October 2008 SemiAnnual GW MonRpt Errata.pdf

Semi-Annual Report October 2008 Groundwater Monitoring

Bitterroot Valley Sanitary Landfill Ravalli County, Montana

Prepared for:

National Institutes of Health Division of Safety Environmental Protection Branch

Building 13, Room 2W64 Bethesda, Maryland 20892

Prepared by:

Tetra Tech

2525 Palmer Street Suite 2 Missoula, Montana 59808 Tetra Tech Project No. 9732221B

April 2009

National Institutes of Health Semi-Annual Report, October 2008 Groundwater Monitoring, BVSL

Tetra Tech i Errata- April 2009

EXECUTIVE SUMMARY

Waste laboratory chemicals, including chloroform and other volatile organic compounds (VOCs), were disposed of at the Bitterroot Valley Sanitary Landfill facility (BVSL) between 1981 and 1985, and contaminated groundwater was discovered at the facility in 1987. Results of early investigations by the National Institutes of Health (NIH) indicated that VOCs had affected portions of the groundwater system between the landfill and the Bitterroot River by 1992.

NIH has instituted several interim remedial actions (IRAs) at the facility since 1992. Initial IRAs completed in 1994 included excavation and treatment of VOC-impacted soil in the source area and installation of an initial (Phase I) groundwater removal and treatment system. Nineteen alternative water supply wells were installed on private properties in the area during 1996 and 1997. The alternative water supply systems have provided residents with water that is free of VOCs originating from the BVSL. In 1998 NIH installed the Phase IIA groundwater removal and treatment system (Maxim 1999a) near Meridian Road to decrease the time required until water quality improvements would be observed downgradient of Meridian Road. The Phase IIA system was expanded in 2000 to include well R-9D located near the source removal area to accelerate clean up of deeper groundwater downgradient of the original source area. In July 2004, an additional recovery well (R-10) was added to the Phase IIA system. Well R-10 was installed between well R-9D and Meridian Road to remediate groundwater in this portion of the facility and began pumping when the system was reactivated on September 28, 2004. Removal and treatment of contaminated soil and groundwater has resulted in significant improvements in groundwater quality between the BVSL and the Bitterroot River.

This report describes methods and results of semiannual groundwater monitoring completed at the BVSL in October 2008. Monitoring was conducted according to procedures specified in the December 2002 Amended Final Groundwater Monitoring Work Plan (Maxim 2002e). Objectives for the monitoring program include:

1. Track temporal and spatial trends in groundwater flow and quality.

2. Evaluate the effect of NIH's 1993-94 soil removal action and effects of NIH’s Phase IIA groundwater remediation system on groundwater flow and quality.

3. Document VOC water quality relative to Montana groundwater quality standards.

4. Operate and maintain the Phase IIA groundwater treatment system.

5. Monitor the effectiveness of water treatment system’s reduction of iron and manganese at the point of use for replacement domestic cells (during the summer monitoring events).

Data collected at the facility will also be used to support periodic refinement of an existing numerical groundwater flow and contaminant transport model.

During October 2008 groundwater monitoring, Tetra Tech measured depth-to-water in 92 wells/piezometers and collected groundwater samples from 53 wells (56 samples). Samples were sent to Northern Analytical Laboratories, Inc. (NAL) in Billings, Montana, for analysis of VOCs. Analytical data were compared to Circular WQB-7 groundwater standards published in September 1999 (WQB-7, DEQ 1999), which are referenced in DEQ's Record of Decision (DEQ

Tetra Tech ii Errata- April 2009

2002). The analytical data compiled from this sampling event are presented in Appendices E, F, and G and historical well data is presented in Appendix H on a CD.

Key Findings from the October 2008 Groundwater Monitoring Event

The following key findings from the October 2008 monitoring event are presented in terms of the five objectives listed on the preceding page. BVSL hydrostratigraphic terminology referenced below is defined in Appendix A.

1. Tracking temporal and spatial trends in groundwater flow and quality.

Groundwater Flow

• Unit A groundwater generally continues to flow in an easterly direction, and Unit D groundwater generally continues to flow in a north-northeasterly direction. These flow directions are consistent with observed spatial and temporal long-term trends.

Cones of depression are well developed in both the shallow and deep portions of Hydrostratigraphic Unit A due to nearly continuous operation of Phase IIA remediation system recovery wells since September 28, 2004.

Chloroform in the Shallow Portion of Unit A

• Chloroform has not been detected in any sample from wells completed in the shallow portion of Unit A east of U.S. Highway 93 since July 2000.

• The shallow portion of Unit A remediation well samples that contained chloroform were collected from wells R-1 and R-2 at 14 micrograms per liter (µg/L) and 7.6 µg/L, respectively.

• With the exception of a slight increase in R-2, BR-GW-87S, and BR-GW-89S all detected chloroform concentrations in the shallow Unit A wells were lower in October 2008 when compared to September/October 2006.

• Chloroform concentrations in samples collected from wells BR-GW-2, BR-GW-37S, and R-1 continue to exhibit a generally declining trend.

• Chloroform was not detected in the sample from shallow recovery well R5-S. R5-S was not sampled in September/October 2006.

• The aerial distribution of the chloroform plume in the shallow portion of Unit A remains similar to that observed over the last several monitoring events; however the peak concentrations in the center of the plume continue to decline in response to the 1993-94 soil removal and treatment and operation of the Phase IIA groundwater remediation system.

Chloroform in the Deep Portion of Unit A

• Chloroform concentrations in the deep portion of Unit A continue to attenuate, particularly east of U.S. Highway 93, as a result of remedial actions and natural dilution effects.

Tetra Tech iii Errata- April 2009

• Comparison of the chloroform concentrations observed in groundwater samples from the wells completed in the deep portion of Unit A collected in October 2008 verses samples collected in September/October 2006 revealed the following:

A slight increase in the chloroform concentration in wells BR-GW-09 (6.1 µg/L to

7.5 µg/L), and SA-16 (15 µg/L to 16 µg/L).

Well D-101, not sampled in September/October 2006, contained chloroform at a concentration of 2.9 µg/L.

A significant increase in the chloroform concentration in wells BR-GW-36D (13 µg/L to 93 µg/L), SA-13 (50 µg/L to 84 µg/L), and SA-14 (<0.5 µg/L to 18 µg/L).

