Construction and performance of a field-scale permeable reactive barrier using the deep-soil mixing technique

C. L. Geiger,*1 M. Chopra,2 D. R. Reinhart, 2 S. Burwinkel, 3 J. Quinn, 4 C. A. Clausen, 1 and A. Sonawane3

1 Chemistry Department, University of Central Florida 2 Department of Civil and Environmental Engineering, University of Central Florida, Orlando, FL

32816-2450 3 Camp, Dresser, and McKee

4 Kennedy Space Center, National Aeronautic and Space Administration

Abstract A field-scale permeable reactive barrier (PRB) was installed at Launch Complex 34

(LC 34) at the Cape Canaveral Air Station in Florida. During this installation process, zero-valent iron (average 16%) was mixed with native soil (approximately 70%) and gravel (approximately 10%) using the deep-soil column mixing technique. This novel installation technique provides for increased worker safety (less exposure to contaminants) and little or no materials for hazardous waste disposal at a lower cost than traditional emplacement methods. The concentrations of contaminants at the installation site were as high as 2.6 mg/l for trichloroethylene, 38 mg/l of cis-dichloroethylene and 4 mg/l of vinyl chloride. The concentrations at observation wells inside the PRB approached maximum concentration limits (MCLs) or non-detection limits and, with the exception of one downstream monitoring well, all contaminants were below detection limits downstream of the PRB at 900 days after installation. The design, field installation, and performance of the LC 34 PRB are described in this paper.

Keywords: permeable reactive barrier; deep soil mixing; zero-valent iron; PRB performance

1. Introduction A significant environmental problem facing society today is the contamination of soil

and groundwater by chlorinated solvents. Chlorinated solvent contamination is a result of past disposal practices as well as spills and leaks from storage tanks or pipes. The Fax: 407-823-2252 E-mail address: cgeiger@pegasus.cc.ucf.edu (C. L. Geiger)

most conventional method used for groundwater remediation extracts the groundwater and pumps it to the surface for treatment (pump and treat). A relatively new method for in situ groundwater remediation of chlorinated solvents is a permeable reactive barrier (PRB).

PRBs utilize natural groundwater flow to transport contaminated groundwater through a reactive medium that is capable of degrading the contaminant of concern. This innovative technique, which has been the focus of recent laboratory, pilot-scale and field-scale studies, uses zero-valent metals such as iron to promote reductive dehalogenation of chlorinated hydrocarbons (Gillham and Burris, 1992). PRB technology is advantageous over conventional pump-and-treat systems because no aboveground treatment equipment is necessary. Therefore, operation and maintenance costs are reduced dramatically and the land above the PRB can be used for other purposes.

A field-scale zero-valent iron PRB was installed in the spring of 1998 at the Cape Canaveral Air Station (CCAS). The site, Launch Complex 34 (LC 34), was used in support of NASA’s Apollo program during the 1960’s. Prior to launch, Saturn rocket parts were cleaned on the launch pad with trichloroethylene (TCE). The TCE was not contained and subsequently contaminated the subsurface.

After considering several alternatives, the Deep Soil Mixing technique (DSM) was selected to construct the PRB. DSM, which is typically used for soil improvement or contaminant containment, offers a method of PRB construction that reduces the volume of contaminated soil requiring special disposal and minimizes construction worker exposure to hazardous materials. In addition, the DSM can readily each depths of 46 m and has proven to be a cost effective alternative to PRB construction (Quinn, 1999).

2. Background LC 34 is located on CCAS, as shown in Figure 1. CCAS is itself located on an

island, bordered by the Atlantic Ocean on the east and the Banana River on the west, on the eastern coast of central Florida. The soil immediately below the surface consists of medium to fine sands with some shell and silt. The soil is primarily sandy with shell fragments and traces of silts to depths up to 9.2 m (30 ft). Below 9.2 m (30 ft), there is an increasing amount of clay and silt present in the samples. As evident in numerous soil borings, soil below 9.2 m (30 ft) is stratified with layers of clay and fine sands. Beyond a depth of 30.5 m (100 ft), limestone fragments ranging from 20 to 50% are found within the clay and sandy soils.

Groundwater in the surficial aquifer, the primary location of contamination, was found to flow radially from an area just northwest of the blockhouse and southwest of the launch pad as shown in Figure 2. In the PRB location (area west of the Engineering Support Building ESB), groundwater flow is towards the west-southwest.

