Final SWMU B-3 Soil Vapor Extraction Operations And Maintenance Report

Prepared for:

Camp Stanley Storage Activity
Boerne, Texas
 

APRIL 2003

 AFCEE/ERD QAE
Brooks AFB, Texas

 Contract Number F11623-94-d0024
RL74 and RL83

SECTION 1 INTRODUCTION

This report summarizes operations and results for the first 12 months of compliance monitoring activities for the soil vapor extraction (SVE) system at solid waste management unit (SWMU) Burn Area (B-3).  The continued monitoring activities performed were intended to gather additional data to supplement data collected during the pilot tests, and to evaluate performance of the system utilizing all 18 vapor extraction wells (VEW) in the extraction configuration.  A secondary objective of the continued monitoring task was to repair any identified defect in the existing system, and to upgrade the existing blower with a new, larger blower, which would increase the extraction capacity of the SVE system for possible future long-term use at the site.  Recommendations for future SVE applications at the SWMU B-3 site are developed based on results of the SVE treatability study findings described in the SVE Treatability Test Report (Parsons, 2001) and from observations made during the operation and monitoring activities described in this report.

    This document was prepared as the final report to the SVE pilot test work plan.  The purpose of this work was to evaluate the first 12 months of system monitoring results, assess the overall performance of the system, determine the timeframe for continued operation of the system, and if appropriate, recommend modifications to the system to improve its contaminant removal rates.  An interim Operation and Maintenance (O&M) Assessment Report covering the first 5 months of O&M activities was prepared and submitted to CSSA on July 26, 2000. 

Activities performed during the operations and monitoring include:

1.      Installation of a new, more powerful extraction blower;

2.      Initial soil gas testing after the system was idle for at least 2 weeks (field screening only);

3.      Preliminary flow rate adjustment to provide relatively uniform flow from all 18 VEWs;

    4.      Bi-weekly system checks of the extraction pressures and flow rates at each    VEW;

5.      Monthly soil gas monitoring visits to measure hydrocarbons and flow rates at specific VEWs; and

6.      Collection of soil gas samples for laboratory testing at startup and after 5 months, and after 10 months of operation to quantify specific contaminant levels in blower exhaust and in-line emissions.

The SVE pilot test system was constructed at the SWMU B-3 at Camp Stanley Storage Activity (CSSA) in February 1996.  A limited, 2-week initial pilot test demonstrated that an SVE system operated at the site could reduce the volatile organic compound (VOC) concentrations present in the trench area.  The results also indicated that the subsurface soils at the site are very complex, and that it would be difficult to extrapolate pilot test results across the entire site without the collection of additional data.  Some of this complexity was uncovered during an interim removal action and pre-excavation investigation of the SWMU B-3 trenches conducted in 2002 (Foster Wheeler Corporation, 2003), which discovered that the west trench is actually composed of multiple trenches aligned parallel to each other.

An addendum to the original pilot test work plan (Parsons, 1996a) was prepared to describe the data collection activities planned to further evaluate the efficiency of the SVE pilot system, and to determine optimal operating parameters for long-term operation of an expanded system (Parsons, 1996b).  The layout of the expanded SVE system is presented on Figure 1.1.  A soil vapor test report that describes the construction and layout of the expanded system was prepared, and discusses the major results, conclusions, and recommendations (Parsons, 2001).  Completion of this report was delayed due to concerns over validity of the off-site laboratory test data, which resulted in a resampling effort in 2000.

In addition, CSSA initiated cleanup actions at SWMU B-3 in August 2002 to remove source areas of contaminated soil and debris in the east trench of the former disposal area.  The B-3 SVE system was taken out of service during the removal action to facilitate excavation of the contaminated material.  During the 2002 removal action it was discovered that disposal activities at SWMU B-3 occurred in five narrow trenches rather than two wide trenches as originally thought.  The impacts of the actual configuration of the trenches on the SVE performance was not evaluated during this study.  An evaluation of potential remedial techniques for addressing residual contamination in bedrock and groundwater was performed and is summarized in this SVE report.

This report describes work performed under two projects.  The first 6 months of O&M and preparation of the Interim O&M Assessment Report was completed under contract F11623-94-D0024, delivery order (DO) RL74 (Parsons project number 734521.05000).  The second 6 months of O&M and preparation of this final O&M Assessment Report was conducted under DO RL83 of the same contract (Parsons project number 736071.05000).  Preparation of the O&M Plan and procurement/installation of the new blower for the SVE system was also completed under DO RL83.  Evaluation of remedial options was also conducted under DO RL83.

This final report is organized into five sections, including this introduction.  Section 2 describes the methods and protocol employed to perform the bi-weekly monitoring activities.  Results and data evaluations from the monitoring activities are detailed in Section 3.  Section 4 presents an evaluation of applicable remedial techniques for future use at the B-3 site.  Section 5 summarizes the significant findings, including sustained contaminant removal rates, and provides recommendations for future actions.  References are included in Section 6.

SECTION 2 OPERATIONS AND MAINTENANCE TESTING PROTOCOLS

2.1       Overview

The purpose of this section is to summarize SVE monitoring activities performed during the first 12 months (January 2000 - January 2001) of operation at SWMU B-3.  Before restarting the extraction system, a diagnostic and structural check of the system was performed as part of the O&M task.  Several small portions of the aboveground plumbing network that manifolds the VEWs to the blower were damaged and were replaced.  As part of the diagnostic check, the connections at each wellhead and flow control valve were thoroughly inspected and repaired as necessary.

In December 1999 the existing Gast Model R5 regenerative blower used for the start-up tests, was replaced with a new, more powerful R6 regenerative blower during the initial system check.  The R6 series blower is capable of exerting greater extraction pressures and maintains higher flow rates than the R5 model.  Once system repairs and upgrades were complete and initial soil gas samples were collected, the new blower was started and initial blower settings were established.  Flow rates from all 18 VEWs were checked and adjusted to obtain relatively uniform flow from all VEWs.

The primary activities associated with first 12 months of O&M included bi-weekly monitoring of system performance, collection of emission and soil gas samples during three periodic sampling events (initial, 5-month, and 10-month), and general system maintenance.  Additional data collection was performed during the second 5 months (July - November 2000) of testing, including measuring the percolation rate of rainwater into and through the main trench at SWMU B-3.