A slight decrease in the chloroform concentration in wells BR-GW-90D (8.5 µg/L to 5.8 µg/L), BG-GW-91D (1.5 µg/L to 1 µg/L), R-6D (11 µg/L to 8.5 µg/L), SA-17 (45 µg/L to 39 µg/L), and BR-GW-34D (17 µg/L to 14 µg/L1).

A significant decrease in the chloroform concentration in wells BR-GW-31D (57 µg/L to 4.7 µg/L), BR-GW-51D (19 µg/L to 10 µg/L), BR-GW-82D (5.9 µg/L to <0.5 µg/L), BR-GW-92D (18 µg/L to 8.6 µg/L), R-8D (28 µg/L to 13 µg/L), R-9D (112 µg/L to 5.8 µg/L) and R-10 (86 µg/L to 37 µg/L).

Chloroform in Unit B

• Chloroform concentrations in samples from well BR-GW-61DD have decreased significantly since the previous sampling event two years ago (167µg/L to105 µg/L).

• Chloroform was not detected in the samples from Unit B wells BR-GW-56DD, BR- GW-84D, and D-39.

Chloroform in Units C and D (Replacement Wells)

• Chloroform or other VOCs were not detected in samples from any of the 13 replacement domestic wells monitored in Unit C (BR-GW-65DD, -73DD) and Unit D (BR-GW-62DD, -66DD, -67DD, -68DD, -69DD, -71DD, -72DD, -74DD, -77DD, and - 80DD). Well BR-GW-63DD was not sampled in October 2008.

• The reported chloroform concentration from domestic replacement well BR- GW-70DD in the first laboratory report received was 14 µg/L1 (a first time detection for this well); however further discussion with the laboratory QA/QC officer indicated that this result may have represented water from BR-GW-34D (which was in the same laboratory batch and was run directly before BR-GW-70DD). The well was re-sampled on December 16, 2008 to confirm this suspicion of batch mix-up at the laboratory. The re-sample did not contain any chloroform or other VOCs.

1 Well BR-GW-70DD re-sampled on December 16, 2008 due to laboratory mix up of sample with BR-GW-34D.

Re-sample result (<1 µg/L) replaces original reported concentration for BR-GW-70DD (14µg/L), and original reported concentration is applied to RBR-GW-34D (see more detailed description of the laboratory error in Appendix G).

Tetra Tech iv Errata- April 2009

Other VOCs

• Vinyl chloride (VC) was the only other VOC detected in October 2008 samples at concentrations in excess of the DEQ’s 1999 Circular WQB-7 standards (BR-GW- 39S, and R-8D).

• Comparison of the Tetrachloroethene (PCE) plumes in Unit A in October 2008 with September/October 2006 is similar in distribution and concentration. The shallow PCE plume centered on well BR-GW-2 and BR-GW-39S, is based on 2.2 µg/L and

1.5 µg/L, PCE concentrations respectively. The PCE plume in the deep portion of Unit A west of U.S. Highway 93 is centered on recovery well R-8D and is based on

1.9 µg/L PCE.

• PCE was detected in the Unit B aquifer well BR-GW-61DD; however the concentration was below the WQB-7 standard. No other nearby wells contained detectable quantities of PCE during the October 2008 sampling event.

2. Evaluating the effect of NIH's 1993-94 soil removal action and effects of NIH’s Phase IIA groundwater remediation system on groundwater flow and quality.

• Cones of depression are well developed around Phase IIA remediation system recovery wells. These cones of depression indicate that Phase IIA recovery wells are effective in capturing nearby groundwater within the shallow and deep portions of Unit A. Captured groundwater is then treated through the Phase IIA air stripper prior to release to Bear Creek.

• Chloroform was not detected in shallow Unit A groundwater east (downgradient) of the Phase IIA groundwater remediation system, indicating the ongoing effectiveness of Phase IIA remedial activities in improving shallow Unit A groundwater quality.

• Chloroform concentrations generally continue to improve in Unit A as a direct result of source removal and the Phase IIA groundwater remediation system.

• Significant increases in the chloroform concentration in deep Unit A wells (BR-GW- 36D, SA-13, and SA-14) may indicate the need to adjust pumping rates on nearby remediation wells in order to optimize plume recovery. The affected wells should be closely monitored over the next couple of monitoring events to determine if the sample results are the beginning of a long term trend or are a result of operation and maintenance issues with the R-9D pumping schedule.

• Chloroform concentrations continue to decrease in other portions of deep Unit A as a result of the on going natural attenuation and active pumping in recovery wells R-8D and R-10.

3. Documenting VOC water quality relative to Montana groundwater standards.

VOC concentrations detected in the following wells sampled during October 2008 exceeded groundwater standards (shown below in parentheses):

• Chloroform (60 μg/L): BR-GW-36D, BR-GW-61DD, and SA-13

Tetra Tech v Errata- April 2009

• Vinyl Chloride (0.15 µg/L): BR-GW-2, BR-GW-39S, BR-GW-61DD, R-8D, R-9D, and R-10

4. Operating and maintaining the Phase IIA groundwater treatment system.

Major maintenance performed or system information over the last two years (December 2006-present) is summarized as follows:

• Well R-3S was not operational over the two year monitoring period between semiannual monitoring events because of insufficient water in the well casing.

• The pitless adapter O-ring in well R-7d was replaced when irregular flow rates were noticed in well R-7d on 10/4/07.

• A new Grundfos® Rediflow-3 pump and CU-300 pump controller were replaced on 10/31/07 on well R-10 due to mechanical and electrical failure.

• The step-down voltage transformer that controls the solenoids on the water lines from the upper wells (R-1, R-2, R-9d and R-10), and the two solenoid valves were replaced on 2/19/08 due to electrical failure.

• New pumps and motor controls were installed on wells R-4d and R-8d on 3/28/08 due to electrical failure.

• New stainless steel stripper tray clamps were replaced on 5/15/08 due to mechanical failure of 4 clamps which led to stripper sump alarm and shutdown.

• A new PVC valve on the manifold piping for well R-9d was replaced on 8/28/08 because it started leaking in the off position during routine cleaning of the paddle wheel impeller on the flow sensor.

• New electrical relays to control the stripper fan and pump operations during alarm conditions were installed in 11/13/08 due to electrical and mechanical failure.

5. Monitoring the effectiveness of water treatment systems on replacement domestic wells in reducing concentrations of iron and manganese at the point of use.

