the second site, and also reduction of nuclear fuel demands that led to consistent uranium mineral surplus.

At present alternative solutions are being evaluated in order to fulfil economic and environmental protection requirements for the simultaneous exploitation of both orebodies.

2. GENERAL CHARACTERISTICS

The two sites of Novazzo and Valvedello are located in Northern Italy in the Central Alps (Fig. 1). They are only ten kilometres apart as the crow

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FIG.l. Scheme of the uranium mining areas of Novazza and Valvedello.

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FIG.2. Geological layout of the uranium mining areas of Novazza and Valvedello.

flies, in a mountainous area characterized by rugged topography (narrow valleys, steep slopes, and high erosion rates).

The geological layout of the area is shown in Figs 2 and 3 and is characterized by the following stratigraphic sequence:

(a) Crystalline basement (Archean — Paleozoic) made of gneiss, micaschist, phyllites, etc.

(b ) Basal carboniferous conglomerate. (c ) Collio formation (Permani Age). Thick volcano-sedimentary sequence

(sandstone-pelitic facies interbedded with rhyolitic volcanics). (d) Permian volcanics (lavas, ignibrites, tuffs) mainly of rhyolitic composition. (e) Lombard Verrucano formation (Upper Permian) conglomerate and red

sandstones composed of volcano elastics. ( f ) Triassic limestone dolomites. (g) Recent and quaternary continental deposits.

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The area, as usual for the Alpine Range, is characterized by medium to high relief, ranging in elevation from 600 to 2500 m.

The surface hydrology within the area is characterized by the steep morpho­logy, the spring melting of snow, and the consistent rains which occur mainly in the late summer period. Such conditions give rise to uneven surface runoff, principally in small creeks with highly variable flow. High flow is accompanied by high stream velocity, favouring erosion rather than sedimentation.

The area is sparsely populated with a very uneven distribution. Villages are mostly clustered along or near the Serio River valley, totalling about 5000 people; in the Vedello valley, villages total 3000 people within a radius of 10 km from the Vedello mine site.

The main activities in the area are cattle raising, milk and cheese production, winter and summer tourism; there are also a few small industries in the area, and many small and medium size hydroelectric power plants.

The climate is typical of the Alpine Range, dominated by altitude and by the dynamics of the high and low pressure weather systems which are characteristic of central Europe.

Summer rain is determined by the southern air stream from North Africa and the Mediterranean Sea. The climate is humid with mild summers and cold winters.

Prevailing winds are from the west, south and north. The narrow valleys enhance wind speed and substantially alter the prevailing direction of air flow on higher altitudes. There is rain in late summer, while snow in winter ranges from a few centimetres in the valleys to two metres above an altitude of 1800 m.

There are conifer woods up to 1500 to 1800 m, grassland tundra above that, and therefore wind erosion is effective only to a small extent where bedrock emerges above the soil cover.

The valleys are narrow and winding with a creek or river at the valley floor. There are numerous woods- and pastures.

Agriculture is limited to small patches around the villages. Mining and industrial districts have been active for many decades up to 30 km southward along the lower Serio River valley. It is worthwhile noting the consistent degradation of the surrounding environment, river bed, water and landscape due to industries. Such past deleterious practice has led to strict demand for conservation of the upper Serio River valley. Its inherent aesthetic value and its potential tourist resources are an attractive alternative to young people migrating towards the industrialized areas.

3. PRE-OPERATION AL STUDIES

The assessment of the environmental situation prior to the exploitation of the mines, and to the installation of the mill plant and the disposal of uranium

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FIG.3. Geological section along the line connecting the uranium mining areas of Novazza and Valvedello.

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mill tailings (UMT), was carried out between 1976 and 1980. In Italy, environ­mental protection regulations are very poor. Standards and technical experience are lacking; responsibility is divided among different administrative bodies that exert control only through external technical services belonging to other administrations.

Such a situation is characterized by inefficiency and slowness. The Italian government, therefore, envisages the adoption of EEC guidelines, which will require an 'Environmental Impact Assessment' for any industrial activity, as soon as they are issued [1 ] .

Public opinion is now aware of the environmental impacts produced by industrial activities and it has therefore been envisaged that uranium mining and milling activities should be carried out on the basis of an advanced approach to environmental management and conservation, taking into account the latest regulations adopted by foreign countries [2—4].

The pre-eminence of consideration required for potential radioactive contamination elicited a substantial contribution from the national nuclear energy agency (ENEA, formerly CNEN). It offered its support in the fields of regulation, environmental geochemistry, natural radioactivity, inquiry research on dietary habits and local food chains (jointly with the National Institute for Nutrition, Rome), radiation protection consulting, and co-ordination and supervision of the other studies to outline an 'Impact Evaluation', transferring its expertise from the radioactive field to the general environment.

Accurate geological surveys (1:5000) have demonstrated (with more detail than the general geological map of Italy [1:100 000]) the characteristics of the area in relation to the potential changes resulting from the installation of the mill plant and the UMT disposal. The work may be reviewed in two different sections on a time-scale basis. The first part covers the period from 1976 to 1979 and is focused on the Novazza mine site, the mill plant and the UMT disposal, all located in the immediate vicinity. The second part covers the period from 1979 to today, when the relative importance of Valvedello over that of Novazza led to the development of an alternative option. This alteration of strategy has helped to alleviate public concerns that the first project, whose proximity to villages was troublesome in relation to the potential impact on the environment and on the health of the local population.

In the first part (1976—1979) studies of the general environment in the area of the Novazza mine site were carried out [5,6] to characterize with sufficient detail the flora and fauna of the area.

Hydrogeological studies [7—9] were also carried out to define precisely the hydrology of both surface and underground water, and their physicochemical characteristics. Geotechnical studies were also undertaken specifically [10,11] to support UMT disposal proposals, owing to requirements for long-term management and disposal of tailings.

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ON

TABLE I. VALUE RANGES OF THE PHYSICOCHEMICAL PARAMETERS MEASURED AT NOVAZZA AND ° VALVEDELLO MINING SITES

Temp. pH

Conductivity 10"6 S/cm

Ca Mg Na K HC0 3 SO4 CI F Si0 2

°C pH

Conductivity 10"6 S/cm

10"6 eq/L mole/L

Surface water 6.2-13 7.2-! 3.2 24-210 14- 1900 45--660 12--63 3- 16 80-2100 25-510 7--34 1-9 30-100

Ground water 4.5-12 6.3-1 3.5 25-250 28- 2000 50--710 8--80 2--30 140-2300 13-370 2--44 1-6 35-150

o r

Cu Zn Pb HM U 2 2 2 Rn 2 2 6 Ra § H

W

ug/L pCi/L & 05

Surface water 0.03-0.4 0.5-4.6 0.001-0.2 11-800 0.04-1.2 0.1-0.3

Groundwater 0.1-1 0.2-10 0.001-0.4 11-9000 0.05-1.9 40-450 0.1-0.3

Cu Zn Pb U

ppm

River sediment, 6-83 40-880 10-170 0.5-29 soil

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Natural levels of potentially relevant chemical elements (both stable elements and radioactive), their fluctuations in time and their movement in the environ­ment have been assessed. Element transfer has been considered only through natural water pathways. It has, in fact, been recognized that this is the main pathway of environmental dispersion of pollutants, the air pathway contribution being negligible, except at very short distance, in this specific environment.

Water analyses have included the physicochemical parameters (temperature, pH-value, electrical conductivity) and the major dissolved constituents (Ca, Na, Mg, K, H C 0 3 , S 0 4 , CI, S i 0 2 ) , as well as potentially toxic trace elements (F, U, HM, Cu, Zn and Pb) which may potentially be released into the waterway by the mill operation.

Periodic sampling to investigate fluctuations in time has considered about 60 sampling points (rivers, creeks, wells, springs, water supplies) with special concern for the water bodies expected to receive treated mill effluents. The sampling period covers the years 1977 to 1980.

Soil from cultivated areas and sediment from the rivers and creeks have also been sampled. The relevant findings are:

(a) Element levels, and their correlation, show low mineral content (<0.1 g/L) as would be expected for natural waters at the beginning of their hydrological cycle in these headwaters. Their chemistry is dominated by the presence of Ca and Mg bicarbonates.

(b ) The radioactive elements, U, Ra, and Rn, show low levels, apparently in contrast to the high geochemical background of this area. This should be related to the high silicization of the uranium-enriched orebodies, that renders them very resistant to leaching. Furthermore, the hydrodynamic conditions of the mountain environment produce a poor water-rock inter­action, therefore contributing little to the mobilization of such elements through dissolution by natural waters.

(c ) Potentially toxic stable elements (P, Cu, Zn and Pb) show low levels, with little fluctuation.

(d ) U, Pb, Cu and Zn levels in the local river sediments are usually about the same as levels normally found in the region. Only a few sampling points showed higher values, and are attributed to anthropogenic origins.

(e ) U, Pb, Cu and Zn levels in soils are within the variability range of these elements in the lithological formations encountered within the area. The value ranges related to the various samples are given in Table I.

External dose (both cosmic and terrestrial) has been measured in the area of the two mine sites, and ranges between 8 and 18 juR/h. In Italy, about 70% of the population receive an external gamma dose of about 8 to 13 juR/h, while in the high background areas in central Italy the external gamma dose reaches 50 /xR/h [12]. Therefore the external exposure within the area taken into account

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TABLE II. RANGES OF THE RESULTS OBTAINED FOR 2 2 2Rn AND ITS DAUGHTER LEVELS

Type of measurement 2 2 2 Rn 2 2 2 Rn daughters

Open air 0.1--0.6 (pCi/L) 10" 4 -10" ' 3 (WL)

Indoor 0.7--3.5 (pCi/L) 10~ 3-10" •3 (WL)

Exhalation rate from soil ( i o -• "C i -cm^-s - 1 ) 0.7-12

is only slightly higher than the national average, but not exceeding that encountered in the high background areas where about 30% of the Italian population lives. This modest increase is, of course, attributed primarily to the average altitude of the area, and in the second instance and to a lesser extent to the higher natural radio­activity background of this area.

2 2 2Rn and its daughters have been widely monitored as follows:

(a) in open air; (b) in dwellings; (c) exhalation rates from soil.

The results obtained (Table II) are well within the range of normal natural background levels, taking into account higher variability due to geological and meteorological factors.

On the basis of the results gathered through the aforementioned studies, it has been recognized that any disturbance of the environment which might be caused by mining, milling and tailings disposal would affect only the local environment through local air and water pathways. Consequently, impacts on local food-chains would also be restricted to the local environment.

Therefore, a survey of potential food-chain contamination has been carried out in the region of the Novazza mine where there are about 5000 people living within a 3 km radius. The other mine site (Valvedello) and the site recently selected for the mill and mill tailings disposal are in fact at least 7—10 km away from the nearest village and are also far from pasture areas.

A preliminary survey of dietary habits has been carried out by the National Institute for Nutrition to ascertain the contribution of locally produced food to the diet of the population around the Novazza mine.

A critical group of potentially exposed people residing in the area has been selected, including farming people as well as sedentary village and town people.

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TABLE III. 2 1 0 P b , 2 1 0 P o AND 2 2 6 Ra INTAKE RANGES (pCi/d) FOR THE CRITICAL GROUP AT THE N O V A Z Z A MINE SITE

TABLE IV. 2 1 0 P b , 2 1 0 P o AND 2 2 6 Ra INTAKE RANGES (pCi/d) FOR THE ITAL IAN POPULATION

TABLE V. CONCEN­TRAT ION O F 2 1 0 P b A N D 2 1 0 P o (pCi/L) IN THE URINE OF SUBJECTS OF THE CRITICAL GROUP

210T J Pb, 2 1 0 P o

2 2 6 R a

3-20

0.5-6

2 1 0 P b , 2 1 0 P o

2 2 6 R a

0.4-8

0.5-1.2

°Pb

°Po

0.4-1.2

0.1-1.1

By means of interviews and diet surveys, a detailed picture of the dietary habits, and of the consumption of locally produced foodstuffs has been obtained for the critical group; foodstuffs liable to contribute markedly to increased intakes of radionuclides disposed or dispersed from mining, milling and tailings disposal have been identified.

Grain-based foodstuffs (bread and pasta) and rice, even if they are primary diet items, are not produced locally. Vegetables, meat, milk, cheese and eggs were shown to be critical foods. On the basis of the results of the dietary survey, foodstuffs have been sampled and their 2 1 0 Pb , 2 1 0 Po and 2 2 6 Ra levels have been measured to evaluate the ingestion rate of these radionuclides for the critical group as shown in Table III.

As a reference, the results of a wide survey in many large and small towns all over Italy have been considered [13—15] and are reported in Table IV.

A figure of ingestion higher than normal for the Italian population seems reasonable owing to the high consumption of locally produced foods (~50%). Within the critical group, the subjects selected for diet sampling have been submitted to a urine sampling for assay of 2 1 0 Pb , 2 1 0 P o ; the results are shown in Table V.

In the first instance, it was concluded that pre-operational activities at the sites have so far not resulted in any substantial impact on the environment or any detectable impact on public health.

As mentioned above, requirements for environmental and public health protection are rather meagre in Italy and a detailed'Environmental Impact State­ment (EIS) is not required to license uranium mining and milling activities.

Nevertheless, various tentative evaluations have been carried out to reassure the public that are opposed to the licensing of these activities [16]. None of these studies may be considered as part of a detailed impact evaluation. The most accurate and detailed showed that milling and mill tailings disposal operations would cause a modest impact as regards radioactive effluents [16]. However,

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Ore process rate 800 t/d

Average ore grade (% U 3 O g ) 0.08 % Ore activity of 2 3 8 U and each daughter in secular equilibrium 220 pCi/g

Ore storage time 7 days

Operating days for year 230

Uranium recovery 96 % Average annual production 130 tu 3 o 8

Dry solid waste 800 t/d

Tailings density 1.7 g/cm3

Area of tailings disposal 40 000 ™ 2 m

FLOCCUIAHT

FILTRATION TAILINGS P ILE i, DISPOSAL

ORE

CRUSHING

WATER

WET GRINDING

SULFURIC ACID

SODIUM CHLORATE _ +

LEACHING

AMINE KEROSENE ALCOHOL i _

SOLVENT EXTRACTION

RAFFINATE RECYCLED

TO LEACHING

I — STRIPPING

AMMONIA

PRECIPITATION

FILTRATION

ORYING

YELLOW CAKE FACKAGIG

PRODUCT

FIG. 4. Flow diagram for the acid leach process.

TABLE VI. PRINCIPAL CHARACTERISTICS OF THE MILL PLANT

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REAGENTS

ORE

MI L L TAILINGS

LIQUID EFFLUENTS

NEUTRALIZATION

FILTRATION

Ra-BARIUM COPRECIPITATION

WASTE WATER TO BE RECYCLED WITHIN THE PLANT OR DISPOSED IN THE R IVER

FIG.5. Flow diagram of tailings production and waste water recycling.

more accurate evaluations carried out in the light of the latest experience indicated that the siting of the mill and especially the mill tailings disposal area had to be reconsidered, in the absence of special remedial actions, owing to their proximity to the villages. Furthermore, this shortcoming proved to be important on the basis of the long-term management and disposal of the tailings, especially regarding dispersion of stable toxic elements from the mill tailings through water seepage and physicochemical processes.

The best attempt to achieve an estimate of the potential impacts of the proposed operations has been provided by these environmental studies which have been carried out. The preoperational conditions are in fact characterized by very low sources of natural contamination and their very fast transfer from the environment [9 ] . Environmental radioactivity is only slightly above normal background levels and well within the range of the average exposures of the Italian population.

A consistent increase above natural fluxes might therefore be expected through the discharge into the environment of gaseous and liquid effluents from the mill and tailings, even if at concentration levels lower than those foreseen by national regulations. Regulations do not provide standards on the quantities that may be freely disposed of but only on the concentrations (with the exception of radioactive substances). It is therefore clear that the disposal of effluents which contain contaminants at concentration levels which comply with national standards but which are characterized by fluxes higher than those of the natural environment, although legally permissible, are to be discouraged.

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566 CLE MEN TE et al.

4. PLANT CHARACTERISTICS AND IMPACT

The main characteristics of the plant and the projected material balance as estimated in project studies [16] are given in Table VI . The acid leach process will be used (see flow diagrams in Figs 4 and 5).

The expected average mineral composition of ore to be fed into the mill is shown in Table VI I , while in Table VI I I the additives needed for the leaching process are shown in units of flow rate.

Liquid wastes expected to be produced by the mill have been estimated as shown in Table IX, where both flow rates and concentrations are given.

TABLE VII . AVERAGE MINERAL

% ppm

u - 900

Si0 2 75.1 -A1 2 0 3 13.6 -K 2 0 3.3 -Na 2 0 0.22

CaO 0.44

C0 2 0.40

so4 0.85

F 890

CI 400

Al 820

Pas ( P 2 O s ) 600

INPUT COMPOSITION

% ppm

F e 2 0 3 0.8

Zn 0.66

Ti 0.15

Pb 630

V 125

Zr 100

Mn 90

Mo 85-200

Cu 45-60

Rb 100

Sr 100

TABLE VIII . ADDITIVES REQUIRED FOR ACID LEACH PROCESS (kg/t • h)

Sulphuric acid

Calcium carbonate

Calcium hydroxide

Sodium chloride

Sodium chlorate

49

30

19

0.5

4

Barium chloride

Ammonium sulphate

Amine

Alcohol

Kerosene

0.05

0.25

0.04

0.02

0.7

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H 2 0

NH 3

NaCl

NaS0 4

CaS0 4

Flocculant

F

CI

As

Zn

Pb

V

kg/h

60 000

0.11

55

38

28

2

3

1.3

3

28

0.2

0.04

mg/L

50

22

50

470

3

0.7

kg/h mg/L

Mo 0.7 10

Cu 0.2 3

Rb 1 17

Cs 1 17

Unat 0.026

juCi/h pCi/L

2 2 6 Ra 0.3 5 2 i o p b 0.3 5

2 1 0 Po 0.3 5

2 1 0 Bi 0.3 5

The expected composition of mill tailings is reported in Table X, while in Table X I other emissions potentially produced by the mill are given.

Finally, in Table XI I an overall estimate of the radioactive emissions from tne mill is given.

5. ALTERNATIVES

Based on the aforementioned discussion and on the extension of uranium resources at the Valvedello site, a solution has been developed to minimize environmental impacts and to optimize the operations at both mines and mills [17].

As mentioned before, this site (Cascina del Campo) is remote from villages (the nearest is about 7 km away) and is located at about 1300 m above sea level on a wide plain connecting three valleys. It is only 1.5 km away from Valvedello and 15 km from the Novazza mine.

An alternative that has been adopted is preliminary crushing to reduce ore to a size range of 10 to 100 mm followed by radiometric sorting. This enables rejection of about 30% of the ore feed retaining an average recovery of 8 6 % if a cut-off of 240 ppm is adopted.

Further studies are in progress to gather information needed to ensure that operation of the mill and tailings disposal at this site can be carried out without appreciable impact on the environment. The reduction of volume of the mill tailings should enable the adoption of a more effective system for providing for

TABLE IX. ESTIMATED LIQUID WASTES GENERATED BY THE MILL (pH 7)

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TABLE X. ESTIMATED COMPOSITION OF SOLID TAILINGS PRODUCED BY THE MILL

kg/h ppm

Total weight 48 000

H a O 11 700

CaS0 4 -2H 2 0 2 650

Mo0 4Ca 2.6

Fe(OH) 3 353

U 2 0 7 Ca 0.3

NH 3 0.03

NaCl 37

Na 2 S0 4 11

Ca(OH) 2 54

CaC0 3 86

CaS0 4 24

U 0 3 1.4

MoO 3 8.5

Si0 2 25 000

A1 2 0 3 4 500

K >

Na predominantly

Mg

Ca > 354

S0 4 as hydroxides As

P >

52

9

kg/h % ppm

F 26 550

CI 12 250

As 24 500

Zn 250 0.53

Ti 50 0.11

Pb 20 420

V 4 84

Zr 3 63

Mn 3 63

Mo 6 130

Cu 2 40

Rb 1.5 30

Cs 1.5 30

U 3 0 8 1.4

mCi/h % pCi/g

Unat 1.2 0.003 17

Ra-226 8.5 180

Th-230 8.5 180

Pb-210 8.5 180

Po-210 8.5 180

Bi-210 8.5 180

their long-term stability. The main points to be taken into account to obviate long-term institutional control are:

(a) geological stability of the site; (b ) hydrogeological control; (c ) mechanical stability of the tailings; (d) chemical stability of the tailings; (e ) provision of a soil cover and vegetation, thus providing protection against

wind erosion and radon emission.

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TABLE XI. EMISSION POTENTIALLY GENERATED BY THE MILL

Emission Emission source Rate (kg/h)

Ore dust Ore storage and crushing/grinding 0.3

u 3 o 8 Product drying and packing 0.07

Tailings dust Tailings pile -Organic solvent (kerosene) Solvent extraction ventilation system 0.1

Sulphur dioxide and sulphur acid fumes

Acid leach tank ventilation system 0.4

S0 2 Burning of fuel oil 50

N 0 2 Burning of fuel oil 10

Noise Crushing/grinding - 100 dBA at 1 m

C0 2 Acid leach ventilation system 140

c o 2 Effluent neutralization 450

HC1, HF Acid leach ventilation system 10

TABLE XII. RADIOACTIVE EMISSION GENERATED BY THE MILL

Emission source Particulate (mCi/a)

2 2 2 Rn (Ci/a)

Ore hauling and storage pad Ore crushing and grinding

Yellow cake drying and packaging

Tailings pile

Dispersed ore and tailings

2 3 4U

0.2

300

2 3 0 T h

0.2

1.5

2 2 6 Ra 210p b

2 1 0 Po

0.1

0.3

100

negligible

4700

40

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The geomorphological condition of the Cascina del Campo site, in the light of the studies so far carried out, seems to cater adequately for the first requirements.

Concerning leaching of potentially toxic elements from the tailings by rain water, the mineralogical and chemical composition of the tailings indicates that appreciable leaching is very unlikely to occur. Nevertheless, in the period ranging from one to three decades, it is strongly suggested that a monitoring programme be instituted to focus on the characteristics of drainage from tailings containment. It should monitor pH-value, radionuclides and stable toxic elements (heavy metals, As, etc.) in the ground and surface waters around the tailings site, in order to assess the effectiveness of the containment system adopted.

The atmospheric release of radon is a significant pathway to be considered in the assessment of long-term suitability of tailings management. The remoteness of the site might be taken as a reassuring argument. But it has to be kept in mind that any forecasts about population distribution trends in the area in the long term are beyond present planning capability. It is therefore envisaged to provide an adequate soil and vegetation cover over the tailings at the end of the operations.

The wet climate characterizing the site through abundant precipitation, provides sufficient surface moisture to ensure a permanent vegetation cover.

Winter snow cover and surface freezing will also consistently lower average radon emission.

6. REGULATORY ACTIONS

As mentioned above, in Italy regulations have been established concerning only occupational health protection of workers. Guidelines for environmental protection for industrial and mining activities are lacking. In the past the Ministry of Health has carried responsibility and CNEN has provided technical support. However, since 1978, local health authorities also have been responsible for the public health protection and for environmental monitoring of radioactivity.

It is clear that an adequate licensing and regulatory regime is needed not only to provide for assessment of the potential environmental impacts due to mining, milling and to tailings management, but also to provide a starting point for establishing practices needed for safe management of uranium mining and milling operations.

In the interim it is necessary, as in the past, that all uranium exploitation operations be carried out to a high technical standard to comply as far as possible with prospective future regulations, and to provide ongoing experience on which regulatory bodies can base their actions.

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ACKNOWLEDGEMENTS

The authors wish to express their gratitude to all who have contributed to

the sometimes difficult procedure involved in the preparation of this paper.

In particular the authors wish to thank AGIP-S.p.A. and its co-operation

SIMUR, for their technical support, field data and for having made available

information on mining and milling plant characteristics.

The authors also thank G. San tori and A. Renzetti for the 2 1 0 P b - 2 1 0 P o

analysis, P. De Cassan and G. Paganin for graphics aids, and S. Giuliani for typing

and editing.

The authors address special thanks to P. Rafferty for having presented the

paper. Among them, G. Mastino, who was unable to attend the symposium,

expresses his particular personal gratitude.

REFERENCES

[1] PEN, Piano Energetico Nazionale, Ministero dellTndustria Commercio ed Artigianato, Rome (1981).

[2] AECB, the Cluff Lake Board of Inquiry Final Report (1977). [3] USNRC, Final Generic Environmental Impact Statement on Uranium Milling, Rep.

NUREG-0706, U.S. Nuclear Regulatory Commission, Washington (1980). [4] PANCON, The JabilukaProject Draft Environmental Impact Statement, Pancontinental

Mining Ltd. (1977). [5] PIROLA, A., CEDRARO, V., Lineamenti della vegetazione della zona di Gromo -

Novazza - Val Seriana, ENI Int. Rep. (1978). [6] AGIP-GEDA, Relazione Indagine fanistica e microfaunistica, Agip-Geda Int. Rep.,

San Donato Milanese, Milano, Italy (1979). [7] POZZI, Studio Ideologico della zona di Novazza, ENI Int. Rep. (1977). [8] CNEN, Studio delle acque naturali della Valvedello con particolare riferimento agli

elementi naturali radioattivi, Int. Rep. Lab. Geochimico Ambientale of CNEN (1979). [9] CNEN, Ricerche sperimentali di campo e di Laboratorio sulle condizioni ambientali e

sui consumi alimentari della zona di Novazza, CNEN Int. Rep. (1980). [10] ECO SOL, Studio preliminare di fattibilita - Discarica di Foppa (1977). [11] ECOSOL, Studio di affidabilita tecnica - Discarica di Foppa (1978). [12] CARDINALE, A., CORTELLESSA, G., GERA, F., ILARI, O., LEMBO, G., "Distribution

in the Italian population of the absorbed dose due to the natural background radiation", in Natural Radiation Environment II, Vol. 1, Rep. CONF-720805-P1 (1972) 421.

[13] MASTINO, G.G., SANTARONI, G.P., "Ra-226 levels in Italian drinking waters and foods", in Natural Radiation Environment III (Proc. Symp. Houston, 1978) DOE Symposium Series 51 CONF-780422 (1980) 800.

[14] MASTINO, G.G., SANTARONI, G.P., "The exposure of the Italian population to natural radioactivity in drinking water and food", Proc. Seminar on the Radiological Burden of Man from Natural Radioactivity in the Countries of the European Communities, Le Vesinet, Paris, 1979, CEC. Luxembourg (1980).

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[15] CLEMENTE, G.F., RENZETTI, A., SANTORI, G., BREUER, F., "Assessment of 2 1 0 Po exposure for the Italian population" (Proc. 5th IRPA Int. Conf., Jerusalem, 1980) Vol.3 (1980)303.

[16] STEC, Rapport d'impact sur l'environment de l'usine de traitement de minerai d'uranium de Novazza, STEC Rep., Societe Technique d'Entreprise Chimiques, Sevres, France (1978).

[17] AGIP, Progetto VALVE-NOVA, Rapporto di fattibilita; Progetto preliminare, AGIP S.p.A., servizio PROU (1981).

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FINDING AND EVALUATING POTENTIAL RADIOLOGICAL PROBLEMS IN THE VICINITY OF URANIUM MILLING SITES*

W.A. GOLDSMITH Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee

W.G. YATES Monsanto Research Corporation, Mound Facility, Miamisburg, Ohio, United States of America

Abstract

FINDING AND EVALUATING POTENTIAL RADIOLOGICAL PROBLEMS IN THE VICINITY OF URANIUM MILLING SITES.

The Oak Ridge National Laboratory (ORNL) has been performing radiological surveys at former uranium and thorium milling and processing sites since 1975. Tailings at inactive milling sites usually have a low frequency of human occupancy but continuously generate 2 2 2 Rn into the atmosphere. Thus, independent 2 2 2 Rn surveys are conducted at the inactive mill sites and their environs by the Mound Facility. Measurements of airborne 2 2 2 Rn and 2 2 2 Rn flux are made on the sites to define the tailings source term. Concurrently with these measurements, an ambient 2 2 2 Rn monitoring network is established off-site and a meteorological station is established at or near the mill site. Unfortunately, tailings are not always confined to the milling site. Radioactivity can migrate to areas outside of site boundaries by wind and water erosion, groundwater transport, spillage of incoming ore, and removal of tailings or other material for private purposes. In order to identify and assess off-site radioactivity on properties in the vicinity of milling sites, a combination of aerial and ground-level radiological monitoring techniques are used. The ground mobile gamma-ray scan is conducted using a vehicle equipped with sensitive gamma-ray detectors. The detectors are shielded so that gamma radiation input is viewed through only one side of the vehicle. This system is capable of precisely locating properties which have anomalously high gamma radiation levels caused by the presence of tailings. Subsequently, these properties are identified as candidate vicinity properties and are scheduled for radiological surveys subject to the property owner's consent. The comprehensive radiological surveys conducted at these vicinity properties determine the amount, type, and location of tailings materials. Radiological surveys are conducted by measuring and documenting as many components of

* Research sponsored by the Office of Operational Safety, United States Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corporation, and No. DE-AC04-76-DP-00053 with Monsanto Research Corporation.

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the radiation fields as is practical at a given site. Structures on a vicinity property are carefully surveyed to determine the presence or absence of construction-related uses of tailings. If structural uses of tailings are found, air samples are analysed for 2 2 2 Rn progeny, short-term continuous 2 2 2 Rn monitoring is instituted, and 2 2 2 Rn flux rates from tailings are estimated. If warranted, long-term 2 2 2 Rn and progeny measurements are made.

1. INTRODUCTION

In response to the demand for uranium about three decades ago, large scale uranium mil l ing and processing operations were in i t i a t ed at many locations in the western United States. The operations at each of the s i tes generated large quantities of process residues cal led ' t a i l i n g s ' . When most of the early mi l l s were vacated, insuf f ic ient attention was given to the t a i l i ng s p i l e s which were impounded on the s i t e s . These t a i l i n g s pi les represent a large area source of technologically-enhanced natural rad ioact iv i ty and continuously generate 2 2 2 R n into the atmos­phere. The area surrounding the inactive mill s i tes usually have a low frequency of human occupancy; however, some s ites are located within or near major population centers.

In 1974, the Atomic Energy Commission (AEC), now the Department of Energy (DOE), in i t i a ted a study of 22 inactive ura­nium mill s i tes in cooperation with the Environmental Protection Agency (EPA) and health authorit ies in the eight affected western s t a t e s . [ 1 ] This study developed into the Uranium Mill Tai l ings Remedial Action Program (UMTRAP) under authority of the Uranium Mill Tai l ings Radiation Control Act of 1978 (Publ ic Law 95-604). The purpose of this program is to conduct an engineering assess ­ment of exist ing conditions at these s i t e s , determine the reme­dial action required, develop plans and speci f icat ions for implementing remedial act ion, perform the necessary remedial act ion, veri fy the r e su l t s , and re lease the s i tes for unrestr icted or limited use, as required.

Within the DOE, respons ib i l i ty for various aspects of the remedial action programs have been assigned to the Assistant Secretary for Environmental Protection, Safety, and Emergency Preparedness (ASEP), and to the Assistant Secretary for Nuclear Energy (ASNE). The ASEP, through the Off ice of Operational Safety (00S) , is responsible for i n i t i a l radiological characterization and designation of s i tes for remedial action, health and safety overview, and ce r t i f i ca t i on of compliance of remedial action with appropriate standards. A more complete

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description of the ac t i v i t i e s assigned to each assistant secre­tary may be found e lsewhere . [1 ] Within 00S, a contractor asso­c iated with the Remedial Action Survey and Cert i f i cat ion Ac t i v i ­t i e s (RASCA) program performs the radio logical survey duties.

Under the ongoing program, which included other government agencies [notably the Housing and Urban Development (HUD) and EPA], a l l of the primary UMTRAP s i tes have undergone comprehen­sive radio logical assessments. The assessments included measure­ments of airborne 2 2 2 R n and 2 2 2 R n flux at the t a i l i n g s s i tes to define the source terms, and a 2 2 2 R n monitoring network was used to determine the ambient concentrations in the surrounding areas. The 2 2 2 R n surveys were performed by the Monsanto Research Corporation (Mound F a c i l i t y ) .

As a result of the program a c t i v i t i e s , i t was determined that secondary contamination of pub l ic , r e s i dent i a l , commercial, and industr ia l properties in the v ic in i ty of many of the s i tes ( v i c in i t y propert ies ) had occurred. The migration of the con­taminated materials was found to be due to any of the fo l lowing: (1 ) wind or water transport of the t a i l i n g s , (2) using contamin­ated building materials or the t a i l i ng s in bui lding construction, or ( 3 ) for f i l l in outdoor areas. The use of the t a i l i ng s for pr ivate construction purposes, such as in Grand Junction, Colorado, resulted in the transport of the materials away from the or ig inal s i t e .