2.2       Initial soil gas and Flow adjustments

Prior to beginning the O&M effort, the system was idle for more than 3 weeks (21 consecutive days).  To establish the initial flow rates, the initial soil gas sampling event was performed on January 5, 2000.  This was accomplished following replacement of the extraction blower and before turning on the system.  Initial soil gas sampling was performed to acquire baseline data prior to reinitiating air extraction.  Initial soil gas samples were collected from each of the 18 VEWs and six vapor monitoring points (VMP) installed at SWMU B-3 for field measurements.  Oxygen, carbon dioxide, and total volatile hydrocarbons (TVH) testing were measured on each of the samples collected.

During startup, extraction was initiated from all 18 VEWs.  Flow and TVH levels from each VEW were monitored and the flow control valves adjusted to balance the flow as much as reasonable.  It was not possible to create a balanced flow from all 18 VEWs because some (VEW-11, VEW-14, VEW-15, VEW-17, and VEW-18) appear to have been installed in low permeability soils.  However, it was possible to adjust the flow rates in a relatively narrow range from 75 feet per minute (fpm) in VEW-14 to 400 fpm in VEW-01, VEW-02, VEW-03, and VEW-05.  The measured flow from the main exhaust was targeted at 4,000 fpm, or 87.2 cubic feet per minute (cfm).  System settings for the initial flow rates are presented in Table 2.1.

Table 2.1    
Initial Flow Rate Setting, January 6, 2000
SWMU B-3 SVE O&M Assessment

Monitoring Point

Air Speed (fpm)

Flow Rate (cfm)

Extraction Pressure (In. H20)

VEW-01

400

8.72

-15.0

VEW-02

400

8.72

-2.00

VEW-03

400

8.72

-0.15

VEW-04

360

7.82

-0.60

VEW-05

400

8.72

-0.60

VEW-06

390

8.50

-5.00

VEW-07

320

6.98

-1.00

VEW-08

350

7.63

-1.00

VEW-09

350

7.63

-1.10

VEW-10

370

8.07

-0.60

VEW-11

100

2.18

-52.0

VEW-12

360

7.82

-1.70

VEW-13

340

7.41

-0.55

VEW-14

75

1.64

-50.0

VEW-15

100

2.18

-52.0

VEW-16

350

7.63

-0.80

VEW-17

180

3.92

-52.0

VEW-18

200

4.36

-54.0

Main Exhaust

4000

87.20

-5.50

    Using the settings listed in Table 2.1, soil gas readings were collected from the operating extraction system to measure hydrocarbon levels in the flow streams from each of the wells and the main exhaust.  These data were evaluated to estimate initial hydrocarbon removal rates from specific VEWs, and to possibly assist with selection of VEW lines for analytical testing.  The estimated hydrocarbon levels are presented on Table 2.2.  The rate of TVH removal indicated from the main exhaust line (3,959 ppmv/min) agrees favorably with the cumulative sum of the TVH flow rates (approximately 4,110 ppmv/min).  This correlation instills a high degree of confidence in the use of the field screening data to monitor relative removal rates from the wells.

After final adjustment of the SVE system was complete on January 6, 2000, the system was shut down and allowed to sit idle for at least 72 hours prior to collecting soil gas and emission samples (Section 2.4).

Table 2.2        
TVH Estimated Levels
at Initial System Settings, January 6, 2000
SWMU B-3 SVE O&M Assessment

Monitoring Point

Flow Rate (cfm)

Hydrocarbon Level (ppmv)

TVH Flow Rate (ppmv/min)

VEW-01

8.72

110.0

1,683

VEW-02

8.72

119.0

1,166

VEW-03

8.72

1.9

14.4

VEW-04

7.82

9.3

70.7

VEW-05

8.72

53.3

335.8

VEW-06

8.50

58.2

378.3

VEW-07

6.98

2.4

31.4

VEW-08

7.63

15.6

170.0

VEW-09

7.63

8.3

87.2

VEW-10

8.07

0.0

0

VEW-11

2.18

14.4

13.0

VEW-12

7.82

4.5

54.0

VEW-13

7.41

0.0

0

VEW-14

1.64

23.4

21.1

VEW-15

2.18

0.0

0

VEW-16

7.63

3.8

24.7

VEW-17

3.92

3.5

60.9

VEW-18

4.36

1.5

1.4

Main Exhaust

87.20

44.3

3,959

    Flow and pressure readings were monitored on a bi-weekly basis to determine if there were significant fluctuations in the key operating parameters.  Results from the bi-weekly sampling are presented in Section 3.

2.3       Bi-Weekly System Checks and Monthly Monitoring

Bi-weekly system checks were conducted to assure that system operations continued to perform satisfactorily.  The bi-weekly system checks involved recording blower performance data on a log sheet, measurement of flow rates and vacuum pressures at each VEW, and general inspection of the condition of the aboveground plumbing.  Accumulated drainage water from the moisture separator was drained from the tank into an adjacent evaporation pan as necessary during each bi-weekly visit.

Every other bi-weekly system check corresponded with the monthly monitoring effort.  The monthly monitoring visits included direct measurements of TVH, oxygen, and carbon dioxide in the individual flow streams, and emissions from the main blower exhaust, in addition to the bi-weekly system checks.  The schedule of activities completed during the 12-month O&M assessment period is presented in Table 2.3

Table 2.3        
Schedule of Completed O&M Activities,
SWMU B-3 SVE O&M Assessment

Activity

Begin Date

Completion Date

Completed Activities

 

 

1.     Work Plan Addendum preparation (RL83)

Draft
Final

 

September 21, 1999

 

September 20, 1999
December 23, 1999

2.     Procure Blower (RL83)

November 5, 1999

December 8, 1999

3.     Shut Down (Idle) SVE Blower (RL74)

December 15, 1999

Same as begin date

3.     Initial Startup & System Check (RL74)

January 4, 2000

January 6, 2000

4.     Initial Sample Collection (RL74)

January 10, 2000

January 12, 2000

5.     Biweekly System Check (RL74)

January 28, 2000

Same as begin date

6.     Monthly Visit & Biweekly Check & Resample Initial Air Samples (RL74)

February 14, 2000

February 15, 2000

7.     Biweekly System Check (RL74)

February 25, 2000

Same as begin date

8.     Monthly Visit & Biweekly Check (RL74)

March 21, 2000

Same as begin date

9.     Biweekly System Check (RL74)

April 6, 2000

Same as begin date

10.   Monthly Visit & Biweekly Check (RL74)

April 24, 2000

Same as begin date

11.   Biweekly System Check (RL74)

May 5, 2000

Same as begin date

12.   Monthly Visit & Biweekly Check (RL74)

May 22, 2000

Same as begin date

13.   Biweekly System Check (RL74)

June 2, 2000

Same as begin date

14.   Monthly Visit & Biweekly Check plus 5-Month Emission & Air Samples(RL74)

June 19, 2000

June 21, 2000

15.   Biweekly System Check (RL74)

June 30, 2000

Same as begin date

16.   Monthly Visit & Biweekly Check (RL74)

July 13, 2000

Same as begin date

17.   Prepare Interim O&M Report (RL74)

Draft
CSSA/AFCEE review
Final

 