• Samples for total coliform bacteria and iron/manganese were not collected during this semiannual sampling event. Water quality sampling of the 14 replacement domestic supply wells is scheduled for the next semiannual monitoring event. The tentative schedule for semiannual monitoring is the second week of July 2009.

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY................................................................................................................. i

1.0 INTRODUCTION

1.1 REVIEW OF SEPTEMBER/OCTOBER 2006 GROUNDWATER MONITORING

RESULTS

2.0 METHODS

2.1 WATER LEVEL MEASUREMENT

2.2 GROUNDWATER SAMPLING AND ANALYSIS

3.0 DATA PRESENTATION AND INTERPRETATION

3.1 GROUNDWATER ELEVATION AND FLOW

3.2 GROUNDWATER EXCEEDING STANDARDS

3.3 CHLOROFORM DISTRIBUTION AND TRENDS

3.4 CURRENT EXTENT OF CHLOROFORM PLUME

3.5 OTHER VOCS

3.6 COLIFORM BACTERIA, TOTAL IRON AND MANGANESE IN GROUNDWATER

4.0 DATA VALIDATION

4.1 FIELD QUALITY ASSURANCE/QUALITY CONTROL

4.2 LABORATORY QUALITY ASSURANCE/QUALITY CONTROL

5.0 REFERENCES

LIST OF FIGURES

FIGURE 1. Location and Vicinity Map FIGURE 2. Facility Map FIGURE 3. Hydrographs for Wells Potentially Influenced by Phase IIA System Pumping FIGURE 4. Potentiometric Map, Shallow Portion of Unit A FIGURE 5. Potentiometric Map, Deep Portion of Unit A FIGURE 6. Potentiometric Map, Unit D FIGURE 7. Chloroform Concentrations vs. Time for Selected Monitoring Wells FIGURE 8. Chloroform Concentrations in Shallow Portion Unit A – October 2008 FIGURE 9. Cross Section of Chloroform Plume in Unit A FIGURE 10. Chloroform Concentrations in Deep Portion Unit A – October 2008 FIGURE 11. Chloroform Concentrations in Shallow Portion Unit A – 60 µg/L Isopleth FIGURE 12. Chloroform Concentrations in Deep Portion Unit A – 60 µg/L Isopleth FIGURE 13. Tetrachlorethene Concentrations in Shallow Portion Unit A FIGURE 14. Tetrachloroethene Concentrations in Deep Portion Unit A FIGURE 15. Trends in Selected VOCs in Wells R-8D and BR-GW-2

LIST OF TABLES

TABLE 1. Pre-CWSS Wells Monitored, October 2008 TABLE 2. Summary of October 2008 Groundwater Data

TABLE OF CONTENTS (CONTINUED)

LIST OF APPENDICES

APPENDIX A Hydrostratigraphic Terminology APPENDIX B Well Inventory Database APPENDIX C Field Sampling Logs APPENDIX D October 2008 Water Elevation Data APPENDIX E October 2008 Groundwater Volatile Organic Compound Data APPENDIX F October 2008 Groundwater Physical Parameter Data APPENDIX G October 2008 Laboratory QA/QC Review and Laboratory Sample Confusion

Letter APPENDIX H Historical Groundwater Volatile Organic Compound Data (CD)

Tetra Tech 1 Errata- April 2009

1.0 INTRODUCTION

Waste laboratory chemicals, including chloroform and other volatile organic compounds (VOCs), were disposed of at the Bitterroot Valley Sanitary Landfill (BVSL, Figures 1 and 2) facility between 1981 and 1985, and contaminated groundwater was discovered at the facility in 1987. Results of early investigations by the National Institutes of Health (NIH) indicated that VOCs had affected portions of the groundwater system between the landfill and the Bitterroot River by 1992.

NIH has instituted several interim remedial actions (IRAs) at the facility since 1994. Initial IRAs completed in 1994 included excavation and treatment of VOC-impacted soil in the source area and installation of an initial (Phase I) groundwater removal and treatment system. Nineteen alternative water supply wells were installed on private properties in the area during 1996 and 1997. The alternative water supply systems have provided residents with water that is free of VOCs originating from the BVSL. In 1998 NIH installed the Phase IIA groundwater removal and treatment system (Maxim 1999a) near Meridian Road to decrease the time required until water quality improvements would be observed downgradient of Meridian Road. The Phase IIA system was expanded in 2000 to include well R-9D located near the source removal area to speed clean-up of deeper groundwater downgradient of the original source area. In July 2004, an additional recovery well (R-10) was installed between well R-9D and Meridian Road to remediate groundwater in this portion of the facility. The well was added to the Phase IIA system in September 2004. Removal and treatment of contaminated soil and groundwater has resulted in significant improvements in groundwater quality between the BVSL and the Bitterroot River.

Since 1992, Tetra Tech Inc. (and its predecessors) has monitored groundwater conditions on behalf of NIH on a regular basis. Groundwater monitoring was conducted quarterly between 1994 and 1997 and semiannually between January 1998 and September/October 2006.

Without notification to DEQ, semiannual monitoring was discontinued for two years in order to focus the remaining budget on maintaining the pump and treatment system and maintenance of domestic replacement well treatments. This is the first semiannual monitoring event since 2006 sampling. Reports by Chen-Northern, Huntingdon, Maxim, and Tetra Tech, listed in Section 5.0, provide detailed background information and monitoring results for the BVSL project.

This report describes methods and results of semiannual groundwater monitoring completed at the BVSL in October 2008. It includes analytical results for samples from ten groundwater recovery/interception wells, two demonstration monitoring wells, and several source area characterization and monitoring wells installed in 1998 in association with the Phase IIA groundwater remediation project (Maxim 1999a, 1999c, and 2000d).

The October 2008 monitoring event was conducted according to procedures specified in the December 2002 amended final groundwater monitoring work plan (Maxim 2002e). The 2002 work plan establishes monitoring procedures for two distinct periods that are delineated by certification of completion for a community water supply system (CWSS) by the Montana Department of Environmental Quality (DEQ). The first time period is the period prior to completion of the CWSS (pre-CWSS). The second time period is the period following DEQ issuance of a certificate of completion for the CWSS (post-CWSS). The October 2008 monitoring event was conducted in general accordance with pre-CWSS requirements, since plans for a CWSS have been put on indefinite hold by DEQ.