The process and methodology used by a RASCA contractor, Oak Ridge National Laboratory (ORNL), to identify the spec i f ic v i c i ­nity properties which may contain t a i l i ng s material and to con­duct the comprehensive radiological survey to define the extent of t a i l i n g s involvement on those properties are described in this paper. The 2 2 2 R n monitoring networks and long-term indoor 2 2 2 R n and progeny monitoring by the Mound F a c i l i t y , ' another 00S contractor , are also described. These contractor ac t i v i t i e s pro­vide the necessary information to assess the radiation exposure and to support the ASEP determinations of the need for remedial act ion .

2. FINDING CANDIDATE PROPERTIES

Approximately 85% of the original rad ioact iv i ty in uranium ore can be found remaining in the t a i l i n g s . When t a i l i ng s impoundments are vacated and l e f t uncovered for an extended period of time, natural and human forces can cause migration to

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o f f - s i t e locat ions . Pr imari ly , these poss ib le transport mecha­nisms are : (1) wind erosion, (2 ) surface water erosion, (3) groundwater t ransport , (4 ) sp i l l a ge of incoming ore , and (5) removal of t a i l i ng s or other material for pr ivate purposes. Once the t a i l i n g s have been moved from the confines of the storage area , they are subject to further movement or d is t r ibut ion as a result of human act iv i ty ( e . g . street and road repair or construction, pipel ine construction, e t c . ) .

Since t a i l i n g s may be transported for many kilometers before being used for private purposes, large areas (several square ki lometers) around each mil l ing s i t e must be surveyed i f a l l of the v ic in i ty properties where t a i l i ng s may have been used are to be i dent i f i ed . I n i t i a l l y , a DOE contractor conducts comprehen­sive aer ia l gamma-radiation surveys around each or ig inal mil l ing s i t e . The survey provides a preliminary indication of the pre­sence of contaminated materials on the v ic in i ty propert ies .

Results of the comprehensive aer ia l survey can be used to plan a detai led ground-level mobile gamma-ray scanning survey. This type of radiological survey consists of a methodical ground-level gamma-scanning of a property or ser ies of properties by a vehicle equipped with Nal detectors and associated analyzers and recorders. The purpose of this mobile gamma-scanning survey is to accomplish one or more of the fo l lowing: (1 ) veri fy aerial radio logica l survey resu l t s , (2) identi fy a spec i f i c location of rad ioact iv i ty on the ground as indicated by the aer ia l r ad io log i ­cal survey, and/or (3) identify the location of other radiation anomalies that did not appear on an aeria l scan. This type of radio logica l survey requires input of pertinent information such as h istor ica l information, maps, and photographs, and requires a radio logica l survey plan prior to in i t i a t i on of the survey.

The gamma-ray detection system now employed in the ORNL scanning vehicle consists of three 10 x 10 x 40-cm Na l (T l ) Polyscin" log c rys ta l s , each with an integral 8.9-cm photo-mul t ip l i e r tube. The crystals are housed in a lead-shie lded steel frame to provide a 30-cm x 40-cm detector surface area for acceptance of gamma-rays through one side of the survey vehic le . The detector and shield height can be varied with a hydraulic l i f t mechanism to optimize the detector f i e l d - o f - v i e w .

The detector output is transferred to a computer-controlled eight-channel discriminator and inter face , designed and f a b r i ­cated at ORNL. This unit provides for continuous analysis of data inputs for correlat ion of anomaly location with count rate information. Six separate energy reg ions -o f - in te res t are ana­lyzed and a 2 2 6 R a - s p e c i f i c algorithm is employed to identify locations containing residual radium-bearing mater ia ls . Data on

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other natural ly-occurr ing radionuclides (such as k 0 K and 2 3 2 T h ) are obtained for comparison as part of the ana lys i s . Mult i ­channel analysis capab i l i t i e s are included in the system for additional qua l i ta t ive radionuclide i dent i f i c a t i on . The system is operator -control led through keyboard instructions to an on­board mini-computer. Data output is provided on the computer video screen, dual-channel s t r ip chart recorders, and a graphic p r inte r . Data storage is provided by a dual floppy disc system.

Mobile scanning from roadways requires that vehicle travel speed and source-to-detector distance be maintained at a minimum for optimum resu l t s . This is accomplished by dr iv ing the vehicle next to the street curb and by maintaining scanning speeds of less than 8 km/h. In areas to be scanned, a l l access ib le roads would be traversed, and properties scanned from as many views as poss ib le ( e . g . f ront , a l l ey , and side s t r e e t s ) . When access to properties can be gained by other public thoroughfares ( e . g . parking l o t s ) , this additional information is obtained.

Radiation anomalies are ident i f ied by the mobile system by comparison of the instantaneous count rate information with a background level establ ished for the area being scanned. Various methods of data analysis are provided to discriminate for the radionuclide contaminants of concern, including on-board multi ­channel analysis capab i l i t i e s and s t a t i s t i c a l analysis of the input data. Documentation of scanning survey results is t yp i ­ca l l y in the form of s t r ip charts or computer generated data summaries.

By using this mobile scanning system, properties may be iden­t i f i e d as having anomalously high gamma radiation l e ve l s . Furthermore, the nature of the material giving r i se to the e l e ­vated gamma-ray leve ls can be surmised by obtaining spectral information. In this manner, properties which contain excessive 2 2 6 R a (which is typical of uranium mill t a i l i n g s ) and those for which the elevated gamma-ray anomaly is due to other radioactive sources can be ident i f ied in a cos t - e f f ec t ive manner. These propert ies , so ident i f ied as having t a i l i n g s envoivement, can then be subjected to a detai led radiological survey to assess the extent of t a i l i ng s involvement.

3. EVALUATING CANDIDATE PROPERTIES

The comprehensive radiological survey includes obtaining suf­f i c i en t radiological measurements and environmental samples to fu l l y characterize the radiological condition of the s i t e and to define the boundaries of contamination to support the determin­ation of need for remedial actions. The comprehensive r ad io log i ­cal survey is performed to provide a su f f ic ient level of detail

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such that no further radiological work is required for ASNE to perform engineering and environmental assessments of possible remedial action options. The spec i f ic objectives of a comprehen­sive radiological survey are to determine i f there is radioactive contamination on - s i t e , and i f so, determine the fo l lowing: (1) the identity of the contamination, (2) where the contamination is located, (3) the areal and vert ical extent of the contamination, (4 ) estimates of the volume of contaminated mater ia l , (5) the degree of contamination re la t ive to background radiation leve ls and appropriate regulatory guide l ines , (6 ) the potential for of f -s i t e migration of contamination, and (7) estimates of the poten­t i a l for health ef fects to res idents , employees and/or the general pub l ic .

A comprehensive radiological survey plan is prepared for each large property or group of properties which is ident i f ied during the ground mobile scanning. After the property owner gives his consent for a survey to be conducted, any necessary preparatory work (such as clearing vegetation) is completed pr ior to i n i ­t i a t i on of the survey. The comprehensive radio logica l survey is in i t i a ted by preparing or adapting a map or diagram of the s i t e . This f igure is used for locating al l essential features of the s i t e ( s t ructures , streams, e t c ) , visual documentation of radiation levels on-s ite ( including contaminated a r e a s ) , locating samples (water, s o i l , sediment, e t c . ) and/or marking the progression of the survey. Many of these f igures are formalized and presented in the survey report. A gr id system may be establ ished over the s i te and included in the f igure to aid in denoting locations of samples or contamination.

The survey usually consists of: (1 ) scanning to locate and define areas of anomalous radiation leve ls (potent ia l ly contam­inated a r ea s ) ; (2) systematic radiation measurements and samples taken over the s i te (usually at grid po ints ) to provide repro­ducible measurements at precisely defined locations and to deter­mine average radiation levels on the s i t e ; (3) biased samples and measurements (samples biased with respect to locat ion) taken where anomalous radiation levels were observed during scanning to further define areal extent of contamination and degree of con-tamiantion; (4) subsurface investigations including d r i l l i n g , logg ing , and sampling to determine the vert ica l extent of contam­inat ion; and (5) taking other measurements or samples (such as radon and radon daughters, vegetation, sediment, e t c . ) to meet s i t e - or survey-speci f ic ob ject ives .

Once the comprehensive radiological survey is completed, the s i t e is restored to the condition it was found pr ior to the sur­vey ( i . e . f i l l i n g a l l holes, remove gr id markers, e t c . ) . Following the survey and analyses of samples, a complete report

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of a l l measurement and sample analytical r e su l t s , and estimates of contaminated material volume and potential health effects wi l l be submitted to 00S/D0E for review. Following the input of review comments, a f inal report of the comprehensive radiological survey wi l l be submitted to 00S/D0E by the RASCA contractor.

4. SURVEY METHODOLOGY

The fol lowing section b r i e f l y describes various functions and a c t i v i t i e s which may be performed during a radio logica l survey. A more rigorous description of each act iv i ty is provided in References [ 2 ] and [ 3 ] .

4.1 Background Measurements and Samples

Background measurements and samples are co l lected to provide basel ine data for purposes of comparison to measurements and data co l lected at a s i t e . The background measurements and samples should be s i t e - or a r ea - spec i f i c , and for every type of measure­ment or sample taken on a survey, a comparable reference back­ground radiation level should be known. The source of these background radiation levels may be either from an appropriate reputable document or taken by the RASCA contractor either prior to or during the radiological survey of the s i t e . A measurement or sample would be considered to be at background only i f i t were taken from an area not affected (or as nearly so as poss ib le ) by anthropogenic sources of r ad ioact iv i ty , excluding f a l l o u t . Although no minimum number of background measurements and samples of each type to be taken is defined, the number should be suf­f i c i en t l y representative for purposes of averaging. These background radiation leve ls should be presented in the r ad io log i ­cal survey report , and provided during the discussion of the radio logica l survey resu l t s .

4.2 Scanning Measurements

Scanning is the process by which portable radiation detection instrumentation is used to methodically measure the radiation leve ls of a surface ( i . e . ground, wa l l , f l o o r , equipment, e t c . ) . The purpose of scanning is to locate and define the areal extent of radiation anomalies. Scanning at properties suspected of having t a i l i n g s involvement normally requires instrumentation sens i t ive to gamma radiat ion. Scanning is performed by moving

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the survey probe slowly over a surface, until a l l the surface or a representative portion of the surface has been covered. During the surface scanning, the probe should be kept as close to the surface as poss ib le . Any s igni f icant changes in radiation levels above background are indicated by a change in the pitch of audio response in the instrument headphones. The locations of these radiation anomalies are further investigated by the use of biased measurements and sampling.

4.3 Grid Point Measurements and Samples

After a grid system has been establ ished over an area, d i s ­crete radiological measurements or samples are taken at the intersection of grid l ines (gr id po in t s ) . The purpose of taking these measurements or samples is to provide de f in i t i ve radiation leve ls at precisely defined locat ions . These measurements permit the calculation of average radiation levels within a given area (by averaging the individual measurements or sample analytical r e su l t s ) which are used for purposes of comparison to other areas or to estimate potential health ef fects to people occupying that area.

Grids are establ ished on outdoor areas and indoor areas. The s ize of the grid is determined by the s ize and shape of the area to be surveyed. Measurements made at indoor gr id locations may include alpha, beta-gamma, and gamma radiation f i e l d s . Smears may be taken i f the presence of long - l ived ac t i v i ty is suspected in indoor areas. Outdoor measurements are usually limited to determinations of gamma-ray exposure rates at the surface and at 1 m above the surface. Surface soi l samples (<15 cm deep) are taken at randomly selected grid points. The desired type of sample is obtained as near to the grid point as reasonably poss ib le and is labeled and removed for the appropriate analyses.

4.4 Biased Measurements and Samples

At locations where anomalous radiation leve ls are observed, biased radiological measurements and samples (b iased with respect to their locat ion) may be taken. The purpose of these measure­ments and samples is to define further the areal extent of poten­t i a l contamination and determine maximum radiation levels within an area. Biased measurements normally include alpha, beta-gamma, and gamma radiat ions ; however, at these locations other measure­ments not usually taken ( a t y p i c a l ) , such as radon flux or gamma spectrographic measurements, may also be taken. A i r , water, soil and smear samples may typ ica l ly be taken at these locat ions , or atypical samples of vegetation, radon f lux , or sediment samples

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may be appropriate. The location of biased measurements and samples is selected so they can best define the areal l imits of the elevated radiation l eve l s . All sample and measurement loca ­t ions and results are recorded.

4.5 Subsurface Measurements and Samples

Subsurface investigations consist of measurements and samples taken beneath the ground or f loor surface. The purpose of these invest igat ions is to locate subsurface contamination and define the vert ical extent of the contamination. These investigations are conducted by excavating into the f loor or ground surface (by trenching, augering, coring, shoveling, or other means) to depths that are either below a contaminated soi l layer or to a natural formation (beneath anthropogenic f i l l i n g a c t i v i t i e s ) . The sub­surface investigations include logging or scanning of the ver­t i ca l surfaces with shielded or unshielded gamma radiation detection instrumentation. Excavated material or material from the sides of the vert ical wal ls may be sampled for radionuclide analyses , and water in the excavated hole may be sampled for radionuclide content. The number of excavations and the type of measurements or samples to be obtained w i l l be selected according to the type of contamination present, l imitat ions in the f i e l d condit ions, type of instrumentation a va i l a b l e , and objectives of the survey plan.

4.6 Radon and Radon Daughter Measurements

At s i tes contaminated with t a i l i ng s near a structure , i t may be necessary to sample for radon and radon daughter concentra­t ions in indoor a i r . The purpose of these measurements is to estimate instantaneous or short-term concentrations inside structures on a s i t e to determine the need for long-term radon and radon daughter monitoring. In the absence of long-term moni­tor ing data, these short-term data may be used to estimate poten­t i a l health ef fects to structure occupants. These measurements may be made by a variety of methods and equipment types. The instantaneous and short-term measurements are typ ica l l y used to indicate the potential for s ign i f icant health ef fects or the need for long-term measurements. Measurements are typ ica l l y taken indoors in high-occupancy areas when the structure has been closed to maximize radon and radon daughter concentrations.

4.7 Other Measurements and Samples

Other ( a typ i ca l ) measurements, samples and/or methodologies may be required to f u l f i l the designed objectives of the radio ­log ica l survey. These ac t i v i t i e s are selected either during the

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preparation for the radiological survey or as extraordinary con­dit ions ar i se during the survey. Often these samples or measure­ments are col lected to indicate potential migration of contam­inated material from a s i t e . Purpose, method, and results of these atypical samples and measurements are reported or re fe r ­enced in the survey report.

5. RADON MONITORING PROGRAM

Monsanto Research Corporation - Mound has been under contract with OOS to perform radon/radon progeny monitoring at inactive uranium mil l ing s i tes for approximately three years . Currently, Mound is conducting radon/radon progeny surveys at the former Vitro Manufacturing Company's Rare Metals Plant (Canonsburg Industrial Park) in Canonsburg, Pennsylvania, and the former Vitro Plant in Salt Lake City, Utah. Plans are to i n i t i a t e radon/radon progeny surveys at Durango, Colorado, before the end of Fiscal Year 1982. Mound's e f fort represents one segment of the overal l ce r t i f i ca t ion process required by the Uranium Mill Ta i l ings Radiation Control. Act of 1978.

The objectives of Mound's radon monitoring program are to : (1 ) assess what the local concentrations of radon are in and around the environs of the s i t e ; (2) determine the impact the s i t e has on these local radon concentrations; (3 ) perform radon/radon progeny screening surveys at v ic in i ty properties con­sidered candidates for remedial act ion; (4) perform radon/radon progeny surveys at v ic inity properties designated for remedial act ion, and (5) perform 1, 2, and 4 before, during, and after remedial action to bring properties within appl icable EPA guide­l ines for ce r t i f i ca t ion for unrestricted or l imited use.

5.1 Outdoor Radon Monitoring

5.1.1 Site Radon Emanation Rate Survey

Radon flux measurement techniques are u t i l i z ed to determine emanation rates at the s i t e . General ly , charcoal canisters are used to adsorb the radon emanating from the s o i l . These canisters are placed in a grid system covering the area of the s i t e . Gamma-ray spectroscopy is u t i l i z ed to determine the radon emanation rate . Measurements are conducted seasonally to deter-

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mine as accurately as possible the annual emanation rate . Thus, the s i t e as a source term for radon emanation is determined.

5.1.2 Site Perimeter Monitoring

An appropriate number of radon monitors are ins ta l l ed around the perimeter of the s i t e . The radon monitor deployed is a passive environmental radon monitor (PERM). This instrument u t i ­l i z e s thermoluminescent dosimeters (TLD). Over a measurement period which is generally one week, an integrated weekly averaged radon concentration is provided. Thus, the f i r s t detection l ine is establ ished to determine radon transport from the s i t e to the contiguous environs.

5.1.3 O f f - s i t e Outdoor Radon Monitoring Network

The o f f - s i t e radon monitoring network encompasses these e l e ­ments in i ts design: (1) the topography of the area around the s i t e , (2 ) meteorological conditions of the s i t e area, and (3) previous radon data col lected in the o f f - s i t e environs, i f any.

Knowledge of the topography can aid in determining the i n f l u ­ence of radon transport on the area around the s i t e . It a lso provides some idea as to the acces s i b i l i t y of radon monitors placed in the o f f - s i t e environs. The co l lect ion of meteoro­log ica l data, such as wind d i rect ion , wind speed, and temper­ature , aids in determining the anticipated radon transport . Correlat ions with radon emanation rate , radon transport phenomena and the development of dispersion modeling can also be made.

A 360° grid system is placed over the topographic map of the s i t e area and i ts adjacent environs. The s i t e is the center of the grid system. This grid system contains concentric c i rc les of 500 m increments from the center out to i ts extremity of 3000 m. The c i rcu la r grid is divided into 16 sectors of 22.5 degrees each.

Radon monitors (PERM's) are deployed throughout the system to determine radon transport concentrations leaving the s i te and to assess what the local background concentrations are in the con­tiguous environs of the s i t e . In some cases the remote or back­ground monitors wi l l be placed outside the grid system.

Concurrently with the implementation of the outdoor radon monitoring system, a meteorological station is insta l l ed at the s i t e . Meteorological parameters of wind d i rect ion , wind speed, p rec ip i ta t ion , temperature, re l a t ive humidity, and solar radia ­tion are col lected simultaneously with the radon data.

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5.2.1 Screening Surveys

Radon/radon progeny screening surveys are performed by Mound at v ic in i ty properties that are potential candidates for remedial act ion. The screening surveys are conducted based on data generated by the RASCA contractor. The report made by Mound to 00S/D0E then recommends whether or not more comprehensive radon/ radon progeny measurements are warranted at the v ic in i ty property for purposes of designating s i tes for remedial act ion.

The screening survey of a v ic in i ty property encompasses a comprehensive series of grab sampling techniques for radon and i t s progeny. Spatial and temporal conditions are considered. Other factors noted in the survey are building mater ia ls , heating and a i r conditioning systems, the number and age of human occupants, rooms most frequently occupied, and time per day rooms are occupied by the inhabitants.

Radon/radon progeny data generated in the survey are compared to exist ing DOE and EPA guidelines for radon and i t s progeny. Reports submitted to the DOE's Office of Operational Safety indi ­cate whether the v ic in i ty property is within or above these guidel ines and recommend whether or not long-term radon/radon progeny monitoring is required for "remedial act ion" designation.

5.2.2 Indoor Remedial Action Monitoring

General ly , when indoor radon/radon progeny measurements are warranted at "remedial action" v ic in i ty propert ies , data are co l lected before, during, and a f ter the correct ive action. Typica l ly , integrating techniques for radon and i ts progeny are used along with supportive grab sampling. The data are col lected for a period of time to y ie ld an annual average for the radon daughter measurements.

6. SUMMARY

To identify a l l of the v ic in i ty properties which may have become contaminated by t a i l ings from a mi l l ing s i t e , a broad program of direct public inqu i r i es , aer ia l surveys, and mobile gamma-ray scanning was in i t i a ted . Aerial surveys, which define areas of elevated gamma ac t i v i ty , have been completed for most of

5.2 Indoor Radon/Radon Progeny Monitoring

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the suspect areas. Mobile gamma-ray scanning techniques are being used to verify the aeria l survey results and to identify the spec i f i c v ic in i ty properties which contain materials l ike ly or ig inat ing from the original uranium mill t a i l i n g s s i t e s .

To estab l i sh the data necessary to define the remedial action requirements, a comprehensive formal radio logica l survey act iv i ty is implemented for each of the v ic in i ty properties which are suspected of being contaminated. The spec i f ic objectives of a comprehensive radio logical survey are to determine i f there is radioact ive contamination on - s i t e , and i f so , determine the fo l lowing : (1) the identity of the contamination; (2) where the contamination is located; (3) the areal and vert ical extent of the contamination; (4) estimates of the volume of contaminated mater ia l ; (5) the degree of contamination re l a t i ve to background radiat ion levels and appropriate regulatory gu ide l ines ; (6) the potential for o f f - s i t e migration of contamination; and (7) e s t i ­mates of the potential for health e f fects to res idents , employees, and/or the general publ ic .

The survey usually consists of: (1 ) scanning to locate and define areas of elevated radiation leve ls (potent ia l ly contam­inated a r ea s ) ; (2 ) systematic radiation measurements and samples taken over the s i t e ; (3) biased samples and measurements (samples biased with respect to locat ion) taken where anomalous radiation leve ls were observed during scanning to further define areal extent of contamination and degree of contamiantion; (4) subsur­face investigations including d r i l l i n g , logging, and sampling to determine vertical extent of contamination; and (5) taking other measurements or samples (such as radon and radon daughters, vegetat ion, sediment, e t c . ) to meet s i t e - or survey-speci f ic ob ject ives .

An additional program is also underway to perform radon, radon f lux , and radon progeny measurements at inactive uranium mill t a i l i n g s s i tes and v ic in i ty propert ies . Both outdoor and indoor measurements are made before, during, and a f ter remedial act ion. Results of these monitoring programs are used by DOE in the overal l ce r t i f i ca t ion process required by the Uranium Mill Ta i l ings Radiation Control Act passed by Congress in 1978.

REFERENCES

[ 1 ] U.S. DEPARTMENT OF ENERGY, "Background Report for the Uranium Mill Tai l ings Sites Remedial Action Program", DOE/EP-0011 (April 1981).

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[ 2 ] BERVEN, B. A . , COTTRELL, W. D., LEGGETT, R. W., MYRICK, T. E., GOLDSMITH, W. A . , HAYWOOD, F. F., "Generic Radiological Survey Plan for In i t i a l Characterization and Post Remedial Action Measurements at Private and Public Properties Associated with the Department of Energy's Remedial Action Programs", ORNL/TM-7850, Draft Report.

[ 3 ] MYRICK, T. E., BERVEN, B. A . , COTTRELL, W. D. , GOLDSMITH, W. A . , "Procedures Manual for the ORNL Remedial Action Survey and Cert i f i cat ion Act iv i t i es (RASCA) Program", Oak Ridge National Laboratory, ORNL-6000, Draft Report.

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RADIATION MEASUREMENTS

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Chairman

J. FITCH Australia

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MONITORING RADON AROUND URANIUM MINE AND MILL SITES WITH PASSIVE INTEGRATING DETECTORS

J.E. GINGRICH, R.A. OSWALD, H.W. ALTER Terradex Corporation, Walnut Creek, California, United States of America

Abstract

MONITORING RADON AROUND URANIUM MINE AND MILL SITES WITH PASSIVE INTEGRATING DETECTORS.

A large number of integrated radon measurements have been made around uranium mine and mill sites with the passive Track Etch® radon detection system. Measurements have been made for pre-operational base-line studies, for operational mines and mills and for personnel. Track Etch detectors are well suited for such measurements, particularly in remote mining areas since they are completely passive, have no batteries or electronic components and can integrate exposure for times ranging from a few days to a year or more if desired. Several different types of Track Etch detectors have been developed to meet the various application requirements. They have been calibrated at exposures ranging from 17.35 (pCi/L)-d to 13019 (pCi/L)-d. The calibration data are discussed and the lower limit of detection is presented for each detector configuration. In a year-long radon monitoring programme around one operating mine/mill complex, twelve sampling stations were established and the radon detectors were left in place for a month at a time. Results show large monthly variations depending on activities at the facility and changing weather patterns. Maximum variations were typically two to three times the average concentrations, and they varied by factors of 5 to 10 from the highest months to the lowest months at the same locations. On-site measurements for the year averaged 2.65 pCi/L while the site boundary averaged 1.18 pCi/L and the off-site averaged 0.89 pCi/L. The year-long average radon concentrations showed typical fall-off with distance from the centre of the mine/mill complex. A small, compact Track Etch detector has recently been developed which is suitable as a personnel monitor. Field tests with this detector indicate that it should be satisfactory as an indicator of radon progeny exposure. The field tests were conducted for times up to 170 hours under typical mine conditions with changing Working Levels and Working Level Ratios. A large number of Track Etch detectors have been used for monitoring radon in ordinary homes and buildings. The results show some surprisingly high radon concentrations. Data indicate that a significant number of homes may have radon concentrations higher than those observed around uranium mines and mills.

1. INTRODUCTION

Over 50 000 environmental radon measurements have been made with pass ive , integrat ing Track Etch radon detectors ( 1 ) . Measure­ments have been made for pre-operational base - l ine s tud ies , and for

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TRACKS ARE RETAINED

DETECTOR IS ETCHED

ETCHED TRACKS BECOME VISIBLE

*PATENTED

FIG. I. The Track Etch process.

operational mines ( 2 ) . These detectors have a lso been used exten­s ive ly for home monitoring ( 3 ) . The indoor data show leve ls com­parable to those observed around uranium mines and mil ls ( 4 , 5 , 6 ) . Other applications of the technique include radon so i l gas measure­ments for uranium explorat ion, earthquake pred ict ion , geothermal explorat ion, and fundamental geological and geophysical studies ( 7 , 8 ) . Track Etch detectors are now being used in numerous appl ications where there is a need to know exact radon concentrations ( 9 ,10 ) .

2. THE TRACK ETCH PROCESS

With the Track Etch technique, a p l a s t i c nuclear track detector is mounted in a p l a s t i c cup with a f i l t e r permeable to radon over the open end. This device is exposed to the atmosphere to be measured. Alpha par t i c l es from radon in the a i r , or from radon daughters plated out on the inside of the cup, penetrate the detector and cause radiation damage tracks that are subse­quently revealed by an etching process (F ig . 1 ) . The number of

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alpha tracks counted per unit area (T/sq.mm) is proportional to the average radon exposure (eg . (pC i/L ) -hours ) . Exposure times can range up to a year or more, i f des i red , using these detectors which retain alpha tracks without fading for very long per iods.

Track Etch detectors have several features that make them pa r t i cu l a r l y a t t rac t ive for environmental radon monitoring. They are simple, small and l ightweight ; and they have no moving par t s , e lectronics or power suppl ies . They are a lso sens i t ive only to alpha par t i c l es and are not sens i t ive to gamma or beta rad iat ion . Since the detectors are so small and have no moving par t s , they can be ea s i l y used for making unobtrusive radon measurements on personnel and in work areas. The etched detectors a lso provide a permanent, re t r ievab le record for future reference.

3. TRACK ETCH DETECTOR CONFIGURATIONS

Several Track Etch detector configurations have been developed for d i f f e rent app l icat ions . Four configurations are described below:

3 .1 . F i l te red Cup Systems (Type F and Type M)

The Type F Track Etch detector system consists of a small p l a s t i c cup with the detector attached to the inside bottom of the cup (F ig . 2 ) . The opening of the cup is covered with a hydrophobic, microporous f i l t e r which permits rapid and complete i n f i l t r a t i o n of the gaseous radon isotopes but discriminates against the nongaseous radon daughters. Because of i t s high sens i t i v i ty to radon, the Type F configuration is useful in a l l radon-only appl icat ions where thoron is not an important com­ponent.

The Type M Track Etch detector system is the same as the Type F except that the opening of the cup is covered with a semi­permeable p l a s t i c membrane (11 ,12 ) . This membrane, sometimes ca l l ed a Thoron F i l t e r , slows the normal di f fusion of noble gases into the cup and thus discriminates against radon-220 (thoron) that has a 55 second h a l f - l i f e while permitting 60 to 70% of radon-222 (which has a 3.8 day h a l f - l i f e ) to enter the cup. The membrane covered cup system is used primari ly for so i l gas measurements for mineral exploration appl ications to eliminate thoron interference and water accumulation in the cup. I t , too , prevents the entrance of radon daughters and thus measures radon only.

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FIG.2. Track etch radon detector positioned at bottom of plastic cup. The cup may be equipped with the hydrophobic microporous filter or the Thoron Filter.

3.2. Mini-cup Systems (Type SF and Type SM)

Recently two new detector configurations have been developed and ca l ib rat ion results have been obtained on the two systems (F ig . 3 ) . In the two new configurations ( i d en t i f i ed as Type SF and Type SM), the Track Etch detector is mounted in a consider­ably smaller cup which is 3 cm in diameter and 2 cm high. The opening of the cup is covered by the hydrophobic microporous f i l t e r (Type SF) or the Thoron F i l t e r (Type SM). These miniature cups are ideal for use as personnel radon detectors or as devices

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FIG. 3. Type SF Track Etch personnel radon detector. The filter can be seen beneath the protective grid on the cap. This detector can also be equipped with a Thoron Filter.

to measure radon in homes or in other appl ications where a very small passive device is needed.

4. CALIBRATIONS OF TRACK ETCH RADON DETECTORS

During 1981 various configurations of Terradex Track Etch radon detectors were ca l ibrated in four d i f f e rent radon exposure f a c i l i t i e s . These were the U.S. Department of Energy's Environ­mental Measurements Laboratory in New York City , the U.S. Bureau of Mine's radon chamber in Denver, the Austral ian Radiation Laboratory 's radon chamber in Yal lambie, V ictor ia and the U.S. Environmental Protection Agency's Arden Fac i l i ty in Las Vegas. These exposures constitute part of the continuing program of ca l i b ra t ion of Terradex's radon detectors. The portion of this ca l ib ra t ion work deal ing with Types F and SF is discussed below.

Radon exposures covering four orders of magnitude were de l ivered to the detectors . The exposures ranged from 17.35 (pCi/L) -days to 13019 (pCi/L ) -days . Table I l i s t s the re levant exposure information. For each of the detector conf igurat ions, 14 to 20 rep l icates were exposed in each run.

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TABLE I . EXPOSURE PARAMETERS FOR 1981 CALIBRATION OF TRACK ETCH RADON DETECTORS

Radon Radon Exposure Concentration Duration ((pCi/L)-days) (pCi/L) (Days)

Australian Radiation 390.2 39.98 9.76 Laboratory 1218.6 111.6 10.92

7830 438.9 17.84 13019 523.3 24.88

U.S. Bureau of Mines 870 290.0 3.0 298.8 98.3 3.04 1752 584.0 3.0 597.9 199.3 3.0

U.S. E.P.A 17.35 3.47 5.0 61.9 5.63 11.0 87 5.80 15.0 125.8 5.99 21.0

U.S. Environmental 476 59.5 8.0 Measurements Laboratory 1168 46.8 24.96

1547 47 32.92 1792 47 38.13

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S 1.0

1 i • AUSTRALIAN RADIATION LABORATORY

• U.S. BUREAU OF MINES

•A.U.S.E.P.A. ARDEN FACILITY

t U.S. ENVIRONMENTAL MEASUREMENTS

LABORATORY

2 5 10 2

RADON EXPOSURE KpCi/L) • DAYS)

FIG.4. Calibration results for Type Fradon detector, 1981. The calibration factor obtained for each radon exposure has been normalized to the presently used calibration factor. The horizontal dashed lines represent 95% confidence limits for the current calibration factor. Error bars are also 95% confidence limits.

The ca l ib ra t ion factors were calculated by dividing the net track density by the radon exposure reported to us by the c a l i ­bration laboratory . These 1981 ca l ib rat ion factors were then compared to those currently in use by Terradex ( 13 ) . This was done by dividing the ca l ib ra t ion factor obtained in each run by the current Terradex value. The results of the comparison are shown in Figs . 4 and 5. The results of the 1981 ca l ib rat ions are quite consistent with those of previous ca l i b r a t i ons . We a n t i c i ­pate combining these most recent results with a l l the previous ca l ib ra t ion data to ref ine our ca l ib rat ion values even further. Furthermore, the graphs of the normalized ca l ib ra t ion factors indicate good consistency among the four chambers involved in the exposures. A l so , the l i nea r i ty of the Track Etch detectors for a wide range of exposures is demonstrated by these data.