July 11, 2000
July 26, 2000
August 8, 2000

 

July 25, 2000
August 8, 2000
August 22, 2000

18.   Biweekly System Check (RL74)

July 27, 2000

Same as begin date

19.   Monthly Visit & Biweekly Check (RL83)

August 11, 2000

Same as begin date

20.   Biweekly System Check (RL83)

August 24, 2000

Same as begin date

21.   Monthly Visit & Biweekly Check (RL83)

September 8, 2000

Same as begin date

22.   Biweekly System Check (RL83)

September 25, 2000

Same as begin date

23.   Monthly Visit & Biweekly Check (RL83)

October 5, 2000

Same as begin date

24.   Biweekly System Check (RL83)

October 23, 2000

Same as begin date

25.   Monthly Visit & Biweekly Check, & Collect 10-Month Samples (RL83)

November 2, 2000

November 7, 2000

26.   Monthly Visit & Biweekly Check(RL83)

December 1, 2000

Same as begin Date

27.   Biweekly System Check (RL83)

December 15, 2000

Same as begin date

28.   Monthly Visit & Biweekly Check(RL83)

December 28, 2000

Same as begin date

29.   Biweekly System Check (RL83)

January 12, 2001

Same as begin date

30.   Monthly Visit & Biweekly Check (RL83)

January 25, 2001

Same as begin date

31.   Monthly Visit & Biweekly Check (RL83)

February 22, 2001

Same as begin date


    The bi-weekly system checks were initiated on January 28, 2000 and were originally scheduled to be conducted through 10 months of operation.  However, following completion of the 10-month sampling event on November 7, 2000, CSSA decided to extend the monthly and bi-weekly sampling activities through January 2001 to cover 12 months of operation.  During this extended period, system checks and the system monitoring activities were performed during each site visit.  Also, one additional monthly site visit was conducted on February 22, 2001.  

2.4       Collection of Air Emission Samples

Soil gas air samples were collected from the system and submitted for laboratory analysis during initial testing and startup, after 5 months of continuous operation, and after 10 months of operation.  The VEWs that contributed most to VOC mass removal during the 1997 multiple configuration tests were selected for analytical sampling during this O&M task.  Samples were collected from the selected sampling points (VEW-01, VEW-03, VEW-04, VEW-10, VEW-12, and VEW-15) during each sampling event to allow for direct comparison of results.  Based on the initial soil gas testing results (see Table 2.2), these points represent locations with high, medium, and low levels of TVH in the flow stream and variable vacuum extraction pressures.

During each sampling event, emission samples were collected from the system exhaust at approximately 1-, 8-, and 24-hour intervals after restarting the SVE system.  One duplicate sample was collected from the second emission sample (8-hour) during the first sampling event.  During the June 2000 sampling event the duplicate sample from the third emission sample (24-hour) was analyzed in place of the original sample due to integrity problems associated with the air canister in the original sample.  All emissions and soil gas air samples were tested for VOCs using Environmental Protection Agency (EPA) Method TO-14.  The Statement of Work for both DOs requested analysis of air samples to include ethane, ethene, and methane.  Since only exhaust emission samples were planned for this 12-month O&M effort, analysis for these three parameters was not necessary, and would provide little usable data, these parameters were deleted from the requested analysis.  The CSSA quality assurance (QA) plan was followed for sample collection, analysis, and data validation.

Initial emission samples were collected on January 10-11, 2000 after the new blower system was checked and final adjustments were complete.  The blower was operated for approximately 6 hours during system adjustment performed on January 5-6, so the system was shut down on January 6 to allow the soil gas conditions to equilibrate in preparation of the January 11 sampling event.  Samples from the VEW flow lines were collected immediately after collection of the 1-hour emission sample.

The laboratory was unable to complete the analysis within the prescribed holding time, so the initial soil gas sampling activities had to be repeated during the monthly monitoring visit performed on February 14-15.  The 5-month and 10-month sampling events were performed on June 19-21 and November 6-7, 2000, respectively.  The blower was shut down at least 24 hours prior to each sampling event so the sampling intervals for the emission samples matched the intervals used for the initial sampling event.

2.5       Air Emissions

A modification to CSSA�s standard air exemption (Registration No. 32405 SVE System) for the B-3 SVE system was approved by the Texas Commission on Environmental Quality (TCEQ, formerly known as Texas Natural Resources Conservation Commission) on February 22, 1999 to allow extraction to pull from up to 18 VEWs.  Biweekly system checks verified that the maximum extraction flow rates did not exceed the permitted limit of 110 standard cubic feet per minute (scfm).  Emission samples were collected during initial startup (or resampling), after 5 months, and after 10 months of continuous operation.  These emission samples were tested for contaminants of concern to provide for periodic monitoring of contaminant levels in the system exhaust.

2.6       Water Level Measurements

During the multi-configuration testing of the expanded SVE system, the airflow generated in the soil material was lower than observed during previous testing.  The testing followed a rainfall event and the reduction in airflow was attributed to an increase in water content in the pore spaces of the trench soils.  An increase in water content within the pore spaces reduces the volume of pore space available for airflow, and as a result, a decrease in airflow immediately following a rainfall event is expected, but in the case of the observed instance, the reduction in airflow persisted longer than expected.  As a result, an evaluation of groundwater accumulation and drainage in the B-3 trenches was conducted. 

From October 5 through December 1, 2000, a pressure transducer was placed in VEW-01 to evaluate movement of groundwater into and out of the trenches.  The transducer was placed in VEW-01 following a rainfall when water was found to be present in the VEW.  Rainfall data were also collected over the same time period to assess rate of accumulation following rainfall events.

Additionally, groundwater levels were measured in select VEWs in July 2002 to evaluate the accumulation of groundwater in the trenches following a period of heavy rainfall and flooding at the beginning of July.  Water levels were measured in wells VEW-01, VEW-02, VEW-03, VEW-04, and VEW-15.  Water levels were measured to assess the accumulation of groundwater following the heavy rainfall/flooding event at the beginning of July 2002 and prior to the initiation of removal actions at B-3.