Bitterroot Valley Sanitary Landfill

USGS 7.5' Victor Topographic Quadrangle

FIGURE 1

Location MapBitterroot Valley Sanitary Landfill

Cr ea ted by

: P atr ici a A

. W illia ms P rin ted

: D ate

C oo rdi na te Sy ste m:

N

AD

M on tan a S tat e P lan e, me ter

³ 0 2,000

SCALE IN FEET

Victor, Montana

G:

\E nv iro nm en tal \B

VS

L\a rcm ap

\m xd

\lo ca tio n.m xd

Montana

Victor Missoula

§̈¦15

§̈¦94

§̈¦90§̈¦25

Tetra Tech 4 Errata- April 2009

Objectives for the pre-CWSS monitoring program include:

1. Track temporal and spatial trends in groundwater flow and quality.

2. Evaluate the effect of NIH's 1993-94 soil removal action and effects of NIH’s Phase IIA groundwater remediation system on groundwater flow and quality.

3. Document VOC water quality relative to Montana groundwater standards.

4. Operate and maintain the Phase IIA groundwater treatment system.

5. Monitor the effectiveness of water treatment systems on replacement domestic wells in reducing concentrations of iron and manganese at the point of use (during the July semiannual monitoring events).

Data will also be used to support periodic refinement of an existing numerical groundwater flow and solute transport model of the facility. The schedule for the next modeling update is unknown, however it is hoped that frequency can be negotiated with DEQ prior to development of the next long-term groundwater monitoring work plan. It is Tetra Tech’s opinion that annual updates to the numerical groundwater flow model are unnecessary.

During October 2008 groundwater monitoring, Tetra Tech measured depth-to-water in 92 wells/piezometers and collected 56 groundwater samples. Samples were sent to Northern Analytical Laboratories, Inc. (note: Pace Analytical as of December 1, 2008) in Billings, Montana, for analysis of VOCs. Analytical data were compared to Circular WQB-7 groundwater standards published in September 1999 (WQB-7, DEQ 1999), which are referenced in DEQ's Record of Decision (DEQ 2002). The analytical data compiled from this sampling event are presented in Appendices E, F, and G and historical well data is presented in Appendix H on a

CD.

1.1 REVIEW OF SEPTEMBER/OCTOBER 2006 GROUNDWATER MONITORING

RESULTS

Prior to October 2008, the most recent comprehensive groundwater monitoring event was completed during September/October 2006 (Tetra Tech 2007), and involved measuring depth to groundwater in 92 wells/piezometers and collecting 54 groundwater samples for laboratory analysis of VOCs. Important findings from the September/October 2006 monitoring event are listed below. Terminology for the hydrostratigraphic units at BVSL referenced in this summary is defined in Appendix A.

• Groundwater flow direction in both the shallow aquifer (Unit A) and deep aquifer (Unit D) were consistent with observed spatial and temporal long-term trends. Cones of depression were well developed in both the shallow and deep portions of Hydrostratigraphic Unit A due to nearly continuous operation of Phase IIA remediation system recovery wells.

• Chloroform had not been detected in any sample from wells completed in the shallow portion of Unit A east of U.S. Highway 93 since July 2000.

Tetra Tech 5 Errata- April 2009

• The shallow portion of Unit A remediation well samples that contained chloroform were collected from wells R-1 and R-2 at 27 micrograms per liter [µg/L] and 7 µg/L, respectively.

• With the exception of BR-GW-48S, all detected chloroform concentrations in the shallow Unit A wells were lower in September/October 2006 when compared to three previous year’s summer sampling results.

• Chloroform concentrations in samples collected from wells BR-GW-2, BR-GW-37S, and R-1 continued to exhibit a generally declining trend.

• The aerial distribution of the chloroform plume in the shallow portion of Unit A remained similar to that observed over the last several monitoring events; however peak concentrations were considerably less than those exhibited during the 2003 and 2004 monitoring events. This was due, in part, to the onset of pumping in September 2004 of R-10.

• Chloroform concentrations in the deep portion of Unit A continued to attenuate, particularly east of U.S. Highway 93, as a result of remedial actions and natural dilution effects.

• Chloroform concentrations in wells near the source area continued a long-term declining trend.

• Chloroform concentrations in samples from well BR-GW-61DD decreased over the past three sampling events.

• Chloroform was not detected in the samples from Unit B wells.

• Chloroform or other VOCs were not detected in samples from any of the 14 replacement domestic wells monitored in Unit C and Unit D...

• Vinyl chloride (VC) was the only other VOC detected in September/October 2006 samples at concentrations in excess of the DEQ’s 1999 Circular WQB-7 standards.

• Comparison of the Tetrachloroethene (PCE) plumes in Unit A in September/October 2006 with July 2005 data indicated a decrease in the plume dimensions in both the shallow and deep interpretations.

• Although concentrations of VOCs have slightly fluctuated between January 2003 and September/October 2006, the overall downward trend appeared to have stabilized at steady state threshold values

• Cones of depression were observed in both the shallow and deep portions of Hydrostratigraphic Unit A due to nearly continuous operation of Phase IIA remediation system since September, 2004. These cones of depression indicated that Phase IIA recovery wells should be effective in capturing nearby groundwater within the shallow and deep portions of Unit A.

Tetra Tech 6 Errata- April 2009

The following sections of this report describe groundwater monitoring methods, present water level and water quality data from the October 2008 monitoring event, and interpret the data.

Later sections of the report discuss data validation for October 2008 samples and list cited references. The most recent hydrostratigraphic terminology developed for the project and a generalized hydrogeologic cross section of the facility are presented in Appendix A. Other supporting information including water level, VOC, and physical parameters are contained in Appendices B through H.

Tetra Tech 7 Errata- April 2009

2.0 METHODS

Tetra Tech conducted semiannual groundwater monitoring between October 20 and October 27, 2008. Groundwater monitoring methods are described below.

2.1 WATER LEVEL MEASUREMENT

Field staff measured depth to water in wells listed in Table 1 (well locations are shown on Figure 2) using a decontaminated electric water level indicator. Water level measurements were recorded on field sampling logs (Appendix C) and entered into the project database (Appendix D).

Several replacement domestic wells (BR-GW-66DD, -67DD, -68DD, -71DD, -72DD and -74DD;

Figure 2) exhibited groundwater levels above the top of well casing and required the use of a manometer to measure shut in pressure head.