We are continuing to obtain ca l ib rat ion data at various radiation f a c i l i t i e s at a variety of exposure rates and exposure times. Our intention is to continue to demonstrate the wide

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1.5 _

• AUSTRALIAN RADIATION LABORATORY

T Y P E S F • U.S. BUREAU OF MINES

_U.S.E.P.A AROEN FACILITY

^ U.S. ENVIRONMENTAL MEASUREMENTS

LABORATORY

0 I | , i I I l_ 1 1 I I I 1 _ _ _ _ _ _ _ _ _ _ _ _ - _ 10 2 5 1CT 2 5 10 2 5 10 2 5 10

RADON EXPOSURE ((pCi/L) • DAYS)

FIG.5. Calibration results for Type SF radon detector, 1981. The calibration factor obtained for each radon exposure has been normalized to the presently used calibration factor. The horizontal dashed lines represent 95% confidence limits for the current calibration factor. Error bars are also 95% confidence limits.

dynamic range and s t a b i l i t y of Track Etch detectors by u t i l i z i n g the broadest range of exposure parameters ava i l ab l e .

5. LOWER LIMITS OF DETECTION FOR TRACK ETCH RADON DETECTORS

The U.S. Nuclear Regulatory Commission's Regulatory Guide (14) suggests that the lower l imi t of detection (LLD) be based upon the standard deviation of the background d i s t r i but ion . Freidland et al (15) have shown that this reduces to LLD = 4.66 ap, for passive detectors where ag is the standard deviation of the background s i gna l . With this def in i t ion in mind LLD's have been establ ished for several integrat ing radon detector configurations. In the case of p l a s t i c track detectors the standard deviation of the background is re lated to the background track density Tb and counting area A by

T r

provided the background track density is Poisson d i s t r ibuted .

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TABLE I I . LOWER LIMITS OF DETECTION* FOR TRACK ETCH RADON DETECTORS

LLD (pCi/L)-months Configuration for various counting areas

1.15 mm 2 5.75 mm 2 17.25 mm'

TYPE F 0.59 0.27 0.16

TYPE M 0.99 0.45 0.26

TYPE SF 1.5 0.69 0.40

TYPE SM 1.6 0.75 0.43

* LOWER LIMIT OF DETECTION (LLD) is defined as 4.66 times the standard deviation of the background.

We ve r i f i ed by Chi-square tests that the number of tracks counted in our standard counting area is Poisson d i s t r ibuted . The value of Tg = 0.10 tracks/mm2 was found to be a good representative value. This is actual ly a s l i g h t l y high value and w i l l therefore lead to a conservative measure of LLD.

This standard deviation was then converted to an equivalent radon exposure by means of the ca l ib ra t ion factor expressed in (tracks/mm 2 )/( (pCi/L)-month) fo r each detector configuration. Furthermore, since ag depends upon counting area according to Eq. ( 1 ) , we performed the same calculat ions for our other two standard counting areas. The resu l ts of a l l these calculat ions are presented in Table I I . By integrat ing radon exposure for appropriate lengths of time v i r t ua l l y any radon exposure rate can be measured with the Track Etch detectors.

6. FIELD RESULTS

Track Etch detectors are presently being used to make measurements in a var iety of environmental monitoring s i tuat ions . The l a rges t use is for house and bui ld ing monitoring, mostly in selected areas where high radon concentrations are expected. Other appl ications include monitoring around operating uranium mines, mine t a i l i ng s and mill s i t e s , phosphate and radium pro ­cessing f a c i l i t i e s and radium storage areas. Track Etch technology has a l so been useful in base l ine studies around planned uranium mi l l s and in measuring so i l gas. Three examples of the use of Track Etch detectors for environmental monitoring are described below.

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FIG. 6. Type F radon detector being placed in its protective canister for outdoor radon measurements.

6.1. Outdoor Surveys - The Shir ley Basin Mine.

To make outdoor radon measurements, the Type F detector configuration is usual ly employed. In this appl icat ion i t i s often placed in a canister to protect i t from the weather elements (see Fig. 6 ) . The Track Etch detectors are idea l l y suited for outdoor measurements since they can make long, time-averaged measurements and require no power supplies or maintenance. These features are of pa r t i cu la r value in the outdoor environment near uranium mining and mi l l ing f a c i l i t i e s where the radon leve ls vary

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TABLE I I I . RADON CONCENTRATIONS AT SHIRLEY BASIN MINE (pCi/L) (1980-81)

Date 1 2 3 4 5 6 7 8 4R 10R 19 2R 7R

Apr 2.11 0.72 2.26 1.34 0.41 0.10 3.19 -- 0.87 0.41 0.57 0.70 0.25 May 1.71 0.83 0.98 1.86 0.25 1.71 2.00 — 1.27 0.69 1.56 0.86 1.92 June 3.54 0.11 3.23 1.98 1.51 1.20 4.78 — 1.36 1.98 2.29 1.98 1.04 July 1.67 1.04 1.82 1.51 0.58 0.26 6.19 — 1.04 0.42 2.91 1.36 0.11 Aug 1.86 1.27 2.44 1.42 1.56 1.27 4.34 — 1.71 1.42 0.39 1.09 0.95 Sept 2.21 2.37 4.95 2.05 2.21 1.56 8.01 — 0.76 0.27 0.60 1.12 0.62 Oct 1.51 0.81 1.94 1.23 1.23 0.95 1.94 — 0.67 0.95 0.95 0.67 1.23 Nov Dec -- — 6.13

2.63 4.12 — 3.44 0.76

1.12 1.96

1.12 1.56

0.45 1.83 —

0.78 1.43

Jan 2.37 4.55 0.71 0.60 1.08 0.76 1.08 Feb 0. .29 0.47 0.99 0.32 1. .33 0.29 1.20 -- 0.47 0.29 0.64 0.29 0.29 Mar 1, .51 1.36 1.82 1.20 1, .20 0.89 1.90 -- 0.89 1.61 1.16 0.86 1.01

MEAN 1. ,81 1.00 2.62 1.43 1. .15 0.92 3.87 0.74 1.07 0.98 1.18 1.00 0.89

great ly as a function of production a c t i v i t y , weather and season, and where a temperature- insensit ive passive device is e s sent i a l .

A set of measurements performed at Pathfinder Mines Cor­porat ion 's Shir ley Basin Mine i l l u s t r a t e s the usefulness of the method. The major radon sources were expected to be in the uranium mill and in the major open p i t area. Most stations were f ixed posit ions at a height of 3 m using protect ive canisters . One detector was attached to the backhoe that was in nearly • continuous operation in the mine p i t and was exposed to the maximum of the outdoor radon l e ve l s . Data accumulated over a year of monthly measurements are given in Table I I I . The detectors were l e f t in place for a month at a time. Data from three typical sampling stat ions are shown in Fig. 7. At each stat ion i t can be noted that there is a f a i r l y large month to month var iat ion depending on the a c t i v i t i e s at the f a c i l i t y and the changing weather patterns. The maximum var iat ions are typ ica l l y two to three times the average concentrations, and they vary by factors of 5 to 10 from the highest months to the lowest months at the same locat ions . Normally the on -s i te measurements were s i gn i f i c an t l y higher than e i ther the s i t e boundary or the of f -s i t e measurement. The on - s i te measurements fo r the year averaged 2.62 pCi/L while the s i t e boundary averaged 1.18 pCi/1 and the o f f - s i t e averaged 0.89 pCi/L. I t is interest ing to note, however, that during the month of May the o f f - s i t e location had a s l i g h t l y higher average radon concentration than the other two s i t e s .

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A s t r ik ing pattern emerges i f the locations of the monitoring s i tes are corre lated with the expected sources of radon. In Fig. 8 we compare the average annual reading at each of the 13 monitoring s i tes with the distance from the mill or the primary mining area , whichever is nearer. A c l ea r monotonic decrease occurs with distance and approaches the background concentration defined by the two o f f - s i t e locat ions .

6.2 Fie ld Test Results of Track Etch Type SF Personnel Radon Detectors in the Twi l ight Mine.

The purpose of this f i e l d test ing is to demonstrate that i t i s poss ib le to determine exposures to radon progeny with reason­able accuracy from measurements of radon exposure as o r i g i na l l y suggested by Bres l in ( 16 ) . The basis f o r this approach is the existence of an adequate corre lat ion between radon exposure and radon progeny exposures in typical mine environments. This corre lat ion results from the r e l a t i v e l y good s t a b i l i t y of Working Level Ratio observed in typical mine environments (16, 17) .

In a b l ind tes t of this concept, th i r ty Type SF Track Etch Personnel Radon Detectors were exposed in the Twil ight Mine, the U.S. Bureau of Mines tes t mine located near Grand Junction, Colorado. The detectors were divided into two groups of f i f teen detectors , and each group of f i f teen was placed at a d i f f e rent location in the mine. At each location the detectors were deployed in groups of f i ve at three d i f f e rent times. The exposure times ranged from four to seven days.

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ONE-YEAR-LONG READINGS

0 6000 12000 18000

DISTANCE FROM URANIUM MILL (FEET)

FIG. 8. Variation of atmospheric radon concentration with distance from mill.

RADON CONCENTRATION

LOCATION: AC

1000

SO 100 TIME (HOURS)

FIG. 9. Variation of Working Level (WL), Working Level Ratio (WLR) and radon concentration with time at location AC.

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LOCATION: HAUL

0.01 I i ' ' i I i ' • ' I ' ' ' ' 1 L—J 1 0 50 100 150

TIME (HOURS)

FIG. 10. Variation of Working Level (WL), Working Level Ratio (WLR) and radon concentration with time at location HAUL.

During the exposure period the radon concentration, Working Level (WL) and Working Level Ratio (WLR) were varied at each location by one or two orders of magnitude. Also these quantit ies were measured continuously by radon and radon daughter monitoring devices during the exposure period.

Upon completion of the exposures, the detectors were returned to Terradex Corporation where they were evaluated for radon exposure. Radon progeny exposure was then calculated using an assumed WLR of 0.25. These results were reported to the U.S. Bureau of Mines.

Figures 9 and 10 present the WL, WLR and radon concentration data taken at the two locations in the Twi l ight Mine during the tes t . The radon progeny exposures (WLM) actua l ly received by each SF detector were computed by using the data in Figs. 9 and 10 and the deployment locations and times. In order to observe the extent to which WLM can be predicted from radon exposure measurements, we then calculated for each detector the WLR which would have to be used in order to predict correct ly the Bureau

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TABLE IV. OPTIMUM VALUES OF WLR TO USE AT EACH LOCATION TO OBTAIN WLM FROM RADON EXPOSURES

Number of Percent Location Detectors Mean WLR Standard Deviation

AC 15 0.208 20%

HAUL 15 0.244 17%

AC & HAUL 30 0.226 20% (whole mine)

of Mines WLM from Terradex's radon exposure. Table IV shows mean values of these optimum WLR's at each locat ion. In addi t ion , the ent i re mine may be characterized by the grand mean of the optimum WLR values at the AC and HAUL locat ions , 0.226.

F ina l l y , the exposures to progeny were recalculated using the optimum 0.226 WLR. To present the resu l t ing agreement between the progeny exposures predicted from the radon exposure measurements and the progeny exposures according to the Bureau of Mines data, the graph in Fig. 11 was p lotted. This graph shows the ra t io of the Terradex WLM to the Bureau of Mines WLM versus the Bureau of Mines WLM. These values should idea l l y be d i s t r i b ­uted about 1.00 and, indeed, they are .

6.3 Indoor Surveys

For comparison purposes data from several indoor surveys are presented in Table V. Numbers of homes surveyed varied from about f i f t een in Northern Ca l i forn ia to thousands in Sweden.

A s i gn i f i cant number of the homes measured in Eastern Pennsylvania and Sweden have radon concentrations exceeding 20 pCi/L (0 .1 WL, assuming a WLR of 0.5) ( 3 ) . This is a concen­t rat ion at which there may be a s i gn i f i cant concern about an increase in l i f e t ime lung cancer r i sk . The highest concentrations measured in a number of homes are at l eve l s unacceptable for workers in uranium mines. In addi t ion , mean values of radon concentrations in the homes in Eastern Pennsylvania, Maine, Canada and Sweden are s imi la r to the average concentration found around the Shir ley Basin Mine. Certain homes in these areas showed values many times higher.

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• LOCATION AC

• LOCATION HAUL

0.1 RADON PROGENY EXPOSURE (WLM) (ACCORDING TO U.S. BUREAU OF MINES)

FIG.11. Results of determinations of radon progeny exposures (WLM) by means of Terradex Type SF radon detectors. The Terradex WLMs were determined from measure­ments of radon exposure using a WLR of 0.226. These data are distributed with a per cent standard deviation of 21%.

7. CONCLUSIONS

The results from ca l ib ra t ion tests and f i e l d measurements demonstrate that the Track Etch technique for radon monitoring provides adequate sens i t i v i ty and reproducib i l i ty for both indoor and outdoor measurements. The technique is a lso pract ical and easy to use when making l a r g e - s c a l e , long-term radon measurements. The completely passive nature of the detectors makes the Track Etch technique pa r t i cu l a r l y a t t ract ive for making measurements in any locations where i t is necessary that they be l e f t unattended for a period of time. The use of se lected types of Track Etch

1-9° — — _ _ —

Page 619: Management of Wastes from Uranium Mining and

Location-Season Mean Range pCi/L Radon Radon Daughters

Working Level Mean Range

Percent Greater Than

20 pCi/L

N. Calif, winter-summer 0.5 Houston fall-winter 0.4 No. East U.S. summer 0.3 E. Penna. winter 2.4 Maine fall-spring 1.1 Canada winter-spring 3.6 Sweden winter-summer 2.1 Sweden spring-summer 4.1 Sweden fall-winter 8.5 Sweden winter 10.0 Sweden winter-spring 9.5

0.1- 2 0.1- 2 0.1- 3 0.1- 91 0.1- 133 0.1- 34 0.4- 22 0.2- 106 0.2- 520 0.5- 466 0.5-1140

2.1 2.7 3.6

0.002 0.002 0.002 0.01 0.006 0.02 0.01 0.02 0.04 0.05 0.05

0.0005-0.01 0.0005-0.01 0.0005-0.02 0.0005-0.46 0.0005-0.66 0.0005-0.17 0.002 -0.11 0.001 -0.53 0.001 -2.6 0.002 2.3 0.002 -5.7

0 0 0 15 3 4 4 4 14 15 12

* Expressed in Average Radon or Radon Daughter Concentrations and Assuming Working Level Ratio of 0.5.

detector systems permits the se l ec t ive measurement of radon only and the elimination of thoron response.

Fie ld use of two d i f f e rent detector types has been demon­strated around an operating uranium mine/mill complex, in a mine, and in nearly 40 000 indoor locat ions . The results from the measurements around the uranium mine/mill complex indicate that the average monthly radon concentrations change by s i g n i f i ­cant amounts (a factor of 5 to 10) and that the average concen­trat ion decreases away from the mine s i t e as might be expected. The highest radon concentrations near the mill were below the concentrations measured fn many homes. Fie ld tests with a new radon detector configuration designed for personnel monitoring indicates that i t should be sat i s factory as an indicator of radon progeny exposure. This work a lso demonstrates that the radon concentrations in s i gn i f i c an t numbers of homes exceed 20 pCi/L (0 .1 WL). This concentration approaches the maximum permitted exposure in uranium mines. Should current attempts to reduce the 4 WLM mine l imi t to 0.7 WLM be success fu l , up to 50 percent of homes monitored in the current work would exceed the mine standard.

This paper could not have been written without the kind cooperation of the fol lowing organizat ions , under whose sponsor­ship the work was done: U.S. Environmental Protection Agency,

ACKNOWLEDGEMENTS

TABLE V. INDOOR TRACK ETCH RESULTS*

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Statens Provningsanstalt , Austral ian Radiation Laboratory, Path­f inder Mines Corporation, U.S. Bureau of Mines, General E lect r ic Company and Pennsylvania Power and Light Company.

REFERENCES

(1 ) ALTER, H.W., PRICE, P .B . , "Radon Detection Using Track Registration Mater ia l " (1972) U.S. Patent 3,665,194.

(2 ) GINGRICH, J . E . , "F ie ld Measurements with the Passive Inte ­grating Track Etch System", (Proc. 3rd Symposium on Uranium Mill Ta i l ings Management, 1980) 29.

(3 ) ALTER, H.W., OSWALD, R.A., Health Phys. ( in p r e s s ) .

(4 ) MCGREGOR, R.G., VASUDEV, P. , LETOURNEAU, E.G., MCCULLOUGH, R.S. , PRANTL, F.A. , TANIGUCHI, H., Health Phys. 39 (1980) 285.

(5 ) STRANDEN, E., BERTEIG, L. , UGLETVEIT, F., Health Phys. 36 (1979) 413.

(6 ) HOLLOWELL, C D . , BOEGEL, M.L., INGERSOLL, J .G . , NAZAROFF, W.W., Trans. Am. Nucl. Soc. 33 (1979) 148.

(7 ) GINGRICH, J .E . , FISHER, J .C . , "Exploration for Uranium Ut i l i z i ng the Track Etch Technique", (25th Int . Geo!. Cong. 1976),(unpublished).

(8 ) KING, C.Y. , Nature 271 (1978) 516.

(9 ) ALTER, H.W., FLEISCHER, R.L. , GINGRICH, J .E . , MURDOCK, S . , "Passive Integrating Measurements of Radon and Thoron", Radiation Hazards in Mining: Control , Measurement, and Medical Aspects (Proc. Int . Conf. Golden, Colorado, 1981 Manuel Gomez, E d . ) , Society of Mining Engineers of American Inst i tute of Mining, Metal lurgical and Petroleum Engineers, I n c . , New York (1981) , 581.

(10) ALTER, H.W., "Passive Integrating Radon Monitor for Environmental Monitoring", The Natural Radiation Environ­ment (Proc. Second Special Symp. Bombay, Ind ia , 1980). (unpublished).

(11) WARD, W.J . , "A Convenient Method for Reducing the Radon-220 Background in Uranium Exploration" (1977) U.S. Patent 4,064,436.

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(12) WARD, W.J. , FLEISCHER, R.L. , MOGRO-CAMPERO, A . , Rev. Sc i . Instrum. 48 (1977) 1440.

(13) ALTER, H.W., FLEISCHER, R.L. , Health Phys. 40 (1981) 693.

(14) U.S. Nuclear Regulatory Commission Regulatory Guide, Off ice of Standards Development, "Measuring, Evaluating, and Reporting Radioactivity in Releases of Radioactive Materials in Liquid and Airborne Effluents from Uranium M i l l s " , Regulatory Guide 14.4 (1977).

(15) FREIDLAND, S . S . , RATHBUN, L., GOLDSTEIN, A.M., "Radon Monitoring: Uranium Mill Fie ld Experience with a Passive Detector" , (Proc. of the IEEE Nuclear Science Symposium, San Francisco, Ca l i f o rn i a , 1979).

(16) BRESLIN, A . J . , GEORGE, A .E . , WEINSTEIN, M.S., " I nve s t i ­gation of the Radiological Characterist ics of Uranium Mine Atmospheres", HASL-220, United States Atomic Energy Commission, New York (1969).

(17) DOMANSKI, T . , CHRUSCIELEWSKI, W., DOBRZYNSKA, K., Health Phys. 36 (1979) 448.

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STATISTICAL DECISION PROCEDURES FOR URANIUM MILL TAILINGS REMEDIAL ACTION

L.P. SANATHANAN* , R.R. MacDONALD, C.J. ROBERTS, W.E. KISIELESKI Argonne National Laboratory, Argonne, Illinois, United States of America

Abstract

STATISTICAL DECISION PROCEDURES FOR URANIUM MILL TAILINGS REMEDIAL ACTION.

Statistical and computer contouring procedures are examined relative to their use in decision making for remedial action at uranium mill tailings sites (UMTRAP sites). The problem of defining the boundary between the remedial action region and the no-remedial-action region at such sites is discussed. Criteria are proposed for site classification, determination of sample type and size, and setting of guidelines. Examples are given of computer mapping and statistical decision procedures applied to data from the Vitro site at Salt Lake City, Utah.

Radiological survey data that w i l l be considered in making decisions r e l a t i ve to the need for remedial action at inact ive uranium mill t a i l i n g p i l e s in the United States are currently being compiled and updated by the Environmental Impact Studies Division of Argonne National Laboratory under the DOE-sponsored Uranium Mil l Ta i l ings Remedial Action Program (UMTRAP). In addition to consideration of costs and r isks associated with remedial-action decis ions, choice of appropriate decision c r i t e r i a must r e f l e c t the uncertainties caused by v a r i a b i l i t y and gaps in the rad io log ica l data. S t a t i s t i c a l procedures for analyzing such data uncertainties and incorpora­t ing them into corresponding remedial-action decisions are described in this paper.

Radiological data such as gamma exposure rate and radium concentration in the so i l at the UMTRAP s i tes have both spat ia l and temporal components. The manner in which the rad io log ica l phenomena vary with time and location may i t s e l f be non-uniform. The nature of th is spat ia l and temporal var iat ion casts this problem into the f i e l d of geographic sampling. An UMTRAP s i t e i s sampled, and estimates of the "true population values" are

* Now with Abbott Laboratories, North Chicago, Illinois, United States of America.

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made on the basis of the co l lected data. Estimates based on any given sample are dist inguished by two propert ies : accuracy and precis ion. Accuracy refers to correctness in estimating the population value; precis ion re fers to the spread of estimates of the population value around the true value. The prime requirement of any sampling procedure is to achieve accuracy with r e l a t i ve e f f ic iency of the data -co l l ect ion process. For an UMTRAP s i t e , the object ive is to determine the " t rue rad io ­log ica l conditions" with minimum sampling so as to keep the costs reasonable.

Tests of the accuracy of sampling are based on what is known about the population being sampled. The pr incipal basis for the s t a t i s t i c a l evaluation of UMTRAP s i tes is the fact that each s i t e exhibits cont i gu i ty or spat ia l autocorrelat ion in i t s radiat ion f i e l d . Contiguity or spat ia l autocorrelat ion means that the data values have spat ia l proximity and the di f ference in measurement between location is a s t a t i s t i c a l function of distance. Contiguity of the radiat ion f i e l d at an UMTRAP s i t e implies that areas of high exposure rate can be expected to grade into areas at background exposure l eve l s . Thus, there i s a t rans i t ion zone around each area of high radiat ion. Conditions at an UMTRAP s i t e can cause the t a i l i n g s material to be moved around, g iving r i s e to these t rans i t ion zones; however "hot spots" l ike those associated with randomly scattered pieces of uranium ore do not f i t a simple spatia l autocorre lat ion model.

The s t a t i s t i c a l analysis described in this paper r e l i e s on the contiguity of the radiat ion f i e l d , but does not require any assumption about the nature of the spatia l autocorre lat ion. At the simplest l e v e l , the decision procedure for UMTRAP s i t e s is to c l a s s i f y locations into regions that require remedial action and regions that require no action. C l a s s i f i ca t ion is the ordering of objects ( e . g . measured values of a given parameter) into groups ( s e t s ) on the basis of the i r measured value and spatia l proximity. The proposed guidel ines of 20 uR/h for gamma exposure rate and 5 pCi/g for radium concen­t ra t ion in so i l are the bas is for such a c l a s s i f i c a t i o n in th i s study. Regions or zones where the radio log ica l exposure rate or the concentration of radium in soi l exceeds the guide­l i ne values should idea l l y be c l a s s i f i e d as requir ing remedial action. Implementation of these decision c r i t e r i a requires a s t a t i s t i c a l l y va l id procedure for determining the boundary of the remedial action region and a lso guidel ines for the choice of an economically e f f i c i en t sample s i ze .

In th is paper, two procedures for spa t i a l l y dependent analyses have been considered for appl icat ion to decision

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making for UMTRAP s i t e s : ( 1 ) isarithmic techniques (contouring) for describing continuous surfaces by transforming data into the form of a continuous va r i ab l e ; and ( 2 ) grouping analysis for c luster ing datum points into regions of contiguous sets of s imi lar p laces . In grouping ana lys i s , the value and proximity of data points are evaluated in the formation of c lus te r s . In the case of the UMTRAP s i t e s , the object ive is to define the boundary between the regions of remedial action and no remedial act ion ; therefore the value of any procedure depends on how well i t can accomplish this task.

In isarithmic methods, or contouring, there is the need to judge how much of the information transmitted by the map may be regarded as " s i gna l " and how much as " n o i s e " - - i . e . , the contouring of data can show more detai l than is actua l ly warranted on the bas is of the ava i l ab le data. Areal data often present such ambiguit ies, and the most obvious manner in which to t reat them is to attempt to disentangle the smooth, broader regional pattern of var iat ion from the non-systematic var ia t ions . Thus, the regional var iat ion is commonly viewed as a smooth, regular d i s t r i but ion termed a "trend sur face" , and the local perturbations are referred to as res iduals or deviat ion.

As a t es t case, a contouring procedure was appl ied to the ava i l a b l e data from the V i t ro s i t e in Sa l t Lake City by use of the Kansas Geological Survey's computer program SURFACE I I [ 1 ] and i t s nearest-neighbor and Kriging options. Upon examina­t i on , no apparent di f ference was observed in the contour maps generated by use of these two options. Fig. 1 is a map of the V i t ro s i t e ; Figs. 2 and 3 are contour maps (using the nearest-neighbor option) of the radium concentration in surface soi l at the s i t e . The ver t ica l distance between two successive contour l ines is termed the contour interva l . Fig. 2 has a contour interval of 50 pCi/g and i s used to provide an over­view of the radium concentration data and to ident i fy hot spots , which are characterized by closed c i r c l e s ( " h i l l tops " ) in the contour l ines . Fig. 3 has a contour interval of 5 pCi/g and focuses on values around the 5 pCi/g zone. Al l values above 25 pCi/g have been omitted from this map, which is used to ident i fy the general location and character i s t ics of the remedial -action zone.

An examination of the contour maps of exposure rate and radium concentration in the so i l for the Sa l t Lake City s i te indicates that areas of uncertainty can be highl ighted using th i s contouring method. Fig. 3 shows a we l l -de f ined boundary on the east and south sides and a poorly defined boundary on the west and north sides of the V i t ro s i t e . The contouring

Page 626: Management of Wastes from Uranium Mining and

FIG. I. Map of the area around the Salt Lake City Vitro site. (Heavy line indicates perimeter of the study area. The map is adapted from Ford, Bacon & Davis, Utah, 1976, "Phase II -Title 1, Engineering Assessment of Inactive Uranium Mill Tailings, Vitro site, Salt Lake City, Utah". Dashed lines indicate findings reported in that document.)

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- 1 0 0 0 - 5 0 0 0

FIG.2. Contour map of radium concentration in the surface soil at the Vitro site. (The contour interval is 50 pCi/g.)

method is highly dependent on the f i e l d sampling pattern used to gather the rad io log ica l data at the s i t e and lacks the in fe rent ia l powers needed for decision making r e l a t i ve to the need for remedial action. A uniform sample pattern was found to g ive the best resu l ts and an intersect ing traverse sample pattern (based on polar coordinates) was found to give the poorest. A s t a t i s t i c a l analysis technique such a Kriging (which was applied to the Frenchman Lake region of the Nevada Test Site by Barnes et a l . [ 2 ] ) incorporates an assumption about the autocorre lat ion structure that reduces i t s useful appl icat ion to UMTRAP S i tes .

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FIG.3. Contour map detailing the 5 pCi/g zone for the Vitro site. (The contour interval is 5 pCi/g.)

A s t a t i s t i c a l decision procedure for defining the remedial action region was developed with the use of spat ia l c luster ing or grouping of data points and test ing of hypothesis regarding the c luster averages. This procedure c l a s s i f i e s locations at an UMTRAP s i t e as "remedial action required" ( R ) , "no remedial action necessary" ( N ) , and "action uncertain" (U ) where further sampling is needed. The procedure enta i l s the fol lowing steps (us ing gamma measurements as the example) which were applied to log transforms of the radio log ica l data. Log transformation was warranted by the nature of the d i s t r ibut ion of the rad io ­log ica l data. The steps are:

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1. Data points are c lustered into homogeneous groups through the use of the S ta t i s t i ca l Analysis System (SAS) procedure Cluster [3] and an appropriate c luster ing c r i t e r ion based on spat ia l proximity and s imi la r i ty of gamma measurements.

2. Various s t a t i s t i c a l character i s t ics such as the mean, standard e r ro r , and T value (computed with the use of the SAS procedure MEAN) are used for test ing the hypothesis that the mean ( i n or ig ina l uni ts ) = 20 pR/h (the proposed l imit ing value for gamma rad iat ion ) for each c luster [ 4 ] .

NNNN

NNNN N N NNN NN

N N N N N N N N N N NN N N_N N_NN Nj"NU N N "S NN

R II U N NN U U UU U N NR

N N NN N NN N N NNN NNN

N NNN NN N N ft

- N NN N MRRRR R N NN N N N NN N N RR N N N N N JU R

NN N N N NU] U RRR N NN N N N N N N N N NN N

NN

U UU U UUUURRR U URRR Nl RR R N R RR UURR R R

R R R R

UU U u R UU R R U R R R U R R R R RR 1

R R R

H UUU <u u u

N h NNNR N NNN

R R

R R R

RRRRRRNNNN NN R RR NNNfi N

RR R NN NN R M

R R R RR

RRRR R R

R RR RRR R R R RR R N NN NNNj

R iH RRR iH R R

1 NN N N NN N N NNN N N N N N

N N N N N N N N N N N

N

Legend

R Remedial Action Required U Uncertain: Sampling Required N No Remedial Action Necessary

-1500 -1200 -900 -600 -300 0 300 600

DISTANCE FROM VITRO SITE SMOKESTACK (meters)

900 1200

FIG. 4. Remedial-action decision map based on the 20-pR/h guideline for gamma exposure rate.

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T 1000-

fl 500H T

0 -

-500-i

1250

N

N N N

N N N N

" R R

R R 8

500 250

X LOCATION (METERS)

R REMEDIAL ACTION REQUIRED U UNCERTAIN: SAMPLING REQUIRED N NO REMEDIAL ACTION NECESSARY

FIG. 5. Remedial-action decision map based on the proposed 5 pCi/g guideline for radium concentration in surface soil.

3 . Decisions based on the s t a t i s t i c a l tests applied in step 2 are then coded as R, N, or U for each c lus te r , with the fol lowing interpretat ion.

( a ) R means that there is a high p robab i l i ty ( a t l eas t 9 5 % ) , based on the character i s t ics of the group, that the c r i t e r ion of 2 0 uR/h i s exceeded, indicating that remedial action i s necessary.

( b ) N means that there i s a high p robab i l i ty ( a t l eas t 95%) that the c r i t e r ion i s not exceeded, indicating that no remedial action is necessary.

( c ) U means there is uncertainty whether the average exposure rate of a c luster is below or above the c r i t e r i on value, indicating that further sampling i s necessary in that location before a va l i d c l a s s i f i ­cation can be made.

Page 631: Management of Wastes from Uranium Mining and

x !

- x

N N N

R R

JLfi_

•n X

I X

Legend

REMEDIAL ACTION REQUIRED UNCERTAIN: SAMPLING REQUIRED NO REMEDIAL ACTION NECESSARY ADDITIONAL RADIUM MEASUREMENT LOCATIONS

DISTANCE FROM VITRO SITE SMOKESTACK (meters)

FIG. 6. Suggested sampling scheme for the Vitro site.

A map of the c l a s s i f i c a t i on from grouping analysis of the Sa l t Lake City s i t e identi fy ing locations as R, N, or U on the bas i s of a comparison of gamma measurements to the c r i t e r i on of 2 0 uR/h i s shown in Fig. 4. The map of the c l a s s i f i c a t i on shows the suggested region of remedial action as bounded by so l i d l ines and the suggested region of uncertainty bounded by broken l ines . With additional sampling in the region of uncertainty, the appropriate decision as to c l a s s i f i c a t i o n could be assigned. Locations beyond 1000 m from the center of the Sa l t Lake City s i t e are assumed to be c lassed as N and were not included in the grouping analys is .

The method of c luster ing in the grouping analys is used here has certa in advantages over the Kriging technique in that i t i s not as sens i t ive to assumptions of r egu la r i ty in the spat ia l d i s t r i but ion of the sample data points.

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Fig. 5 is a c l a s s i f i c a t i on map for the Vi t ro s i t e i dent i ­fying locations as R, N, or U on the basis of a comparison of radium concentration in surface so i l to the c r i t e r ion of 5 pCi/g. The suggested region of remedial action is bounded by so l id l i ne s , and the suggested region of uncertainty i s bounded by broken l ines . A comparison of the areas for which remedial action i s indicated can be made by examining Figs. 4 and 5. Such a comparison reveals that the extent of the "R" zone indicated by the radium concentration data is l a rger in a l l d irect ions than that defined by the gamma radiat ion measurements, suggesting that the 5 pCi/g c r i t e r ion for radium concentration is more str ingent than the 20 uR/h c r i t e r ion for gamma radiat ion. This observation is consistent with the ca lcu lated re lat ionship between uniform radium contamination in so i l and the resu l t ing exposure rate above the surface.

To complete the analysis of an UMTRAP s i t e and determine where remedial action i s necessary, subsurface, water, and a i r measurements may have to be considered. The number of ava i l ab l e water and a i r measurements i s too small for any s t a t i s t i c a l analys is for the Sa l t Lake City s i t e . By the addition of the th i rd dimension, depth, to the grouping ana lys i s , the subsurface radium measurements could be c l a s s i f i e d in a manner s imi lar to the surface data.