2.7       Groundwater Sampling

Groundwater samples were collected from the SVE system to evaluate contaminant concentrations partitioning into the groundwater within the B-3 trenches.  These samples were collected by CSSA environmental personnel, and results were provided to Parsons for inclusion into this report.  Samples were collected from VEW-01, VEW-02, VEW-04, VEW-10, VEW-12, and the drain port on November 7, 2000.  Well VEW-01, which contained the highest concentrations in the November 2000 sampling event, was re-sampled on July 19 and July 23, 2002 following a flood event earlier that month.  Results of the groundwater samples provided information regarding the location and relative concentration within the trench, and contaminant levels that may be migrating into the underlying bedrock. 

SECTION 3 RESULTS AND DATA EVALUATION

This section summarizes results of 12 months of bi-weekly system checks including monthly soil gas monitoring.  Results from the soil gas and exhaust emission samples collected during the initial startup, after 5 months, and after 10 months of operation are also included in this section.  These results are important because they allow for a comparison with other periodic sample results from this O&M task, and from results obtained during the pilot test activities of the SVE system.  A brief evaluation of the possible implications or conclusions of test results are included in the associated summaries.

3.1       Initial Soil Gas Results

Air extraction was shut down on December 15, 1999 by CSSA in anticipation of starting the 1 year O&M program for the SVE system.  Initial soil gas in each of the SVE monitoring points (and VEWs) was measured using field instruments on January 5, 2000, and the results are presented on Table 3.1.  Also included in Table 3.1 are results from the initial soil gas screening events performed during the initial pilot test, and during the expanded system treatability study.  Initial soil gas points were field screened for oxygen, carbon dioxide, and TVH using field instruments.

Screening results indicated that anaerobic conditions continued to persist at several of the tested subsurface locations within the main trench, primarily at depths of 10 feet or greater.  In fact, oxygen levels in some of the test points sampled in January 2000 (VEW-01, VEW-02, VEW-03, VEW-05, MPA-10, MPC-14, and MPD-15) returned to levels originally reported in the initial soil gas testing event performed in March 1996, while some oxygen levels remained significantly higher (VEW-04, VEW-07, VEW-08, VEW09, and MPA-05).  Meanwhile, TVH levels continued to maintain a pattern of decreasing values from March 1996 to January 1997, and then to January 2000.  The only exceptions were found in MPC-05 where the levels rose from 16 to 30 ppm between 1997 to 2000, and in MPD-10, where levels rose slightly from 133 (1997) to 140 ppm (2000).

These results are indicative of continued biological activity, despite the decreasing TVH levels observed in the subsurface soil gas.  There was no pattern observed with the carbon dioxide gases throughout the three test events, but some of the highest levels (12 to 25 percent) encountered in initial soil gas to date were noted in several test points measured in the January 2000 event.  These values provide further evidence of the ongoing biological activity.  According to the results, the greatest levels of biological activity were observed in VEW-01, VEW-03, VEW-11 to VEW-18, and in the deeper intervals at MPA, MPC, and MPD.  These findings are consistent with previous test results, which indicated that anoxic conditions are more prevalent in the deeper zones of the trench near the center and western edge of the defined treatment area.

3.2       Bi-weekly System Checks and Monthly Monitoring Results

Continued operation of the SVE system began on January 11, 2000.  Air flow measurements and vacuum pressures were obtained at each VEW to ensure that the settings established during the system adjustment (Section 2.2) were maintained.  During the 12 months following system startup, personnel from Parsons performed system checks on an approximate 2-week schedule to ensure that continuous air extraction remained relatively uninterrupted, and that blower operating parameters remained stable.  Measurements of extraction pressure and air flow velocity at each VEW and at the blower were collected as specified in the SVE Test Plan, Second Addendum.  Results from this data collection through February 22, 2001 are compiled in Table 3.2 (extraction pressures) and Table 3.3 (air flow), respectively.  Temperatures of the blower�s main exhaust emissions were also measured and recorded in Table 3.2.  Flow and pressure results are not included for the March 10, April 24, and May 22 bi-weekly checks because either the data were not recorded, or the records were misplaced.

Only minor manual adjustments were made to modify flow rates from any of the 18 VEWs.  Some of the VEWs were slightly damaged during soil resampling performed at the site in April 2000, so minor repairs and flow adjustments were performed to maintain flow rates for individual VEWs near levels established during the initial set up.  As seen in Table 3.2, extraction pressures remained relatively stable, although some VEWs experienced sharp increases in the extraction pressures beginning in April and persisted into August 2000.  From August to November there was a general decrease in extraction pressures in most wells, after which the pressures increased.

From the beginning of the bi-weekly system checks until the August 11th system check, flow rates appeared to remain relatively stable during each check.  Beginning August 24, a significant increase in flow rates was observed at most VEWs.  In many VEWs, the increased flow rates continued to the end of the bi-weekly monitoring in February 2001.  The decreased pressures and increased flow rates beginning in August are likely the result of generally warmer and drier subsurface soil.  This period corresponds with a period of drought at the CSSA site.  Between June 13 and November 5, a total of 2.78 inches of rainfall was recorded at CSSA.  A majority of the rainfall during this period came in infrequent small rainfall events of 0.5 inches or less separated by extended periods of no rainfall.  Therefore, the increase in flow rate and decrease in pressure may be the result of an increase in permeability due to lower water content (less water occupying pore spaces).  The change could also have been exacerbated by the creation of soil cracks through desiccation thereby increasing the secondary porosity of the soils.  Historically at this site, higher extraction pressures (and lower flow rates) were associated with wetter subsurface soil conditions, as experienced during the second multiple configuration test (MCT-2) performed during a rainy period in 1997 (Parsons 2001, Soil Vapor Extraction Test Report).