BR-GW-5 and BR-GW-21 are located on private land without access and were not measured during the October 2008 sampling event. Other wells surveyed during this sampling event which were which sampled due to insufficient water in the well casing include BR-GW-41S, - 49S, -58S, P-1, and P-2.

2.2 GROUNDWATER SAMPLING AND ANALYSIS

On October 20 through October 27, 2008, Tetra Tech collected groundwater samples from 53 wells. Samples were not collected from wells typically included in the semiannual sampling program for the following reasons:

• BR-GW-63DD could not be sampled because the well house was locked, the distribution line drained, and the house vacant.

• BR-GW-41S, BR-GW-49S, BR-GW-58S, could not be sampled because there was insufficient water in the well during the time of sampling.

A summary of the wells that were sampled is provided in Table 1.

Tetra Tech 8 Errata- April 2009

TABLE 1.

Pre-CWSS Wells Monitored, October 2008

Well Number

Well Type DTW VOCs Bact., Fe, Mn, Well

Number Well Type DTW VOCs

BR-GW-2 M � � SA-8 M �

BR-GW-3 M � SA-9 M �

BR-GW-8 M � � SA-13 M � �

BR-GW-9 M � � SA-14 M � �

BR-GW-10 M � � SA-16 M � �

BR-GW-30S M � SA-17 M � �

BR-GW-31D M � � D-39 O � �

BR-GW-32S M � � D-101 O � �

BR-GW-33S M � � BR-GW-1 O �

BR-GW-34D M � � BR-GW-5 O NA

BR-GW-35S M � BR-GW-21 O NA

BR-GW-36D M � � BR-GW-62DD DD � �

BR-GW-37S M � � BR-GW-63DD DD �

BR-GW-38D M � � BR-GW-65DD DD � �

BR-GW-39S M � � BR-GW-66DD DD � �

BR-GW-40D M � BR-GW-67DD DD � �

BR-GW-41S M dry dry BR-GW-68DD DD � �

BR-GW-42D M � BR-GW-69DD DD � �

BR-GW-43S M � BR-GW-70DD DD � �

BR-GW-46S M � BR-GW-71DD DD � �

BR-GW-48S M � � BR-GW-72DD DD � �

BR-GW-49S M dry BR-GW-73DD DD � �

BR-GW-50D M � � BR-GW-74DD DD � �

BR-GW-51D M � � BR-GW-75DD DD �

BR-GW-52S M � BR-GW-76DD DD �

BR-GW-53S M � BR-GW-77DD DD � �

BR-GW-54D M � BR-GW-78DD DD �

BR-GW-55S M � BR-GW-79DD DD �

BR-GW-56DD M � � BR-GW-80DD DD � �

BR-GW-58S M dry BR-GW-84D DD � �

BR-GW-59S M � BR-GW-90D M � �

BR-GW-60S M � BR-GW-91D M � �

BR-GW-61DD M � � BR-GW-92D M � �

BR-OW-01D M � R-1 R � �

BR-OW-02S M � R-2 R � �

BR-GW-81S M � � R-3S I � �

BR-GW-82D M � � R-4D I � �

BR-GW-83D M � R-5S I � �

BR-GW-85 M � R-6D I � �

BR-GW-86D M � R-7S I � �

BR-GW-87S M � � R-8D I � �

BR-GW-88S M � � R-9D R � �

BR-GW-89S M � � R-10 R � �

Tetra Tech 9 Errata- April 2009

TABLE 1 (continued)

Well Number

Well Type DTW VOCs Bact., Fe, Mn, Well

Number Well Type DTW VOCs

SA-1 M � P-1 M dry SA-2 M � P-2 M dry

SA-3 M � P-3 M �

SA-4 M � INF Influent -- � SA-5 M � EFF Effluent -- �

Notes:

DTW Depth to water VOCs Volatile organic compounds INF Phase IIA system influent

M Monitoring well I Interception well EFF Phase IIA system effluent

O Other well R Recovery well -- Not applicable

DD Replacement domestic well NA Not accessible Bact., Fe, Mn

Total coliform bacteria, total iron, and total

Each well was purged of approximately three casing volumes of water prior to sampling. During and after well purging, groundwater was directed through an instrumented cell where physical parameters such as pH, temperature, specific conductance, oxidation-reduction potential [Eh], and dissolved oxygen were measured with a QED Hydrolab® meter. Field parameter data were recorded on groundwater sampling logs for each well (Appendix C). Groundwater samples collected for VOC analysis were packed in ice and shipped with chain-of-custody documentation to NAL in Billings, Montana for VOC analysis by EPA Method 524.2.

Several samples were incorporated into the October 2008 sample train for quality assurance/quality control (QA/QC) purposes, including:

• Temperature blanks for each cooler were shipped to the laboratory.

• One field blank was prepared for VOC analysis.

• Two trip blanks prepared by the laboratory were shipped with the sample containers for VOC analyses.

• Three blind field duplicates were collected from wells BR-GW-36D, BR-GW-88S, and BR-GW-89S for VOC analyses.

Details of QA/QC procedures are provided in Section 4.0.

Tetra Tech 10 Errata- April 2009

3.0 DATA PRESENTATION AND INTERPRETATION

This section presents results of October 2008 semiannual groundwater monitoring. Field sampling logs, water elevation data, groundwater VOC data, and groundwater physical parameter data are provided in Appendices C through G, respectively. Groundwater flow and quality data collected from the current reporting event, along with Tetra Tech’s interpretations of the data, are discussed below.

3.1 GROUNDWATER ELEVATION AND FLOW

The Phase IIA remediation system had been in near continuous operation since 1998 with the exception of the shutdown study from April through September 2004; resulting in mature, well-developed cones of depression in the vicinity of recovery wells. Depth to water and groundwater elevation data for October 2008 are presented in Appendix D.

Groundwater hydrographs for the period from 1996 through October 2008 for a group of wells potentially influenced by the Phase IIA remediation system are shown on Figure 3. Each hydrograph includes a dashed vertical line denoting the day the Phase IIA system was shut down (April 28, 2004). Groundwater elevations were higher in October 2008 than September 2006 for each well shown on Figure 3, with the exception of wells BR-GW-38D and -39S which were dry during both events.