The rate of groundwater movement, an important factor in PRB design, is dependent on the hydraulic gradient of the surficial aquifer. The gradient for the entire site ranges from 10-3 to 10-4 m/m. Additional gradient measurements, calculated from water levels measured in piezometric wells installed at LC 34, concluded that the gradient does not vary significantly with time in both direction and magnitude. Tests were also conducted to examine the effect of the ocean tide on groundwater levels. The results show no signs of local tidal influence on the groundwater level.

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The primary contaminants at LC 34 are TCE and its degradation products. Prior investigations of groundwater contamination conducted at this site had found TCE concentrations as high as 310 mg/l just south of the blockhouse (see Figure 1). At the general location of the PRB discussed in this paper, the TCE concentrations were found to range from less than 0.005 to 59 mg/l. Groundwater samples collected between April 1997 and May 1998 found TCE concentrations near the PRB as high as 12 mg/l. In the present investigation, the highest concentrations were found at depths between 4.6 and 9.1 m (15 and 30 ft) below land surface (bls). During previous studies, a few locations exhibited maximum TCE concentrations around 2.1 to 3.1 m (7 to 10 ft) bls. The same was also found for the daughter products of TCE, for example cis-1,2-dichlorethene (cis-DCE) had maximum concentrations in the stratum between 4.6 and 9.1 m (15 and 30 ft) bls in both investigations.

3. Design of the PRB The two primary factors that influence PRB design are the permeability and hydraulic

retention time of the wall. The PRB permeability can be controlled by the addition of bulking material such as gravel. Several proposed mixtures composed of iron, gravel, coarse sand, and native soil were tested using the constant-head permeability test (ASTM D2434). The selected mix consisted of 16% iron (Peerless Metal Powders & Abrasives, Detroit, MI), 5% gravel, and 79% native soil by weight. This composition had an estimated hydraulic conductivity of 3.7 x 10-3 cm/sec, compared with surrounding native soils values of 3.6 x 10-4 to 3.9 x 10-3 cm/sec. The hydraulic retention time of the contaminated groundwater was calculated to verify that sufficient time for TCE and by-product degradation had occurred. Since TCE degradation by zero-valent iron has been found to follow first-order kinetics (Gillham and O’Hannesin, 1994), the hydraulic retention time must be greater than the required degradation time. The required degradation time of 5.7 days for TCE removal is easily met by the estimated hydraulic retention time within the wall of 35 days.

The selected PRB design employed a continuous pattern consisting of eleven 1.2-m (4-ft) diameter, overlapping columns for a total barrier length of 12.2 m (40 ft). Depth of the PRB was 12.2 m (40 ft), ending just above an impermeable clay stratum. Overlapping columns ensured a continuous DSM PRB that reduced the possibility of contaminants by-passing the wall. Mixing was also provided upstream from the barrier to maintain parallel flow lines entering the PRB.

4. Field Installation of PRB

The construction method consisted of driving hollow steel casings 12.2 m (40 ft) into the subsurface. The hollow casings, equipped with removable steel points, were filled with zero-valent iron and gravel. The steel points were removed before the casings were extracted, leaving columns of reactive material. The DSM auger then mixed the material with the native soil. Prior to casing installation, less than a meter of soil was removed to account for the expected volume increase. The mixing resulted in a higher hydraulic conductivity of the columns relative to the surrounding soil and consequently a slight increase in the capture zone of the wall.

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4.1. Casing Installation

The final design required the installation of 44, 25-cm (ten-inch) steel casings (four

per mixing column) for material introduction into the subsurface. The casings were guided into the subsurface to assure casing installation was vertical and within the DSM auger limits. A supporting bracket was attached to a backhoe that guided the casing for the first 6.1 to 9.1 m (20 to 30 ft) into the subsurface as shown in Figure 4. A vibratory hammer performed the driving of the casings. The displacement of soil by the casing installation caused compaction of the surrounding soil. This compaction resulted in increased time for casing installation and consequent construction delays. Initially, casing installation took less than one hour but gradually increased to two hours due to local soil compaction. In addition, casing installation was significantly more difficult for depths of three to eight meters where denser soils were evident. To reduce construction time, the soil was mixed using the DSM rig prior to casing installation. Following mixing, casings were installed in less than 20 minutes.