Monthly soil gas monitoring was performed at each well to assess relative contaminant and degradation indicator parameter concentrations.  Monthly soil gas monitoring included measurements of oxygen, carbon dioxide, and TVH at each VEW and the main exhaust.  The oxygen, carbon dioxide, and TVH measurements were collected using field instruments.  During the June 19, 2000 system check, the Photovac 2020 was not functioning properly, so the soil gas measurements for this event were completed on June 20.  Results from field screening measurements from the VEWs are presented on Table 3.4.  Soil gas readings were also collected from the VMPs on January 5, February 14, June 20, and November 6, 2000, and are presented in Table 3.5

Soil gas readings show wide variability, with oxygen levels generally increasing through the initial 4 to 5 months of operation before reaching a relatively constant level.  The oxygen level in most VEWs exhibited a decrease beginning in November and continuing to the end of the monitoring period.  Carbon dioxide levels showed a general decrease over time at most monitoring points through November, after which an increase in concentrations was observed coinciding with the decrease in oxygen levels.  In general, TVH levels showed a decrease over time with the exception of a brief increase in many VEWs from June to August, which corresponds to a draught period at the site.  A few exceptions do exist, such as the June 19, 2000 oxygen readings at VEW-09 and VEW-16, which both experienced significant oxygen losses.  Several other VEWs also exhibited lower oxygen levels on June 19, 2000 than in the proceeding monitoring visit. 

Generally, oxygen increases occur in response to improved ventilation (air circulation) and delivery of oxygen from the surface as a result of displacement of soil gas caused by physical extraction processes and decreases in biological activity resulting from reductions in contaminant concentrations.  Conversely, oxygen decreases are typically associated with increased biological activity caused by improving metabolic conditions so air flow is no longer adequate to maintain higher oxygen levels (due to increased biological consumption), or because the air circulation system has been impaired.  Poor air circulation is usually caused by increased moisture content (reduced air-filled porosity) in the soil, or by a decrease in the effective extraction (screened) interval due to rising water levels.  Meteorological data from CSSA�s weather station indicates significant rainfall events through June 14 preceding the June 19 sampling event.

3.3       Soil and Gas Air Emission Results

3.3.1        Contaminant Removal Rates

A total of 18 soil gas and nine exhaust emission samples were collected for analytical testing during the first 10 months of O&M.  The samples were collected during three sampling events.  Each sampling event consisted of six in-line samples from individual VEWs and three emission samples collected from the system�s main exhaust.  The individual soil gas samples were collected from the same VEWs during each sampling event.  Emission samples were collected after 1 hour, 8 hours, and 24 hours of continuous operation (after being shut down for at least 72 hours prior to restarting the system).

Results of the analytical testing events are summarized in Table 3.6, and are arranged to allow for direct comparison between the three sampling events.  Data validation summaries for the laboratory data are included in Appendix A of this report.  Also included in Table 3.6 are the estimated pounds per hour calculated for each data point using the estimated flow rate.  Calculations for these results are presented in Appendix B.

All laboratory data collected as part of the SVE O&M assessment were validated using the AFCEE Quality Assurance Project Plan (QAPP), version 3.0 to ensure generation of defensible data.  Data validation reports are provided in Appendix A of this report for all sampling events.  All samples submitted to the laboratory were prepared and analyzed within the specified holding times using the EPA-approved analytical procedures with the following exceptions.

bullet

Samples collected during the initial sampling event (January 10-11, 2000) were not analyzed within the AFCEE QAPP 14-day holding times.  As a result, resampling was performed on February 14-15, 2000. bullet

The sample collected for Emission #3 was received at the laboratory without any pressure, indicating that the canister had leaked.  The duplicate sample (DUP-1) was collected from this same location and time interval, so it was analyzed as Emission #3.  There was no duplicate sample for this batch of samples.

    With the exception of PCE, the levels of contaminants detected in the main exhaust stream showed a significant reduction over the three sampling events.  Contrary to this finding, several of the individual VEWs sampled indicated higher removal rates (lbs/hr) for cis-1,2-DCE and TCE with time.  The decrease in the removal rate from the main exhaust is likely caused by a reduction in the cumulative contaminant levels from the 12 VEWs not sampled for this study.  Vinyl chloride removal rates were very low in samples collected from both testing events, but experienced an almost 10-fold reduction in the concentration reported in the main exhaust.  This sharp reduction can be attributed to continuing extraction on the complete 18-VEW system.  Vinyl chloride encountered in the trench is generated from biological degradation of more complex chlorinated hydrocarbons including TCE, PCE, and cis-1,2-DCE , which are present at the site.  Results indicate that vinyl chloride removal rates are greater than the rates at which it is generated.  It is also possible that reductions in vinyl chloride are found because the extraction process is capable of pulling atmospheric air into the treatment zone making aerobic biological degradation a contributor to reductions in vinyl chloride levels.

    Monthly field screening results were used to compare TVH removal rates during the 12-month O&M assessment.  Table 3.7 presents a comparison of TVH removal rates for monthly screening from January 6, 2000 to February 22, 2001.  No other records exist that include both TVH and flow rates for performing this evaluation.  Of particular concern is the variability of the flow rate over time.  Many VEWs exhibited a general trend toward lower flow rates from January 6 through August 11, 2000.  In the September 8 monitoring data, the flow rates from all the VEWs exhibited a significant increase which was generally followed by a gradual downward trend in the flow rates through the remainder of the monitoring period.

The TVH removal rates from the VEWs exhibited considerable variability between monitoring events with a general trend toward lower rates over time.  The data indicate that several VEWs are contributing higher amounts to the removal rates.  These VEWs, (VEW-01, VEW-02, VEW-04, VEW-05, and VEW-06) typically showed TVH removal rates significantly higher than the remaining VEWs.  The increased removal rates observed in these VEWs is likely attributable to the higher flow rates maintained at these points.

The variability of the flow and removal rates observed in the data are likely attributable to the drastic fluctuations in saturation levels of the shallow material, annual temperature variations, and the geologic complexities of the B-3 site.  Sudden groundwater fluctuations have been observed at the site following rainfall events.  Temperatures at the site can vary between a wide range over the course of the year and can have a significant impact on the volatility of the contaminants and therefore, the removal rate.  Also, the geologic conditions appear quite complex with the presence of clayey soil material with varying composition overlying a highly fractured bedrock unit.  Given the magnitude of some of the removal rates experienced in the November 2000 sampling event, it is more likely that the radius of influence of each VEW has grown into adjacent areas with greater contaminant concentrations.  Reduced moisture and higher temperatures may be facilitating this expansion. 

3.3.2    Air Emissions Summary

The results of air emissions sampling are presented in Table 3.8 with estimated removal rates and total quantities removed included for the February, June, and November sampling events.  The hydrocarbon meter was malfunctioning during the February event, so no TVH data were collected.  The total maximum removal rates were observed for TCE at 0.0256 pound per hour (lb/hr) during the February testing event.  The estimated cumulative mass of TCE removed during this 24 hour extraction period tested was 0.735 pounds.

