UNFTED STATES ENVIRONMENTAL PROTECTION AGENCYREGION III

841 Chestnut BuildingPhiladelphia, Pennsylvania 19107

SUBJECT: New Castle Spill SuperfundConstruction Completion

06- gf\FROM: Thomas C. Voltaggio, Dire or "" ^ H—)!

Hazardous Waste Management Division if/

TO: Edwin B. EricksonRegional Administrator

We have prepared the attached Interim Closeout Report forthe New Castle Spill Superfund site. The limited action remedyselected in the September 27, 1989, Record of Decision for thissite called for monitoring to ensure that natural attenuation ofthe contaminant of concern ( 2-chloropropyl-phosphate or "tris")would continue as observed in the remedial investigation.

We have recently determined that no additional monitoringwells, beyond those used during the remedial investigation willbe required for implementation of the remedy. Since noadditional construction activity will be required, we are nowable to get credit for construction completion.

I recommend that you sign the attached Interim CloseoutReport for the New Castle Spill Site.

INTERIM CLOSEOUT REPORTNEW CASTLE SPILL SUPERFUND SITE

NEW CASTLE, DELAWARE

*• Summary of Site Conditions

Background

The New Castle Spill Site is located approximately 0.5 milenorth of the City of New Castle and 0.5 mile west of the DelawareRiver. The site covers approximately six acres in area andconsists of the former Witco Corporation manufacturing plantproperty; the New Castle Board of Water and Light (NCBWL)property; and an adjacent marsh area west-northwest of the twoproperties (see Figure 1).

The Witco Corporation facility was formerly a manufacturingplant which utilized tris (2-chloropropyl)-phosphate (tris) inthe production of plastic foams. However, the plant is no longerin use, and access is limited by a fence around the WitcoCorporation property.

The NCBWL property was formerly used as a treatment plantfor an on-site production well of the Potomac (deep) aquifer anda shallow infiltration gallery system for the Columbia (shallow)aquifer. This system served as part of the potable water supplyfor the City of New Castle until its closure in 1978.

The marsh area consists of emergent and forested wetlandsthat support diverse flora and fauna. The marsh is drained byway of the man-made Narrow Dyke Canal. The flow of water throughthe canal is regulated by sluice gates located at the confluenceof the major drainage ditch and the Delaware River.

The site is located within the 100-year flood plain of theDelaware River. Surface water drainage from the site follows thegently sloping topography to the west-northwest and discharges tothe marsh which drains to the south via the Narrow Dyke Canal andeventually the Delaware River.

There are two aquifer systems at the site: the shallowColumbia aquifer and the deep Potomac aquifer. A thick claylayer at the top of the Potomac formation separates the twoaquifers so that they are not hydraulically connected. Theshallow Columbia aquifer discharges to freshwater non-tidalstreams and to the Delaware Bay and Atlantic Ocean. The groundwater flow from this aquifer varies from the north and southsections of the site. In the northern section of the site, theground water flows northerly at a rate of approximately 1.0ft/day; while in the southwestern section, the ground water flowswesterly at a rate of about 0.5 ft/day. The Columbia aquifer is

31006-01-06

Figure 1New Castle Spill Site Map

WETLANDS/MARSH AREA

Brick ft ConcreteBlock Building

SO 25 0 50 100a—-gaScale in Feet

E X P L A N A T I O N

--*- Chain Link Fence

<s— Fence Gate

not currently used as a potable water source in the area of thesite. The Potomac aquifer discharges primarily through pumpingfor municipal and industrial purposes. The Potomac aquifer isused as a potable water supply for New Castle County.

The area surrounding the site is a mixed commercial andresidential area. The Castle Ford garage and car dealership islocated immediately south of the NCBWL property. The nearestresidence is located approximately 250 feet west of the site onthe other side of the marsh. It is part of a residentialcommunity which receives its potable water supply from wells inthe Potomac aquifer.