Clusters from the c l a s s i f i c a t i o n procedures may be used to suggest additional sampling points. For example, analysis of the radium concentration data from the Vi t ro s i t e suggests that about 15 more radium measurements be made at locations ident i f i ed with an "X" in Fig. 6. The rat iona le for the choice of sample s ize and locations i s as fo l lows. I f the seven radium data points located in the northwestern and northern s t r i p s (an area characterized as U) are combined, the mean radium concentration i s 5.06 pCi/g, with a standard error of 1.3, a T value of 0.05, and an u n c e r t a i n l y level of 0.96. To reduce the uncertainty to 0.20 with a T value = 1.0, at l e a s t 100 more data points would be needed, even i f the true mean were to be 4.5 pCi/g. However, i f the data point with the 13.3 pCi/g value at the extreme end of the northern s t r i p ( see Fig. 7) were omitted, the c l a s s i f i c a t i on would change dramatical ly. One point having a very bad f i t with i t s neighbors very strongly influences the grouping analysis c l a s s i f i c a t i ons . These data points , as well as the surrounding area, need to be examined again in the f i e l d . I f the grouping analysis is done again based on the s ix remaining data points , the area would now be c l a s s i f i e d as N with a mean of 3.9 pCi/g and an uncertainty level of 0.08. An addit ional sample point i s suggested at the lower end of this s t r i p to cover a spat ia l gap.

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1 0 0 0

5 0 0

1 ' ' ' 1 m — r

• IS.4

H S t . i + 1 1 . 8

T t - t t r

+ 1 . 6 * J « .

+ 6 . 0

• J . 4

+ 7 - 5 + S 0 . 9 + * ' - 0

10 0 0-_l I

5 0 0

1 0 0 0

5 0 0

FIG. 7. Map of data values for radium concentration (pCi/g) in the surface soil at the Vitro site.

To define the R-boundary, one needs N-points surrounding it. The clustering pattern, the associated means, and uncer­tainty levels suggest that one needs about four or five points averaging about 4 pCi/g to define N clusters. The additional sampling locations have been chosen in a manner that is most likely to yield such N-points. The data for this test study on the radium concentration in the soil for the Salt Lake City site are shown in Fig. 7.

One of the problems in determination of sampling needs is that a suitable confidence level has not been defined. The present EPA guidelines provide maximum values without specifying the level of confidence required to meet these criteria. A realistic confidence level should be established on the basis

5 0 0 0

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of the many uncertainties inherent in measuring the radio log ica l conditions at UMTRAP s i t e s . The appl icat ion of s t a t i s t i c a l concepts to evaluate this confidence level r e l a t i ve to spat ia l and temporal va r i a t ion , as well as instrument var ia t ion , would provide ins ight into this problem. Addi t iona l ly , some consid­erat ion should be given to the costs involved in achieving a given confidence l eve l .

REFERENCES

[ 1 ] SAMPSON, R.J. , SURFACE I I Graphics System, Kansas Geological Survey, Lawrence, KA (1975, Rev. 1978).

[ 2 ] BARNES, M.G., et a l . , NTS Radiological Assessment Project : Results for Frenchman Lake Region of Area 5, Desert Research In s t i tu te , University of Nevada, U.S. Department of Energy Rep. D0E/DP/01253-17 (1980).

[ 3 ] ANON. SAS User ' s Guide; 1979 ed i t ion , SAS Ins t i tu te , I nc . , Cary, NC (1979).

[ 4 ] BROWNLEE, K.A., S ta t i s t i ca l Theory and Methodology in Science and Engineering (2nd e d i t i o n ) , John Wiley & Sons, I n c . , NY (1965).

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AN IN SITU GROSS ALPHA MONITORING TECHNIQUE FOR DELINEATING FUGITIVE MILL TAILINGS*

WJ. SMITH, F.W. WHICKER Department of Radiology and

Radiation Biology, Colorado State University, Fort Collins, Colorado, United States of America

Abstract

AN IN SITU GROSS ALPHA MONITORING TECHNIQUE FOR DELINEATING FUGITIVE MILL TAILINGS.

In situ gross alpha counting of soils is an effective technique for measuring uranium mill tailings contamination. In a field test, five minute gross alpha measurements were found to be capable of discerning tailings contamination at a level of 1.5 Bq (total alpha) per gramme of soil (41 pCi/g) in the presence of natural soil radioactivity. This corresponds to 0.28 Bq/g (7.6 pCi/g) for 2 2 6 Ra in tailings (with an assumption of secular equilibrium less 12% of radon and progeny). The equipment is inexpensive, rugged, and truly portable.

1. INTRODUCTION AND SUMMARY

Research and regulatory requirements frequently necessitate the monitoring of soil for tailings contamination. Soil samples collected for laboratory analysis are commonly used to satisfy this need. Considerable time is often involved in obtaining the results of laboratory analyses. Consequently, any work which must be planned on the basis of such analyses may be greatly delayed. To overcome this problem a field radioactivity measurement technique with good detection sensitivity and fast sample throughput is needed.

Two reports 11,21 describe the use of a gross alpha measurement system for evaluating contamination of soil by alpha-emitting radionuclides. Both used the technique in the laboratory with dried and homogenized soil samples. Both studies found that for 5-minute counting times good detection sensitivity and good correlations with more precise gamma spectroscopy or chemical analysis were possible.

* This work has also received support from the Colorado Graduate Fellowship Fund, and from the United States Department of Energy under Contract DE-AC02-79 EV 10305.

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95% CONFIDENCE INTERVAL

3 FROM

4 5 6 TAILINGS DAM (km)

FIG.l. Soil gross alpha radioactivity concentrations measured in situ as a function of distance downwind from a uranium mill tailings impoundment. The line labelled MSCa

marks the cutoff between 'natural' and 'contaminated' soil.

A more efficient use of this technique, we feel, is to make the measurements directly in the field with limited need for sample collection and laboratory analyses.

For in situ gross alpha counting (5-minute counting time) we calculated a 'minimum detectable contaminant concentration' (MDCC a) of 1.5 Bq/g (41 pCi/g) of total alpha contamination in the presence of the natural soil alpha radioactivity (see Section 4 ) . For ^**Ra in uranium mill tailings, the MDCC R a corresponds to about 0.28 Bq/g (7.6 pCi/g) when equilibrium assumptions are used to apportion the observed alpha radioactivity among the several alpha emitters in the tailings.

As examples of the use of the in situ gross alpha technique we present Figures 1 and 2. The data for these Figures is a portion of that collected and fully evaluated in one day of field work. The soil contamination downwind from a tailings impoundment after fifteen years of operation is easily discerned in Figure 1, where the alpha radioactivity of the soil surface is plotted as a function of distance downwind. The 'minimum significant concentration' (MSC Q) is shown (see Section 4 ) , as well as 95 % confidence intervals for each of the five measurements. In Figure 2 soil gross alpha radioactivity is shown as a function of depth, based on measurements made in a 25-cm deep soil profile dug 300 m downwind of a tailings dam. The tailings have been released over a period of about 15 years, yet the depth of significant mixing with soil is only 2 to 3 cm.

Although this report is based on measurements made with soils contaminated by uranium mill tailings, reasonable assumptions allow

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DEPTH IN SOIL (cm)

FIG.2. Soil gross alpha radioactivity concentrations measured in situ as a function of depth below the surface. The depth profile was dug 300 m downwind of a tailings impoundment dam. The line labelled MSCa marks the cutoff between 'natural' and 'contaminated' soil.

estimates of the radioactivity concentrations that may be discerned in soil for other alpha-emitting contaminants. In Table I are estimates of the 'minimum detectable contaminant concentration' (MDCC) for a number of materials. A major assumption is that the variability of natural soil alpha radioactivity is similar to that which we observed. Other assumptions regarding equilibrium of decay chains, radon emanation fractions, and radionuclides of interest are specified in the table.

In situ measurements reduce the overall time and effort for each survey point, but the effects of uncontrolled variables on the quality of the results must receive careful attention. Some potential interferences are contaminant inhomogeneity, soil moisture content, surface roughness, soil density, and disequilibrium of radionuclide decay chains.

The field gross alpha technique requires a certain level of laboratory support, especially corroboration of the identity of the contaminant and spot check verification of the alpha measurements by soil sampling for laboratory analysis.

Perhaps most important in applying gross alpha counting as a monitoring technique is knowledge of the mean and variability of the natural alpha radioactivity associated with the soil. This should be determined for an area as representative of the study site as possible in order to keep the variability to a minimum. The large possible variation in soil alpha radioactivity from place to place requires that we advise others to investigate carefully and to apply our 'MDCC' estimates with caution.

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TABLE I ESTIMATES OF MINIMUM DETECTABLE CONTAMINANT CONCENTRATIONS FOR IN SITU GROSS ALPHA MEASUREMENTS

OS to

Contaminant material Radionuclides assumed to be in equilibrium

effective alphas1

radionuclide of interest

MDCC az

Bq/f (r>Ci/e)

U-tailings 2 3 0 T h - 2 2 6 R a with with 12 % emanation 88 % 2 2 2 R n - 2 1 0 P o , or with 5.5 2 2 6 R a 0.28 (7.6) with 20 % emanation 80 % 2 2 2 R n - 2 1 0 P o 5.2 2 2 6 R a 0.29 (8.0)

U-ore dust 2 3 8 U - 2 2 6 R a ; 80 * 2 2 2 R n - 2 1 0 P o 7.2 2 2 6 R a 0.21 (5.7)

U-concentrate 238^ _ 234^ 2.0 2 3 8TJ 0.77 (21.)

Refined 2 2 6 R a 2 2 6 R a ; 80 % 2 2 2 R a - 2 1 4 P o ; no 2 1 0 P o 3.2 2 2 6 R a 0.48 (13.)

Th-ore dust 2 3 2 ^ _ 212 p o 6.0 2 3 2 T h 0.26 (6.9)

Th-tailings 2 2 8 T h _ 212 p o 5.0 2 2 8 T h 0.31 (8.3)

U-Th mixtures 2 3 8 U - 2 2 6 R a ; 80 % 2 2 2 R n - 2 1 0 P o ; (by radioactivity): and 2 3 2 T h - 2 1 2 P o

10:1 2 3 8 U : 2 3 2 T h 7.8 2 2 6 R a 0.20 (5.3) 1:1 2 3 8 U : 2 3 2 T h 13.2 2 2 6 R a , 2 2 4 R a 0.12 (3.1) 1:10 2 3 8 U : 2 3 2 T h 6.7 2 2 4 R a 0.23 (6.2)

2 3 9 P u (or any single alpha emitter) 1,0 2 3V 1.5 (41.)

1. The effective number of alphas emitted per disintegration of the radionuclide of interest. 2. Defined in Section 4. Based on 5-minute counting times and the soil conditions of our study.

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2. EQUIPMENT AND COUNTING PROCEDURES

2.1. Gross alpha

The gross alpha counting system consists of a portable, battery-powered, single channel analyzer and a 10 cm diameter ZnS scintillation probe with integral photomultiplier tube. The detector/analyzer system is light (4.3 kg), rugged, and amenable to use in the field if care is taken to prevent puncture of the light-tight mylar probe face. Small punctures of the mylar have been repaired in the field with a tiny dot of opaque enamel paint.

Field procedure. The ZnS probe was set directly on the exposed earth. Integral ribs on the probe provide a 1.6-mm spacing between earth and the probe face. Some minor surface preparation was often needed. Twigs, small pebbles and other sharp objects which might have damaged the mylar were carefully removed, and in some cases rough surfaces were flattened with pressure from a metal lid having about the same diameter as the alpha probe.

The particulate progeny of radon emanating from the soil may attach to the aluminized mylar probe face. An elevated detector background results, and suitable correction must be made in subsequent measurements. Because of this, we recommend determining the detector background immediately before each soil count. Repeatable background measurements were made on the clean inside cover of a notebook.

As part of this evaluation, soil samples were taken at each field survey point. The soil sample was approximately 0.5 cm thick and slightly larger than the area covered by the alpha probe, yielding a mass of 60 to 120 g.

Laboratory procedure. The laboratory gross alpha counting equipment was the same as that used in the field. Soil samples were dried, and mixed for homogeneity with mortar and pestle. Uniform counting geometry was provided by 8.8 x 1.3 cm plastic petri dishes, each of which holds a sample of about 100 g. As in the field, each soil sample measurement was preceded by a detector background count to allow proper correction for attached radon progeny.

2.2. Gamma spectroscopy

A computer—based multichannel analyzer and a large (23 x 8.8 cm), shielded (5 cm Pb) Nal crystal were the basis of the gamma spectroscopy system used as the comparison technique for the gross alpha measurements. Each soil sample (60 to 120 g) was sealed in an air-tight metal container (10 x 6 cm can with slip-on lid) and set aside to allow equilibration of the radon progeny. The net counts in the 1.76 MeV 2 1 4 B i and the 2.61 MeV * 0 8 T 1 photopeaks were

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determined. Typical counting times were 1000 s. Radioactivities 214 208

of Bi and Tl were calculated by comparison to reference sources.

3 . GROSS ALPHA CALIBRATION

Three samples were used as calibration check sources for alpha counting. They were kept in unsealed plastic petri dishes with loose fitting covers, and the total alpha radioactivity in each sample was assumed to be that of its equilibrated decay chains less the losses due to the emanation of radon. Counting yields (5-min counting time) for the three check sources were: uranium ore 8.0xl0~ 2 + 0.2xl0~ 2 (c/s)/(Bq/g) ,*

O.OxlO" 3 ± O.lxlO" 3 (c/s)/(pCi/g)), uranium mill tailings 9.7xl0 - 2 + 0.5xl0~ 2 (c/s)/(Bq/g),

(3.6xl0~3 ± 0.2xl0" 3 (c/s)/(pCi/g)), plutonium-spiked sand 8.6x10 2 + 0.5xl0~ 2 (c/s)/(Bq/g),

(3.2xl0~ 3 ± 0.2xl0" 3 (c/s)/(pCi/g)). The values given are the mean plus or minus one standard deviation (x + s). The standard deviations are the propagated uncertainties from each step of sample preparation including mass determinations, pipetting, radioactivity measurements, estimates of radon emanation fraction, and other factors as appropriate to each source. The agreement is excellent considering that the plutonium source is a surface deposit on relatively large sand particles, as opposed to the other two sources which are finely ground and have the radionuclides dispersed throughout the particles.

4. MINIMUM DETECTABLE CONTAMINANT CONCENTRATION

Currie [3] provided a statistical framework allowing the calculation of the level of contamination that may be distinguished from the natural radioactivity of soil. In applying the method we used the observed standard error of 24 background soil samples rather than the counting deviation. The observed standard deviation was about four times as large as the counting error and was a more useful measure of the natural variability. On the other hand, for a single measurement of a contaminated soil sample at the threshold of being distinguished from natural soil, the counting error was used as an appropriate measure of uncertainty.

With the logic presented by Currie [ 31 , we calculated the minimum radioactivity concentration that indicates a contaminated sample (with 5 % risks of false detection and non-detection).

* c/s = counts/s.

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TABLE II BACKGROUND SOIL RADIOACTIVITY

AND ESTIMATED DETECTABLE CONCENTRATIONS

SOIL METHOD 'MSC (£ + s) 'MDCC' UNITS

Nal ( 2 1 4Bi) 0 .18 0.092 + 0.038 0.088 Bq/g ( 2 1 4Bi) 4 .9 2.5 + 1.0 2.4 pCi/g ( 2 1 4Bi)

Field alpha 2 .7 1.2 + 0.7 1.5 Bq/g (total alpha) 73 • 32. + 19.0 41. pCi/g (total alpha)

Herein, this quantity is termed the 'minimum significant concentration' (MSC). If the mean radioactivity of the background toil samples is subtracted from the MSC, the difference represents the 'minimum detectable contaminant concentration' (MDCC). These terms are used merely for convenience and should not be confused with other terms such as 'lower limit of detection' (LLD) or 'minimum detectable concentration' (MDC), which are well-defined and apply to a different concept [4]. (The MDC for the alpha detector is 0.45 Bq/g (total alpha) (12 pCi/g) for typical background counts in 5 minutes.) Table II presents the mean and standard deviation of radioactivity measured in background soils, the MSC's, and the MDCCs for gross alpha counting and gamma spectroscopy.

5. ESTIMATING TOTAL ALPHA RADIOACTIVITY (Nal)

To allow direct comparisons between gamma spectroscopy and gross alpha measurements it was necessary to estimate the total alpha radioactivity of a sample based on the concentrations of 2 * 4 B i 208 and Tl. This was done by calculating the effective number of alpha emissions due to their respective equilibrated decay chains. Correction was made for the emanation of Rn by a reduction of alpha radioactivity due to lost radon and progeny. The emanation

222 fraction for Rn was estimated using a method similar to that of Austin and Droullard [5], and averaged 0.12 + 0.04 (1 SD) for 19 samples.

For soils contaminated by uranium mill tailings the 2 * 4 B i must be partitioned between the natural *J°JJ chain and the truncated

230 chain headed by Th. The partitioning was made using the mean 214

Bi radioactivity of natural soils, but only for samples where the total 2 1 4 B i content exceeded M S C B i .

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-•.' ' ' i , , , , , , , , , i , , , , 0 10 20 30 40 50

LABORATORY ALPHA (Bq/g)

FIG.3. Regression of soil gross alpha radioactivity concentrations measured in situ versus those measured on sampled soil in the laboratory. The 95% confidence intervals based on counting error are shown for a few sample data points. The 99% confidence band on the fitted line is shown as well as the least squares regression fit. The line labelled MSCa marks the cutoff between 'natural' and 'contaminated' soil. The circle represents 29 data points which fall too close together to be plotted separately.

6. COMPARISON OF FIELD ALPHA TO OTHER TECHNIQUES

Field alpha versus laboratory alpha. A regression of the calculated radioactivities (Bq/g (total alpha)) for field alpha measurements (Y) against those for laboratory alpha measurements (X) indicated excellent overall agreement between the two techniques. Figure 3 shows the data and the fitted regression line: Y = - 0.523 + 0.983X, The coefficient of determination, R 2, is 91.2 %, and the intercept is not statistically different from 0. If both techniques were equivalent in measuring the gross alpha radioactivity an intercept of 0 and a slope of 1 would be expected. The experimental results are consistent with this expectation.

Field alpha versus gamma spectroscopy A regression of the field alpha values (Y) (Bq/g (total alpha)) against the gamma spectroscopy (X) estimates of total alpha radioactivity (Bq/g (total alpha)) gave a regression line: Y = 0.294 + 1.28X, with R 2 = 88.9 % and with a standard deviation of Y about the regression line of + 3 . 0 (Bq/g (total alpha)).

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A useful comparison may be made by regressing the laboratory alpha values (Y) against the same gamma spectroscopy estimates of total alpha radioactivity (X): Y = - 0.824 + 1.31X. Here, R 2 is 97.7 % and the standard deviation of Y about the regression line is + 1 . 3 (Bq/g (total alpha)).

There was much more variability in the field alpha measurements than in the laboratory alpha measurements, as indicated by the differences in their coefficients of determination and by the considerably larger standard deviation of the field measurements about the regression line.

We attempted to investigate the variability due to two potential interferences: contaminant inhomogeneity and soil moisture content. The conditions at our study site were such that neither had a significant effect. The deposited tailings were relatively old and well weathered into the soil. If fresh surface deposits were monitored and subsequently evaluated against homogenized samples in the laboratory, significant differences would be expected. Soil moisture may reduce the number of alpha particles received by the detector. The soils we studied were very dry (40 of 61 samples contained 3 % moisture or less), and no effect of moisture on alpha detection could be observed.

Relative ability to detect contamination. Of the 61 samples assayed by Nal gamma spectroscopy, 27 were found to exceed MSCg^. The field gross alpha technique succeeded in identifying 23 of these samples, as well as an additional 6 samples not identified as contaminated by gamma spectroscopy. Although a sample size of 61 is small, these data allow some corroboration of the 5 % risks of false detection and non-detection used in calculating the MSC's. Assuming no error in the decisions made on the basis of gamma spectroscopy, the observed false detection was 9.8 % and the non-detection was 6.6 %.

7 . FIELD GROSS ALPHA AS AN ESTIMATOR OF * x o R a

Dreesen and Wienke [2] used gross alpha net counts/minute from 226

5-minute counts as an estimator of Ra in samples. The same use may be made of the field alpha measurements from this study. Regression of the radium content (Bq/g) (Y) (assumed to equal the equilibrium 2 1 4 B i content) against the field gross alpha data (net c/s) (X) gives Y = -0.09 + 1.40X, with R 2 =89.5%. The intercept is not statistically different from zero.

An alternative method is to recalculate the alpha counting yield as if all of the observed alpha radioactivity in the cali­bration check sources were due to Ra. When this is done for the uranium ore and mill tailings check sources, the reciprocal of the

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counting yields gives 1.57 (Bq/g)/(c/s) for each source. This is quite close to the slope in the above regression, as expected.

The values of MDCC a are expressed as Bq/g of total alpha. For equilibrated uranium mill tailings, 6 alpha emitters of the truncated uranium decay chain headed by 3^Th contribute to the total alpha radioactivity. So, in effect, each member of the chain may be detected at a level of MDCC a/6. When the emanation of radon is taken into account the effective number of alphas is less, in our case about 5.5 rather than 6. Thus the MDCC R a, for example, may be stated as 0.28 Bq/g (7.6 pCi/g).

8 . THE IMPACT OF IGNORING THE 2 3 2 T h DECAY CHAIN

Dreesen and Wienke [2] made no correction for the contribution 232

of alpha emitters of the Th decay chain to the gross alpha measurements, and did not consider the effect on predictions of

Ra. The implication was that the •"^Th content of the samples was either very low or highly correlated with the Ra content.

208 214 In our data the Tl and Bi contents were strongly

914 correlated (r - 0.87, df = 26) for samples having Bi concentrations greater than MSCg^, but weakly correlated (r = 0.42, df = 31) for samples below that level. We conclude that background soils contain the uranium and thorium chains in no consistent proportions, while in the mill tailings the two chains occur in a reasonably predictable ratio.

With a reasonably constant radioactivity ratio between the 23 0

thorium and uranium ( Th in tailings) chains, the presence of thorium alpha-emitting progeny will not impair the ability to relate gross alpha measurements to the 2 2 ^ R a content of tailings. In fact if the ratio is known, accounting for the thorium chain alpha emitters may enhance the MDCC R a. For our contaminated samples the U ( 2 3 0 T h ) : Th radioactivity ratio was about 6:1. On this basis it may be argued that an effective 6.5 alphas, rather than 5.5, are expected per disintegration of 2 2 ^ R a . The resulting MDCC R a is 0.24 Bq/g (6.4 pCi/g).

In the absence of a strong correlation (consistent ratio) between the two major decay chains, the effectiveness of detecting 'contaminated' samples is not impaired, but some interference and increased uncertainty in predictions for specific radionuclides will result. 9. CONCLUSIONS

The in situ gross alpha monitoring technique proved to be a fast and effective means for delineating windblown uranium mill

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tailings. It has potential for the quantitative evaluation of other alpha emitting contaminants in the environment.

Our field measurements exhibited greater variability than comparable laboratory alpha measurements on soil samples. The effect of uncontrolled variables apparently reduces the quality of the field measurements. Other investigators should consider carefully, for conditions at their sites, the potential effects of soil moisture and contaminant inhomogeneity.

Our future uses of the field alpha technique may include 1) mapping, in a relatively short period of time, the tailings deposition on large areas near a tailings impoundment, 2) investi­gation of the tailings deposition near, under the canopy of, and in the lee of large sagebrush plants without disturbing the soil by sampling, and 3) monitoring for residual radioactivity in reclamation areas to assure compliance with the 5 pCi/g ( 2 2^Ra) proposed standard [6],

ACKNOWLEDGEMENTS

A number of people have assisted with various parts of this investigation. We appreciate the aid of Gary Whicker with the field alpha survey, Bill McGinnies with the sample preparation and laboratory alpha measurements, and Shawna Flot with sample preparation for gamma spectroscopy. Dr. Shawki Ibrahim provided valuable assistance in the investigation of gross alpha calibration sources. We gratefully thank Dr. Keith Schiager for constructive reviews of this report, and for giving assistance with the statistical analyses.

KEFEIENCBS

[1] AHLQDIST, A.J., UMBARGER, C.J., STOKER, A.K. , Recent devel­opments for field monitoring of alpha-emitting contaminants in the environment, Health Physics 34 5 (1978) 486-489.

[2] DREESEN, D.R., WIENKE, C.L. , Gross alpha activity as an esti­mator of radium-226 activity in soils and tailings at an inactive uranium mill tailings site, Los Alamos Scientific Laboratory LA-7529-MS (1978).

[3] CURRIE, L.A., Limits for qualitative detection and quantitative determination, Anal. Chem. 40 (1968) 586-593.

[4] WATSON, J.E.(ed.), Upgrading environmental radiation data, U.S. Environmental Protection Agency, Office of Radiation Programs EPA-520/1-80-012 (1980) 6.24-6.31.

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[5] AUSTIN, S.R., DROULLARD, R.F. Radon emanation from domestic uranium ores determined by modifications of the closed-can gamma-only assay method, U.S. Dept. of Interior, Bureau of Mines Report of Investigations RI-8264 (1978).

[6] Draft environmental impact statement for remedial action standards for inactive uranium processing sites (40 CFR 192), U. S. Environmental Protection Agency t EPA/520/4-80-011 Appendix D (1980) 7.

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A COUNTING SYSTEM AND RESULTANT DATA FROM FIELD DETERMINATIONS OF 2 2 6 Ra AT TWELVE URANIUM MILL TAILINGS SITES*

H.L. RARRICK, D.M. MINNEMA, L.W. BREWER Sandia National Laboratories, Albuquerque, New Mexico, United States of America

Abstract

A COUNTING SYSTEM AND RESULTANT DATA FROM FIELD DETERMINATIONS OF 2 2 6 Ra AT TWELVE URANIUM MILL TAILINGS SITES.

A nuclear counting system has been developed and placed in service to determine the radium-226 content of soils within and beneath uranium mill tailings piles. Minimum detectable activity is approximately 3 pCi 2 2 6Ra/g of soil in a 0.5 mR/h background with a 3-minute count. The counting system consists of a lead shield for holding core barrel samplers, a Nal crystal coupled to a photomultiplier (PM) tube, a preamplifier and amplifier, two single-channel analysers (SCAs), a programmable calculator, and a 500 W portable generator. The counting system, installed in a delivery van, was used to count 2773-samples during 10 months under extreme field conditions. Approximate cost of the system excluding vehicle is US $8000. Vertical profile holes of the tailings piles exhibited 2 2 6 Ra activities from over 2000 pCi/g to 15 pCi/g. 2 2 6 Ra contamination levels in the soil beneath the tailings varied from 1000 pCi/g to background.

INTRODUCTION

Public Law 95-604, "The Uranium Mill Tailings Radia­tion Control Act of 1978," assigns the Department of Energy (DOE), other federal agencies, and involved states and Indian Tribes responsibilities for remedial action at 24 inactive mill tailing sites. The Department of Energy has established the Uranium Mill Tailings Remedial Action (UMTRA) Project to stabilize and control the tailings in a safe and environmentally sound manner according to standards set by the Environmental Protection Agency.

Sandia National Laboratories (SNL), acting on behalf of the DOE, contracted with Mountain States Research of Tucson, AZ, to perform sampling and analysis of 12 of the tailing sites (Fig. 1) to determine the economic feasibility

* Work performed at Sandia National Laboratories supported by the United States Department of Energy under Contract No. DE-AC04-76DP00789.

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FIG.l. Inactive uranium mill tailings sites.

of reprocessing the tailings for recovery of minerals. Additional studies for geochemical characterization, soil stability and Ra-226 contamination beneath the tailings were performed simultaneously with the site sampling.

Sandia National Laboratories developed and placed in service a mobile counting system to determine the Ra-226 activity of soil samples removed from the tailing piles.

INSTRUMENTATION

The counting system (Fig. 2) consists of a 136 kg (300 lb) lead shield for insertion of core-barrel samples and a 5 cm diameter x 2.5 cm Nal scintillation crystal coupled to a high resolution photomultiplier (PM) tube. The electronic pulse output of the PM tube is proportional to the energy of the gamma ray absorbed in the Nal crystal. A preamplifier and amplifier strengthens and conditions the electronic pulse which is then routed through two single channel ana­lyzers (SCAs). If the energy of the gamma ray as repre­sented by the pulse is within the window setting on the SCAs, the pulse passes through to a scaler where it is recorded. The number of counts (pulses) recorded in a specified time in a given energy window is proportional to the total radioactivity in that window and by comparison with standard sources one can determine the amount of a radioisotope in a sample.

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HIGH VOLTAGE POWER SUPPLY

PREAMPLIFIER POWER SUPPLY

- 2 4 V

- 1 6 0 - 375 keV WINDOW

SIGNAL

I— AMPLIFIER SINGLE

CHANNEL ANALYZER

SCALAR

TIMER

>— AMPLIFIER SINGLE

CHANNEL ANALYZER

SCALAR

CHANNEL A

CHANNEL B

BICRON 1 " x 2 " Na I (Tl) CRYSTAL WITH PREAMPLIFIER

-220 - 260 keV WINDOW

COMPONENTS: -110 VAC POWER GENERATOR - HONDA E-500 -HIGH VOLTAGE POWER SUPPLY - ORTEC 478 -AMP + SINGLE CHANNEL ANALYZER <X2) - ORTEC 4808 -Na I (Tl) CRYSTAL - BICRON 2 Ml/2 PLP -SCALAR + TIMER - ORTEC 776 -SCALAR - ORTEC 871 -BATTERY POWERED BACKUP SCA - LUDLUM MODEL 2200

FIG.2. Two-channel core barrel radium assay instrument.

N N O R M A L I Z E D Nal(TI) SPECTRA N FOR U R A N I U M T A I L I N G S A N D £ T H O R I U M O R E SHOWING

0.01 —/ 0 128 256 384 512

GAMMA ENERGY (keV)

FIG. 3. Normalized Nal(Tl) spectra for uranium tailings and thorium ore.

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e = THORIUM EFFICIENCY IN CHANNEL B IpCi/g) TB

counts c = RADIUM EFFICIENCY IN CHANNEL A IpCi/gl

counts RADIUM EFFICIENCY IN CHANNEL B (pCi/g)

B = BACKGROUND COUNTS IN CHANNEL A (counts) A

B = BACKGROUND COUNTS IN CHANNEL B [counts] B

C = TOTAL COUNTS FROM SAMPLE IN A (counts) A

C = TOTAL COUNTS FROM SAMPLE IN B (counts) B

THE CHANNEL RESPONSES CAN BE DESCRIBED AS:

C„ = e „ „ R + e,.„T + B . A RA TA A

C = € R + € T + B„ B RB TB B

THESE EQUATIONS CAN BE SOLVED FOR R YIELDING:

1 E (C — B ) - c (C - B ) TB A A TA B B

pCi/g

FIG.4. Core barrel radium assay - Calculation of the thorium correction.

For the analysis of Ra-226, the energy windows were set to a range from 160-375 keV and 220-260 keV. Window "A" includes the gamma rays from Ra-226 at 186 keV, and from Pb-214, a daughter of Ra-226, at 242 keV, 295 keV and 352 keV. Window "B" ranges from 220 keV to 260 keV to detect the 239 keV gamma rays from Pb-212, a daughter of Th-232 (Fig. 3 ) . The width of the windows compensate for the broad peaks resulting from a detector resolution of about 10%.

The total counts from the two SCAs, the count from a standard source and the background count are entered into a

CORE BARREL RAOIUM ASSAY INSTRUMENT

-DERIVATION OF THORIUM CORRECTION USING 2 SCA WINDOWS:

LET:

R = RADIUM CONCENTRATION (UNKNOWN) IpCi/g]

T = THORIUM CONCENTRATION (UNKNOWN) IpCi/g)

counts e- = THORIUM EFFICIENCY IN CHANNEL A [pCi/g]

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FIG.5. Instrument van.

calculator that has been programmed to determine the Ra-226 content of the sample (Fig. 4 ) . The resulting determination is printed out for a permanent record.

The entire system was calibrated using standard sources that contain known amounts of Ra-226 and Th-232, which approximate the physical nature of the samples to be analyzed. The sources were fabricated from mill tailings analyzed by Argonne National Laboratory and blended with very low background foundry sand to the desired concen­trations. These standard sources were then sealed in pipes chosen to simulate the physical dimensions and attenuation characteristics of the core barrels used for obtaining the samples.

The counting system was designed to operate in a back­ground radiation such as exists on a uranium mill tailing pile (up to one mR/h) , to count the soils in the core barrel samplers and to perform the counts in a minimum time

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in order to minimize the delay in the drilling schedule. The system is permanently mounted in a delivery van (Fig. 5 ) . Power is supplied by a 500 w gasoline powered electric generator. With a 3-minute counting time, the Minimum Detectable Amount (MDA) of Ra-226 is approximately three pCi/g of soil in a 4.5 cm T . D. split spoon sampler in a background of 0.5 milliroentgens per hour. Increasing the size of the sample, increasing the counting time or decreasing the background lowers the MDA.