The iron and gravel mixture was introduced into the casings from a cement truck. Initially, the iron and gravel was combined and mixed in the truck and then placed in the casings using a chute. However, the density difference between the iron and gravel caused some separation of the mixture resulting in unequal distribution of the iron and gravel in the columns. Subsequently, the iron and gravel were added separately to individual steel casings and the DSM was used to combine them with the native soil.

Prior to casing removal, a solution of 1-2% sulfuric acid was added to the iron columns to remove oxidation products from the iron surface and increase the reactivity of the iron. Laboratory testing had shown that a sulfuric acid bath with a pH of two could significantly improve the reaction kinetics of the iron. The iron filings received an overnight in-situ acid wash prior to removal of the steel points from casings. Laboratory testing also indicated a rise in pH of the acid wash from two to five in the presence of iron filings because of the cleaning process. Therefore, the acid solution was released into the subsurface at a pH of approximately five. High alkalinity levels at the site (257 mg/L as CaCO3) maintained a neutral pH within the PRB.

4.2. Deep-Soil Mixing

The DSM rig used at the site was an ICE Model 55AT hydraulic top drive auger with

roller guides. A 235-kW generator that applied 75 kN-m of torque powered the mixer. The auger blades were 15° off horizontal. Four teeth were located on each of the two mixing paddles. Four mixing blades were located above the mixing paddles and were not equipped with teeth. The auger had a 1.2-m (4-ft) mixing diameter and two “pilot teeth” located at the bottom of the auger.

The iron and gravel columns were mixed with the surrounding soil by two mixing passes of the DSM auger. A mixing pass is defined by the movement of the auger to the desired depth (12.2 m) and back to the surface. Initially water was injected to aid the mixing process but was unsuccessful and air was subsequently used. In order to assure vertical columns, the DSM rig was equipped with devices that guided the auger through the soil. A steel frame that supported the auger, shaft, and motor was suspended from a

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boom crane. Braces on the steel frame were used to keep the auger shaft from moving laterally. The steel frame was kept vertical by the use of steel posts, attached to the frame bottom. The posts penetrated the soil surface and kept the frame vertical. Finally, a stabilizing frame was attached to the DSM frame and the bottom of the crane. Because of the removal of the topsoil, there was no investigation-derived waste produced during the entire construction process and consequently there were no off-site disposal costs.

5. Construction Evaluation In order to provide an immediate idea of the effectiveness of the construction

technique, standard penetration tests (SPT), soil sampling, slug tests and nuclear density tests were performed. SPT results from within and outside the wall showed the effect DSM mixing had on the soil. Monitoring wells, locations shown in Figure 5, were installed within and outside the PRB. The wells inside the PRB were labeled observation wells (OW) while those in the native soil around the PRB were called monitoring wells (MW). The results from within the PRB, shown in Table 1, ranged from a minimum SPT blow count (N) value of one to a maximum of 14. The results from outside the wall, shown in Table 1, ranged from six to 31. A high N value as observed for pre-construction soils has been commonly associated with a high relative density (Das, 1994)

Soil samples of the PRB were collected to evaluate the effectiveness of the DSM technique in mixing the iron with the soil. The samples were obtained from two sources: split-spoon samples and drummed cuttings from monitoring well drilling. Drill cutting samples were collected during the installation of an observation well within the PRB and other locations within the wall. The iron composition was determined by separation of soil and reactive material with a magnet. Table 2 presents the findings of these tests for each sample from the split spoon samples, while Table 3 presents those from the drill cuttings.

The average iron percentage was consistent with the 16% iron content design. The wide variability of the split-spoon samples compared with the consistent results from the drill cuttings questions the reliability of the split-spoon samples to accurately measure DSM effectiveness. One difference in the methods is the amount of soil collected. Split-spoon samples are collected from a 3.5-cm (13/8-inch) diameter probe, whereas drill cuttings are collected from a 25-cm (10-inch) diameter auger sample. Consequently, the samples from the split-spoon may not be as representative as those obtained during well drilling.