Generally, contaminant concentrations would be expected to decrease over the initial 24 hours of extraction after restarting an inactive system.  Despite idling the system for at least 72 hours prior to performing the air emission sampling, no apparent trend was observed in the three test events.  During the February event, the emissions exhibited a decreasing trend for the four contaminants of concern with the only exception noted by a slight increase in the 24 hour sample for cis-1,2-DCE over the 8-hour sample.  For the June test event TCE and TVH concentrations increased with time while the other parameters showed variability over the test intervals.  During the November test event the TVH concentrations showed a decrease with time, whereas all other parameters showed variability with time.

Although these findings seem rather inconsistent, they indicate that emissions from the SVE system continue to behave as observed in the treatability test completed in 1997 (Parsons, 2001).  During the 1997 test, three tested configurations demonstrated that TCE levels increased in emissions during the initial 24 hours of testing, and then behaved with little or no trend during the following 96 hours.  The O&M emissions data collected under this project lead to the same conclusion, that continuous operation of the SVE system will remove more contaminants over time than pulsing the system.

Given that the contaminant levels appear to remain relatively constant in the exhaust emissions, the total mass of contaminants removed by the SVE system during the initial 12 months (365 days or 8,760 hours) of O&M was estimated using the average removal rates (see Table 3.8).  The estimated cumulative mass of each contaminant removed by SVE operations during the 12 months of O&M activities (January 11, 2000 through January 10, 2001) are as follows:

bullet

TCE = 161.18 pounds (8,760 hr x 0.0184 lb/hr), bullet

Cis-1,2-DCE = 77.09 pounds (8,760 hr x 0.0088 lb/hr), bullet

PCE = 50.81 pounds (8,760 hr x 0.0058 lb/hr), and bullet

Vinyl Chloride = 0.96 pounds (8,760 hr x 0.00011 lb/hr).


    Based on the data collected from the emissions samples, the 18-VEW extraction system does not result in contaminant emissions above the standard exemption for the B-3 SVE system.  It is interesting to note that TCE is the primary contaminants removed by conducting SVE in the western trench, whereas waste characterization and closure confirmation data collected from the eastern trench during excavation activities suggested that the primary contaminant present in the remediation soils, and in the liquid waste drums uncovered, was PCE.

3.4       Groundwater Evaluation results

3.4.1        Groundwater Elevation Measurements

Field observations reveal that water percolation, drainage and infiltration into the trench area can create significant negative impacts to the SVE system operation.  Observations made during routine bi-weekly visits identified the presence of groundwater in some VEWs immediately following a rainfall event.  Groundwater has been observed in VEW-01, VEW-04, VEW-10, VEW-12 and VEW-15 following rainfall.  Water levels have risen to as high as 3 feet below grade (or up to 15 feet water column in the measured VEWs) within the trench following significant rainfall events (July 2002).

The accumulation of groundwater in the VEWs can have a significant impact on the performance of the SVE system.  With groundwater in the well, the length of well screen open to extract soil gas from the surrounding material is reduced.  Additionally, groundwater flowing through the subsurface will follow the more permeable material, thereby reducing the ability of the system to extract soil gas from these permeable zones.  The increasing humidity and saturation of pore spaces also can reduce and negatively impacts the removal rates.

In November 2000, Parsons installed a pressure transducer in VEW-01 to monitor the rise and fall of groundwater in the well following rainfall events.  Analysis of the data indicates a strong correlation between rainfall events and water levels in the trench.  The water level in VEW-01 increased immediately after rainfall events and then declined slowly with time.  The slow drop in water levels following a rainfall event suggests that the material within the west trench has a low permeability.  Additionally, as indicated on Figure 3.1, there appears to be an almost immediate increase of the water level in the well for rainfall events greater than 1.5 inches in a 24-hour period.  This immediate response for rains greater than 1.5 inches may be attributable to flooding around the well and leakage into the well.  It has also been theorized that water recharges and accumulates inside the trenches due to recharge, percolation, and draining from water transmitted through horizontal bedding layers within the upper limestone formation.  The trenches may actually function as a break in the drainage path, allowing the water to accumulate temporarily within the less permeable trench materials. 

 3.4.2    Groundwater Sampling

Groundwater samples were collected from wells VEW-01, VEW-04, VEW-10, VEW 12 and the drain port on November 7, 2000.  Analytical results of the samples identified the presence of several VOC constituents.  Of note, cis-1,2-dichloroethene and trichloroethene were present in the sample from VEW-01 at concentrations of 27,000 and 2,900 �g/L, respectively.  Cis-1,2-dichloroethene and TCE were present at much lower concentrations in the other samples.  PCE, vinyl chloride and other volatile constituents were present at low concentrations.  Table 3.10 presents a summary of the groundwater sample results from B-3.

On July 19 and 23, 2002, groundwater samples were again collected from VEW-01 following a heavy rainfall and flooding event in early July.  Sample results revealed the presence of TCE, cis-1,2-dichloroethene, trans-1,2-dichloroethene, 1,1-dichloroethene, and vinyl chloride.  Cis-1,2-dichloroethene was detected at much higher concentration than the other analytes, and was present at a concentration of 12,100 �g/L in the July 19 sample and at 8,190 �g/L in the July 23 sample. 

Comparison of the concentration trends from the 2000 and 2002 sampling events indicates that biodegradation is occurring at B-3.  The ratio of cis-1,2-dichloroethene to TCE has increased from the November 2000 to the July 2002 sampling events.  This increase in the cis-1,2-dichloroethene to TCE ratio indicates that the source material continues to be degraded to daughter products, which is consistent with the decrease in PCE and TCE concentrations observed in the samples.  Also, the presence of vinyl chloride in the samples suggests that complete degradation of the chlorinated compounds is occurring and not terminating at an intermediate stage, although the high levels of cis-1,2-dechloroethene relative to the vinyl chloride levels suggests that this process is not vigorous.

Table 3.9        

Water Levels in VEWs Following July 2002 Flood SWMU B-3 SVE O&M Assessment Report

Date

VEW-01

VEW-02

VEW-03

VEW-04

VEW-15

July 11, 2002

3.93

4.02

--

6.46

3.52

July 22, 2002

12.62

12.59

9.56

9.00

8.83

July 23, 2002

10.53

--

--

--

--

July 26, 2002

12.10

12.45

12.29

14.11

11.79

July 29, 2002

--

13.51

--

14.64

12.60

August 2, 2002

13.66

14.30

13.76

15.08

13.08

August 7, 2002

14.70

dry

14.45

16.76

14.12

August 23, 2002

14.61

15.28

14.17

17.19

14.18

Water levels reported as depth to water measured in feet.