This system operated reliably under field conditions in temperatures from below freezing to over 40°C (104°F). 2773 samples were counted during a 10 month period. Approximate cost of the system excluding vehicle is $8000 U.S.

SAMPLING

Samples were taken to profile the tailing piles and to characterize the extent of contamination in the soil below the piles. A drilling rig was used to auger a 15 cm hole into the soil and then pound a sampler down the open center of the auger to obtain soil samples below the auger. The samplers are 75 cm long and of three types: (1) Shelby - a 7.5 cm O.D. thin wall tube, (2) split spoon sampler - 3.5 cm I.D. tube, and (3) split spoon sampler - 7.5 cm I.D. tube. Most of the samples col­lected during this project were of the third type. After the samples were analyzed for Ra-226 the samplers were opened, the samples were visually evaluated, and then bagged and sealed for further analysis. Each sample was 75 cm long if complete recovery was obtained; however, some samples were less than 75 cm due to the composition of the sample; i.e., very fine sands, slimes, or cobbles were not retained when the sampler was with­drawn from the sample hole.

At least a 20 cm sample was required for the core barrel analyzer since the detector's field of view was 20 cm. At most sites profile holes were drilled to characterize the Ra-226 activity in the tailings and to locate the interface between the tailings and the subsoil by visual examination of the samples. At a few sites the tailings and subsoil were visually very similar, and the interface was determined by using the counting system. Samples varied from very wet to very dry, depending upon the site and location within the site.

Text cont. on page 641

Page 653: Management of Wastes from Uranium Mining and

HOLE NO. SR-D-061

100.0 100.0 1000.0

RADIUM - pCi/g

FIG. 6. Profile - Shiprock, NM (lower pile).

FIG. 7. Profile - New Rifle, CO.

Page 654: Management of Wastes from Uranium Mining and

10

£ 15 I

I

INTERFACE

10.0 100.0

HOLE NO. VC 030

RADIUM - pCi/g

FIG.-8. Profile - Salt Lake City - Vitro site.

10

15

25

INTERFACE

HOLE NO. OR-C-061

1.0 10.0 100.0

RADIUM - pCi/g

1000.0

FIG.9. Profile - Old Rifle, CO.

Page 655: Management of Wastes from Uranium Mining and

i i i i i i i 1 1 1— 0 2 4 6 8 10 12 14 16 18 20

DISTANCE FROM END OF SAMPLER - I N C H E S

FIG. 10. Non-uniformity of sample.

DISCUSSION

Four conditions were found beneath the piles: (1) rock, with essentially no contamination (Fig. 6); (2) very dry soil with contamination of 1 000 pCi/g above the interface to approximately 60 pCi/g at 225 cm below the interface (Fig. 7); (3) near saturated to saturated soils with contamination of 1000 pCi/g above the interface and 15 pCi/g at 225 cm below the interface (Fig. 8); and (4) saturated soils underlaid by cobbles and water where the water contained very fine particles composed of Ra-226 in suspension (Fig. 9). Vertical profile holes of the piles using 75 cm core barrel samples resulted in tailings activities from 2000 pCi/g to approximately 15 pCi/g. The non-uniformity of samples is illustrated by Fig. 10.

CONCLUSION

A mobile counting system using short counting times has been used to assay Ra-226 in soils collected in core barrel samplers on tailings piles. The system, using basic, inex­pensive components, has been reliable under severe weather conditions and has required minimal maintenance.

Page 656: Management of Wastes from Uranium Mining and

BIBLIOGRAPHY

Brewer, L.W., Rarrick, H.L., Minnema, D.M. SAND82-0288A, MRa-226 Measurements Below Uranium Mill Tailings Piles." To be presented at the Annual Health Physics Society Meeting, 1982.

Ford, Bacon and Davis, Utah. Engineering Assessments of each of the UMTRA Project Sites, 1979.

Minnema, D.M., Rarrick, H.L., Brewer, L.W. SAND82-0287A, "A Counting System for Field Determination of Ra-226 in Soils." To be presented at the Annual Health Physics Society Meeting, 1982.

Page 657: Management of Wastes from Uranium Mining and

NATIONAL RESEARCH AND DEVELOPMENT PROGRAMMES

Page 658: Management of Wastes from Uranium Mining and

Chairman

J. HOWIESON Canada

Page 659: Management of Wastes from Uranium Mining and

RESEARCH ON URANIUM TAILINGS DISPOSAL TECHNOLOGY AT CANMET, OTTAWA

J.M. SKEAFF, G.M. RITCEY, A. JONGEJAN, M. SILVER Canada Centre for Mineral and Energy

Technology, Department of Energy,

Mines and Resources Canada, Ottawa, Ontario, Canada

Abstract

RESEARCH ON URANIUM TAILINGS DISPOSAL TECHNOLOGY AT CANMET, OTTAWA. In this paper, results from three continuing investigations at CANMET on uranium

tailings management are presented. These investigations are: cleaning of tailings by flotation, conversion of municipal wastes into compost for use as topsoil on uranium tailings, methods for the chemical fixation of uranium tailings and a laboratory determination of the rate of release of environmental contaminants from uranium tailings. In order to develop a groundcover that would facilitate revegetation of uranium tailings in areas remote from topsoil, experiments were done on the windrow composting of solid municipal wastes mixed with sewage sludge. Because of severe Canadian winter conditions the effects of low ambient temperatures on this process were estimated from laboratory experiments. The results indicated that a continuous composting operation would slow down considerably during the winter because a part of the windrow would freeze. This problem may be overcome by storing the municipal-waste sewage-sludge mix as hydraulically compacted briquettes which appear to degrade when temperatures permit without producing foul odors. A vegetative cover was established much more easily and with the application of much less fertilizer on a surface layer of the compost on uranium mine/ mill tailings than on the surface of tailings that had only been treated with limestone. Chemical fixation was investigated as a means of reducing the rate of release of contaminants from uranium tailings. Part of the study consisted in mixing samples of uranium tailings with various potential fixating agents and conducting leach tests at various pH-values on the resulting materials in order to estimate their stability. The results indicate that chemical fixation can reduce the amounts of 2 2 6 Ra leached from uranium tailings by factors as high as 23 and, further, that a decrease in pH-value destabilizes the fixated material with respect to 2 2 6 Ra dissolution. The effects of iron-oxidizing bacteria and salt solutions on the elution of 2 2 6 Ra from uranium mine/mill tailings were investigated in lysimeter experiments containing approximately one tonne of tailings. In tests which simulated the precipitation conditions at Elliot Lake, sulphate generated by the bacterial oxidation of sulphide minerals decreased the concentration of 2 2 6 Ra in the effluents from these lysimeters. When a 2M KC1 solution was passed repeatedly through these tailings, the 2 2 6 Ra concentration increased to ~35 000 pCi/L after the fourth passage; further treatment did not result in any increase in the 2 2 6 Ra concentration in the saline effluent. Work is continuing to determine if the 2 2 6 Ra remaining in the tailings is stable with respect to further leaching.

Page 660: Management of Wastes from Uranium Mining and

INTRODUCTION

The environmental concerns associated with the disposal o f uranium mine-mill tailings have been extensively described elsewhere (1,2,3,4,5). In Canada, where precipitation exceeds evaporation at the uranium tailings sites, these environmental concerns are related to the generation o f acidic groundwater by pyrite oxidation and the long-term release into the environ­ment o f radionuclides such as Th-230, Ra-226 and Pb-210 and such elements as As and Ni.

The Canada Centre for Mineral and Energy Technology (CANMET) has a considerable programme directed towards the development of uranium tailings disposal methods which would alleviate these concerns. Elements of the programme to be dis­cussed in this paper are:

i) conversion of municipal wastes into compost for use as topsoil on uranium,

ii) methods for the chemical fixation of uranium tailings and iii) a laboratory determination of the rate of release of

environmental contaminants from uranium tailings.

CONVERSION OF MUNICIPAL WASTES INTO COMPOST

The establishment o f a vegetative covering on tailings areas for esthetic and environmental reasons requires the pres­ence o f organic matter in the top layers to obtain self-sus­taining plant growth. However, the essential absorptive and ion-exchange properties of the required organic matter are lacking in inorganic fertilizers. Organic matter either devel­ops from plant decay or it can be incorporated in the tailings in the form o f compost. The application o f compost may prove to be economic because o f the reduction of time in which self-sustenance o f plant growth can be obtained, and because of potential savings to be realized by reductions in the quanti­ties of fertilizer (200 lb/acre) and limestone (10 tons/acre) used previously (6) in establishing a vegetative cover on pyritic uranium tailings.

Thus in order to aid the development of methods which could be employed to establish a vegetative covering on Canadian uranium and other tailings, CANMET undertook an investigation into the production o f compost from municipal wastes which would be suitable for northern Canadian mining towns.

Compost is a humus-rich material formed by the bacterial degradation of various types of organic matter including munic­ipal wastes in the form o f cellulosic material and sewage. The

Page 661: Management of Wastes from Uranium Mining and

composting process, which is one method of disposing of munic­ipal wastes, is actually very similar to natural humus forma­tion.

A series of experiments was conducted to determine the optimum raw material ratios for the production of compost from municipal wastes (7). Cellulosic municipal refuse, wood waste, sewage sludge-bacterial concentrate slurry and recycled compost were combined in various proportions and cycled in an incubator as follows:

days °C 6 35 3 40

12 45 3 52 4 60 7 45

35

The mixtures were stirred twice weekly for aeration and samples were taken weekly for analysis of volatile matter, B-humus, moisture content, total N (Kjeldahl), ammonia N, urea N, P and K.

The best final degradation products were made from initial compositions in the ranges

cellulosic municipal refuse 50-75% wood waste 0-20% sewage sludge 10-25? recycled compost 10%

These composts had final compositions in the ranges

volatile solids 64.6-72.5 B-humus 1.94-2.42 total N 1.20-2.05 P 1.20-1.43 K 0.32-0.49 g plant material/100 c m 2 3.13-0.0 3

growth surface

Subsequent experiments with a mixture of 65% cellulosic municipal refuse, 5% wood waste, 20% sewage sludge and 10% recycled compost were then conducted by simulating Canadian winter conditions to determine the effect of low ambient tem­peratures on the composting process (8). The results showed that composting in a windrow format at an ambient temperature

Page 662: Management of Wastes from Uranium Mining and

r r Out

A r e a fo r W i n d r o w C o m p o s t i n g or B r i q u e t t e S t o r a g e

f - f Out 11

Os

00

7 0 m

Boler H o p p e r s

Hand Picking Sta t ion

( Waste Conveyor [ ' [ /

M a g n e t i c S e p a r a t o r

Shredder I '--.tr-' • ;B

v A J L A

Maintenance" Shop

3 Ramp

•4-,

A

Centri fuge

Water

• -A Baler

2 0 m

• 5 0 m-

FIG.l. Tentative plan for a composting process plant.

Page 663: Management of Wastes from Uranium Mining and

Sample 1 Sample 2

Approximate Weight Approximate Weight

Element Percent Element Percent

Si high Si 35.1 Al 3 Al 3.3 S 2 Fe« 2.4 (5 .2 )

K 2 K 1.69

Ca 2 Ca 1.41

Fe* 1.5 (3 .2 ) Ti 0.22

Ti 0.3 P 0.05

Na <0.1 Mg 0.07

Mg <0.1 Zn Trace

Pb <0.1 Se Trace

Zn <0.1 Cu Trace

Rb <0.1 Pb Trace

Ni Trace

•Value in brackets gives percentage pyrite in sample i f a l l

iron i s present as FeS 2

XRD analysis of uranium mine ta i l ings

Quartz

Muscovite

or similar mineral

Gypsum

Pyrite

Others present at

70-80%

10-20%

5-10%

l-2%»

<l-2% l eve l

•Wet chemical analysis suggests this value i s low and should

be 4.4%

Table I - Semi-quantitative chemical ana lys is (XRF) o f

uranium mine t a i l i n g s

Page 664: Management of Wastes from Uranium Mining and

Table II - Total solids percentage, percentage dry tailings and flow properties of mixes

Solids

(%)

Dry Tailings Total Dry Weight

(%)

Flow Value* Comment s

Krofchak Cast 72.1 94.1 150 Flows readily Krofchak Filtered — 94.1 128 Placeable by hand

AECL 75.7 75.7 — Flows readily at 165°C Chemfix 1 78.3 94.5 136 Easily placeable; almost

flows Chemfix 2 82.4 94.5 68 Placeable with vibration

IUCS 1 83.5 42.9 — Requires hand or vibratory compaction

IUCS 2 84.7 60.0 — Requires hand or vibratory

compaction

*As per ASTM C 109-77.

Page 665: Management of Wastes from Uranium Mining and

of -20°C was unsuccessful due to freezing to a significantly thick outer layer and the continuation of composting within the core.

Briquetting and indoor winter storage of the compost mix­tures offered a method of avoiding the windrow composting dif­ficulties during the winter. Degradation of the briquettes during winter storage would enable compost to be made year-round. Experiments showed that hydraulically compacted bri­quettes of dimensions 23x51x51 cm containing the above mixture of municipal refuse would degrade at ambient temperatures above 0°C to produce compost without evolving disagreable odours. Subsequent experiments showed that compost formation was favoured by low hydraulic compacting pressures increased sewage sludge contents up to 50% and the addition of a bacterial con­centrate to the mixture (9).

Based on the results of the foregoing experiments, a pro­cess was then designed which would be suitable for producing compost from the municipal waste of Canadian mining towns, of which the Elliot Lake area was taken as an example (10).

The plant, a schematic floor plan of which is shown in Fig. 1, is considered to have a capacity of 50 tons of munici­pal waste per day. The material is entered onto a conveyor-belt from which the 15% by weight considered to be non-compost-ible is hand-removed and the remaining 85% of the material, which is considered to be compostible, is discharged into a primary shredder. The shredded material then passes beneath a magnetic separator which removes the scrap iron. Centrifuge-dewatered sewage sludge is then mixed with the shredded mate­rial in a pugmill-type mixer and the material, to which pre­viously stored briquettes are now added, is then further shred­ded to 1/2-inch particle size, which has been shown by previous experiments to be the optimum size for degradation. The mate­rial produced by the secondary shredder is either discharged to storage to be windrowed during the summer or carried to a baler for briquetting during the winter. Both storage of briquettes and windrow composting would take place in an in-door storage area of 50x70 m. Very preliminary estimates place the 1982 operating cost at ~$400 000/year and the capital cost at $1.34 million.

CHEMICAL FIXATION OF URANIUM TAILINGS (11)

Chemical fixation or solidification has previously been discussed as a possible means of reducing the rate of release

Page 666: Management of Wastes from Uranium Mining and

Table III - Summary of freeze-thaw tests (2 samples of each material tested)

Cycles at end Sample of testing Comments

Krofchak Cast A 0 Turned to mush during saturation period prior to freeze-thaw cycling

B 6 Broke prior to freeze-thaw test; turned to mush after 6 cycles

Krofchak Filtered A 6 Broke after 1 cycle; turned to mush after 6 cycles

AECL A 128 No visual change of surface; some warpage

B 128 No visual change of surface; some warpage

Chemfix 1 A 11 Ends disintegrating; severe spalling on one side

B 11 Ends disintegrating; one side turning to mush

Chemfix 2 A 5 Numerous cracks; shattered B 5 Numerous cracks; shattered

IUCS 1 A 40 Severe spalling and disintegration B 80 Severe spalling and disintegration

IUCS 2 A 98 Severe spalling and disintegration B 98 Severe spalling and disintegration

of contaminants from uranium tailings. The investigation sum­marized here was conducted by the Ontario Research Foundation under contract to CANMET (11).

Four commercially available fixation processes were stud­ied :

a) the Krofchak process: acidic or basic additives, e.g. H2SO4 or Ca ( 0 H ) 2 , are mixed with "siliceous sludges" to form, according to the patent claims, "an inert solid mate­rial";

b) the AECL bituminization process: dry tailings are mixed with molten asphalt at 125°C in a twin-screw extruder and discharged at 165°C;

Page 667: Management of Wastes from Uranium Mining and

Sample Mass of Sample

Weight Dry tails/ Total Dry Weight

Radon Count* Radon Count Per Unit Sample Massf

Radon Count Per Unit Tails Masst

KC 719 g 94.1% 43346 270 287 KF 679 94.1 27121 179 190 AECL 776 75.7 884 5 7 C 1 680 94.5 26230 173 183 C 2 740 94.5 33824 205 217 IUCS 1 704 42.9 8299 53 123 IUCS 2 762 60.0 13618 80 134 Tails 243 100 5420 100 100

*10 minute count that has been corrected for the background and the dilutions when sampling.

fData has been normalized to 100 for untreated tails.

c) the Chemfix process: a solid matrix is produced by the reaction of soluble silicates with silicate setting agents upon mixing with the tailings; and

d) the IU conversion systems (IUCS) process: fly ash and lime-bearing materials are mixed with silica-bearing waste mate­rials to form a final produce similar to Portland cement.

EXPERIMENTAL

The Elliot Lake tailings employed in the present study had analyses as given in Table I, a R a 2 2 ^ content of 352 pCi/g, and a fineness of grind of ~59% minus 200 mesh. The samples of tailings and fixating agent were prepared under the condi­tions given in Table II,

The specimens of fixated tailings were subjected to stand­ard tests for shrinkage, compressive strength, flexural strength, freeze-thaw resistance, porosity and pore size dis­tribution. Rn emanation, agitation leach studies and percola­tion leach studies were also conducted.

RESULTS

The results of the freeze-thaw tests are given in Table III and show that freeze-thaw resistance was in the order AECL>IUCS>Chemfix>Krofchak. As expected, the AECL bituminous samples exhibited no visible changes upon completion of the

Table IV - Radon emanation data

Page 668: Management of Wastes from Uranium Mining and

Table V - Ra-226 dissolved from fixated tailings by leaching for 1 h at various pH levels

pH 1 .5 3 .0 5 .5

F i x a t i o n Head Ra--226 pCi/L Method pC i/g - 3 / 4 "

+1/4 " - 1 / 4 "

- 3 / 4 "

+1/4 " - 1 / 4 "

- 3 / 4 "

+ 1 / 4 " - 1 / 4 "

K r o f c h a k , F i l t e r e d 334 545 - 122 208 305 109

K r o f c h a k , C a s t 355 245 - 90 207 178 145

Chemfix 1 305 161 210 176 80 97 28

Chemfix 2 298 218 412 140 158 76 70

IU 1 144 103 124 60 28 72 16

IU 2 212 85 102 29 55 60 16

AECL 277 159 329 56 39 - 9 1

Denison T a i l i n g s 352 - 360 - 426 _ 374

freeze-thaw tests. The remaining cementitious samples exhi­bited various stages of decomposition at the end of their test periods.

Test results for porosity indicated that cementitious fixa­tion reduced the volume % porosity from 40.0% for unfixated tailings to an average of 34.5%. However, for the AECL bitumen samples, the porosity was only 4.9%.

The results for the radon emanation tests are given in Table IV. The data indicate that, with the exception of the AECL sample, the Rn counts per unit weight of tailings are higher than the count for untreated tailings. This result may be caused by dissolution of Ra-226 during mixing of the water, tailings and binder, and subsequent precipitation of the Ra-226 on a matrix from which Rn-222 emanation is easier than from untreated tailings. On the other hand, the emanation rates from the AECL samples indicate that the bitumen has virtually enclosed the tailings to prevent the release of radon. These results may be related to the porosities of the fixated sam­ples, which as noted above, are not very different among the cementitious samples and untreated tailings, i.e., ~35%, but are only ~ 5 % for the bituminous samples. Further investiga­tion would determine the effect of matrix and surface proper­ties on radon emanation rates.

Page 669: Management of Wastes from Uranium Mining and

The results for the agitation leach tests are given in Table V. For most specimens, the fixation procedures reduced the dissolved Ra-226 concentrations after one hour of leaching at room temperature below those for untreated tailings, e.g. at pH 3.0, 55 and 426 pCi/L for IUCS 2 and untreated tailings, respectively.

In general, the lowest dissolved Ra-226 levels are from those samples produced by the IUCS process, e.g. at a pH of 5.5, the -1/4" IUCS samples yielded levels of dissolved Ra-226 of 16 pCi/L, whereas the untreated tailings yielded dissolved Ra-226 levels of 360-426 pCi/L. This may be due to the binding of the Ra-226 by the alkaline pozzolan reaction within the crystalline lattice of the bulk matrix. For both -3/4, +1/4 inch material and for -1/4 inch material, an increase in pH from 1.5 to 3.0 decreases the levels of dissolved Ra-226, e.g. in the -1/4 inch Chemfix 2 sample, 412 and 158 pCi/L, respec­tively. With the exception of the AECL samples, for -1/4 inch material, increases in pH from 3.0 to 595 decrease the levels of dissolved Ra-226, e.g. in the Cherafix 2 sample 158 and 70 pCi/L, respectively. However, for the -3/4 + 1/4 inch material, the Krofchak and IUCS samples show increases while the Chemfix samples show decreases from 3«0 to 5.5. Further investigation would be required to clarify this effect.

Chemical analysis of the agitation leach solutions showed that the concentrations of Ca, Al and Mg increase with decreas­ing pH and with decreasing particle size.

Percolation leach tests were conducted to give some indica­tion of the effect of rain-water and winter run-off on the fixated materials. The results of these tests are given in Table VI and in general show a decrease in the rate of Ra-226 release as a function of time. Unfortunately, corresponding data for untreated tailings are not available. In agreement with the agitation leach studies, the lowest concentration of Ra-226 at the end of 22 days was from the IUCS 2 specimen, at 9 pCi/L. Twenty-two day concentrations for the KF, KC, Chem­fix, IUCS 1 and AECL specimens were 488, 383, 210, 69 and 100 pCi/L, respectively.

Discussion

The various test results showed that the Krofchak samples were the poorest performers with respect to strength, shrink­age, freeze-thaw resistance, radon emanation and acid leaching. However, preliminary estimates show that the materials cost for the Krofchak process would be the cheapest at $1.50 per ton of

Page 670: Management of Wastes from Uranium Mining and

Table VI - Percolation leach test results

Conditions: Leach Solution pH 4.0 Flow Rate: 0.170 L/Day (Equivalent to 34"/Year)

Fixation Head Day 1 Day 8 Day 15 Day 22

Method pCi/g 2 2 6 Ra pCi/L 2 2 6 Ra pCi/L 2 2 ° Ra pCi/L 2 2 6 Ra pCi/L

Krofchak, Filtered 334 823 474 462 488

Krofchak, Cast 355 668 641 488 383

Chemfix 1 305 271 284 220 210

Chemfix 2 298 256 238 150

IU 1 144 70 31 53 69

IU 2 212 47 17 27 9

AECL 277 62 80 74 100

Page 671: Management of Wastes from Uranium Mining and

El l i o t Midwest Lake* Key Lake*

Component Lake (small (shake (H 2S0 4 leac

column) f lask)

Radium-226 (pCi/g) 170 1650 6090 1090

Uranium (%) 0.007 0.395 0.05 0.004

Thorium (%) 0.025 0.007 - 0.0008

Iron (Total ) (%) 2.82 2.48 1 .83 1.11

Sulphate (% S) 0.72 0.19 0.09 1.26

Total sulphur {%) 3.64 0.80 0.81 1.28

Nickel (%) - 0.77 0.51 0.60

Arsenic (,%) - 1.21 1.08 0.34

Calcium (%) 0.45 0.11 - 2 .23

Total carbon {%) - - - 0.17

Carbonate {%) - - - 0.02

•Tai l ings are the residues from the laboratory scale leaching of the

corresponding ore.

t a i l i n g s . Hence the Krofchak process i s most probably unsu i t ­ab l e for the f ixat ion of uranium mine-mill t a i l i n g s .

Although exhib i t ing very good physical propert ies and low radon emanation r a t e s , the AECL .bituminous processes showed surpr i s ing ly high Ra-226 leach ra tes under ac id i c condit ions . Nevertheless, these leach rates were s i gn i f i c an t l y lower than for untreated t a i l i n g s as we l l as some other treated specimens, and adjustment of the bituminous specimens formation conditions may reduce the Ra-226 concentrations to an acceptably low l e v e l . However, the ext raord inar i ly high cost per ton of t a i l ­ings , $420, would prevent the use o f a bituminous process fo r bulk treatment of the t a i l i n g s , although consideration could be given to providing a bituminous cover.

Fixat ion of t a i l i n g s by the Chemfix process resulted in specimens with some improvement over untreated t a i l i n g s in strength, poros i ty , radon emanation rate and Ra-226 l e achab i l -i t y but with poor freeze-thaw res i s tance . The estimated cost o f the Chemfix process i s $500 000 for set-up and $7 per ton of treated t a i l i n g s .

Table VI I - Chemical ana lys is of uranium t a i l i n g s

Page 672: Management of Wastes from Uranium Mining and

Solidification of tailings by the IUCS process yielded materials with good strength and porosity values and fairly good freeze-thaw resistance. These pozzolanic materials also exhibited the best resistance to radium release by acid leach­ing and the second lowest radon emanation rates. The estimated costs, at $17 per ton of tailings, are the most expensive of the inorganic processes, although considerably less than the bituminization process.

LYSIMETER INVESTIGATIONS OF URANIUM TAILINGS

Lysimeter studies of the weathering of uranium tailings were undertaken (13,14) to enable predictions of

Page 673: Management of Wastes from Uranium Mining and

9 0.01

O 5

0.0001

1 1 1 1 1 1 1 1 1

1 MIDWEST LAKE TAILINGS -- (SULFATE LEACH) -_ SMALL COLUMN _

0.77% Ni

— 1.21 % As —

- tf^ ^"^S>-<v ARSENIC

— —

-

1 1 1 1 1 1 1 1 1

2 3 4 5 6 7 8 9 10

VOLUME OF WATER APPLIED PER kg MASS OF TAILINGS (L/kg)

FIG.3. Dissolution of As and Ni from Midwest Lake tailings.

i) the production of acid and the dissolution of metallic elements by the action of iron-oxidizing bacteria;

ii) the effects of organic solvent extraction reagents (which are used in the uranium purification process and rejected in small amounts with the tailings) on these bacteria; and

iii) the leaching of Ra-226 and other elements and compounds by water percolation through tailings site.

To this end, in adition to previously reported large-scale lysimeter tests (13,14), shake flask and small column tests were undertaken to determine whether small-scale tests could be useful for predicting radium release. Analyses of the vari­ous tailings used in the investigation are given in Table VII.

In the shake flask tests, 25 g of tailings and 250 mL of water were agitated in flasks at 30°C on a mechanical gyratory shaker. Each week the slurry was filtered and the solution was analyzed for Ra-226; fresh water was then added to the solids and the agitation was continued. In the large column tests, water was percolated at the rate of 1.75 L per week through

Page 674: Management of Wastes from Uranium Mining and

Table VIII - Concentrations of Ca, SO4, Fe, Ra-226 and U eluted by 2 M KC1 solution

Cycle pH Ca SC74/S Fe Ra-226 U No. g/L g/L g/L pCi/L g/L

1 3.39 0.027 0.24 0.40 2 000 0.0038 2 3.12 0.027 0.67 0.65 14.300 0.0084

3 4.13 0.012 0.71 0.75 30 900 0.0071 4 4.31 0.033 0.45 0.71 35 900 0.0021

5 4.20 0.035 0.26 0.30 34 300 0.0017 6 4.28 0.052 0.33 0.42 35 300 0.0020

7 4.21 0.059 0.32 0.38 35 400 0.0017 8 4 . 1 3 0.064 0.36 0.43 33 700 0.0023 9 3.92 0.02 0.36 0.36 10 800 0.0012

glass columns of dimensions 9.8 cm diameter by 90 cm containing 12.5 kg of tailings. In the small column tests 0.75 kg of tailings were held in glass columns of diameter 5.6 cm and length 25 cm, with a percolation rate of 200 mL/week. Bacteria were absent from the column tests but present in the shake flask tests.

The data of Figure 2 show the results of shake flask and small column tests on the aqueous dissolution of Ra-226 from leach residues obtained by leaching Midwest and Key Lake ores on a lab scale. Relatively high concentrations of Ra-226 were obtained from the Midwest 6090 tailings, i.e., ~20 000 pCi/L. In all, ~16% of the Ra-226 was dissolved, which is an excep­tionally higher level of dissolution when compared with the Key Lake shake flask test, in which the range of Ra-226 in solution was 800-2900 pCi/L and the total dissolved was only 0.22% of the Ra-226 initially in the tailings.

The data of Figure 3 for the elution of water through a small column of Midwest tailings show that although there is little dissolution of nickel, £0.001 g/L, there is signif­icant and continuous dissolution of arsenic in the range 0.01-0.04 g/L, which, however, is at least one order of magni­tude less than the federal effluent regulation (15).

Experiments conducted by Silver and Andersen (16) showed that 50% of the Ra-226 in washed conventional Elliot Lake tail­ings could be removed by leaching with 2 M KC1 solutions. In

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order to determine whether this would function on a larger scale, dissolution of Ra-226 from a one tonne lysimeter con­taining ~170 yCi Ra-226 was attempted by the continuous recy­cling of 2 M KC1 solution. After each passage, half of the eluted salt solution was treated for removal of Ra-226 by BaCl2 addition, while the remainder was made up to 150 L and 2 M KC1, and recirculated to the lysimeter.

The concentrations of Ca, SO4, Fe, Ra-226 and U are given in Table VIII. It is of interest to note that in cycles 3-8 the Ra-226 concentrations were between 30 900 and 35 900 pCi/L. Upon completion of the ninth cycle, the lysimeter had become clogged with precipitated KC1. However, by this time a total of ~18 iiCi of Ra-226 had been removed from the lysimeter. Further investigation will determine if significantly greater quantities of Ra-226 can be removed from the tailings by this method.

CONCLUSIONS

CANMET research on uranium tailings disposal has shown that compost could be produced from municipal wastes under winter conditions similar to northern Canadian mining towns by storing hydraulically compacted briquettes which degrade without pro­ducing foul odours. Testwork on the chemical fixation of uranium tailings showed that it is possible to reduce the quan­tities of Ra-226 leached from fixated uranium tailings samples by factors as high as 23 over untreated tailings; however, the cost of fixation of all tailings may be prohibitive, although fixation of certain size fractions or pyrite and radionuclide concentrates may be feasible. Lysimeter tests have demon­strated the feasibility of simulating the aging of uranium tailings and that 2 M KC1 is effective in dissolving Ra-226 from a one tonne lysimeter.

Future work is to involve the simulation of central dis­charge. Knight-Piesold and deep lake disposal techniques as well as the development of a correlation between bacterial activity and the extent of pyrite oxidation in an abandoned uranium tailings site and an extension of the investigation on the elution of Ra-226 from uranium tailings by 2 M KC1 solu­tion.

REFERENCES

[1] Moffett, D., "The disposal of solid wastes and liquid effluents from the milling of uranium ores", CANMET Report 76-19, Dept. of Energy, Mines and Resources, Ottawa, Canada (1976).

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[2] James F. MacLaren Ltd., "Environmental Assessment of the Proposed Elliot Lake Uranium Mines Expansion", Vol. 1 and 2, Toronto (1977, 1978).

[3] Bragg, K., "Long term aspects of uranium tailings manage­ment" , in "First Annual Conference on Uranium Mine Waste Disposal", Vancouver, B.C., May 19-21, 1980, C O . Braw­ner, Ed., Soc. Min. Eng. A.I.M.E., New York, N.Y., U.S.A. (1980) .

[4] Tsivoglou, E.C. and O'Connell, R.L., "Waste guide for the uranium milling industry", U.S. Dept. of H.E.W. , P.H.S., Report W 62-12 (1962).

[5] Raicevic, D., CIM Bulletin, 72 (808) , 109 (1979). [6] Murray, D. and Moffett, D., J. Soil and Water Cons., 32

(4), 171 (July/Aug 1977). [73 Jongejan, A., CANMET Division Report MRP/MSL 80-36(IR),

Dept. of Energy, Mines and Resources, Ottawa, Canada (1980).

[8] Jongejan, A., CANMET Division Report MRP/MSL 80-99(IR), ibid. (1980).

[93 Jongejan, A., CANMET Division Report MRP/MSL 8l-62(IR), ibid. (1981).

[10] Jongejan, A., CANMET Division Report MRP/MSL 8l-73(IR), ibid. (1981).

[11] Bruce, R.B., Pinchin, D.J., Lakshmanon, V.I., Berry, E.E., Stott, W.R. and Witte, M.K., Ontario Research Foundation "Physical and chemical properties of chemical­ly fixated uranium mine-mill tailings", Final Report, Contract no. 23440-0-9079, Dept. of Energy, Mines and Resources, Ottawa, Canada (1981).

[12] Weaver, W.S. and Luka, R., CIM Bulletin, Sept., 988 (1970).