Remedial Planning Activities

In the summer of 1977, personnel of the NCBWL noticed areasof dead grass on their property adjacent to the drum storage areaof the Witco facility. This was brought to the attention ofWitco Corporation, who subsequently conducted an investigationwhich determined the presence of tris in the soil in the drumstorage area. It was estimated that approximately 4-5 drums oftris had been spilled onto the ground. Additional samplingrevealed levels of contaminants including polychlorinatedbiphenyls (PCBs), trichloroethylene (TCE), andtetrachloroethylene (PCE) in the shallow infiltration galleries,and low levels of PCBs and TCE in the NCBWL's Potomac aquiferproduction well No. 11. Under the direction of the state ofDelaware Department of Natural Resources and EnvironmentalControl (DNREC), the ground water from the shallow infiltrationgallery was pumped and discharged to the adjacent marsh area.The DNREC then requested the assistance of EPA in theidentification of contaminants in the ground water. Thisinvestigation was conducted in January 1978. The NCBWL ceasedusing the shallow water gallery on January 30, 1978.

In September 1981, the EPA performed a site inspection whichresulted in a Hazard Ranking System score of 39.57 due to thepresence of tris, TCE, chloroform, PCE, and 1,2-transdichloroethylene in the ground water. The site was proposed forinclusion on the National Priorities List (NPL) on December 12,1982, and was finalized on September 3, 1983.

In December 1987, an Administrative Consent Order (AGO) wassigned by Witco Corporation and DNREC to address the performanceof the Remedial Investigation/Feasibility Study (RI/FS) and anEndangerment Assessment (EA) for the site. The purpose of the RIwas to determine the nature, extent, and magnitude of thecontamination at the site. The EA evaluated the risks to humanhealth and the environment posed by the site. The RI and EA werefinalized in May 1989.

As a result of the RI the following contaminants wereidentified. Ground water sampling in the Columbia aquiferindicated detectable and quantifiable levels of tris ranging from17.1 to 110,000 ug/1 in 7 of 17 wells; TCE ranging from 1 to 120ug/1 in 8 of 17 wells; and 1,2-dichloroethylene ranging from 5 to11 ug/1 in 2 of 17 wells. The distribution of tris wasconsistent with the spill source area, and reflected a reducedmobility by it's occurrence primarily in the upper ten feet ofthe Columbia aquifer. The highest concentration of TCE occurredin an off site well located upgradient of the spill source area.The 1,2-dichloroethylene was detected in two wells and isconsidered to be a degradation product of TCE.

Four major contaminants were detected in subsurface soils ata depth of 2-4 feet at the site. The contaminants and theirmaximum concentrations are as follows: tris at 11.8 mg/kg;fluoranthene at 3.6 mg/kg; phenanthrene at 4.4 mg/kg; andbenzo(b) fluoranthene at 2.5 mg/kg.

Two rounds of surface water/sediment sampling occurred inthe marsh wetlands during the RI. During the first round ofsampling tris was detected in surface water at levels rangingfrom 0-42 ug/1. The highest concentration was detected in thesampling location closest to the site. During the secondsampling round tris was detected in surface water from 1.2 to 5.5ug/1. TCE was not detected in the surface water nor were TCE ortris detected in the sediment during the first sampling event.In the second sampling round tris was detected in the sediment at300 and 402 ug/kg at two locations slightly away from the site.TCE was detected at 3 ug/kg at one of the sampling locationsclosest to the site. A wetlands delineation and habitatassessment identified emergent and forested wetlands supporting adiverse flora and fauna which was unaffected by the site.

Several conclusions were drawn from the RI results; l) thesource of tris contamination no longer exists at the site; 2)tris contamination exists in the Columbia aquifer; 3) there is notris contamination in the Potomac aquifer; 4) the source of TCEcontamination was not identified, but it's detection in wellsupgradient of the spill source area indicated an upgradientsource; 5) the contaminant levels in the wetlands are well belowthe Ambient Water Quality Criteria.