-- Water level not measured

SECTION 4 TECHNOLOGY EVALUATION

Use of the SVE system has proven effective in removing VOCs from the landfill and shallow bedrock material at the B-3 area.  Over the course of treatment, an estimated 290 pounds of solvent have been removed.  However, site data suggest that significant amounts of the contaminants remain in the trench areas. 

From August through October 2002, CSSA conducted a partial removal action at the unit to remove the contaminated soil and fill material (Foster Wheeler Corporation, 2003).  The work was temporarily discontinued in October 2002 because the volume of waste material and quantity of hazardous waste generated exceeded original estimates.  Only excavation of the eastern trench was completed.  Landfill remediation efforts for the western trench at SWMU B-3 will be re-initiated as part of an overall remediation effort planned for SWMU B-3.  This planned excavation work will continue until all contaminated material has been removed or until bedrock is encountered. 

In combination with the B-3 removal activities, additional remedial actions will be required to address the residual contamination in the unsaturated bedrock material and in the groundwater.  To address this need, an evaluation of applicable remedial options was conducted to identify suitable technologies.  The preferred technology should be capable of preventing the continued spread of contamination and reduce contaminant levels in the various phases present (vapor, adsorbed, dissolved, etc.).  The evaluation of technologies assumed that the source material (B-3 trench material) would be removed and that there would be no restrictions on accessibility.  Technologies with low capital and low system maintenance technologies were favored over techniques with high costs and high maintenance.  Also, evaluation of remedial techniques must consider transmissivity of groundwater and high fluctuations in groundwater levels observed at the site.

Techniques that were identified for the unsaturated or partially saturated bedrock material include soil vapor extraction, dual phase extraction, and reductive dechlorination.  The techniques evaluated for treating groundwater included reductive dechlorination and injection of zero-valence iron.  Techniques such as conventional pump and treat, air sparging, and containment with slurry walls were not evaluated because they were determined to be inappropriate for use at the site.  Additionally, techniques such as steam extraction, surfactant flooding, and chemical oxidation were not evaluated due to high anticipated costs and concerns for mobilizing contaminants into the fractured and karstic aquifer.  Part of the higher anticipated costs is the need for an expensive investigation to identify the precise locations and an accurate assessment of contaminant mass to assure success of these high cost treatments.

For the unsaturated material, the identified remedial alternatives include soil vapor extraction, dual phase extraction, and enhanced biodegradation.  For contaminants in the saturated zone, the remedial technologies include enhanced biodegradation and reductive dechlorination.  

Probably one of the lowest cost and lowest maintenance remedial techniques for use at B-3 is the combination of soil vapor extraction and waste removal (excavation and off-site disposal).  The SVE system can be used to remove contaminants from the unsaturated zone by extracting soil vapors.  The main disadvantage to the use of SVE at B-3 is the possible fluctuations of groundwater known to occur at the site which might limit its effectiveness in the fluctuation zone.  The former B-3 SVE did prove to be very effective at removing volatiles from the trench area even though some of the wells may not have been optimally located.   Information from the 2002 removal action activities indicates that some of the former VEWs were not located within the disposal trenches (Figure 1.1), whereas a review of the boring logs identified fill material and debris at several of these locations.  Future SVE operations at B-3 would be able to take advantage of the current knowledge of trench configurations to optimize removal efficiencies from the trench material.  Further information regarding the bedrock features (geologic structure, fractures, faults and caves) will assist in making the SVE system more effective in removing contaminants from bedrock.  The added advantage of SVE is that it will increase the oxygen concentration in the formation which will enhance the biological degradation of the contaminants. 

Dual extraction can be used at B-3 to remove soil vapors and groundwater from the partially saturated bedrock.  Dual extraction is a proven technology utilizing liquid ring vacuum pumps capable of extracting both soil vapors and groundwater including dissolved and immiscible phase contaminants.  With this technique, extraction wells would be used to extract soil gas from targeted areas of the fractured bedrock material.  At times when moisture levels in the treatment zone of the fractured bedrock are low, the system would function as a high-vacuum SVE system and extract contaminants in the vapor phase.  As groundwater moves through the fractured bedrock material during recharge events, the dual phase extraction wells would recover the contaminated water percolating through the rock and prevent it from adding to the groundwater contaminant plume.  Contaminated groundwater would be collected into holding tanks and would require treatment prior to discharge.  The dual extraction technology could also provide the flexibility to incorporate various flushing methods to enhance the removal of contaminants.  As with the SVE method, accurate characterization of the subsurface features will be required for the dual extraction technique to be effective.

Zero valence iron has been proven to facilitate the breakdown of chlorinated aliphatic compounds by reductive dechlorination processes.  Typically, this technique consists of installing zero valence iron, in the form of iron filings, in an interceptor trench constructed across the flowpath of the contaminant plume.  Since the depth to groundwater can exceed 150 feet during times of drought conditions, creating an interceptor trench to such a depth to treat the contaminated groundwater would not be economically feasible.  However, iron filings could be injected into the bedrock fractures along the contaminant plume.  Injecting iron filings into the bedrock fractures would require a thorough understanding of the bedrock fracture network and groundwater flow through the fracture network for effective injection and distribution of the filings over the desired treatment area.  Additionally, the impacts of injecting the filings on the groundwater flow must be carefully evaluated to ensure they do not significantly alter the groundwater flow, reducing the effectiveness of the treatment.

Enhanced biodegradation is a very promising technique that appears applicable for use at B-3.  Natural biological degradation of the chlorinated compounds has been proven to be occurring at B-3.  This natural process can be enhanced by the addition of carbon sources that can be utilized in the degradation process.  The mechanism associated with this technical approach is described in a technical memorandum presented during the July 22, 2002 regulatory communication meeting for the B-3 removal action, and is included in Appendix C of this report.  At B-3, lactate, bark mulch, and vegetable oil may prove to be adequate sources of carbon for enhancing the degradation process in the underlying contaminant groundwater plume.  Initially, lactate would be injected to trench areas and allowed to migrate to groundwater.  There the lactate would eventually dissolve into the groundwater and migrate with groundwater flow, enhancing degradation along the migration pathway.  A mixture of bark mulch and vegetable oil would then be added to the ground surface, preferably in an infiltration trench.  The mixture rate for the bark mulch and oil would be selected to ensure the vegetable oil is absorbed to the mulch and not freely mobile.  Water, primarily from rainfall, will enter and migrate through the mixture picking up dissolved and colloids of the organic mixture as it passes.  This mixture would provide carbon source material as water infiltrates and passes through the material into the underlying bedrock material.  The rain water enriched with the oil will migrate downward and enter the groundwater regime where additional degradation will occur. 