6. Wall Performance

To evaluate the performance of the PRB, groundwater samples were collected from

wells located at various points up gradient, down gradient, and within the PRB itself (see Figure 5). The groundwater was analyzed for TCE and its daughter products including DCE isomers, VC, and ethylene. Groundwater sampling was carried out according to US EPA guidelines (US EPA, 1996). The samples were kept in an ice chest during transportation to the UCF Chemistry Department laboratories. The samples were preserved at 40C until time of analysis. Analysis was completed within seven days of sampling. A Hewlett-Packard Model 5890 Gas Chromatograph (GC) equipped with a

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flame ionization indicator (FID) was used for VOC analysis. Five ml of each sample was placed into a purge vial. Helium was bubbled through the sample for 11 minutes, transferring the contaminants to a Tekmar Purge Trap K. Desorbing was done for four minutes to transfer the contaminants to a 0.25-mm i.d., 60-m Vocol capillary column. The GC was programmed to hold at 600C for three minutes then rise at 150C per minute until reaching a temperature of 1800C. Duplicate samples were run for each vial. Calibration curves were run each month for all contaminants. Blank and standard samples were analyzed during each run.

The average concentration of TCE before wall installation was 2.6 mg/L (Farrell, 1999). Figure 6(a) shows the concentration of TCE over time in the wells upstream of the PRB since installation. Similarly, Figure 6(b) and 6(c) shows the TCE concentration over time in the wells inside the PRB and in the wells downstream of the PRB, respectively. For CWI, one of the upstream monitoring wells, TCE concentration has declined from 2.6 mg/L to non-detectable levels (less than 5µg/L). This decline can be attributed to the biotic conversion of TCE. This site appears to be biologically active as suggested by the reduction of TCE (the original pollutant) and the appearance of DCE isomers, VC, and ethylene. Another upstream well, MW-4, consistently contains TCE concentrations of 1.5 mg/L. TCE has never been detected inside or downstream of the PRB since its installation, suggesting that the PRB is efficiently degrading TCE.

Trans-DCE has been observed consistently in upstream wells, CWI and MW-4, where concentrations have averaged 0.9 mg/L and 0.45 mg/L respectively. Since approximately 400 days after installation of the PRB, trans-DCE concentrations have been at non-detectable levels inside of the PRB. Trans-DCE has never been detected in downstream wells MW-1 and MW-2. MW-3 concentration reached the non-detectable level 660 days after PRB installation. These data suggest that trans-DCE is being degraded by the wall.

1,1 DCE has rarely been detected upstream of the PRB, and only at a concentration of less than 0.01 mg/L. 1,1 DCE persisted inside of the PRB for approximately 600 days after wall installation and then declined to non-detectable levels. 1,1 DCE has been non-detectable downstream from the PRB since 300 days after installation. These data suggest that the wall is successfully treating 1,1 DCE.

The most predominant isomer of DCE found on the site was cis-DCE. Although cis-DCE was not discharged in the area, cis-DCE has been found at very high concentrations, most likely due to significant subsurface biological activity. It has also increased over time throughout the PRB area. Most recent data show cis-DCE upstream concentration in the range of 32-38 mg/L (Figure 7(a)). Cis-DCE was non-detectable in the majority of the inside wells (Figure 7(b)). Cis-DCE has been observed in the range of 0.02-0.065 mg/L in OW-4 (inside the wall), but it has always been less than the maximum contaminant level (MCL) of 0.07 mg/L. These higher concentrations found in OW-4 can be attributed to the fact that OW-4 is screened in a zone of higher contaminant concentration. Concentration levels in downstream wells are also below MCL (non-detectable most of the times) with the exception of MW-3 (Figure 7(c)).

Immediately after installation of the PRB, cis-DCE concentration in MW-3 was 2 mg/L. Since 450 days after PRB installation, this concentration has declined, reaching 0.24 mg/L 900 days after PRB installation. MW-3 is screened in a zone of higher contaminant concentration and it is assumed that the cis-DCE originally in the

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groundwater and sorbed to the soil is being displaced by groundwater treated by the PRB slowly moving to MW-3. Calculations based on the hydraulic gradient and hydraulic conductivity support a cis-DCE time of travel of approximately 440 days to MW-3. It is projected that MW-3 will not reach the MCL until 2000 days after PRB installation.

Another daughter product of TCE that must be considered is VC (Figures 8(a-c)). Due to biological activity taking place in the subsurface, VC is found in upstream wells at relatively high concentrations of approximately 1 to 4 mg/L (Figure 8(a)). Compared to other chlorinated compounds, VC is the most difficult contaminant to degrade using zero-valent iron. VC has been found inside the PRB on several occasions as well, although at far lower concentrations than upstream. After 780 days, VC reached non-detectable level inside the PRB (Figure 8(b)).