The EA was conducted to evaluate the risks that compoundsdetected at the site posed to human health and the environment.The EA concluded that a potential human health risk existed frompossible contact (i.e. inhalation, ingestion, and dermal contact)with contaminated ground water if used as a future potable watersource. The noncarcinogenic risk, or Hazard Index (HI) from thispossible future exposure route is 6.68 x 10+1 , which exceeds theEPA recommended value of less than one. This exceedence can becontributed solely to the presence of tris in the ground water.

The lifetime weighted carcinogenic risk for the future groundwater use scenario calculated for upper bound worst case estimatewould be 1 x 10"*, which is within the EPA acceptable range of 1x 10~4 to 1 x 10" . The carcinogenic risk is mainly due to theexistence of TCE in the ground water.

The environmental impact assessment concluded that triscontamination had no adverse impact on the environment in thevicinity of the site.

A Feasibility Study (FS) was conducted in order to evaluatepotential remedies to address the site. The remedialalternatives developed in the FS considered the results of theendangerment assessment as well as these facts established duringthe RI. The shallow Columbia ground water is contaminated withtris; however, the deeper Potomac aguifer is not. There is nointerconnection between the two aquifers in the area of the site.The source of tris contamination no longer exists at the site.The Columbia aquifer is not currently being used as a potablewater supply, but is classified as a Class IIB aquifer which is apotential source for potable water supply. In addition, TCE hasbeen identified in the shallow ground water as originating from asite upgradient of the New Castle Spill site. Finally, the sitedid not present any adverse impact to the environment. Remedieswere evaluated in the FS in order to address the potential threatto human health and the environment under potential future useconditions and to restore ground water to its beneficial use.

The FS was completed in August 1989, and the EPA RegionalAdministrator signed a Record of Decision (ROD) on September 27,1989. The major components of the selected limited action remedyinclude:

- Monitoring the Columbia aquifer on a quarterly basis fortris to ensure the effectiveness of natural attenuation

- Monitoring the Potomac aquifer on an annual basis for tristo ensure that contamination has not occurred in the Potomacaquifer

- Monitoring the surface water of the marsh wetlandsadjacent to the site on an annual basis. Resample in thenext quarter if an anomaly occurs in the results

- Further evaluation and bioassay testing if the triggervalue of 100 ug/1 tris is reached in surface water of theadjacent wetlands

- Monitoring the sediments of the wetlands adjacent to thesite on an annual basis for tris. Resample in the nextquarter if an anomaly occurs in the results

- Further evaluation and bioassay testing if the triggervalue of 1000 ug/kg tris is reached the sediments of theadjacent wetlands

-Institutional restrictions on the placement of wells inthe Columbia aquifer in the vicinity of the site

- A five-year effectiveness review to re-evaluate the site

This ground water response action protects against risks tohuman health and the environment through the use of "to beconsidered" (TBC) criteria for the ground water, surface waterand sediment. The TBC criterion for ground water of 4.4 mg/1tris is the clean up goal; it was derived due to the lack ofARARs for the tris compound. This value was derived by EPA as ahealth based drinking water level calculated from the referencedose (RfD) for tris of 0.125 mg/kg/day being consumed by an adultweighing 70 kg and drinking 2 liters of water a day. The TBCsfor surface water and sediments of 100 ug/1 and 1000 ug/kg,respectively, were established by the National Oceanographic andAtmospheric Administration (NOAA) and are not considered clean upgoals, but act as trigger values which, if reached, require theimplementation of bioassay testing and further wetlandsevaluation.

In September 1990, a Consent Decree (CD) was signed betweenEPA and the Witco Corporation in which Witco agreed to implementthe Remedial Design/Remedial Action (RD/RA) called for in theSeptember 27,1989 ROD. The CD was entered in U.S. District Courton February 11, 1991. Witco Corporation awarded a contract toEnvironmental Resources Management, Inc. (ERM) in October 1990 toperform the work required by the CD.