SECTION 5 CONCLUSIONS AND RECOMMENDATIONS

There are several conclusions that can be drawn from the first 12 months of O&M activities performed at the SWMU B-3 SVE system.  The testing activities demonstrated that SVE is an effective mechanism for removal of VOC contamination present in the trench.  The findings re-emphasize the importance of maintaining continuous extraction to maximize removal of VOCs.

Most of the observations were consistent with what was encountered during the expanded treatability study, with the possible exception of the increased TVH removal rates (Table 3.6) observed in the poor contributing VEWs in the June 2000 sampling event.  Some of the removal concentrations increased more than tenfold, suggesting that the VEWs had widened their radius of influence.  The primary mechanism for this expansion of influence is not known, but decreasing moisture contents in the subsurface soils are suspected to be an important factor.

Flow levels for the system showed a general decrease with time from January through August, even though the vacuum on the system remained relatively constant.  Typically with SVE systems, such a change might be related to an increase in moisture in the subsurface; however, at B-3 the decrease in flow rate does not appear to be related to moisture content.  The reason for the observed reduction in flow levels at observed at B-3 is not well understood.

Based on the initial pilot test and the first 12 months of O&M, operation of the SVE system at SWMU B‑3 resulted in the removal of approximately 290 pounds of VOCs.  Based on these findings, SVE appears to be an effective method for removing VOCs from the B-3 trenches.  Additionally, SVE has been identified as a possible remedial alternative to reduce levels of residual contaminant in bedrock following completion of the current removal action.  The following recommendations are provided for continuing remedial activities at SWMU B-3:

bullet

Conduct a comprehensive investigation to determine the nature and extent of residual contamination in bedrock and groundwater at B-3, and identify and characterize the geologic features that may be controlling the migration of contaminants from the B-3 trenches into the underlying material.  The investigation should incorporate techniques previously utilized at CSSA such as:  borehole geophysics to identify fractures, faults, and other geologic features; soil gas packer tests to assess the horizontal and vertical distribution of VOCs in the unsaturated bedrock material and evaluate the interconnections between fractures, faults and karst features; install and sample groundwater monitoring wells and multi-port wells to determine the hydrogeologic conditions; and evaluate groundwater recharge in the areas to determine its effect on the migration of contaminants. bullet

Perform a detailed evaluation of the applicable remedial alternatives for reducing the levels of contaminants in the bedrock and groundwater.  The evaluation should include the technologies identified in this report, including SVE, dual phase extraction, enhanced biodegradation, and reductive dechlorination.  The evaluation should also include techniques determined to be applicable as a better understanding of site conditions is developed. bullet

Perform an investigation that combines the investigative approach needed to obtain a better understanding of the geologic features and contaminant distribution underlying the B-3 trench with an SVE pilot study focused on removing additional PCE, TCE, and cis-1,2-DCE from the western trenches at B-3 and assessing the radius of influence of an SVE system in the underlying bedrock.  This investigation should include: bullet

(1)   Drilling one boring to 100-150 feet below grade near location where PCE drums were encountered in the eastern trench.  Soil gas packer testing should be conducted on this boring to assess the vertical distribution of contamination and to obtain permeability information on different depth intervals.  Based on findings of the soil gas packer testing, an extraction well or multi-level vapor monitoring point should be installed in the borehole at the appropriate depth interval(s) for use in the pilot test.  bullet

(2)   A limited round of soil gas screening should be performed in the western trench cells to identify areas where high concentrations of VOCs may continue to be present.  Based on this information, up to six additional extraction wells should be installed in the bedrock immediately underlying the trench materials at designated locations to continue the VOC removal process (15-25 ft bgl screened intervals).  Reduction of VOCs in trench materials would be beneficial by reducing contaminant levels so the potential for generating any additional hazardous waste during the removal action would be minimized.  Decreasing the mass of contaminants available for migration to underlying groundwater aquifer should help clean up the groundwater.  The soil gas survey should also include points in the vicinity of the Oxidation Pond to verify that no residual VOC contamination is present underlying that SWMU. bullet

(3)   Drill 2-3 borings to 50 feet below grade in areas near the deeper boring as part of the pilot test monitoring system.  A surface geophysical survey should be considered to help determine the boring locations to focus on key features in the upper 50 feet of the formation and to identify any significant fracturing or faulting in the area.  Soil gas packer tests and geophysical borehole logging should also be performed on each of these boreholes.  These boreholes should be completed as either extraction wells or multi-level VMPs to provide a suitable network of monitoring points for evaluating key SVE test parameters. bullet

(4)   An SVE pilot test study should be conducted to assess the mass of contamination that could be removed from the underlying fractured media using SVE as the sole treatment technology.  The contaminant information collected would be combined with the pilot study findings to determine the appropriate spacing and screened intervals of a full-scale SVE system installed at the site and designed to maximize removal of VOCs from fractured media underlying B-3. bullet

(5)   A second SVE system should be installed and employed for continued removal of VOCs present in the B-3 trench.  While only a limited study of these VEWs is recommended, continued O&M of this system should be performed to maximize the VOCs that can be removed before initiation of the eventual excavation and waste removal activities.  A key parameter to be measured from this study is the emission rate from the fully operational SVE system.

SECTION 6 REFERENCES

Foster Wheeler Corporation, 2003. SWMU B-3 Removal Action Report (pending).

Parsons, 1996a.  Work Plan for SVE Pilot Test System, prepared for the Department of the Army, CSSA, Boerne, Texas, February.

Parsons, 1996b.  Addendum to SVE Test Work Plan for SWMU B-3, CSSA, Boerne, Texas.  December 1996.

Parsons, 1997.  Draft Soil Vapor Extraction Test Report for SWMU B-3, Camp Stanley Storage Activity, Boerne, Texas.  July 1997.

Parsons, 1999a.  Modification to TCEQ Standard Exemption Registration No. 32405, SWMU B-3 SVE Site, Building 27, Building 200.  For the Department of the Army, CSSA, approved February 1999.

Parsons, 1999b.  Second Addendum, SVE Test Work Plan for SWMU B-3, CSSA, Boerne, Texas.  December 1999.

USEPA, EPA Compendium Methods for the Analysis of Toxic Organic Compounds in Ambient Air.