Concentrations of VC in downstream wells have always been variable. Downstream wells MW-1 and MW-2 reached non-detectable levels 450 days after installment (Figure 8(c)). However, prior to day 450, these concentrations varied between 0.02 and 0.05 mg/L. VC is found at high concentrations (1-2 mg/L) in MW-3. Note that the concentrations of cis-DCE in MW-3 declined after 450 days, but at the same time VC concentrations increased in MW-3, suggesting that VC is breaking through the PRB and moving to MW-3. As seen in Table 2, the iron content in the PRB in front of MW-3 may be quite low (approximately 3%). This iron content appears to be sufficient for cis-DCE degradation as suggested by cis-DCE declination in MW-3, but not for VC, as high concentrations of VC persist in MW-3. Unfortunately OW-8, located upstream of MW-3 is screened from 9.14 m to 10.6 m, a stratum characterized by low contamination levels. Therefore, it is not possible to confirm VC behavior in the PRB at the depths where MW-3 is screened. OW-4, located in another part of the PRB and screened in a stratum with high levels of contamination shows efficient removal of VC. Iron concentration was over 10% near the OW-4 screen (see Table 2).

7. Conclusions An innovative method for installing a permeable reactive barrier for groundwater

treatment using zero-valent iron and native soil mixture is presented in this paper. The mixing of the zero-valent iron, gravel, and the native soil was carried out using a deep-soil mixing technique. A permeable reactive barrier installed using the deep-soil mixing technique offers several advantages over other construction techniques and treatment methods. The DSM technique produced no contaminated excavated soils that required special disposal. Exposure of workers to hazardous chemicals was also minimized since the mixing occurred below grade. This is a passive, in-situ remediation technique and above-ground treatment equipment is unnecessary during routine operation.

Monitoring of wall performance suggests that removal of the chlorinated solvents challenging the wall is successfully occurring. TCE and its daughter products are at non-detectable levels within the wall and are declining in downstream wells, with the exception of vinyl chloride. Additional mixing during PRB construction is recommended to provide sufficient iron throughout the treatment barrier capable of complete destruction of TCE and all daughter products.

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Acknowledgement This research was supported by the National Aeronautical Space Administration Grant Number NAG100198 under the project entitled “Permeable Reactive Wall Field-Scale Application” within the Environmental Programs Office, NASA, Kennedy Space Center. References

Das, B.M. (1994). Principles of Geotechnical Engineering. PWS Publishing

Company, Boston, MA. Gillham, R.W. and D.R. Burris (1992) “Recent Developments in Permeable In Situ

Treatment Walls for Remediation of Contaminated Groundwater,” Proceedings of Subsurface Restoration Conference, June 21-24.

Gillham, R.W., and S.F. O’Hannesin (1994). “Enhanced Degradation of Halogenated

Aliphatics by Zero-Valent Metal”, Ground Water, v32, pp. 958-965. Farrell, K.M., (1999). Evaluation of a Field-Scale Zero-Valent Iron Permeable

Treatment Wall. M.S. Thesis, University of Central Florida. Quinn, J. W., (1999). Evaluation of the Constructability of a Zero-Valent Permeable

Treatment Wall using Deep Soil Mixing and Vibro-Installation Techniques. PhD Dissertation, University of Central Florida.

U.S. Environmental Protection Agency Region I, (1996). Low Stress Purging and Sampling Procedure for the collection of Groundwater samples from Monitoring Wells, Revision 2.

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LIST OF FIGURES Figure 1. Site plan of Launch Complex 34 at the Cape Canaveral Air Station Figure 2. Groundwater Contours at LC 34 site Figure 3. Final design layout of field-scale PRB constructed at LC 34. Figure 4 Guiding support for casing installation Figure 5. Groundwater flowlines depicting (a) complete and (b) incomplete capture. Figure 6. Concentration of TCE (a) Upstream of the PRB over Time, (b) Inside of the

PRB over Time, and (c) Downstream of the PRB over Time Figure 7. Concentration of cis-DCE (a) Upstream of the PRB over Time, (b) Inside of

the PRB over Time, and (c) Downstream of the PRB over Time Figure 8. Concentration of VC (a) Upstream of the PRB over Time, (b) Inside of the

PRB over Time, and (c) Downstream of the PRB over Time LIST OF TABLES Table 1. Pre- and Post-Construction SPT results Table 2. Iron content for split spoon samples. Table 3. Iron content for drill cutting samples.