[13] Silver, M. and Ritcey, G.M., "A simulation of effects of bacteria, organics and salt solutions on uranium mine mill tailings from Elliot Lake, Ontario", in "Waste Treatment and Utilization", Vol. 2, Murray Moo-Young, Ed., p 489, Pergamon Press, New York, U.S.A. (1982).

[14] Ritcey, G.M. and Silver, M., CANMET Division Report MRP/MSL 81-36(J).

[15] Report EPSI-WP-77-1, Metal Mining Liquid Effluent Regula­tions and Guidelines, Fisheries and Environment Canada, Hull (April 1977).

[16] Silver, M. and Anderson, J.E., "Removal of radium from Elliot Lake uranium tailings by salt washing", presented at 15th Canadian Symposium on Water Pollution Research in Canada, University of Sherbrooke, Dec. 7, 1979; published in J. Water Pollution Research in Canada (1980).

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THE CANADIAN RESEARCH PROGRAMME INTO THE LONG-TERM MANAGEMENT OF URANIUM MINE TAILINGS

V.A. HAW Canada Centre for Mineral and

Energy Technology, Ottawa, Ontario, Canada

Abstract

THE CANADIAN RESEARCH PROGRAMME INTO THE LONG-TERM MANAGEMENT OF URANIUM MINE TAILINGS.

Canada has embarked upon a three-year intense research programme intended to develop technology that will lead to the safe long-term disposal of uranium mine and mill tailings. Currently there are well in excess of 100 X 106 tonnes of uranium tailings on the surface in Canada, an amount that is expected to triple by the end of the century. A group of experts, who have studied the problem concluded that there was insufficient knowledge at present of the long-term consequences to the environment and man to walk away from uranium tailings after the termination of operations without thought for the future. Recommendations were made to government authorities for a three-pronged research programme that would contribute to a sounder basis for future decisions on requirements for the long-term safe abandonment of uranium tailings. The proposed research programme consists of three interactive parts: (1) Modelling the pathways of radionuclides from the uranium tailings through the environment to man, the objective of which would be to provide a forecasting tool for predicting the long-term behaviour and dispersion of contaminants within and beyond the tailings management area. (2) Measurement of the physical and chemical parameters of interest in the production and control of radioactive wastes, the objective of which would be to provide basic data needed for model building and verification and to establish a national uranium waste management data base. (3) The study of disposal technologies for use in the management of abandoned uranium tailings, the objective of which would be to identify economically feasible methods for closing out tailings areas, which will result in acceptably low adverse effects on the future environment. As part of the programme, it is proposed to conduct detailed measurements on three representative tailings sites, where 1000 holes will be drilled on each site for each of the three years to collect data. A National Tailings Program Office will be established, which will consist of a Directorate and supporting staff to conduct the programme, which is expected to cost in excess of $ 18 million dollars over the three years.

1. INTRODUCTION

Canada has large reserves of uranium. Production in 1981 amounted to about $770 million, about 85% of which was ex­ported. Our nuclear power industry now has a capacity of 5.25 GWe, which is expected to triple in the next 10 years. Clearly, the Canadian uranium industry makes an important contribution to

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the country's economy. Yet the safe disposal of uranium tailings is cause for concern, the magnitude of which is a matter on which there is not unanimous agreement. Tailings contain radionuclides, heavy metals and acid-producing agents that must be controlled to meet environmental standards of regulatory agencies. Current operating practices of the industry in Canada meet existing standards for effluent disposal to the environment; it is the long-term management of abandoned uranium tailings that, in the public perception, poses the potential problem.

High level waste from the nuclear cycle has received a lot of attention in Canada over the past few years, as elsewhere; annual expenditures on research for its safe disposal in Canada are currently close to $30 million. In contrast, at the front end of the cycle, research on uranium tailings in 1980/81 was only about $1.4 million, in fact, total R&D expenditures up to 1980 on record in Canada amounted to only about $7.9 million. The need for a greatly expanded R&D program on the long-term management of uranium tailings is recognized. The goal would be to provide new information and data on the characteristics of tailings and on the pathways of radionuclides from tailings that will aid in de­veloping methods for their safe disposal now and in the future. The results of such work will assist in providing a rational basis for the preparation of guidelines by government agencies for lic­ensing and controlling of uranium mining operations.

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FIG.2. Key Lake mining operations, Canadian shield, northern Saskatchewan.

1.1. Uranium Production in Canada

Uranium is currently being mined in Ontario and northern Saskatchewan. Large low-grade deposits at Elliot Lake, Ontario provide about two thirds of Canadian production. The higher grade deposits of Saskatchewan make up most of the balance. Figure 1 shows the distribution of uranium occurrences in Canada, the open circles indicating possible future operations, the others repre­senting abandoned tailings, although some may be under active management.

The Elliot Lake ore contains about 0.05 to 0.10% uranium of which the main minerals are brannerite and uraninite. The gangue is a quartz pebble conglomerate containing small quanti­ties of feldspar, sericite and chlorite. About 5% pyrite is present, and minor amounts of monazite and traces of other min­erals. There are more than 100 x 10° tonnes of tailings on the surface in Ontario, largely in the Elliot Lake area. The Saskatchewan ores are of much higher grade, some containing from 1 to 3% uranium and are, in general, more mineralogically com­plex. The main uranium constituent is pitchblende with some coffinite and brannerite. Associated mineralization includes

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sulphides, arsenides, and sulpharsenides giving rise to: iron, copper, nickel, lead, zinc, arsenic, antimony and minor molyb­denum and vanadium. The gangue minerals from the host rock are mainly quartz, sericite, chlorite and clay. There are about 20 x 10^ tonnes of uranium tailings in Saskatchewan, although a large proportion of these are under water or disposed of as backfill in the Beaverlodge mine at Uranium City. However, tailings accumula­tion will increase in the future as new mines come on stream.

Of the 120 x 10^ tonnes of surface uranium tailings in Canada about one third are inactive. These tailings are increas­ing by almost 24 thousand tonnes per day at current production rates. It is estimated that the total tailings accumulation will reach 300 x 10^ tonnes by the end of the century.

When considering uranium tailings management in Canada, at least in Ontario and Saskatchewan, both topographic and cli­matic conditions must be recognized. Uranium mining is isolated from populated areas. Both producing areas are located in pre-Cambrian rocks of the Canadian Shield, where topographic relief is generally low, streams and lakes are numerous and the surface is covered with vegetation, Boreal Forest in northern Saskat­chewan and open woods in the Elliot Lake area. Figure 2 illus­trates the type of terrain that is characteristic of the uranium producing areas of both Saskatchewan and Ontario. Temperatures are generally high in summer, up to 25°C and low in winter, down to -30°C; precipitation is moderate in the Elliot Lake area and low to moderate in Saskatchewan.

1.2. The Need for a Uranium Tai l ings Research Program

In 1 9 7 9 , the Canada Centre for Mineral and Energy Technology (CANMET), a branch of the Department of Energy, Mines and Resources examined the possibilities of launching an inte­grated research and development program into the long-term man­agement of uranium tailings in Canada. Although active mining operations are meeting current standards in the 2 2 ^ R a content of effluent to receiving streams, little information is available on what may happen when operations are terminated and the tail­ings are ultimately abandoned. A meeting was convened of those conducting or sponsoring research on uranium tailings, i.e., federal agencies, provincial governments and the uranium mining industry, to obtain their views. As a result, a group of experts on uranium mining and processing was appointed (National Tailings Planning Group (NTPG)) by the Department of Energy, Mines and Resources and given the following terms of reference:

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a) to review present activities and sources of funding; b) to propose a research program structure with priorities and

defined objectives; c) to estimate a program schedule, cost and cashflow; and d) to propose a program management structure.

The Group spent one year studying present practices for tailings management, the condition of abandoned tailings, and the measures adopted by government agencies to regulate the storage and disposal of wastes from mining and milling of radio-active ores. It visited all uranium mining operations in Canada and held discussions with officials from federal and provincial government departments and from companies. At the end of the year's study the NTPG concluded:

"Although active management schemes are used to maintain the emissions from inactive tailing within regulatory limits, the steps which may be required for the safe total abandonment of uranium tailings have as yet not been demonstrated. The problem is to devise such steps based on a better understanding of the mechanism of chemical constituent transport and dispersion. "

As a result the NTPG made recommendations to the Depart­ment of Energy, Mines and Resources which are summarized below:

a) The Federal Government and the Governments of Ontario and Saskatchewan should jointly establish a three-year uranium tailings research and development program.

b) An independent National Tailings Program Office should be established in Ottawa to manage the program.

c) The tailings R&D program should consist of three components: i) Measurement

ii) Modelling iii) Disposal technologies

d) Program objectives to be accomplished by the end of the third year should be:

- the completion and assessment of a preliminary set of models and associated codes;

- the instrumentation of representative tailings basins with two years of field data completed;

- the implementation of a national uranium waste management data base;

- a significant improvement made in accuracy and productivity in analyzing radionuclides;

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- preparation of a preliminary manual for deriving site-specific close-out actions;

- advancement of generic research on disposal technology options, and the site-specific R&D of industry incorporated into the total program.

The NTPG did not envisage that the recommended three-year program would provide definitive answers to the ultimate safe disposal of uranium tailings. However, it believed that the program would be instrumental in determining the extent of the problem of uran­ium tailings disposal and that it would provide a solid informa­tion base from which decisions could be made for future research on tailings and would assist regulatory agencies in establishing interim guidelines for uranium tailings management.

2. PROGRAM DESCRIPTION

To achieve the above objectives the NTPG proposed a three-pronged approach. The highest priority was given to the measure­ment component which is to generate data to assist in defining the extent of the problem and to provide a basis for construction of models of contaminant movement into the biosphere. The second component focusses on modelling of the pathways of radionuclides and other contaminants through the tailings and into the bio­sphere. The third component deals with disposal technology where various disposal options would be studied, the results of which would serve as a basis for guidelines in closing out tailings at the termination of milling operations.

2 . 1 . Measurement Component

The measurement component includes the determination of radio­nuclides and other chemical constituents of mill tailing effluents as they migrate through a number of pathways into the biosphere. Important measurements include dust and radon emanations from tailings surfaces, ground and surface water flow, water table fluctuations and the mineralogical characteristics of the tail­ings. This is by no means a comprehensive list of all the param­eters to be measured; undoubtedly, others will emerge as important to the success of the program as it develops.

2 . 1 . 1 . Objectives

The main objectives of the measurement activities are to:

a) establish environmental baseline data;

b) provide data for model development and verification;

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c) increase the understanding of natural processes which will lead to the design of improved disposal methods;

d) aid in the development of federal and provincial regula­tions;

e) monitor key control variables used to prove the validity of long-term disposal alternatives; and

f) coordinate data gathering activities over time.

The establishment of baseline data prior to mining development is important in order to measure the subsequent environmental impact. A large number and variety of measurements are required for an understanding of the processes in which the tailing con­stituents are active. Model development and verification will require large volumes of data from field and laboratory measure­ments.

2.1.2. Plan

Most of the measurement component will be dedicated to studying three representative tailings areas. It is proposed to drill each site to obtain solid and liquid samples and to deter­mine hydrological flow patterns. It is expected that about 1000 samples will be taken annually from each site during the three-year program which will consist of four parts:

a) sample design, installation of equipment and implemen­tation;

b) analyses of samples;

c) analytical and mineralogical research under controlled laboratory conditions; and

d) data base management.

The sampling program will be designed to yield hydro-logical , hydrogeochemical and biological data needed by the modelling program. It will entail the installation of sampling equipment, the taking and preparation of samples for analysis, and other field measurements.

2.1.3. Research

The NTPG recognized weaknesses in analytical procedures for radionuclides: the length of time for analyses is excessive and the accuracy of determination at low level concentrations is

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inadequate. Since a s i gn i f i cant research e f f o r t in both of these problems would be bene f i c i a l , funds have been earmarked for this purpose. S imi la r ly , i t was f e l t that addit iona l studies o f the mineralogy of the t a i l i n g s would r e su l t in a better understanding of the chemical and physical processes within the t a i l i n g s and should receive support.

2 .1 .4 . Data base

An important aspect of the measurement component i s the establishment of a uranium waste management data base . A mass o f data has already been co l l ec ted , but o f varying standards and for widely ranging ob ject ives . This backlog of data must be ca re fu l l y scrut inized and selected for incorporation into a newly organized data base that w i l l meet uniform standards of a n a l y t i ­ca l accuracy and techniques across Canada. In this manner, data on uranium t a i l i n g s can be gathered, stored and retr ieved in which there w i l l be a high degree of confidence.

2 .2 . Modelling Component

Understanding the interact ion, behaviour and disposal processes of the t a i l i n g constituents and describing them mathe­matical ly constitute the modelling component. The derived models w i l l provide the prediction capab i l i ty to estimate environmental consequences of the contaminants in the future and to evaluate the ef fect iveness of proposed measures for reducing contaminant re l ease . Such models w i l l a lso serve a key ro le in der iving guidel ines and regulations by government agencies for cont ro l l ing future uranium t a i l i n g s management.

2 .2 .1 . Pathways

Ta i l ing materials may be transferred d i rect ly or i nd i ­rect ly to humans through groundwater, surface water and a i r v ia aquatic , t e r r e s t r i a l and a i r pathways. Figure 3 i s a compart-mental model that represents the poss ib le d i s t r i but ion of t a i l i n g contaminants and the interfaces by which they may be transferred from t a i l i n g s to man. To be usefu l , models must be reduced to compartments that can be represented by measurable quant i t i es . Thus, by observation and an understanding of the processes i n ­volved w i l l permit the construction of models making i t poss ib le to predict the future behaviour and loading of contaminants.

The NTPG report ident i f ied 33 separate pathways for the transport of contaminants from t a i l i n g s to humans. Six of these are associated d i rect ly with the re lease of contaminants from the t a i l i n g s :

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FIG.3. Compartmental model, illustrating linkages between tailings and man.

a) release of leached material to groundwater, including radio­nuclides, heavy metals, acid from pyritic oxidation and process chemicals;

b) run-off and seepage through embankments directly to surface water;

c) release of large particles to nearby soils b y surface creep;

d) release of radon gas and small particles by suspension in air;

e) removal of tailings for use as fill or as construction material, resulting in exposure by direct gamma irradi­ation; and

f) direct irradiation by gamma-emitting nuclides from the tailings.

The contaminants migrate by means of aquatic, terrestrial and air pathways, resulting in human exposure by inhalation, ingestion or external irradiation. The relative importance of any of the path­ways is site specific, the major variables being: characteristics of the tailings, construction details of the tailings impound­ments, local geology and climate.

2.2 .2 . Objectives

The main objectives of the modelling component are to pro­vide a forecasting tool for predicting the long-term behaviour

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and dispersion of contaminants within and beyond the tailings areas. Specifically, modelling will provide a basis for:

a) assessing the long-term dosage or concentration of radio­nuclides from both existing and future mill tailings;

b) deciding preferred tailings management strategy; and

c) setting performance standards based on basic environmental criteria.

2.2.3. Plan

Two principal modelling activities are planned: development of models to provide a prediction capability and assessment of tailings disposal options, using the derived models. The success of both activities is highly dependent upon interaction and co­ordination with the other two program components. Observations are needed from the measurement program to understand the proces­ses involved so that empirical models can be assembled and veri­fied under different sets of conditions over time. Conversely, the modelling activity identifies the measurements required to characterize the dispersal of contaminants. Various tailings disposal options will also help to identify the variables that must be measured, which in turn will be used in the construction and verification of the models. Thus, there is a complete inter-dependency among the three program components. In all, there are four proposed activities for work on modelling:

a) model development and validation;

b) code development and verification;

c) data base management;

d) interpretation, assessment and program direction.

Model development will begin with a review of existing data, models and computer codes that are available and may be applic­able to Canadian conditions. It is hoped that this review will provide a basis for a first illustrative assessment that will identify the major components and processes affecting the environ­ment and give direction to future activities in all the program components - measurement, modelling and disposal technologies.

This will be followed by expansion and refinement of the data base. Processes governing the behaviour and migration of the contaminants will be studied in greater detail. These activ­ities will require extensive field and laboratory investigations,

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especially those involving long-term changes occurring in and about the immediate vicinity of the tailings areas. At the same time new data and information will be developed from studies of the tailings disposal options included in the program, which will be applicable to further model development.

As additional data are accumulated from field work and from studies of disposal technology, further assessments of dis­posal options can be made. This is an iterative process by which it is expected that convergence will be achieved between the pre­dictive capabilities of the models and the field measurements.

By the end of the third year model development and assessment will have identified the major contaminants and their short-term impact, identified the effects of some disposal alter­natives and will have evaluated the validity of using model pre­dictions to rank disposal options.

2 . 3 . Disposal Technology

The objective of this component is to identify feasible methods for closing out uranium tailings that, in the long term, will control the release of contaminants from uranium tailings to meet the standards of regulatory agencies. The success in reach­ing the objective will only be determined in the course of history as hard data become available from measurement of radionuclides and other contaminants as they are dispersed into the environment.

2.3.1. Current practice

In the 1950's, when uranium mining grew rapidly, tailings management was adapted from previous mining practices. As time passed it became evident that these methods were unsatisfactory as pollution problems were encountered downstream and corrective measures had to be taken. By the time uranium mining was revived in the early 1970's, from the depressed years following 1959, methods for the management of tailings had succeeded in reducing 2 2 ^ R a to 10 pCi/L or less in the effluent water, a level that was acceptable to federal and provincial regulations. Figure 4 illustrates the general configuration of tailings practice now in use; the effluent from the mill is treated with lime to raise the pH to about 9, which precipitates the iron, thorium, lead and other heavy metals. The decant from the radium tailings pond is treated with barium chloride to collect the 2 2 & R a as a precipi­tate, which forms a sludge at the bottom of the second impound­ment. Measures have also been introduced that have resulted in better control: impermeable barriers at the bottom of tailings

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Stream Precipitation or take P o n d Receiving

Waters

FIG.4. Current uranium tailings practice in Canada.

dams, better care in siting tailings ponds, improved water drain­age and vegetative covers. Apart from some of the older aban­doned tailings where information is lacking, the operation of ac­tive tailing sites meets all current regulatory requirements.

2.3 .2 . Recent innovations

Innovations have been introduced in recent years that show promise of mitigating, at least in part, the potential prob­lems of future tailings management. These apply to the surface disposal of tailings and include: coning, stacking and sub-aerial discharge. Coning is a method by which a thickened discharge -about 70% solids, is deposited in the form of a cone on the tail­ings site. The advantages are reported to be an increase in the capacity of a tailings area, improved surface water drainage, more uniform distribution of the grain size in the tailings, and the final surface contour is thought to provide better conditions for soil stabilization and vegetation. Stacking is another method by which surface drainage is promoted and capacity of the tailings area is increased. It depends on the presence of a natural eleva­tion which serves as a barrier for the enclosed tailings around which dykes are built of tailings, sand, gravel and glacial till to completely enclose the accumulated tailings. The slopes can be increased to ensure optimum drainage, depending on the local topography. Sub-aerial discharge, known as layering by some, is a technique whereby a layer of tailings about 76 mm thick is deposited on a slight slope, and left to dry during which time a similar layer is deposited in another sector of the tailings area. This operation is cycled to permit each layer to dry and become consolidated before another layer is deposited on top.

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The method i s expected to reduce v e r t i c a l permeability to a minimum and increase l a t e r a l f low; the surface of the l aye r s , because of the i r greater cohesiveness, i s l e s s subject to wind erosion.

These three techniques are r e l a t i v e l y new, e spec ia l l y the l a t t e r , and must be evaluated before f i na l conclusions are drawn on their app l i c ab i l i t y to s i t e - s p e c i f i c s i tua t ions .

2 .3 .3 . Proposed research

New research for d isposal technology has not yet been we l l defined. A s t a r t can be made by examining the r e su l t s o f the above innovations and making a c r i t i c a l study of the long -term consequences of more establ ished t a i l i n g s management p rac ­t i c e s . A lso , i t i s expected that some research now underway w i l l be expanded. Research under th i s heading can be categorized as generic and s i t e s p e c i f i c . The NTPG took the view that s i t e -spec i f i c work, in la rge pa r t , can best be performed by the ope r ­at ing companies and should be the i r r e spons i b i l i t y ; generic research w i l l be the pr inc ipa l concern of the National Uranium Ta i l ings Research Program, the r e su l t s of which should have general appl icat ion regard less o f locat ion , type of ore or l o c a l condit ions. However, the report s t resses and i t must be obvious to a l l concerned that the two types of research must be c l o se ly l inked and mutually support ive. Research supported i n i t i a l l y under the heading of disposal technology w i l l include:

a ) The use of synthetic and natural materials to l i ne t a i l i n g s basins and dams in pa r t i cu l a r ; synthetic membranes now being used have long l i f e expectancies but in considering the ha l f l i v e s o f some radionucl ides the durab i l i t y of such l in ings remains undetermined; further study of propert ies , du rab i l i t y and costs o f natural mater ia ls : c lays and g l a c i a l t i l l .

b ) Limiting the access of surface water to t a i l i n g s areas in order to reduce leaching o f t a i l i n g constituents into groundwater; examining s u r f i c i a l geology, divers ion schemes and improving drainage on t a i l i n g sur faces , as described above.

c ) Surface treatment of t a i l i n g s , mainly by vegetat ion.

d) Eliminating or substant ia l l y reducing radionucl ides and acid-producing sulphides in the processing of ore pr ior to discharge to the t a i l i n g s . This would eliminate a l a r ge part of the potent ia l problems. Some work has been done

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along these lines using conventional beneficiation tech­niques before and after leaching for uranium recovery. Alternate methods of acid leaching, using hydrochloric and nitric acids, have shown some promise. Work will continue along these lines.

e) Siting of tailings with regard to surficial geology and the design and stability of retaining structures, i.e., dykes and dams, for very long periods into the future.

Although the ultimate objective of the program is to achieve a walk-away condition from inactive tailings, it will be a very long time indeed before periodic monitoring of the release of contaminants can be abandoned. Methods of monitoring, fre­quency and the key constituents to be monitored will be examined. Other research will include investigations into deep water dis­posal, shallow burial and the use of tailings for backfilling of mines, a practice that has already been introduced but has fur­ther potential. This is by no means a.comprehensive list of items for research under the program but it will undoubtedly serve as a good beginning and as a basis for further development of the program.

3. PROGRAM IMPLEMENTATION

The NTPG report proposed that the program would cover a three-year period at an estimated cost of $18.6 million, divided into four components: measurement - $8.4 million; modelling -$6.9 million; disposal technology - $2.1 million and management of the program - $1.2 million. The report recommended that the entire program be jointly funded by the Federal Government and the Provincial Governments of Ontario and Saskatchewan.

The recommendations included a proposal to have the program managed by a centrally located National Tailings Program Office, with a director in charge and three technical assistants responsible for each of the main program components. It is intended that virtually all the research and associated scien­tific activities will be performed on contract to the private sector, to provincial research councils, and to universities and government laboratories. The uranium industry participation will be largely on site-specific projects that have special signifi­cance to local conditions. However, close cooperation and coord­ination with industry will be necessary. Site-specific informa­tion generated by industry must be incorporated into the national program if maximum benefits are to be realized. It was also proposed that the program directorate be responsible to a board of directors and that a technical advisory committee be appointed

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to assist the director and his staff in formulating the program and in evaluating results.

The report emphasizes and reiterates that the three-year period will not provide a final solution to the long-term manage­ment of uranium tailings. It is anticipated that answers to tailings disposal options will only be found by continual effort over a period exceeding one decade. The main contributing fac­tors to such a long period of time are: the slow rate of pro­gress of contaminants along the pathways and the slow response of the total environmental system to changes in both the contam­inant source characteristics and in the pathway parameters.

The size and scope of the three-year program are con­sidered sufficient to provide solutions to presently perceived problems and should give clear direction to future work. Suf­ficient data and information should also be provided from which interim guidelines can be prepared that will assist both industry and government agencies charged with setting regulations.

ACKNOWLEDGEMENTS

This paper has been based largely on the report of the National Tailings Planning Group, which was under the chairman­ship of Philip A. Lapp, Consultant, Toronto, Ontario. The report was commissioned by the Canada Centre for Mineral and Energy Technology for which the author served as the Scientific Author­ity and participated in many of the Group's field studies and deliberations which led to the report. I wish to acknowledge the contributions made by all members of the National Tailings Planning Group, and especially the work of Dr. D.H. Charlesworth and his colleagues at Atomic Energy of Canada Limited, Chalk River, Ontario, who provided the material on modelling. The re­port itself has not yet been publicly released and this paper attempts only to provide background to the proposed Program and to present the highlights and some of the guiding thoughts behind the proposals made in the report.

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URANIUM MILL TAILINGS MANAGEMENT -A SWEDISH APPROACH

J. EURENIUS

VBB/SWECO Consultants,

Stockholm

A. OSIHN

LKAB,

Stockholm

E. STRANDELL

ASA,

Stockholm,

Sweden

Abstract URANIUM MILL TAILINGS MANAGEMENT - A SWEDISH APPROACH.

During the last years considerable discussions have taken place on the short- and long-term aspects of uranium tailings management. This paper describes the background and the historical development within this area in Sweden. Requirements of regulatory authorities and design criteria are discussed. Two tailings disposal methods proposed for the Ranstad and Pleutajokk projects are described and illustrated. The tailings are handled in a 'dry' condition during disposal. The tailings are covered with more than 3 m glacial till. The tailings will lie above grade at Pleutajokk and below grade and groundwater at Ranstad after the mine operations are terminated. On the results of field tests it has been calculated that the release of radon and gamma radiation will be reduced to background levels. It is estimated that the infiltration through the till cover will vary between 1 and 10% of the precipitation. The till cover has the same durability as natural till covered ground which has been exposed to geomorphological processes since the ice-age 10—15 000 years ago. It is estimated that the changes of the cover in stable areas will be almost negligible during the next 10 —15 000 years or to the next ice-age. The long-term seepage is calculated to less than 0.1 L • s"1 -km"2 at Ranstad and to 0.2-2.0 L • s"1 -km"2 at Pleutajokk. The cost of the tailings handling including rehabilitation has been calculated to about 5% of capital and operation costs.

1. Introduction

A uranium mining waste disposal system in Sweden must be designed to eliminate environmental hazards, to the extent that is reason­ably achievable. License for operating a uranium mine is not granted until the applicant has shown that the risk for pollution by heavy metals and radioactive materials is acceptably low dur­ing and after operation of the mine.

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FIG.l. Sweden.

This paper discusses uranium mine tailings disposal methods suggested for two uranium mine projects in Sweden. The tailings are planned to be handled and disposed in a "dry" condition. After the operations are terminated the tailings will be deposited above grade at one site and below grade and ground­water table at the other site.

2. History

Uranium mineralizations occurring in alum shales and ryolite type rocks have been found in Sweden. Mining is being considered at Ranstad (alum shale) in the southern part of the country and at Pleutajokk (ryolite) in the northern part.(Pig.1.)

The extensive formations of alum shale contain large but low-grade uranium ore reserves. The highest uranium grades have been indi­cated at Ranstad where the alum shale is a part of the practical­ly horizontal series of sediments belonging to the upper Cambrian

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Uranium ore

0 5 10 Km

FIG.2. Ranstad area.

era. The uranium-carrying horizon is 2.5 to 4.0 m thick with a grade varying between 250 and 325 g/t U. The total uranium con­tent in the Ranstad area is over 1 Mt of which it may be possible to recover at least 0.3 Mt on a technical and economic basis.(Fig.2.)

A small uranium mill was constructed at Ranstad and put on stream in 1965. The plant operated at reduced capacity for 3 years pro­ducing about 300 t of yellow cake. Due to the low demand for uranium at that time, eaused by delays in the nuclear power programmes, the plant was closed down in 1969.

Since this time the facilities at Ranstad have been used for pilot-plant testing, developing more efficient technology for the processing of shale-type ores. During the late 1970's a re­fitted production was planned for about 2 Mt of ore per year.

At Pleutajokk the ore grade from the vein type mineralizations is expected to range between 0.05-0.30 %. The ore which dips 70-80 is suggested to be mined in an open-pit to a depth of 20-40 m

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and underground below this level. The production facilities are planned to about 0.7 Mt per year.(Pig.3. )

Sweden had a referendum in 1980 on the nuclear power issue. Parliament has after the referendum accepted a nuclear power program up to a maximum of twelve units. The decision in Parliament also includes a planned cessation of nuclear power generation after the year 2010. The question of uranium mining was not handled in the referendum. There are no mining activi­ties going on and planning activities are at low level.

3. Potential pollutants

Sulphuric acid leaching will be used at both Ranstad and Pleutajokk. At Ranstad about 80 % of the uranium is extracted and at Pleutajokk 95-97 %. With the exception of extracted uranium most of the radionuclides such as thorium -230 remain in the tailings.

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The tailing from Ranstad has a pyrite content of about 13 %. Heavy metals such as Cd, Hg, As, Cu and Zn are present in the pyrite and Ni and V in the shale matrix.

At Pleutajokk the content of heavy m e t a l s is almost negligible.

The following radiation and chemical risks have been considered in the design of the tailings d i s p o s a l system:

o radon release o gamma radiation o airborne dust o seepage of radium o seepage of heavy metals (Ranstad) o seepage of nutrient salts

4. Licensing

As mentioned, a license for uranium mining is not granted until it has been shown that the risk for public health and pollution is acceptably low. The following list summarizes some of the most important measures required by S w e d i s h regulatory authorities at licensing proceedings for the proposed Ranstad and Pleutajokk operations.

o Radon emission and gamma radiation shall be reduced to approximately background levels

o Surface and groundwater shall be protec­ted against pollution from seepage

o Release o f airborne pollutants shall be reduced to as low as reasonably achiev­able

o The tailings deposit shall have a good long-term stability. The area shall be available to the public after the mine is terminated. The surface shall,if possible.be restored to be used as pro­ductive land in the future

Some restrictions must be imposed. Human habitation, construction work and remo­val of materials can only be accepted under proper control.

http://possible.be
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-100 m

FIG.4. Ranstad - test pile.

5. Field testing

Since 1965 tailings have been deposited at Ranstad. They were placed in a 10 m high deposit with steep slopes and no cover. This resulted in pyrite weathering and leakage of water with a high content of iron and heavy metals.

At the beginning of the 1970's it was realized that the weather­ing and the transportation of pollutants could be substantially reduced if the tailings were neutralized by ground limestone and covered by vegetated glacial till.

Field tests to investigate the influence of these measures have been carried out since 1972. About 15 000 tons of tailings with a limestone content of 4 % were placed in a test pile. The ma­terial was placed in three 1 m thick layers. Each layer was com­pacted by vibratory rollers. Half of the surface was covered by 0.3 m limestone less than 10 mm. The other half was covered by 0.3 m till-bentonite mixture (permeability about 10"^ m / s ) . The whole pile was thereafter covered by about 1 m till (permeability

10 ^ m/s) and 0.3 m topsoil which was planted with local grass types.

Inside the pile 16 water collection vessels each with a bottom area of about 0.6 m 2 were installed. Continuous measurements of water flow, weathering and radon attenuation have been carried out (Fig.4) with the following results:

o Below the limestone the infiltration is 13 l/m 2 ,year corresponding to 1 % of the precipitation and below the bento-note-till mixture 3.7 l/m 2 ,year

o The oxygen diffusion down through the cover gives a pyrite weathering of 2-3 g Fe/m 2*year. The weathering zone moves downwards about 1 mm per 30 years

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• Calculated • Measured

FIG.5. Radon emission from test pile.

o The content of radon in the pore spaces is reduced from about 30 000 Bq/m 3 in the tailings to about 75 Bq/m 3 in the upper surface layer. The radon attenua­tion of the cover is about 400. (Fig. 5')

The infiltration through the till with the permeability of 10 ^ and the limestone is remarkably low (1 % of the precipitation). This can probably be explained by the unsaturated conditions of the till. The permeability, 10 ^ m/s,was determined under satura' ted conditions. However,the permeability decreases when the saturation decreases. Capillary forces and negative pore press­ure reduce the permeability. The saturation degree in the test pile till has varied between 40 and 60 %.

This explains why an unsaturated till can resist infiltration almost as well as a bentonitic till with a saturated permeabil-

-9 ity of about 10 m/s.

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6. Design criteria

The tailings disposal system must be constructed to fulfil the environmental requirements. The following criteria,when applic­able, have been used in the design of the proposed projects:

o Mill site selection should be made with regard to the proper location of the tailings disposal area

o The mill process should be designed with consideration to tailings handling technique. The process should give "dry" tailings or tailings which after dispo­sal are dewatered within a short time period

o The tailings handling must be designed to protect surface and groundwater from pollution

o The tailings deposit shall be covered with soil to control dust, radon emis­sion and gamma radiation. The infiltra­tion through the cover shall be so small that the transportation of pollutants from the deposit is acceptably low. The cover shall have a long-term stability.

Both at Ranstad and Pleutajokk the tailings area is selected on the basis of environmental requirements as well as on economic terms. At Ranstad the tailings are backfilled in the worked out parts of the open-pit. At Pleutajokk the tailings are deposited above grade in a relatively small till-covered valley. The mills are sited close to the disposal area so that long transports and contamination with dust are avoided.