Six replacement domestic wells (BR-GW-66DD, -67DD, -68DD, -71DD, -72DD and -74DD) exhibited groundwater levels above the top of well casing and required the use of a manometer to measure groundwater elevation during October 2008. Well locations are shown on Figure 2.

Figures 4, 5 and 6 are potentiometric surface maps for the shallow portion of Unit A, the deep portion of Unit A, and Unit D, respectively, based on October 2008 groundwater elevations.

Groundwater flow in the shallow and deep portions of Unit A illustrate the strong influence the Phase IIA remediation system, with well developed cone of depressions present around the Phase IIA remediation wells. The potentiometric surface of Unit D does not appear to be influenced by the Phase IIA remediation system pumping, and flow direction is generally to the north-northeast.

3.2 GROUNDWATER EXCEEDING STANDARDS

Table 2 summarizes October 2008 groundwater VOC data. Appendices E, F and G contain databases with October 2008 sample data. Several groundwater samples exhibited VOCs concentrations that exceeded the WQB-7 groundwater standards (DEQ 1999) in October 2008.

These groundwater samples are listed below according to their hydrostratigraphic unit with WQB-7 groundwater standards and their respective sample concentrations in parentheses.

Shallow Portion of Unit A

• VC (0.15 µg/L) – Sample from well BR-GW-39S (1.3 µg/L).

Deep Portion of Unit A

• Chloroform (60 μg/L) – Samples from wells BR-GW-36D (93 µg/L) and SA-13 (84 µg/L).

Tetra Tech 11 Errata- April 2009

• VC (0.15 µg/L) – Sample from well R-8D (1.0 µg/L).

Unit B

• Chloroform (60 µg/L) – Sample from well BR-GW-61DD (105 µg/L).

A description of chloroform distribution and trends for each hydrostratigraphic unit follows.

3.3 CHLOROFORM DISTRIBUTION AND TRENDS

Chloroform groundwater quality in most wells generally continued to improve as a direct result of the 1993-94 soil cleanup, 1998-2004 Phase IIA groundwater remediation, and natural attenuation. Recent and historic trends in chloroform concentrations in selected monitoring wells are shown on Figure 7.

Figure 8 is an interpretation of chloroform concentrations in the shallow portion of Unit A.

Figure 9 is a cross section through the center of the chloroform plume. Figure 10 is an isoconcentration contour map based on October 2008 data for the deep portion of Unit A.

Figures 11 and 12 present an interpreted 60 µg/L chloroform isoconcentration contour plume based on October 2008 data for the shallow and deep portions of hydrostratigraphic Unit A, respectively. A discussion of chloroform distribution and trends according to hydrostratigraphic unit based an interpretation of information shown on Figures 7 through 12 follows.

Shallow Portion of Unit A

• Chloroform has not been detected in any sample from wells completed in the shallow portion of Unit A east of U.S. Highway 93 since July 2000 (Figure 8 and Figure 11).

• The shallow portion of Unit A remediation well samples that contained chloroform were collected from wells R-1 and R-2 at 14 µg/L and 7.6 µg/L, respectively.

• With the exceptions of BR-GW-87S, BR-GW-89S, and R-2, all detected chloroform concentrations in the shallow Unit A wells were lower in October 2008 when compared to September/October 2006.

• Chloroform concentrations in samples collected from wells BR-GW-2, BR-GW-37S, and R-1 continue to exhibit a generally declining trend.

• Chloroform concentrations within the plume continue to decline in response to the 1993- 94 soil removal and treatment and operation of the Phase IIA groundwater remediation system. The aerial distribution of the chloroform plume in the shallow portion of Unit A remains similar to that observed over the last several monitoring events; however the peak concentrations in the center of the plume are considerably less than exhibited during September/October 2006 monitoring events.

Chloroform in the Deep Portion of Unit A

• Chloroform concentrations in the deep portion of Unit A continue to attenuate, particularly east of U.S. Highway 93 (Figures 10 and 12), as a result of remedial actions and natural dilution effects.

Tetra Tech 12 Errata- April 2009

• Comparison of the chloroform concentrations observed in groundwater samples from the wells completed in the deep portion of Unit A collected in October 2008 versus samples collected in September/October 2006 revealed the following:

A slight increase in the chloroform concentration in wells BR-GW-09 (6.1 µg/L to

7.5 µg/L), and SA-16 (15 µg/L to 16 µg/L), Well D-101, not sampled in September/October 2006, contained chloroform at a concentration of 2.9 µg/L.

A significant increase in the chloroform concentration in wells BR-GW-36D (13 µg/L to 93 µg/L), SA-13 (50 µg/L to 84 µg/L), and SA-14 (<0.5 µg/L to 18 µg/L).

A slight decrease in the chloroform concentration in wells BR-GW-90D (8.5 µg/L to 5.8 µg/L), BG-GW-91D (1.5 µg/L to 1 µg/L), R-6D (11 µg/L to 8.5 µg/L), SA-17 (45 µg/L to 39 µg/L), and BR-GW-34D (17 µg/L to 14 µg/L1), A significant decrease in the chloroform concentration in wells BR-GW-31D (57 µg/L to 4.7 µg/L), BR-GW-51D (19 µg/L to 10 µg/L), BR-GW-82D (5.9 µg/L to <0.5 µg/L), BR-GW-92D (18 µg/L to 8.6 µg/L), R-8D (28 µg/L to 13 µg/L), R-9D (112 µg/L to 5.8 µg/L) and R-10 (86 µg/L to 37 µg/L).

Chloroform in Unit B

• The chloroform concentrations in samples from well BR-GW-61DD have decreased approximately 37 percent over the last two years and 50 percent over the last eight years.

• Chloroform was not detected in the samples from Unit B wells BR-GW-56DD, BR-GW- 84D, and D-39.

Chloroform in Units C and D (Replacement Wells)

• Chloroform or other VOCs were not detected in samples from any of the 13 replacement domestic wells monitored in Unit C (BR-GW-65DD, -73DD) and Unit D (BR-GW-62DD, - 66DD, -67DD, -68DD, -69DD, -71DD, -72DD, -74DD, -77DD, and -80DD). Well BR-GW- 63DD was not sampled in October 2008.

• Replacement well BR-GW-70DD contained a chloroform concentration of 14 µg/L1 in the initial laboratory report received; however upon review of the results and further discussion with the laboratory QA/QC officer, a potential laboratory error was identified.