Remedial Design/Action Activities

The major component of the limited action remedy consists ofmonitoring of ground water, surface water and sediment. EPA andDNREC have determined that the monitoring wells which arepresently located at the site are sufficient for continuedmonitoring of ground water until the clean up levels areachieved. Therefore, no remedial action construction activitiesare necessary.

A Memorandum of Agreement became effective between the DNRECDivision of Air and Waste Management (DAWM) and the Divisionof Water Resources (DWR) on November 19, 1990 which established aGround Water Management Zone (GMZ) in the area of the New CastleSpill site. This agreement does not allow for any permits forwells installation, other than monitoring wells, to be issued forproperty in the GMZ without joint review and approval by bothDAWM and DWR. This agreement will be effective until bothparties modify or terminate it. EPA will be notified of any

modifications or termination of the agreement.

In May 1991, ERM, Inc. submitted the Field Sampling andQuality Assurance Plan for Remedial Activities at the site.Several revisions have been made to this plan and approval hasbeen given to conduct the first round of post-ROD sampling at thesite. Since the ground water, surface water, and sedimentsampling has not been conducted since the RI/FS, EPA requestedthat thirteen of the monitoring wells and all of the previoussurface water/sediment locations be sampled in order to gatherdata for the selection of future monitoring locations. This datawill be used to gain an overall understanding of theeffectiveness of the natural attenuation process that hasoccurred since the RI/FS. The first round of sampling isscheduled for July 1992.

Future remedial action activities include:

ERM, Inc. will submit to EPA and DNREC the work plan forfield sampling and Remedial Action activities within thirty (30)days of receipt of the first round of sampling data. The workplan will identify future sampling locations for continuedmonitoring of ground water, surface water and sediment.

A revised schedule for future sampling events and submittalsrequired under the Consent Decree, will be developed and willinclude an updated schedule and comprehensive plan for remedialaction activities from onset to completion.

This revision will include a plan for determining when cleanup levels have been achieved. EPA has informed Witco Corp. thatthe present EPA Region III policy or guideline for determiningwhen clean up levels have been achieved is to continue monitoringuntil the analysis confirms that the clean up levels have beenreached throughout the ground water plume and remain at or belowthis level for twelve consecutive quarters (three wet and dryseasons).

Several concerns may need to be addressed prior to sitecompletion. TCE was detected in ground water at the site, butdetermined to be originating from an upgradient source. DNREC iscurrently investigating this upgradient site (Castle Fordproperty); however, no remediation plans currently exist. EPAand DNREC will continue to coordinate efforts to ensure that theTCE is addressed under a separate site investigation andassessment. If the trigger values are reached in the wetlands,surface water or sediment then additional bioassay and wetlandsevaluation will be necessary. This will require coordinationwith the EPA Biological Technical Assistance Group (BTAG) forguidance in the development and implementation of this work, inaddition to, interpretation of the results. The current workplan anticipates this possible future work and indicates that

work plans would be developed in coordination with EPA and theEPA BTAG.

11• Demonstration of OA/OC Activities

All sampling and field activities performed as part of theremedial action will be conducted according to the approved FieldSampling (FSP) and Quality Assurance Project Plan (QAPP) forRemedial Action Activities for the site. The FSP and QAPPincludes plans for sampling activities, field equipment to beused; data quality objectives; the number, times, and location ofsamples to be taken and sample transportation procedures; dataanalysis methods; laboratory quality assurance/ quality controlprocedures; and data validation and reporting procedures.

The QAPP has been reviewed and approved by the EPA RegionIII Central Regional Laboratory for conformance with EPA QA/QCpolicy and guidance.