In the mill processes "dry" tailings are obtained at Ranstad by percolation leaching at Pleutajokk by slurry leaching followed by filtration. The ore is ground as coarse as possible with re­gard to the leaching requirements. From the mill the tailings are transported by conveyors or trucks.

The cover of the tailings must be designed with consideration to the specific conditions of the area. Sweden has a wet climate with a net precipitation and for the construction of cover, till, considered to have very good short and long-term qualities,is obtainable in most parts of the country.

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^- Drainage filter ^ R o c k

FIG.6. Pleutajokk - tailings disposal.

The tailings are in both cases covered by at least 3 m of till. Drainage layers are interbedded to create unsaturated water con­ditions in the till. Based on the results of the field tests at Ranstad it has been calculated that the release of radon and gamma radiation is reduced to background levels. The infiltration is estimated to be between 1 and 10 % of the precipitation (500-800 mm per year).

Till has a very good durability against geomorphological proces­ses. The covered tailings have the same durability as natural till covered ground which has been exposed to such processes since the ice-age 10 to 15 000 years ago. During this period the changes by weathering and erosion have been almost negligible in stable areas. It is therefore judged that the durability of the till cover is acceptable during the next 10 to 15 000 years or to the next ice-age at the proper disposal location.

7. Disposal methods

Several alternative tailings and waste water disposal schemes and layouts have been evaluated for the Pleutajokk and Ranstad projects. The alternatives include wet and "dry" tailings handling with a soil cover of at least 3 m. Comparisons of total construc­tion and operating costs including required reclamation measures showed that "dry" handling in most alternatives is cheaper than wet handling. From an environmental point of view "dry" handling is considered favourable because besides other advantages it allows continuous reclamation of the tailings area during opera­tion. "Dry" handling has therefore been selected in both projects.

At Pleutajokk the tailings are placed above grade. They are transported by conveyor belts to an area where the ground con­sists of 3 to 5 m of till resting on bedrock. The tailings con­sist of a mixture of sand and silt 100 % passing 1 mm and 20 %

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H 2S0 4

1 Rock

FIG.7. Ranstad - uranium ore handling; backfilling of open pit; revegetation of ground surface.

passing 0.05 mm. The water content is about 15 % by weight. Be­fore disposal of the tailings the bottom of the disposal area is covered by compacted till and a crushed rock filter. The compac­ted till has a permeability less than 10 ^ m/s. The bottom is sloped to allow drainage water to flow to a collection pond dur­ing operation. From there it is pumped into a closed water system. Excess water is treated in a purification plant for radium pre­cipitation before release to the environment. The radium preci­pitate is disposed separately.

The tailings are spread and compacted in about 0.2 m thick layers by a dozer. The risk for slides is avoided by using slopes flatter than 1 vertical to 3 horizontal. When the tailings are filled to the final level which is 15 to 20 m above ground level, it is covered by 3 m till with a permeability of less than 10"^ m/s. Most of the cover material is taken within the disposal area ahead, of the disposal front. This technique allows the tailings to be covered 1-2 years after disposal. (Fig.6.)

The surface of the deposit is sloped in such away that permanent water-pools can not be established. Inflow of surface water from the surroundings is prevented by diverting ditches. The ground­water is permanently lowered to a level below the tailings. The surface is planted by natural forest vegetation. (Fig.9»)

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-Till Crushed Limestone -Outside dam Limestone Inside dam

Ground water level

..Compacted till KslO^m/s

FIG.8. Ranstad - surrounding dams.

At Ranstad the tailings consist of material less than 2 mm with 15 % fines (material passing 0.07 mm). The water content is about 17 % by weight. This material can be deposited in the same way as at Pleutajokk. At Ranstad the alum shale has a low per­meability. It is possible to design the disposal so that the see­page and the oxidation will be very small. Therefore,after the operation of the mine is terminated the groundwater is raised above the tailings.

The tailings are transported by trucks to worked-out parts of the open-pit. They are placed on a filter of coarse broken barren alum shale and limestone material. The filter rests on alum shale

-10 -11 with a low permeability, 10 to 10 m/s. The tailings are spread in about 1 m thick layers. Each layer is compacted to avoid future settlements.(See Pig.7») The tailings are surrounded by a double parallel dam structure, see Figure 8. The cover is placed continuously throughout the life of the project. The top of the deposit is covered with at least 0.3 m topsoil. The intent is that the area shall be used for farming in the future. Waste water is pumped to a purification plant during operation.

When the operation is finished water is raised mainly by inflow of groundwater from the surroundings. The water level is deter­mined by the crest of the outer dam. The water pressure in the tailings will be the same as between the outer and inner dam. This means that seepage of waste water will only be through the solid shale below the deposit which has a very low permeability 10 ^ to 10 ^ m/s. The seepage of radium and heavy metals is therefore very small.

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ON

o

FIG.9. Pleutajokk - tailings disposal area.

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The time from the start-up of one section of the open-pit until the section is backfilled and revegetated is about 5 years. The ground surface of the area will than be about 5 m higher than the original surface. (Fig. 10.)

The cost of the tailings handling at Pleutajokk and Ranstad in­cluding rehabilitation is calculated to about 5 % of capital and operating costs.

By using the suggested methods release and dispersion of radio­nuclides are reduced to background levels. However, over a long period of time, thousands of years, water will seep through the tailings. The long-term seepage is calculated to between 0.2 and 2 l/s'km 2 at Pleutajokk and less than 0.1 l/s'km 2 at Ranstad. Radium, heavy metals and other soluble salts will over the long-term period be dissolved slowly and transported by groundwater surface streams and rivers into the oceans where they finally end up in the sediments.

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COLORADO'S PROSPECTUS ON URANIUM MILLING

A.J. HAZLE, G.A. FRANZ, R. GAMEWELL Colorado Department of Health, Denver, Colorado, United States of America

Abstract

COLORADO'S PROSPECTUS ON URANIUM MILLING. The first part of this paper will discuss Colorado's control of uranium mill tailings under

Titles I and II of the Uranium Mill Tailings Radiation Control Act of 1978. Colorado has a legacy of nine inactive mill sites requiring reclamation under Title I, and two presently active plus a number of new mill proposals which must be regulated in accordance with Title II. Past failures in siting and control on the part of federal jurisdictions have left the state with a heavy legacy requiring extensive effort to address impacts to the state's environment and population. The second part of this paper will discuss the remedial action programme authorized under Public Law 92-314 for Mesa Country, where lack of federal control led to the dispersal of several hundred thousand tons of uranium mill tailings on thousands of properties, including hundreds of homes, schools and other structures. Successful completion of the State efforts under both programmes will depend on a high level of funding and on the maintenance of adequate regulatory standards.

With the end of World War II, the United States federal government embarked on a uranium procurement program. The control of radiation and radioactive materials was largely a responsibility of the federal government, particularly the U.S. Atomic Energy Commission (.AEC). In 1959 the Atomic Energy Act of 1954 was amended to enable states to enter into agreements with the AEC for the regulatory control of source, by-product, and special nuclear material. In 1968, Colorado was the 18th state to enter into such an agreement. At the time of Colorado's achieving agreement status, regulatory authority over uranium mills was also transferred in reference to the source material regulatory responsibility for uranium mills.

In 1978 the U.S. Congress passed Public Law 95-604, otnerwise known as the Uranium Mill Tailings Radiation Control Act of 1978, or UMTRCA. The basis for this act is the clean-up of the old inactive mill sites which were generated and regulated by the federal government as the sole buyer of the mill product, and the preclusion of developing another generation of mill site problem situations in the future.

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With regard to the inactive uranium mill sites, there are nine such piles in seven locales in Colorado, and four of the locales involve growing population centers. These are Durango, Grand Junction, Rifle and Gunnison. With the exception of the one pile at Maxell, all piles are in relatively close association with a major stream or river.

Colorado has entered into a cooperative agreement with the U.S. Department of Energy (DOE) for the conduct of the remedial program authorized by Title I of UMTRCA. This agreement addresses the conduct of the program and the inter-relationships and responsibilities of the parties. The Colorado Department of Health is the lead state agency for this program with a coordinating role in the participation of other state agencies and local government.

With the assistance of DOE, Colorado has conducted two potential disposal site evaluation efforts. These involved the areas surrounding Durango and Grand Junction/Rifle suitable for possible relocation of the tailings materials. In the case of Durango, four potentially viable sites were recommended to DOE for consideration under their NEPA (National Environmental Protection Act) requirements. Three of these sites were on privately owned properties and had the preferred geohydrological characteristics. One was a state-owned property in relative close proximity to the old mill site but in a highly erosional environment. Further analysis of the feasibility of these sites is left to DOE engineering studies and the NEPA process. With regard to the Grand Junction/Rifle potential disposal site evaluation effort, this state study is still in progress at the time of this writing. However, due to the extent of federal government land ownership in that area of the state, and the geological and hydrological characteristics, only federal lands are being considered as viable alternatives. In the case of the Gunnison pile, DOE has suggested that an Environmental Assessment be done first to determine if relocation is necessary prior to state effort in a potential relocation disposal site evaluation study.

Due to the unavailability of Environmental Protection Agency (EPA) standards, much of the remedial program cannot proceed at this time. Actual remedial action on the piles themselves in Colorado is not anticipated until FY 83-84 or later. We express concern for suggestions of stabilization in place, particularly of the four locations involving growth centers in the state. The real potential for accidental death due to removal actions and the extra cost for such a program is acknowledged.

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Aside from the actual tailings pile sites, there are vicinity properties that have also been contaminated. DOE must by law designate these sites for consideration of remedial action. To date in Colorado, DOE has neglected to do so. While the major program effort is directed to the tailings piles, the problems with the vicinity properties may be very significant from a health and remedial cost view point. The majority of such properties are located in Grand Junction where remedial action at structures was authorized under earlier federal and state laws as discussed later in this paper. There are also a significant number of such properties at the other locales that could be addressed in a more timely manner. Of particular interest is the preclusion of new construction on off-site tailings. While a building permit survey program has been initiated by Colorado with assistance from DOE, the local governments cannot preclude construction indefinitely if the remedial program is not willing to act in a timely manner. The cost of remedial action after construction can be excessive and unacceptable.

When Colorado took over the regulation of uranium mills in 1968, it quickly identified problem areas in three of the four conventional operating uranium mills previously sited and regulated by the AEC. Upon completion of contracts, the Grand Junction mill was shut down in 1970 and interim reclamation and stabilization of the site occurred in 1972. The new Rifle mill ceased uranium milling in 1972 but it continues to process vanadium solutions. The tailings pile is under active maintenance. These locations are included in the Title I program. The other two problem mills were Union Carbide's mill at Uravan and Cotter Corporation's mill at Canon City, neither of which is addressed under UMTRCA, Title I.

Uravan 1 s history dated back to the days of Madame Curie, World War I, vanadium extraction, the Manhattan Project, the federal uranium procurement program, and then private contracts for uranium production. Uravan's AEC license in 1968 authorized the discharge of up to 90 pCi Radium226/ liter of effluent into the San Miguel River. At one time in Uravan's history the San Miguel River did not contain any biota within the impact of the mill effluent discharge. Additionally, discharge points were diffuse and not controlled. Subsequently, as processes were improved, discharge collection and treatment reduced the mill effluent concentrations to levels orders of magnitude below the AEC and state effluent regulations, and to a fraction of the drinking water standard. In 1979-80, orders were issued by the Department concerning the stability of the tailings impoundments which contained over 10 million tons of tailings located on a cliff above the town of Uravan. These concerns were addressed by

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reberming and buttressing. We are currently awaiting various state and federal agency buy-offs on the acceptabilty of these structures for an additional maximum two years nominal operation and tailings storage. Impoundments for liquid treatment and raff inate disposal are currently located along or in the river channel and were apparently designed to allow seepage into the river. Correction of this situation is envisioned upon the shut down of the mill operation as it currently exists, followed by the removal of the ponds and their residues into the main tailings impoundment. Uravan has recently installed a new product drying and packaging facility. However, concern exists that the 40 CFR 190 off-site dose limits are still being exceeded. Consideration of license renewal will be addressed during 1982.

The Cotter Corporation mill in Canon City was also involved with the federal uranium procurement program but the majority of the tailings were generated under private contracts. The old facility was primarily an alkaline leach process. Other minerals were also extracted. Two major issues were involved with the old mill. These were worker protection, particularly in the product drying and packaging areas, and ground water contamination. With the availability of new milling facilities and impoundments in 1979, worker exposures have been tremendously reduced. This has been demonstrated by inspection and by a NIOSH investigation made at the request of the union local. While Cotter officially states it is not the source of the ground water contamination, they have embarked on an extensive effort to relocate all the old tailings into the new engineered impoundments. By the time of this presentation this relocation will have been completed by rather simple earth moving means without major incident. There was a minor bank cave-in that partially buried a worker and some equipment. Efforts are now underway to remove non-tailings residual contamination to levels approaching background, realizing that continued operation of the facility may provide continuing surface contamination and that these old tailings pile sites will remain a restricted or controlled area under government jurisdiction following closure and reclamation of the entire mill site.

We initially started with a relatively pristine environment in Colorado, proceeded to defile it, and now with the cooperative efforts of the federal government, the state, and the involved industry, we are correcting the sins of the past. Only history will tell if we have been successful.

In recent years Colorado has become involved with several new uranium mill applications. • Homes take Mining Company was licensed in 1981 to build a conventional alkaline circuit mill

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and high tailings dam in a pristine high mountain National Forest area* This action followed exhaustive review of an Environmental Impact Statement and subsequent engineering studies, by several dozen state, local and federal agencies, and a public adjudicatory hearing. This licensing action has withstood all court challenges as of this writing date.

By the time of this meeting, extensive review and hearings will have been completed on an application by Pioneer Nuclear for an acid circuit mill in semi-arid southwestern Colorado. This mill will involve belt dewatering and incremental trench reclamation of the tailings.

Colorado is also reviewing an application for another very large (4500 tons/day) conventional mill with partially underground tailings disposal, and several applications for leach recovery and in-situ extraction operations.

A few additional comments on other aspects of our current uranium mill regulatory program: In October 1980, the U.S. Nuclear Regulatory Commission (NRC) adopted regulations regarding uranium mill tailings and in accord with the requirements of Title II of UMTRCA, Washington, Colorado and Texas adopted equivalent regulations. Hearings that ensued on the EPA proposed standards for the Title I program most probably will result in standards that differ considerably from what was proposed. Action by Congress, based on the envisioned precedence setting impact of EPA proposals and the NRC regulations on the U.S. Department of Defense remedial programs, has deferred action by NRC on implementation of their regulations. Revision of the NRC regulations might be anticipated, based on the anticipated EPA standards. All this came about because goals and objectives were put into regulations.

The situations discussed so far in this paper relate to concerns addressed by Title I or Title II of UMTRCA. Mesa County Colorado has a unique situation stemming from the deliberate use of several hundred thousand tons of tailings for home and other construction purposes throughout major portions of the community.

The discovery of this in August of 1966 initiated an effort to develop an inventory of all the locations where tailings had been deposited and then, to measure the levels of radiation associated with each deposit. Locations that involved structures were of special interest.

It took roughly two and one half years to locate and evaluate existing alpha radiation measuring devices that could be used in the field in homes and businesses to measure radon and

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radon daughter concentrations (RDC) within the structures. It took another year before an acceptable integrating sampling device could be produced that would better define the average RDC levels within structures.

In 1969, radon grab sampling and gamma radiation surveys were performed at structures reported to have used tailings in their construction. Based on the data gathered from the first 250 such locations, an all out effort was begun to locate all locations having tailings deposits. Mobile scanning units traversed all streets and roads in the county noting any gamma anomalies. On foot teams of state and federal workers followed up each anomaly and eventually found that it would be necessary to go door to door down every street and road in the county because these scanning units could not detect deposits shielded by structures and intervening layers of clean soil. Most property owners cooperaLed in allowing these surveys (only 260 refused), and each structure was checked for tailings contamination.

By 1971, over 15 000 locations had been checked, and by the end of 1981, over 30 000 locations had been surveyed.

Initial data indicated that it would be necessary to take integrated RDC measurements due to the highly variable RDC levels measured in individual tailings involved structures. Instrumentation developed by Colorado State University was put into use in 1970, and enough data developed by 1973 to provide a basis for the evaluation of the radiation levels in structures built with or on tailings.

By 1973, over 15 000 locations had been notified as to whether or not they had any tailings deposits affecting their property. Those whose structures were contaminated in some way by the tailings were provided evaluations of the radiation levels observed within and given recommendations as to the need for corrective action based on guidelines provided to the state by the U.S. Public Health Service. These guidelines are known as the Surgeon General's Guidelines.

Late in 1972, an agreement between the federal and state governments provided for a remedial action program under Public Law 92-314 to reduce the levels of radiation in the tailings involved structures where the measured levels of either gamma or alpha radiation exceeded the lower values of the Surgeon General's Guidelines. Based on criteria formulated by the Federal government, a remedial program began corrective action on the first structure (a school building) in 1973.

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The joint state/federal program, conducted by the state with federal concurrence, contracts with individual property owners to do corrective action designed by an architect engineering firm and approved by the two governmental agencies. Private construction contractors bid on the individual jobs.

Even though the program continues to evaluate locations that have applied for consideration by the program, over 560 locations have already been assigned for engineering assessment. It is projected that by 1983 approximately 6b0 locations will be identified as qualifying for corrective ac tion.

Construction contracts have been awarded to 416 locations and 397 have now completed remedial action.

Removal of the contamination is the first choice in remedial corrective methods. There are conditions that exist at some locations that will not allow for complete removal of the tailings deposits. Deposits under the foundation of some structures cannot be safely removed without destroying the structural integrity of the structure. Tailings deposits mixed into the concrete and/or mortar of the foundation and bearing walls of the structure in most instances cannot be removed. We have learned that in some instances epoxy sealants, improved ventilation and special vent systems in crawl spaces or beneath floors can be used to reduce the RDC within the structure.

Filtration of the air by high efficiency filters and electrostatic precipitators was tested but found to be highly dependent on thorough and consistent maintenance if they were going to be consistently effective in keeping the RDC levels down to an acceptable level.

Seventy locations were found to have elevated RDC levels above the program criteria entry levels even after the initial remedial action. Experimentation with different types of remedial measures, developing experience in identifying deposits around a structure that influences the RDC within the structure, and formulating procedures and techniques for locating hidden deposits that were affecting the structure, all contributed to the group of unsuccessful remedial locations. Progress, although slow at times, is being made in improving the engineering assessment that defines and influences the types of remedial measures to be taken on each structure. In this case, experience was the only teacher, as nothing like this had ever been undertaken before.

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The current projection is to complete the remedial action on all eligible locations by the end of 1985, but the level of funding from the state and possibly the federal government could delay the completion until the late 1980s.

The cost of completing the remedial action on those 660 structures projected to require the remedial action, which includes residences, schools, churches and all types of commercial structures, is now estimated to be 22.6 million in 1981 dollars.

In summary, in Colorado's experience, what is needed with regard to the uranium industry is knowledge, intellect and wisdom. Collectively a great abundance of knowledge exists and as all involved are not unintelligent, the apparent problem area has been the unfortunate lack of wisdom exhibited by a majority of the involved parties.

Page 715: Management of Wastes from Uranium Mining and

PANEL DISCUSSION AND CLOSING REMARKS

Page 716: Management of Wastes from Uranium Mining and

Chairman R.W. RAMSEY, Jr.

United States of America

Page 717: Management of Wastes from Uranium Mining and

PANEL DISCUSSION ON WASTE MANAGEMENT IN THE URANIUM MINING AND MILLING INDUSTRY -OBJECTIVES, PROBLEMS AND SOLUTIONS

Chairman: R.W. Ramsey, Jr. (USA)

As regards the objectives, a view was expressed that, while the scope and quality of work done so far has been impressive, demonstrating an acceptable level of safety, unanimity is still lacking on what the objectives should be for waste management in the industry. In papers presented at the Symposium there was no adequate coverage of what inadmissible risks are in the industry, but a few docu­ments which dealt with the risks were reassuring. A principal management objective is to avoid improper reuse of tailings materials. At the same time it would be appropriate to transmit to future generations knowledge of the existence of disposal facilities. Furthermore, it is within the capability of human beings to preserve disposal sites for centuries, to keep control of these in the long term, and to monitor their environment and protect themselves from potential risks. How­ever, it should be left to the future generations to recognize their responsibilities for protecting themselves. Reuse of tailings for certain practical purposes could be considered. It is a responsibility not to encourage countries, particularly less affluent ones, to invest inordinate resources on the long-term aspects of tailings disposal when they need such resources for much more important things.

Presenting the problems being faced by the industry, it was mentioned that the basic requirement for long-term management of uranium mill tailings is to reduce the escape and dispersion of contaminants to acceptable levels. However, a requirement that disposal systems should provide containment and stability that will last for thousands of years (a 'walk away' condition) poses very formidable engineering requirements — that have hitherto been unheard of and are beyond the limits of engineering practice. Furthermore, it is considered unrealistic to relieve future generations of all concern for tailings disposal sites. The perception, whether by members of the public or by government authorities, of the real nature of potential problems or risks posed by uranium mill tailings inevitably has a sub­stantial effect on objectives which may be set for decommissioning and rehabilita­tion of tailings disposal sites. Perceptions may often be emotional and inaccurate,

Panel Members

Mr. R.H. Campbell (USA) Mr. J. Coady (Canada) Mr. R.M. Fry (Australia)

Mr. J. Howieson (Canada) Mr. J. Pradel (France) Mr. R.A. Scarano (USA)

Page 718: Management of Wastes from Uranium Mining and

and may be misleading when efforts to solve tailings management and disposal problems are being considered. A principal feature of decommissioning and rehabilitation programmes is inevitably their cost. It is currently estimated that the 24 inactive tailings sites which are to be rehabilitated in the United States Uranium Mill Tailings Remedial Action Program (UMTRAP) will cost between US $500 to 1000 million. This cost would be substantially less if a re-evaluation of objectives led to more realistic requirements.

In an appraisal of the solutions for the long-term management of wastes from uranium mining and milling, in particular uranium mill tailings, three cate­gories have been considered :

(1) Containment: by various methods (in above- or below-grade facilities) which can be so engineered to reduce the dispersion of contaminants to acceptable levels and prevent the dispersion of tailings material for as long as possible.

(2) Dispersion: by various methods which permit dispersion of contaminants at a limited rate, so long as no unacceptable public health and environmental problems result; in reality it is not a feasible option.

(3) Removal: render tailings 'clean' by removal of contaminants for more secure management (concentration, containment and disposal); such a course would provide an immediate solution to the problem but commercial technologies for removal and alternative management of contaminants have not yet been developed.

Technical solutions for tailings disposal should therefore consider the entire range of options and circumstances, and should preferably aim at establishing passive control mechanisms. Potential public health and environmental problems which may, in general, result from the dispersal of contaminants from tailings are not likely to be of a very serious nature. However, should passive control mechanisms not perform adequately, contaminant releases may create unacceptable problems in certain circumstances. Should institutional controls be relied upon to ensure control in such circumstances, some reliance needs to be placed on the continuation of the institutional control mechanism. In time, as contaminants are removed from a tailings pile by dispersion, the problem will perhaps cease to exist and institutional controls can be phased out.

Commenting on the concern for future generations, it was mentioned that the role of technical administrators has to be quite clear-. The increased pressure that appears to be on technical administrators to be concerned for future generations is not something which is technologically based, but it is a societal demand. Present day society appears, for good or otherwise, to be requiring society, in its decisions, to be more concerned for future generations than appears to have been the case in

Page 719: Management of Wastes from Uranium Mining and

the past. The role of technical administrators is only to ensure that there is a proper technological basis for the concerns which society appears to have over the problems which it addresses. Concern, as it appears in the public perception, for the hazards associated with uranium mill tailings is grossly over-estimated, and is out of all proportion to their real hazards. The role of technical administrators is to provide society and decision-makers with the information that is necessary for them to see this problem in perspective. When seen and understood in its true perspective, perhaps the demands from society for spending inordinate amounts of money to isolate tailings for all time, as though they were major radiological hazards, rather than just a nuisance — which is what in fact they are — will diminish somewhat.

There was discussion on some of these issues. One aspect which emerged is that decision-makers will have to be provided with alternatives. It is necessary to understand what institutional control means and a clear definition of this seems to be lacking. There was a mention that there should be a rationalization between radioactive contaminants originating from non-radioactive materials, such as phosphate rock being used as a fertilizer and mill tailings disposal in respect of dealing with licence applications. There was also a suggestion that improvements are required in public perception and understanding. There was a discussion as to what guidance the Symposium can give regarding the time periods that should be considered. Glaciation provides a terminal control for some reasonable cut-off point according to some opinions.

In conclusion the discussion was quite illuminating. It must be borne in mind that management of this problem must be placed in perspective with other concerns of society. Many objectives are philosophical and related to potential long-term effects and misuse of tailings in the future. One of the best precautions is to transmit current knowledge to future generations so that they can take the actions and be free to make decisions concerning these issues. Views were expressed that many problems may be unrealistic, for example, the 'walk away' objective is a difficult engineering challenge and one that often creates paradoxical situations, particularly with respect to the investment of large resources for small relative benefit. Answers lie in adopting technical solutions for uranium mill tailings management, but the importance of near-term institutional controls must still be borne in mind. An extensive discussion also took place concerning the time scale that is important when trying to maintain control, and whether or not some of the ideas can be considered as really feasible.

Page 720: Management of Wastes from Uranium Mining and
Page 721: Management of Wastes from Uranium Mining and

CLOSING REMARKS

R.A. SCARANO United States Regulatory Commission, Washington, DC, United States of America

It is an honour and a privilege to provide the Closing Remarks for this conference. I am particularly pleased to be the closing speaker at this conference and not at the first international conference on mill tailings held here four years ago.

The atmosphere at the 1978 meeting was very intense. Those of us who were responsible for national radiation protection programmes were being taken to task for allowing, what was perceived then, an extremely hazardous industry to run wild. Those of us who were the technical experts within the national agencies or laboratories were being asked to define the hazards and propose solutions on an immediate time basis. Those of us who issued interim tailings management objectives while the issues were being studied in a more organized manner were being questioned quite vehemently by the industry as to the appropriateness of interim objectives. And last, but not least, the industry felt it was being pulled apart by the public and regulators alike.

Well, the atmosphere has changed. The passion, for the most part, has gone. What seems to prevail at this conference is an atmosphere of reasoned under­standing of the hazards presented by uranium mill tailings and a thorough, open minded discussion of various methods to mitigate the hazards. I have also perceived this change in atmosphere or attitude in numerous meetings with governmental and public groups over the last year or so. I attribute this change in attitude to the large number of competent technical studies related to tailings performed since 1978. Some of these studies have been presented at this conference; they have defined the hazards associated with tailings and have provided perspective to allow the public to weigh the significance of the hazards as well as to develop viable control techniques to minimize the hazards.

With the understanding of a problem comes the ability and confidence to take a reasoned approach to the resolution of the problem. I believe that is the point we have reached at this meeting.

The debate we are having regarding a radon standard I find to be very healthy and an example of the opportunity we now have to take a reasoned technical approach to standard setting. Four years ago this debate could not have taken place. Any of us who would have taken a less conservative stance than we took at that time would have been deemed 'suspect' by the sceptical public. Now that we understand the subject better we realize that there is

Page 722: Management of Wastes from Uranium Mining and

room for debate within the international community relative to the numerical value of a radon standard or even if a radon standard is needed. I should like to interject a word of warning however. We should be careful not to overreact to the opportunity to reassess proposed standards. If we hastily settle on less conservative standards for economic, philosophical, or other reasons, and those standards are not supported by a firm technical basis, I am afraid that the public trust we have acquired over the last few years will erode and we will revisit this issue again in four years in another atmosphere of tension and overreaction.

Notwithstanding this word of caution I should like to return to the positive aspects of the conference and highlight a few of what may be considered the very significant results.

The papers presented at this conference demonstrate a more refined under­standing of the hazards presented by uranium tailings and the development of reasonable, technically sound control measures to minimize the hazards.

We have progressed this far because there seems to be general agreement on a number of primary objectives to be met by an acceptable tailings management programme. The first of these objectives that have been generally accepted is that 'groundwater should be protected'. Methods utilized to accomplish this objective, as we have seen during this symposium, vary greatly depending on climate and ore types. In the United States of America, impermeable liners are utilized to prevent seepage from the impoundment to the groundwater table. In Canada, a very innovative scheme to utilize a highly permeable liner is being considered to channel groundwater around the impoundment. Evidence of other advances in technology that have been discussed throughout the course of this symposium which would facilitate the accomplishment of ground and surface water protection relates to areas such as: groundwater contaminant transport modelling; investiga­tion of various types of natural and synthetic liners; consideration of in-situ and process dewatering techniques; and consideration of specific constituents in ore bodies, such as pyrite.

Another objective that seems to have been generally accepted is that 'siting and reclamation design should be such that containment can be assured for a long time frame'. The length of time differs among countries but, for the most part, it seems that internationally we are agreeing on at least hundreds if not thousands of years.

In an effort to develop methods to achieve this objective, siting features such as geology, surface water and groundwater hydrology, and geomorphologic influences are being considered in developing tailings management programmes, as demonstrated by numerous papers presented in the symposium.

We also heard papers on how appropriate engineering techniques can be applied to the design of a tailings management system, taking into consideration site specific features. The practical application of these techniques has resulted in tailings containment schemes ranging from disposal in mined out pits to deep lake disposal.

Page 723: Management of Wastes from Uranium Mining and

The third objective on which we appear to have reached general agreement is that 'tailings should be reclaimed such that continuous active care is minimized'. It is recognized, however, by the countries agreeing with the 'walk away' objective that it is prudent to utilize some institutional controls as an added measure of assurance. Institutional controls such as routine surveillance, monitoring and land use controls are under consideration. Our colleagues from France, though not subscribing to a 'walk away' disposal, are looking into the possibility of turning disposal sites into useful areas such as national parks. This concept will offer a challenge to social scientists with respect to public acceptance. Assuming this concept is accepted, there will be a continuing expenditure of public funds for upkeep of the area; however, public benefit through use of the area may make such expenditures cost effective.

As discussed in numerous papers, research has been underway related to final tailings stabilization covers such as vegetation and rock layers which are intended to contribute to the walk-away, no maintenance objective.

In the next few years we can look forward to a better data base in the areas of long-term stabilization, groundwater protection and environmental monitoring. As noted in several papers presented here, there is comprehensive research being conducted in these areas. There will also be, I hope, the establishment of national mill tailings standards in numerous uranium producing countries. In this regard I would encourage you to use whatever influence you may have to motivate your respective countries to issue standards. There now exists a sufficient body of knowledge to establish standards, it just takes a little boldness to get out on that limb and make decisions. We will never reach a point where we know everything there is to know about mill tailings and therefore be able to develop perfect standards. As we get smarter, standards can and should be modified. Do not, however, put off issuing the initial set of standards too long.

As most of you know, the USNRC was one of the first, if not the first, governmental organization to establish tailings management objectives and require the industry to develop programmes which addressed these objectives. Formal regulations were issued soon after. As the forerunner in this area, we became a very good target for criticism. We did not expect to write perfect regulations; some modifications may be needed. This is not surprising. I can tell you without any reservation that if we at the NRC had to do it all over again, we would respond in the same manner; that is, by issuing requirements quickly utilizing the best body of knowledge available at the time. However, we would do this recognizing that somewhere down the path, modification would be necessary either for purposes of clarification or other revision as later determined to be appropriate. I would encourage you to do the same.

As noted during the panel session this morning, the reports of the joint NEA/IAEA working groups on mill tailings will be available in the near future. These reports promise to be a comprehensive compilation of the body of knowledge available related to mill tailings.

Page 724: Management of Wastes from Uranium Mining and

In the next several years we can also look forward to the reclamation of several tailings sites. So far we all have been talking about stabilization concepts. It should be very interesting to see the results of real experience in stabilization of mill tailings.

Based on the proceedings of this conference and the invaluable informal discussions we have had during this week, I believe we can express the current status of the uranium mill tailings issue in the following way. Through extensive studies, experience and debate conducted over the last several years, the international scientific community has gained an understanding of the potential hazards related to uranium mill tailings and is confident that viable control mechanisms can be developed and implemented that would assure public health and safety and the protection of the environment.

Mr. Chairman I am sure that my colleagues in the audience join me in commending the OECD and IAEA and particularly Mssrs Thomas and Rafferty in co-ordinating the efforts of the international scientific community in addressing and moving well toward the resolution of the hazards related to disposal of uranium mill tailings.

Page 725: Management of Wastes from Uranium Mining and

CHAIRMEN OF SESSIONS

Session I

Session II

Session III

Session IV

Session V

Session V I

Session VI I

R.W. RAMSEY, Jr.