NAL indicated that samples may have been mixed up in laboratory. The chloroform result from BR-GW-70DD may in fact represent water from BR-GW-34D (which was in the same laboratory batch and was run directly before BR-GW-70DD on October 28, 2008). The samples were re-run on October 30, 2008 and BR-GW-70DD was re-

1 Well BR-GW-70DD re-sampled on December 16, 2008 due to laboratory mix up of sample with BR-GW-34D. Re-sample result (<1 µg/L) replaces mix-up concentration, and reported concentration for BR-GW-70DD (14µg/L) is applied to RBR-GW-34D (see more detailed description of the laboratory error in Appendix G).

Tetra Tech 13 Errata- April 2009 sampled on December 16, 2008 and analyzed for chloroform to confirm this suspicion of batch mix-up at the laboratory. No chloroform was detected in BR-GW-70DD from the re-run analysis on October 30, 2008 and BR-GW-34D contained 14 µg/L. The re-sample from BR-GW-70DD on December 16, 2008 was below the chloroform reporting limit (<1 µg/L). A copy of the laboratory write up of the potential sample confusion is included in Appendix G.

3.4 CURRENT EXTENT OF CHLOROFORM PLUME

Figures 11 and 12 are our interpretation of the current extent of chloroform-affected groundwater exceeding the DEQ groundwater standard of 60 µg/L in the shallow and deep portions of Unit A, respectively. The current extent of the shallow and deep portion of Unit A chloroform plumes, bounded by concentrations exceeding 1 µg/L, is shown in Figures 8 and 10, respectively. The affected area within the 1µg/L chloroform isoconcentration line in both the shallow and deep portions of Unit A is estimated to be approximately 16.0 and 84.8 acres, respectively.

NOTES:

930 (y-axis) - Relative Groundwater Elevation (feet)

Phase I system operated April through October 1995 through 1997

Phase IIA system operated July through October 1998 & December 1998 through July 2003

Recovery well R-9 went on-line March 2000

Hydrographs for Wells Potentially Influenced by Phase IIA System Pumping

Bitterroot Valley Sanitary Landfill Victor, Montana

FIGURE 3

Phase II system shut down on April 28, 2004, reactivated September 28, 2004 (indicated by dashed red line)

BR-GW-38D

BR-GW-39S

BR-GW-58S

Dry

BR-GW-40D

BR-GW-82D

BR-GW-8

BR-GW-54D

BR-GW-3

BR-GW-81S

BR-GW-49S

Dry

BR-GW-55S

BR-GW-37S

BR-GW-50D

Deep Unit A Wells Near R-9D

GW-5 GW-21 GW-36D GW-83D SA-13

BR-GW-31D

Dichloro-benzene

Dichloro-ethane

1,4- 1,1- Dichloro-ethane ethene Dichloro- Dichloro-ethene ethene Dichloro-benzene Ethyl-chloride Methylene-ethene chloro-

Toluene ethane Trichloro-ethene Trichloro-methane Fluoro-

Chloride Vinyl

Xylenes Total

Tetra- Trichloro-1,2- 1,1- Cis-1,2- T-1,2- 1,1,1 nese Manga-

Total

TABLE 2

SUMMARY OF OCTOBER 2008 GROUNDWATER DATA

Bitterroot Valley Sanitary Landfill

DateLocation

Carbon chloride Tetra- Chloro-benzene Chloro-ethane

Sample Benzene

Bromo-methane

Chloro-methane

Chloro-form

Dichloro-difluoro-methane

Iron Total

Coliform Total

BRGW-2 10/23/2008 2.2 0.5 1.5 5.5

BRGW-8 10/22/2008 1.5

BRGW-9 10/21/2008 0.9 1.5 7.5

BRGW-10 10/22/2008 1.5

BRGW-31D 10/22/2008 1.5 4.7

BRGW-32S 10/22/2008 1.5

BRGW-33S 10/22/2008 1.5

BRGW-34D 10/21/2008 1.5 14 **J

BRGW-36D 10/22/2008 1.5 93

BRGW-37S 10/23/2008 1.5 21

BRGW-38D 10/22/2008 1.5

BRGW-39S 10/22/2008 1.5 1.3 1.6 1.5 1.4

BRGW-48S 10/23/2008 1.5 25

BRGW-50D 10/24/2008 1.5

BRGW-51D 10/22/2008 1.5 10

BRGW-56DD 10/21/2008 1.5

BRGW-61DD 10/21/2008 1.7 1.5 105 J

BRGW-62DD 10/20/2008 1.5

BRGW-65DD 10/20/2008 1.5

BRGW-66DD 10/20/2008 1.5

BRGW-67DD 10/20/2008 1.5

BRGW-68DD 10/20/2008 1.5

BRGW-69DD 10/24/2008 1.5

BRGW-70DD 10/21/2008 1.5 1 **<

BRGW-71DD 10/22/2008 1.5

BRGW-72DD 10/20/2008 1.5

BRGW-73DD 10/20/2008 1.5

BRGW-74DD 10/24/2008 1.5

BRGW-77DD 10/20/2008 1.5

BRGW-80DD 10/20/2008 1.5

BRGW-81S 10/22/2008 1.5

BRGW-82D 10/22/2008 1.5

BRGW-84D 10/20/2008 1.5

BRGW-87S 10/24/2008 1.5 5.6

BRGW-88S 10/24/2008 1.5 14

BRGW-89S 10/24/2008 1.5 7.2

BRGW-90D 10/22/2008 1.5 5.8

BRGW-91D 10/21/2008 1.5 1

BRGW-92D 10/21/2008 1.5 8.6

R-1 10/24/2008 1.5 14 R-2 10/24/2008 1.5 7.6 R-3S 10/27/2008 1.5 R-4D 10/27/2008 1.5 R-5S 10/27/2008 1.5 R-6D 10/27/2008 0.5 1.5 8.5 0.6 R-7S 10/24/2008 1.5 R-8D 10/27/2008 1.9 1 1.4 1.5 13 2.2 1.7 R-10 10/24/2008 0.6 0.6 1.5 37 1.4 D-101 10/22/2008 1.5 2.9 D-39 10/22/2008 1.5

SA-13 10/23/2008 1.5 84

SA-14 10/23/2008 1.5 18

SA-16 10/23/2008 1.5 16

SA-17 10/23/2008 1.5 39

G:\DatabaseInfo\BVSLDbase\705Event\bvsl2k.mdb <Table_2_Summary.rpt> Tetra Tech

Montana GW Standard 5 48 3 --100 75 -- 4 728 60 1,400 70 100 700 5 5 1,000 200 5 10,000 0.15 10,000

NOTES:

- All concentrations in micrograms per liter

- Montana GW (Groundwater) Standard from WQB-7 (9-99)- Blank cell indicates not detected above the practical quantitation limit

- Compounds listed are those that have been detected at least once since 1992 - Shading indicates over Montana GW Standard

30050 <1 PER

100ml

** - Well BR-GW-70DD re-sampled on December 16, 2008 due to laboratory mix up of sample with BR-GW-34D.

Re-sample result (<1 µg/L) replaces mix-up concentration, and reported concentration for BR-GW-70DD (14µg/L) is applied to RBR-GW-34D (see more detailed description of the laboratory error in Appendix G).