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Building

Blockhouse

Launch Pad AtlanticOcean

N

Not to Scale

PRB

Engineering Support

Figure 1. Site plan of Launch Complex 34 at the Cape Canaveral Air Station

10

July 1993

Not to ScaleN

AtlanticOcean

Figure 2. Groundwater Contours at LC 34 site

11

Figure 3. Final design layout of field-scale PRB constructed at LC 34.

Permeable DSMColumns

Upstream Mixing

GroundwaterFlow

12.2 m (40 ft)

1.2 m (4 ft)

1.2 m (4 ft)

12

Figure 4. Guiding support for casing installation.

13

Figure 5. Location of PRB Observation and Monitoring Wells

14

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 200 400 600 800 1000

Days since Wall Installation

Con

cent

ratio

n (m

g/L)

CWI MW-4

Figure 6(a). Concentration of TCE Upstream of the PRB over Time.

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0 200 400 600 800 1000Days since Wall Installation

Con

cent

ratio

n (m

g/L)

OW-1 OW-4 OW-6 OW-8 Figure 6(b). Concentration of TCE Inside the PRB over Time.

15

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 200 400 600 800 1000Days since Wall Installation

Con

cent

ratio

n (m

g/L)

MW-1 MW-2 MW-3

Figure 6(c). Concentration of TCE Downstream of the Wall over Time.

16

0

10

20

30

40

50

60

0 200 400 600 800 1000

Days since Wall Installation

Con

cent

ratio

n (m

g/L)

CWI MW-4

Figure 7(a). Concentration of cis-DCE Upstream of the PRB over Time.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000

Days since Wall Installation

Con

cent

ratio

n (m

g/L)

OW-1 OW-4 OW-6 OW-8Figure 7(b). Concentration of cis-DCE Inside the PRB over Time.

17

0.0

0.5

1.0

1.5

2.0

2.5

0 200 400 600 800 1000

Days since Wall Installation

Con

cent

ratio

n (m

g/L)

MW-1 MW-2 MW-3

Figure 7(c). Concentration of cis-DCE Downstream of the PRB over Time.

18

0.00.51.01.52.02.53.03.54.04.55.0

0 200 400 600 800 1000

Days since Wall Installation

Con

cent

ratio

n (m

g/L)

CWI MW-4

Figure 8(a). Concentration of VC Upstream of the PRB over Time.

0.000

0.005

0.010

0.015

0.020

0.025

0 200 400 600 800 1000Days since Wall Installation

Con

cent

ratio

n (m

g/L)

OW-1 OW-4 OW-6 OW-8Figure 8(b). Concentration of VC Inside the PRB over Time.

19

0.0

0.5

1.0

1.5

2.0

2.5

0 200 400 600 800 1000Days since Wall Installation

Con

cent

ratio

n (m

g/L)

MW-1 MW-2 MW-3Figure 8(c). Concentration of VC Downstream of the PRB over Time.

20

.

Table 1. Pre- and Post-Construction SPT results

Inside Wall Outside Wall Depth (m) OW-4 OW-6 MW-2 MW-4

Pre-construction

3 5 3 − 12 50

4.6 1 2 26 20 29

6 − − 21 12 29

7.6 8 5 14 10 9

9.1 14 9 6 − 8 Note: OW refers to observation wells within the PRB and MW refers to

monitoring wells around the PRB (Burwinkel, 1998).

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Table 2. Iron content of split-spoon samples.

Depth OW-1 OW-4 OW-6 OW-8

7 − 9.0% 62.1% −

10 6.2% − − −

15 − 10.4% 1.3% 3.6%

20 16.7% − − −

25 − 11.1% 5.1% 6.3%

30 1.4% − 7.4% −

35 − 14.9% − 3.2%

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Table 3. Iron content for drill cutting samples.

Location Sample 1

Sample 2 Total

OW-1a 16.9% 16.4% 16.5%

OW-1b 20.5% 20.8% 20.5%

OW-1c 20.1% 22.1% 20.9%

Random 1 16.7% − 16.7%

Random 2 18.7% − 18.7%

Random 3 11.9% 16.5% 13.5%

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