III. Community Relations Activities

During the RI/FS phase interviews were conducted with thecommunity and local municipal officials to familiarize the publicwith the site and the findings of the RI and EndangermentAssessment (EA). In compliance with Section 113 and 117 of theSuperfund Amendments and Reauthorization Act (SARA) of 1986, theAdministrative Record, the body of documents used by EPA andDNREC in the remedy selection process, was made available forpublic viewing in the DNREC office at 715 Grantham Lane, NewCastle, DE. The Proposed Plan was advertised in the Wilmington-based News Journal newspaper, which has state-wide circulation,to inform public of the alternative being proposed for selection.A 30-day comment period was established from August 22, 1989 toSeptember 22, 1989 to allow the public an opportunity to reviewand comment on the Proposed Plan and documents in theAdministrative Record. A public meeting was held on September 6,1989 to discuss the Proposed Plan and the findings of the RI, EA,and FS. The public was encouraged to comment either at themeeting or in writing. The comments were summarized andresponses were provided in the Responsiveness Summary section ofthe ROD.

The EPA will continue to keep the community informed ofmonitoring results and remedial action activities. The citizenswill be notified when the clean up goals have been achieved andwhen the site is proposed for deletion.

8

IV- Summary of operations and Maintenance

Remedial action activities which occur during the timerequired for natural attenuation to achieve clean up goals arenot considered operation and maintenance (O&M) activities. Theremedial action, which consists of monitoring to ensure thatnatural attenuation will achieve the clean up goals, isconsidered a Long Term Response Action (LTRA). The remedialaction will continue until the clean up goals are achieved. Atthat time the wells will be abandoned and no O&M activities willbe warranted.

V. Summary of Five-Year Review Activities

Section 300.430(f) of the National Oil and HazardousSubstances Pollution Contingency Plan (NCP) stipulates thatstatutory five-year reviews will be conducted when contaminantsremain at a site above levels that allow for unlimited use andunrestricted exposure. At the completion of remedial action thelevel of tris contamination will not pose an unacceptable risk tohuman health or the environment. However, EPA's policy is toconduct five-year reviews for sites at which the remedial actionwill require more than five years to complete. The time requiredto reach the clean up level of 4.4 mg/1 of tris was estimated atfour years in the ROD. This time estimate was based on theestimated half-life of the tris compound which was determined byreviewing the time period (1983-1988) it took for tris to degradefrom 10,100 mg/1 to 110 mg/1 and comparison to DDT, which has asimilar aqueous structure. EPA does not currently know if thetime period for remedial action will exceed this four yearestimate. In addition, EPA specified in the ROD that it willconduct a review within five years to verify that the selectedremedy remains protective of human health and the environment.

EPA, in consultation with DNREC, will develop a work planfor this review. Based on the review, EPA in consultation withDNREC, will determine whether human health and the environmentare being protected by the limited action alternative. The five-year reviews will occur no less often than once each five yearsafter initiation of the remedial action. These reviews can beterminated when EPA determines that the clean up levels have beenachieved throughout the area of attainment; and if requirementspromulgated or modified after the ROD that are considered ARARsdo not result in a determination that the remedy is no longerprotective.

VI. Protectiveness

The Columbia aquifer is currently not used as a potablewater source, therefore, the conditions at the site do not

currently pose a threat to human health. The establishment ofthe Ground Water Management Zone offers additional assurance thatthe limited action remedy is currently protective of human healthby reducing the potential for human contact with the contaminatedground water. The monitoring of ground water, surface water, andsediments during the remedial action will enable EPA to monitorthe effectiveness of the natural attenuation process in achievingthe clean up levels. EPA will continually review the monitoringdata and conduct the five-year reviews to verify that theselected remedy remains protective of human health and theenvironment.

This interim closeout report will be amended when theremedial action is completed, and at least one five-year reviewis conducted. A final closeout report along with all thesupporting documentation will then be prepared.

Approved by:

s*——>JUL

Edwin B. EricksonRegional Administrator

Date

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DO NOT use this form as a RECORD of approvals, concurrences, disposals,clearance*, and similar actions

FROM: (Name, org. symbof, Agency/Post) Room No.—Bldg.

Phone No.

8041-102

* US t;PO: 1990-262-080

OPTIONAL FORM 41 (Rev. 7-76)Prescribed by GSAFPMR (41 CFR) 101-11.206