TABLE 2

SUMMARY OF SEPTEMBER/OCTOBER 2008 GROUNDWATER DATA

Bitterroot Valley Sanitary Landfill

DateLocation

Carbon chloride Tetra- Chloro-benzene Chloro-ethane

Sample Benzene

Bromo-methane

Chloro-methane

Chloro-form

Dichloro-difluoro-methane

Dichloro-benzene

Dichloro-ethane

Dichloro-ethane ethene

Dichloro- Dichloro-ethene ethene

Dichloro-benzene

Ethyl-chloride

Methylene-ethene chloro-

Toluene ethane Trichloro-ethene Trichloro-methane Fluoro-

Chloride Vinyl

Xylenes Total

Tetra- Trichloro-1,4- 1,1- 1,2- 1,1- Cis-1,2- T-1,2- 1,1,1 nese Iron Manga-

Total Total

Coliform Total

BRGW-2 10/23/2008 0.5 0.5 0.51 2.2 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 25.5 0.5 1 1 0.50.5 BRGW-8 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-9 10/21/2008 0.5 0.5 0.51 0.9 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 27.5 0.5 1 1 0.50.5 BRGW-10 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-31D 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 24.7 0.5 1 1 0.50.5 BRGW-32S 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-33S 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-34D 10/21/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-36D 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 293 0.5 1 1 0.50.5 BRGW-37S 10/23/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 221 0.5 1 1 0.50.5 BRGW-38D 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-39S 10/22/2008 0.5 0.5 0.51 1.5 0.5 0.5 1.30.51.6 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1.4 0.50.5 BRGW-48S 10/23/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 225 0.5 1 1 0.50.5 BRGW-50D 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-51D 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 210 0.5 1 1 0.50.5 BRGW-56DD 10/21/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-61DD 10/21/2008 0.5 0.5 0.51 1.7 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 2105 0.5 1 1 0.50.5 BRGW-62DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-65DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-66DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-67DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-68DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-69DD 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-70DD 10/21/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 214 0.5 1 1 0.50.5 BRGW-71DD 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-72DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-73DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-74DD 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-77DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-80DD 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-81S 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-82D 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-84D 10/20/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 BRGW-87S 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 25.6 0.5 1 1 0.50.5 BRGW-88S 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 214 0.5 1 1 0.50.5 BRGW-89S 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 27.2 0.5 1 1 0.50.5 BRGW-90D 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 25.8 0.5 1 1 0.50.5 BRGW-91D 10/21/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 21 0.5 1 1 0.50.5 BRGW-92D 10/21/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 28.6 0.5 1 1 0.50.5 R-1 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 214 0.5 1 1 0.50.5 R-2 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 27.6 0.5 1 1 0.50.5 R-3S 10/27/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 R-4D 10/27/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 R-5S 10/27/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 R-6D 10/27/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 28.5 0.6 1 1 0.50.5 R-7S 10/24/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 R-8D 10/27/2008 0.5 0.5 0.51 1.9 0.5 0.5 10.51.4 1.50.5 0.50.5 0.5 1 213 2.2 1 1.7 0.50.5 R-9 10/27/2008 0.5 0.5 0.51 0.6 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 25.8 0.5 1 1 0.50.5 R-10 10/24/2008 0.5 0.5 0.51 0.6 0.5 0.5 0.50.50.6 1.50.5 0.50.5 0.5 1 237 0.5 1 1.4 0.50.5 D-101 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 22.9 0.5 1 1 0.50.5 D-39 10/22/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 20.5 0.5 1 1 0.50.5 SA-13 10/23/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 484 0.5 1 1 0.50.5 SA-14 10/23/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 218 0.5 1 1 0.50.5 SA-16 10/23/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 216 0.5 1 1 0.50.5 SA-17 10/23/2008 0.5 0.5 0.51 0.5 0.5 0.5 0.50.50.5 1.50.5 0.50.5 0.5 1 239 0.5 1 1 0.50.5

G:\DatabaseInfo\BVSLDbase\705Event\bvsl2k.mdb <Table_2_Summary.rpt> Tetra Tech

Montana GW Standard 5 48 3 --100 75 -- 4 728 60 1,400 70 100 700 5 5 1,000 200 5 10,000 0.15 10,000

NOTES: - All concentrations in micrograms per liter- Montana GW (Groundwater) Standard from WQB-7 (9-99)- Blank cell indicates not detected above the practical quantitation limit

- Compounds listed are those that have been detected at least once since 1992 - Shading indicates over Montana GW Standard

30050 <1 PER

100ml

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C h lo ro fo rm

C o n c e n tr a ti o n μ g /L

BR-GW-51D

1,000

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C h lo ro fo rm

C o n ce nt ra tio n μ g /L

BR-GW-41S

Data from well GW-58S

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C h lo ro fo rm

C o n ce n tr a tio n (μ g /L

BR-GW-31D

1,000

1,200

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C h lo ro fo rm

C o n ce nt ra tio n μ g /L

BR-GW-82D

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C h lo ro fo rm

C o n ce n tr a tio n μ g /L

BR-GW-2

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C hl or of or m

C on ce nt ra tio n (μ g/ L)

BR-GW-51D

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C h lo ro fo rm

C o n ce n tr a tio n μ g /L

BR-GW-34D

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 '06 '07 '08 '09

C hl or of or m

C on ce nt ra tio n (μ g/ L)

BR-GW-61DD

'92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '02 '03 '04 '05…