R.V. OSBORNE R.M. F R Y

R.M. FRY J. PRADEL

J. PRADEL H.I. LINDHOLM

D.H. GROELSEMA

J. SCHMITZ

J. FITCH J. HOWIESON

United States of America

Canada Australia

Australia France

France Sweden

United States of America

Federal Republic of Germany

Australia Canada

Session VI I I R.W. RAMSEY, Jr. United States of America

SECRETARIAT OF THE SYMPOSIUM

Scientific K.T. THOMAS Division of Nuclear Secretaries: Fuel Cycle, IAEA

P. RAFFERTY Division of Radiation Protection and Waste Management OECD/NEA

Page 726: Management of Wastes from Uranium Mining and

M. McCLARY

H.L. RARRICK

G. SEILER

B. KAUFMANN

United States Department of Energy,

Washington, DC

Sandia National Laboratories,

Albuquerque, New Mexico

Division of External Relations, IAEA

Division of Publications, IAEA

Page 727: Management of Wastes from Uranium Mining and

LIST OF PARTICIPANTS

AUSTRAL IA

Fell, R.

Fitch, Jill

Folwell, K.

Fry, R.M.

Pidgeon, R.T.

Ring, R.J.

Sorentino, CM.

Coffey & Partners Pty Ltd, Consulting Engineers, 12 Waterloo Road, North Ryde, NSW 2113

South Australian Health Commission, P.O. Box 1313, GPO, Adelaide, South Australia 5001

Minatome Australia Pty Ltd , 61 Macquarie Street, Sydney 2000

Office of the Supervising Scientist, P.O. Box 387, Bondi Junction, NSW 2022

School of Physics and Geosciences, Department of Geology & Geophysics, Western Australian Institute of Technology, Hayman Road, South Bentley, Western Australia 6102

Australian Atomic Energy Commission Research Establishment,

Lucas Heights Research Laboratories, Private Mail Bag, Sutherland, NSW 2232

Denison Australia P.L., P.O. Box 1334, North Sydney, NSW 2060

BRAZIL

Novais Santiago, T. National Nuclear Energy Commission, Rua General Severiano, 90, Botafogo, 22294 Rio de Janeiro, RJ

Page 728: Management of Wastes from Uranium Mining and

CANADA

Averill, D.W. Environmental Protection Service, Environment Canada, Wastewater Technology Centre, Canada Centre for Inland Waters, P.O. Box 5050, Burlington, Ontario, L7R 4A6

Boyd, J.M. Golder Associates, 3151 Wharton Way, Mississauga, Ontario, L4X 2B6

Bragg, K. Atomic Energy Control Board, 270 Albert Street, P.O. Box 1046, Ottawa, Ontario, KIP 5S9

Caza, C. Institute for Environmental Studies, Haultain Building, University of Toronto, Toronto, Ontario, M5S 1A4

Chakravatti, J.L. Denison Mines Limited, P.O. Box B-2600, Elliot Lake, Ontario, P5A 2K2

Chart, E.J. MacLaren Engineers, Inc., 1220 Sheppard Avenue East, Willowdale, Ontario

Coady, J. Atomic Energy Control Board, 270 Albert Street, P.O. Box 1046, Ottawa, Ontario, KIP 5S9

Dave, N.K. Canada Centre for Mineral and Energy Technology,

Dept of Energy, Mines and Resources Canada, P.O. Box 100, Elliot Lake, Ontario, P5A 2J6

Gorber, D.M. SENES Consultants Limited, 499 McNicoll Avenue, Willowdale, Ontario, M2H 2C9

Halbert, B.E. SENES Consultants Limited, 499 McNicoll Avenue, Willowdale, Ontario, M2H 2C9

Page 729: Management of Wastes from Uranium Mining and

Haw, V.A. Canada Centre for Mineral and Energy Technology,

Dept of Energy, Mines and Resources Canada, 555 Booth Street, Ottawa, Ontario, K1A 0G1

Howieson, J. Dept of Energy, Mines and Resources Canada, 580 Booth Street, Ottawa, Ontario, K l A 0E4

Hynes, T.P. Amok Ltd/Cluff Mining, P.O. Box 9204, Saskatoon, Saskatchewan S7K 3X5

Kalin, M. Institute for Environmental Studies, Haultain Building, University of Toronto, Toronto, Ontario, M5S 1A4

Lahaye, G.J. Ontario Ministry of Environment, 455 Albert Street East, Sault Ste. Marie, Ontario, P6A 5JA

Lush, D.L. Beak Consultants Limited, 6870 Goreway Drive, Mississauga, Ontario, L4V 1L9

Marsden, D. Occupational Health and Safety Division, Special Studies and Services Branch, 400 University Avenue, Toronto, Ontario

Moffett, D. Eldorado Nuclear Limited, 255 Albert Street, Suite 400, Ottawa, Ontario, K IP 6A9

Ogilvie, K.B. Environmental Protection Service, Ontario Region, 25 St Clair Avenue East, Toronto, Ontario, M4T 1M2

Osborne, R.V. Atomic Energy of Canada Limited Research Company,

Chalk River Nuclear Laboratories, Health Sciences Division, Chalk River, Ontario, K0J 1J0

Page 730: Management of Wastes from Uranium Mining and

Snodgrass, W.J.

Vasudev, P.

Woods, R.J.

University of Toronto, Department of Chemical Engineering and

Applied Chemistry, Toronto, Ontario, M5S 1A4

Saskatchewan Department of the Environment, Mines Pollution Control Branch, 800 Central Avenue, P.O. Box 3003, Prince Albert, Saskatchewan, S6V 4V1

Mining Environmental Consultant, 274 Riverside Drive, Oakville, Ontario, L6K 3N4

University of Regina, Dept of Physics and Astronomy, Regina, Saskatchewan, S4S 0A2

Canada Centre for Mineral and Energy Technology,

Dept of Energy, Mines and Resources Canada, 555 Booth Street, Ottawa, Ontario, K1A 0G1

The Johns Hopkins University, Dept of Geography and Environmental

Engineering, Ames Hall, Homewood Campus, Baltimore, Maryland, 21218, USA

Environment Canada, Environmental Protection Service, Place Vincent Massey, Ottawa, Ontario, K1A 1C8

University of Saskatchewan, Dept Chemistry & Chemical Engineering, Saskatoon, Saskatchewan, S7N 0W0

DENMARK

Pilegaard, K. Risd National Laboratory, Postbox 49, DK-4000 Roskilde

CANADA (cont.)

Phillips, C.R.

Potter, C.

Pullen, P.F.

Robertson, B.E.

Skeaff, J.M.

Page 731: Management of Wastes from Uranium Mining and

FINLAND

Eerola, P.I. Outokumpu Oy, Mining Technology Group, SF-83500 Outokumpu

FRANCE

Andrieux, C.

Angel, M.

Bautin, F.

Blum, J.

Bordes-Pages, H.

Boulicault, M.

Chameaud, G.J.

Chapot, G.

Cohen, P.

CEA, CEN Saclay, Service de Protection contre les rayonnements, B.P. 2, F-91191 Gif-sur-Yvette Cedex

Minatome, 69-73, rue Dutot, F-75738 Paris Cedex 15

Societe des Mines de 1'Air "Somair", B.P. 303, Arlit, Republique du Niger

Soci6te Uranium Pechiney Ugine Kuhlmann, 6, avenue Bertie Albrecht, F-75008 Paris

Commissariat a Tenergie atomique, B.P. 510, F-75752 Paris Cedex 15

Ministere de l'industrie, Direction de la qualite et de la securite

industrielles, 99, rue de Grenelle, F-75007 Paris

Cogema,

B.P. l,F-87640 Razes

Cogema,

2, rue Paul Dantier, B.P. 4, F-78141 Velizy Villacoublay S.I.S.A., 9, rue Fernand Leger, F-91190 Gif-sur-Yvette

Page 732: Management of Wastes from Uranium Mining and

F R A N C E (cont.)

Descamps, B. CEA, CEN Cadarache, DPr/SERE, B.P. 1, F-13115 St-Paul-lez-Durance

Duchamp, C.G. Compagnie miniere Dong-Trieu, B.P. 1, F-87360 Lussac-les-Eglises

Fourcade, N. CEA, CEN Fontenay-aux-Roses, Service de protection technique, IPSN/DPr/STEP, B.P. 6, F-92260 Fontenay-aux-Roses

Grisez, F. Cominak, B.P. 114, F-78153 Le Chesnay Cedex

Halna du Fret ay, O. S.I.M.O., Usine de l'Ecarpiere, B.P. 36, F-44190 Getigne

Hugon, J. CEA, CEN Cadarache, B.P. 1, F-13115 St-Paul-lez-Durance

Lavie, J.-M. Commissariat a l'energie atomique, Agence nationale pour la gestion des

dechets radioactifs (ANDRA), B.P. 510, F-75752 Paris Cedex

Lesty, S. Compagnie Francaise de Mokta, Tour Maine Montparnasse, 33,avenue du Maine, F-75755 Paris Cedex 15

Pradel, J. (see also under ENS)

CEA, CEN Fontenay-aux-Roses, Services de protection techniques, IPSN/DPr/STEP, B.P. 6, F-92260 Fontenay-aux-Roses

Zettwoog, P. CEA, CEN Fontenay-aux-Roses, Service de protection technique, IPSN/DPr/STEP, B.P. 6, F-92260 Fontenay-aux-Roses

Page 733: Management of Wastes from Uranium Mining and

GERMANY, FEDERAL REPUBLIC OF

Gehnes, P.

Landsiedel, K.

Rosenkranz, R.

Schmitz, J.

Bundesanstalt fur Geowissenschaften und Rohstoffe (BGR),

Postfach 510153, D-3000 Hannover 51

Uranerzbergbau GmbH, Kolnstrasse 367, D-5300 Bonn 1

Saarberg-Interplan Uran GmbH, P.O. Box 73, D-6600 Saarbriicken

Kernforschungszentrum Karlsruhe GmbH, Hauptabteilung Sicherheit, Postfach 3640, D-7500 Karlsruhe

HUNGARY

Csovari, M. Mecsek Ore Mining Enterprise, Research Institute, 39-es Dandar ut 19, H-7633 Pecs

INDIA

Kharbanda, J.L.

Raghavayya, M.

Bhabha Atomic Research Centre, Waste Management Division, Trombay, Bombay 400085

Health Physics Unit (BARC), P.O. Jaduguda Mines, Singhbhum, Bihar 832102

IRAQ

Murad, M. State Enterprise for Phosphate, Alkaim

ISRAEL

Levin, I. Nuclear Research Center Negev, P.O. Box 9001, Beer Sheva

Page 734: Management of Wastes from Uranium Mining and

Rossing Uranium Ltd, Private Bag 5005, Swakopmund, 9000 South West Africa/Namibia

Chamber of Mines, Research Organization, P.O. Box 809, Johannesburg 2000

Rossing Uranium Ltd, P.O. Box 22391, Windhoek, South West Africa

Junta de Energia Nuclear, Avenida Complutense, 22, Madrid-3

Fabrica de Uranio "General Hernandez Vidal' Apartado 93, Andujar (Jaen)

SWEDEN

Eurenius, J. VBB/SWECO, P.O. Box 5038, S-10241 Stockholm

Lindholm, I. Swedish Nuclear Fuel Supply Co. P.O. Box 5864, S-102 48 Stockholm

Sodermark, B. Swedish Environmental Protection Board, P.O. Box 1302, S-17125 Solna

UNITED STATES OF AMERICA

Ausmus, B.

Baggett, D.

Bechtel National, Inc., P.O. Box 350, Oak Ridge, TN 37830

Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Jooste, A.W.J.

Lloyd, P.J.

Vernon, P.N.

SPAIN

Gasos, P.

Perarnau, M.

Page 735: Management of Wastes from Uranium Mining and

Baker, C.E. Energy Fuels Nuclear, Inc., Three Park Central, Suite 900, 1515 Arapahoe Street, Denver, CO 80202

Ball, D.M. Department of Energy, UMTRA Project Office, P.O. Box 5400, Albuquerque, NM 87115

Barber, W. Jacobs Eng., 3601 Central N.E., Albuquerque, NM 87110

Bickmore, R. Controls for Environmental Pollution, Inc., P.O. Box 5351, Santa Fe, NM 87502

Bingham, F. Sandia National Laboratories, Albuquerque, NM 87185

Blanchfield, D.M.

Borak, T.B.

U.S. Department of Energy, P.O. Box 2567, Grand Junction, CO 81501

Colorado State University, Department of Radiology & Radiation Biology, Colorado State University, Fort Collins, CO 80523

Boyden, T.A. NUEXCO, 3000 Sand Hill Road, Menlo Park, CA 94025

Bramlitt, E.T. Field Command, Defense Nuclear Agency, Kirtland, NM 87115

Brandvold, G.E. Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Breese, K. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Brewer, L.W. Sandia National Laboratories, Dept 3310, P.O. Box 5800, Albuquerque, NM 87185

Page 736: Management of Wastes from Uranium Mining and

Brough, T.G. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Brown, C.A. Bechtel National, Inc., P.O. Box 350, Oak Ridge, TN 37830

Campbell, R.H. Uranium Mill Tailings Remedial Actions Project Office (UMTRA/PO),

U.S. Department of Energy, Albuquerque Operations Office, P.O. Box 5400, Albuquerque, NM 87115

Christiansen, T. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Cokal, E.J. Environmental Science Group, Los Alamos National Laboratory, P.O. Box 1663, MS-K495, Los Alamos, NM 87545

Coobs, J.H. Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37830

Dayal, R. Brookhaven National Laboratory, Department of Nuclear Energy, Upton, NY 11973

Dieckhoner, J. U.S. Department of Energy, Washington, DC 20545

Dinges, R. Texas Department of Health, Bureau of Radiation Control, Division of Environmental Programs, 1100 W. 49th Street, Austin, TX 78756

Dreesen, D.R. Environment Science Group, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545

Page 737: Management of Wastes from Uranium Mining and

Ellett.D.M. Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Ennis, M.E., Jr. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Ensminger, J.T. Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37830

Fisher, C.J. Fisher, Harden & Fisher, 2904 Leopard Street, Corpus Christi, TX 78408

Flot, S.L. Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

Gardner, F. Chem-Nuclear Systems, P.O. Box 1866, Bellevue, WA 98009

Gee, G.W. Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352

Gingrich, J.E.

Gisler.W.D.

Terradex Corporation, 460 N. Wiget Lane, Walnut Creek, CA 94598

Bendix Field Eng. Corp., P.O. Box 1569, Grand Junction, CO 81501

Goldsmith, W.A. Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37830

Gonzalez, D.D. Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Groelsema, D.H. U.S. Department of Energy, Washington, DC 20545

Page 738: Management of Wastes from Uranium Mining and

Hamill, K.

Hansen, M.V.

EDA Instruments, Inc., 5151 Ward Road, Wheat Ridge, CO 80033

U.S. Nuclear Regulatory Commission, Washington, DC 20555

U.S. Department of Energy, P.O. Box 2567, Grand Junction, CO 81502

Harmon, K.M.

Hartley, J.N.

Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352

Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352

Hazle, A.J.

Heggen, R.J.

Colorado Department of Health, 4210 East 11th Avenue, Denver, CO 80220

Department of Civil Engineering, University of New Mexico, Albuquerque, NM 87131

Henderson, J.T.

Hill, T.M.

Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

United Nuclear Corporation, Mining and Milling Division, 113 Sixth Street NW, Albuquerque, NM 87102

Hinton, T.G.

Hunter, D.

Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

USAF Hospital Kirtland, SGPER, Kirtland AFB, NM 87117

Ibrahim, S.A. Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

Grover, S.

Page 739: Management of Wastes from Uranium Mining and

Ikenberry, T. Department Radiology and Radiation Biology, Colorado State University, Fort Collins, CO 80523

Kaye, G.E. Sandia National Laboratories, Albuquerque, NM 87185

Kisieleski, W.E. Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439

Krishnan, R. Jacobs Engineering, 251 S. Lake Avenue, Pasadena, CA 91101

Landa, E.R. U.S. Geological Survey, Water Resources Division, P.O. Box 25046 - Mail Stop 424, Denver, CO 80225

Landauer, C. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Lewis, D. Jacobs Engineering, 3601 Central N.E., Albuquerque, NM 87110

MacDonald, R.R. Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439

Marcus, D. Gulf Research and Development Company, P.O. Drawer 2038, Pittsburgh, PA 15230

Markos, G. Geochemistry and Environmental Chemistry Research, Inc.,

2693 Commerce Road, Rapid City, SD 57701

Marple, M.L. Texas Department of Health, Bureau of Radiation Control, 1100 West 49th Street, Austin, TX 78756

Page 740: Management of Wastes from Uranium Mining and

it.)

Uranium Mill Tailings Remedial Actions Project Office (UMTRA/PO),

U.S. Department of Energy, Albuquerque Operations Office, P.O. Box 5400, Albuquerque, NM 87115

Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Sandia National Laboratories, Div. 4733, P.O. Box 5800, Albuquerque, NM 87185

Roy F. Weston, Inc., Weston Way, Westchester, PA 19380

Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Sandia National Laboratories, Div. 3312, P.O. Box 5800, Albuquerque, NM 87185

Davy McKee Corporation, 2700 Campus Drive, San Mateo, CA 94403

Controls for Environmental Pollution, Inc., P.O. Box 5351, Santa Fe, NM 87502

Sandia National Laboratories, Organization 4413, P.O. Box 5800, Albuquerque, NM 87185

Rogers and Associates Engineering Corporation, P.O. Box 330, Salt Lake City, UT 84110

Matthews, M.L.

McKiernan, J.

Merritt, M.L.

Metry, A.

Millard, J.B.

Miller, A., Jr.

Minnema, D.M.

Morgan, P.V.

Mueller, J.I.

Muller, A.B.

Nielson, K.K.

Page 741: Management of Wastes from Uranium Mining and

Oakley, D.T. Los Alamos National Laboratory, P.O. Box 1663, MS F671, Los Alamos, NM 87544

O'Brien, P.D. Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Oswald, R.A. Terradex Corporation, 460 N. Wiget Lane, Walnut Creek, CA 94598

Owen, P.T. Oak Ridge National Laboratory, P.O. Box X, Building 2001, Oak Ridge, TN 37830

Phoenix, D.R. Roy F. Weston, 3601 Central Avenue, N.E., Albuquerque, NM 87110

Pillay, K.K.S. Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545

Preusse, M.J. Texas Department of Health, Bureau of Radiation Control, 1100 West 49th Street, Austin, TX 78756

Price, W.C. Texas Department of Health, 1100 West 49th Street, Austin, TX 78756

Ramsey, R.W. U.S. Department of Energy, Washington, DC 20545

Rarrick, H.L. Sandia National Laboratories, Div. 4772, P.O. Box 5800, Albuquerque, NM 87185

Relyea, J.R. Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352

Riddle, L. Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Page 742: Management of Wastes from Uranium Mining and

Rogers, V.C. Rogers and Associates Engineering Corporation, P.O. Box 330, Salt Lake City, UT 84110

Savignac, N.F. Noel Savignac, Inc., 130 Louisiana N.E., Albuquerque, NM 87108

Scarano, R.A. U.S. Nuclear Regulatory Commission, Washington, DC 20555

Schumm, S.A. Colorado State University, Department of Earth Resources, Fort Collins, CO 80523

Schwendiman, L.C. Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352

Sejkora, K.J. Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

Simpson, S. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Skinner, D.J. Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

Smith, W.J. Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

Snell, W.D. Texas Department of Health, Bureau of Radiation Control, 1100 West 49th Street, Austin, TX 78756

Roberts, C.J. Argonne National Laboratory, Division of Environmental Impact Studies, 9700 S. Cass Avenue, Argonne, IL 60439

Page 743: Management of Wastes from Uranium Mining and

Staub, W.P. Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37830

Stewart, G. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Stewart, L. U.S. Department of Energy, Washington, DC 20585

Thiel, J.F. Texas Department of Health, Bureau of Radiation Control, 1100 West 49th Street, Austin, TX 78756

Thode, E.F.

Thomson, B.M.

Tierney, M.

Department of Management, New Mexico State University, P.O.Box 3DJ, Las Cruces, NM 88003

Department of Civil Engineering, University of New Mexico, Albuquerque, NM 87131

Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Topp, A. Radiation Protection Bureau, Environment Improvement Division, P.O. Box 968, Santa Fe, NM 87504

Torma, A.E. New Mexico Institute of Mining and Technology, Socorro, NM 87801

Volpe, R.L. R.L. Volpe & Associates, 110 Atwood Ct., Los Gatos, CA 95030

Waligora, S.J., Jr. Eberline, 3807 Academy Parkway, Albuquerque, NM 87109

Walker, E. Bechtel National, Inc., P.O. Box 350, Oak Ridge, TN 37830

Page 744: Management of Wastes from Uranium Mining and

Wangen, L.E.

Weart, W.D.

Whicker, F.W.

Williams, J.M.

Williams, R.

Winsor, G.

Wogman, N.

Wolff, T.A.

Yates, W.G.

Zimmermann, L.

Environmental Science Group, Los Alamos National Laboratory, P.O. Box 1663, MS-G734, Los Alamos, NM 87545

Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Colorado State University, Department of Radiology and Radiation Biology, Fort Collins, CO 80523

Environmental Science Group, Los Alamos National Laboratory, P.O. Box 1663, LS6, MS-K495, Los Alamos, NM 87545

Uranium Mill Licensing Branch, 7915 Eastern Avenue, Silver Spring, MD 20910

UNC Nuclear Industries, 2900 George Washington, Richland, WA 99352

Battelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352

Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185

Mound Facility, Monsanto Research Corporation, P.O. Box 32, Miamisburg, OH 45342

Bendix Field Engineering Corporation, P.O. Box 1569, Grand Junction, CO 81502

ZAMBIA

Chitumbo, K. Radioisotopes Research Unit, National Council for Scientific Research, P.O. Box CH 158, Lusaka

Page 745: Management of Wastes from Uranium Mining and

ORGANIZATIONS

EUROPEAN NUCLEAR SOCIETY (ENS)

Pradel, J. CEA, CEN Fontenay-aux-Roses, (see also under France) B.P. 6,

F-92260 Fontenay-aux-Roses, France

NUCLEAR ENERGY AGENCY OF THE OECD

Olivier, J.-P. 38, boulevard Suchet, F-75016 Paris, France

Page 746: Management of Wastes from Uranium Mining and
Page 747: Management of Wastes from Uranium Mining and

AUTHOR INDEX

Alter, H.W.: 589 Averill, D.W.: 353 Balu, K.: 325 Barnes, E.: 127,353 Baudin-Jaulent, Y.: 523 Beedlow, P.A.: 429 Boyd, J.M.: 141 Bragg, K.: 85 Brewer, L.W.: 633 Buelt, J.L.: 429 Bush, K.J.: 231 Capobianco, J.: 285 Caries, J .C: 535 Carter, T.G.: 141 Cartier, Y.: 523 Caza, C : 385

Chakravatti, J.L.: 127,157,417 Cherry, J.A.: 215 Clemente, G.F.: 553 Cline.J.F.: 429 Coffman, F.E.: 3 Cokal, E.J.: 311 Costa, J.E.: 111 Culver, K.B.: 141, 157 Dall 'Aglio.M.: 553 Dave, N.K.: 215 Davis, J.B.: 157 Delmas, J.: 535 Descamps, B.: 523 Dreesen, D.R.: 311 Dubrovsky, N.: 215 Eapen, K.P.: 541 Eurenius, J.: 679 Flot, S.L.: 339 Foulquier, L.: 523

Fourcade, N.: 169 Franz, G.A.: 693 Freeman, H.D.: 429 Fry, R.M.: 41, 71 Gamewell, R.: 693 Gee, F.J.: 247 Gee, G.W.: 429 Gillham, R.W.: 215 Gingrich, J.E.: 589 Goldsmith, W.A.: 573 Gorber, D.M.: 157 Gragnani, R.: 553 Grant, M.W.: 197 Groelsema, D.H.: 9 Halbert, B.E.: 127 Hamel, P.: 21 Hamill, K.: 103 Hartley, J.N.: 429 Haw,V.A. : 663 Hazle, A.J.: 693 Heggen, R.J.: 373 Howieson, J.: 21 Hugon, J.: 535 Ibrahim, S.A.: 339 James, A.: 85 Jongejan, A.: 645 Kalin,M.: 385 Kharbanda, J.L.: 325 Kisieleski, W.E.: 609 Knapp, R.A.: 141, 157 Knox,J .C: 111 LaRocque, E.: 417 Levins, D.M.: 247 Lim, T.P.: 215 Lush, D.L.: 285,483

Page 748: Management of Wastes from Uranium Mining and

MacDonald, R.R.: 609 Marcus, D.: 449 Markos, G.: 231 Markose, P.M.: 541 Mastino, G.G.: 553 Matthews, M.L.: 403 Mauch, M.L.: 197 McKee, P.: 483 Merrell, G.B.: 197 Minnema, D.M.: 633 Moffett, D.: 353 Morin, K.A.: 215 Morison, I.W.: 41 Nielson, K.K.: 197 O'Brien, P.D.: 311 Osborne, R.V.: 471 Osihn, A.: 679 Oswald, R.A.: 589 Panicker, P.K.: 325 Pidgeon, R.T.: 263 Potter, C : 85 Pradel, J.: 55 Raghavayya, M.: 541 Ramsey, R.W., Jr.: 367 Rarrick, H.L.: 633 Reades, D.W.: 417 Relyea, J.R.: 429 Rich, D.C.: 197 Ring, R.J.: 247 Ritcey, G.M.: 645 Roberts, C.J.: 505,609 Robinsky, E.I.: 417

Rogers, V.C.: 197 Sanathanan, L.P.: 609 Sandquist, G.M.: 197 Sangrey, D.A.: 449 Santaroni, G.P.: 553 Scacco, F.: 553 Scarano, R.A.: 707 Scharer, J.M.: 127 Schmidt, J.W.: 353 Schumm, S.A.: 111 Sciocchetti, G.: 553 Silver, M.: 645 Skeaff, J.M.: 645 Smith, W.J.: 621 Smyth, D.J.A.: 215 Snodgrass, W.J.: 285,483

Srivastava, G.K.: 541 Strandell, E.: 679 Tamura, T.: 429 Thode, E.F.: 311 Thomson, B.M.: 373 Toy, T.J.: 111 Venkataraman, S.: 541 Vivyurka, A.J.: 215 Wangen, L.E.: 311 Warner, R.F.: 111 Webber, R.T.: 353 Whicker, F.W.': 339, 621 Williams, J.M.: 311 Yates, W.G.: 573 Yuan, Y.C.: 505 Zettwoog, P.: 169

Page 749: Management of Wastes from Uranium Mining and

INDEX OF PAPERS BY NUMBER

Paper Symbol Page IAEA-SM-262/

1 85 2 385 3 417 4 127 5 141 7 157 9 483

10 353 12 •645 13 663 14 215 16 609 17 505 18 169 20 523 21 535 22 679 23 231 25 589 26 247 27 541 29 325 30 471

Paper Symbol Page IAEA-SM-262/

32 339 35 621 39 429 40 71 41 553 42 403 43 197 44 693 45 633 49 449 50 111 51 373 53 103 54 285 56 311 58 263 60 9 61 21 62 41 64 55 65 367 67 57.3

Page 750: Management of Wastes from Uranium Mining and

HOW TO ORDER IAEA PUBLICATIONS

•

A n exclusive sales agent for I A E A publications, to w h o m all orders

and inquiries should be addressed, has been appointed

in the fo l lowing count ry :

UNITED STATES OF AMERICA UNIPUB, P.O. Box 433, Murray Hill Station, New York, NY 10016

In the fo l lowing countries I A E A publications may be purchased f r o m the sales agents or booksellers listed or through your major local booksellers. Payment can be made in local currency or w i t h U N E S C O coupons.

ARGENTINA

AUSTRALIA BELGIUM

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ITALY

JAPAN NETHERLANDS

PAKISTAN POLAND

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SPAIN

SWEDEN

UNITED KINGDOM

U.S.S.R. YUGOSLAVIA

Comision Nacional de Energi'a Atomica, Avenida'del Libertador 8250, RA-1429 Buenos Aires Hunter Publications, 58 A Gipps Street, Collingwood, Victoria 3066 Service Courrier UNESCO, 202, Avenue du Roi, B-1060 Brussels S.N.T.L., Spalena 51 , CS-113 02 Prague 1 Alfa, Publishers, Hurbanovo namestie 6, CS-893 31 Bratislava Office International de Documentation et Librairie, 48, rue Gay-Lussac, F-75240 Paris Cedex 05 Kultura, Hungarian Foreign Trading Company P.O. Box 149, H-1389 Budapest 62 Oxford Book and Stationery Co., 17, Park Street, Calcutta-700 016 Oxford Book and Stationery Co., Scindia House, New Delhi-110 001 Heiliger and Co., Ltd., Scientific and Medical Books, 3, Nathan Strauss Street, Jerusalem 94227 Libreria Scientifica, Dott. Lucio de Biasio "aeiou", Via Meravigli 16, 1-20123 Milan Maruzen Company, Ltd., P.O. Box 5050, 100-31 Tokyo International Martinus Nijhoff B.V., Booksellers, Lange Voorhout 9-11, P.O. Box 269, NL-2501 The Hague Mirza Book Agency, 65, Shahrah Quaid-e-Azam, P.O. Box 729, Lahore 3 Ars Polona-Ruch, Centrala Handlu Zagranicznego, Krakowskie Przedmiescie 7, PL-00-068 Warsaw llexim, P.O. Box 136-137, Bucarest Van Schaik's Bookstore (Pty) Ltd., Libri Building, Church Street, P.O. Box 724, Pretoria 0001 Diaz de Santos, Lagasca 95, Madrid-6 Diaz de Santos, Balmes 417, Barcelona-6 AB C.E. Fritzes Kungl. Hovbokhandel, Fredsgatan 2, P.O. Box 16356, S-103 27 Stockholm Her Majesty's Stationery Office, Agency Section PDIB, P.O.Box 569, London SE1 9NH Mezhdunarodnaya Kniga, Smolenskaya-Sennaya 32-34, Moscow G-200 Jugoslovenska Knjiga, Terazije 27, P.O. Box 36, YU-11001 Belgrade

Orders f r o m countries where sales agents have not y e t been appointed and requests for in format ion should be addressed direct ly t o :

^ Division of Publications g Internat ional A t o m i c Energy Agency

Wagramerstrasse 5, P.O. Box 100, A-1400 V i e n n a , Austr ia

Page 751: Management of Wastes from Uranium Mining and
Page 752: Management of Wastes from Uranium Mining and

INTERNATIONAL SUBJECT GROUP: II ATOMIC ENERGY AGENCY Nuclear Safety and Environmental Protection/Waste Management VIENNA, 1982 PRICE: Austrian Schillings 1200,-


National Inventory on Hazardous and Other Wastes ...

National Inventory on Hazardous and Other Wastes ...

Design and Utilization Wastes in Construction

Design and Utilization Wastes in Construction

Uranium Mining in Africa

Uranium Mining in Africa

URANIUM DEPOSITS IN PROTEROZOIC QUARTZ-PEBBLE ...

URANIUM DEPOSITS IN PROTEROZOIC QUARTZ-PEBBLE ...

Composting of Sugar Mill Wastes: A Review

Composting of Sugar Mill Wastes: A Review

Shape of Roll-type Uranium Deposits

Shape of Roll-type Uranium Deposits

Conversion of leather wastes to useful products

Conversion of leather wastes to useful products

Batan Tek mengembangkan uranium - Badan Pengawas ...

Batan Tek mengembangkan uranium - Badan Pengawas ...

Calculation of electron-positron production in supercritical uranium-uranium collisions near the Coulomb barrier

Calculation of electron-positron production in supercritical uranium-uranium collisions near the Coulomb barrier

Uranium tailings sampling manual

Uranium tailings sampling manual

MINING PLA

MINING PLA

Mining DP1314

Mining DP1314

Dasa Uranium Project

Dasa Uranium Project

URANIUM FISSION CAUSES SUNLIGHT

URANIUM FISSION CAUSES SUNLIGHT

Uranium accumulation by aquatic plants from uranium-contaminated water in Central Portugal

Uranium accumulation by aquatic plants from uranium-contaminated water in Central Portugal

uranium deposit development, exploration, resources

uranium deposit development, exploration, resources

Uranium and Potentially Toxic Metals During the Mining, Beneficiation, and Processing of Phosphorite and their Effects on Ground Water in Jordan

Uranium and Potentially Toxic Metals During the Mining, Beneficiation, and Processing of Phosphorite and their Effects on Ground Water in Jordan

Metal bioaccumulation, genotoxicity and gene expression in the European wood mouse (Apodemus sylvaticus) inhabiting an abandoned uranium mining area

Metal bioaccumulation, genotoxicity and gene expression in the European wood mouse (Apodemus sylvaticus) inhabiting an abandoned uranium mining area

Management ^ ^ of Gaseous Wastes from Nuclear Facilities

Management ^ ^ of Gaseous Wastes from Nuclear Facilities

Elemental analysis of mining wastes by energy dispersive X-ray fluorescence (EDXRF

Elemental analysis of mining wastes by energy dispersive X-ray fluorescence (EDXRF