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September 1994 Groundwater Monitoring Report

March 1995

Report Summary

Groundwater monitoring was performed at the Camp Stanley Storage Activity (CSSA), located south of Boerne and northwest of San Antonio (Bexar County), Texas, during September 1994. This report presents a summary of previous groundwater monitoring and describes the September 1994 activities and results. The CSSA groundwater monitoring program is tasked under Armstrong Laboratory/OEB (AL/OEB) contract F33615-89-D-4003, order 67, mod 2, with Parsons Engineering Science, Inc. (Parsons ES) of Austin, Texas.

Monitoring of CSSA wells was initiated in August 1991, when routine water well testing by the state indicated the presence of dissolved tetrachloroethene (PCE), trichloroethene (TCE), and 1,2-dichloroethene (DCE) in well 16 above the respective constituent maximum contaminant levels (MCLs). Additional testing of other wells for halogenated volatile organics (HVOs) was performed in August and December 1991, October and November 1992, May 1994, and September 1994.

Monitoring actions include measurement of water levels, observation of current well conditions, and collection of grab samples by bailer or by well pump. Sample analysis has been performed in accordance with EPA method SW8010 for HVOs. September 1994 analytical results indicated the presence of PCE and TCE in well 16 and well D above MCLs. DCE was found in well 9 at a low concentration (1.0 micrograms per liter; ug/L), below the DCE MCL. Methylene chloride, a common laboratory contaminant, and chloroform, a well sterilization by-product, were detected in some groundwater samples at low concentrations (3 to 17 ug/L). The September 1994 analytical results are consistent with historical data trends: a gradual increase of PCE and TCE concentrations in wells 16 and D since December 1991. Data from the existing wells are not sufficient to the extent of the groundwater contamination.

Groundwater Monitoring Synopsis

Site Description

CSSA is a subinstallation of the U.S. Army Red River Army Depot and is located approximately 10 miles south of Boerne and 19 miles northwest of downtown San Antonio in Bexar County, Texas. It is approximately 1/2 mile east of Interstate-35 off Highway 3351, also identified as Ralph Fair Road, and adjoins Camp Bullis Military Reservation lands to the east and southeast (Figure 1). The primary mission of CSSA is maintenance, storage, and issuance of ordnance materiels.

The CSSA water supply is entirely from Army water wells located at CSSA and Camp Bullis. Historically, nineteen water wells have been completed at CSSA (Figure 1). Seven wells are abandoned (wells 5, 6, A, B, C, E, and F). Of the remaining water wells, four are active water supply wells (wells 1, 9, 10, and 11), three in the north pasture are leased to the USDA-ARC for livestock water use (wells G, H, and I), and the others are inactive water supply (well 16) or unused livestock wells (wells 2, 3, 4, and D). Well 1 is the only CSSA well on Camp Bullis property.

Exact dates of well completion and contracted water well drillers are not known for the majority of CSSA wells. Available well information such as public well records and well histories are in the Hydrogeologic Report for Evaluation of Groundwater Contamination.

Site Background

Monitoring of CSSA wells was initiated in August 1991, when TDH performed routine testing of active CSSA water wells. Analytical results indicated the presence of dissolved concentrations of PCE, TCE, and 1,2-DCE (cis- and trans-1,2-DCE were reported together bby TDH) in CSSA well 16 above the respective constituent MCLs. The well 16 pump was turned off, and two weeks later TDH resampled the well. Results confirmed the presence of PCE, TCE, and DCE in well 16. TWC also tested CSSA well 16 and nearby wells 4 and D on December 4, 1991. In January 1992, TWC reported to CSSA via telephone that concentrations of PCE, TCE, and DCE were detected in well 16 and that DCE was detected in well D. Table 1 presents historical analytical results and constituent MCLs.

CSSA retained Parsons ES under AL/OEB contract in October 1992 to perform a preliminary evaluation of groundwater contamination. Field actions including groundwater monitoring took place from October through December 1992 and were discussed in the Hydrogeologic Report.

October 1992 water level measurements used to calculate groundwater elevations indicated a general flow direction to the southeast with an average gradient of 0.015 foot/foot. It was observed during a downhole camera survey (December 1992) that zones of water perched above the water table were cascading into some of the wells (see previous casing depth versus total depths in Table 2). In September 1994, CSSA water wells 2, 3, 4, 16, and D were upgraded with additional casing to seal off perched zones for monitoring of the middle Trinity aquifer. Therefore, depths to water measured before September 1994 are considered to be approximate static water levels. A list of groundwater elevations is shown in Table 2.

Ten wells were sampled during October and November 1992 for analysis of HVOs by SW8010; a bottom sample was also collected from well D. Sampling procedures were similar to previous state of Texas agency procedureds, i.e., samples were collected at the taps for those wells with pumps or were collected with a bailer for wells without pumps. For those wells with pumps, the samples were collected from the pump intakes which are located near the bottoms of the wells. Analytical results indicated PCE and TCE concentrations above respective MCLs in groundwater samples from wells 16 and D, while PCE and TCE concentrations below MCLs were detected in the well 4 sample. The bottom sample from well D contained PCE and TCE in approximately the same concentrations as found in the top sample. Concentrations of PCE below its MCL were also found in wells 2 and 3.

Seven potential source areas (previous burn areas and an oxidation pond) were proposed for further investigation by the preliminary evaluation. These areas are shown in Figure 1. Investigation of potential source areas has not been performed as of the date of this report, as the EPA is reviewing the proposed plans of action for site investigation of the groundwater contamination. Thus, a source of the HVO contamination is not known at this time.

September 1994 Groundwater Monitoring and Results

Current Well Conditions

The surface completions at active water supply wells 1, 9, 10, and 11 appear to be in good condition. Well 11 was shut off for chlorination, and wells 1, 9, and 10 were pumped periodically for supply water. Wells 10 and 11 contain airlines and wells 1 and 9 contains a PVC pipe for water level measurements.

Wells G, H, and I, located in the north pasture, are leased to USDA-ARC. As well H was obstructed near the surface, a water level measurement was not possible. Grease from the sucker rod pump (previously reported as a turbine pump) was also observed within well H casing near the surface.

Wells 2, 3, 4, 16, and D were upgraded for monitoring of the middle Trinity aquifer. In these wells, surface casing was installed to depths ranging from 195 to 205 feet below ground level (Table 2). In addition, surface completions were upgraded at the above well sites.

CSSA wells were surveyed in November 1992, but the survey measurement points are no longer observable. Therefore, the Parsons ES field team marked the most appropriate measuring point on the north side and calculated the measuring point elevation at each well. Measuring point elevations of upgraded monitoring wells were also calculated this way.

Water Level Measurements and Groundwater Gradient

Well water levels were measured with a 500-foot electric line which was decontaminated between measurements. In active water wells 1 and 9, a PVC tube has been installed that allows insertion of the electric line. In wells 10 and 11, there are air lines which provide estimates of water levels. There is no access for water level measurements in well H.

Depths to water were measured in eleven wells in September 1994 and varied from 201.99 feet below top of casing (BTOC) to 390.64 feet BTOC (Table 2). These depths to water were generally 100 feet deeper than depths recorded during May 1994. Calculated groundwater elevations ranged form 940.48 feet above mean sea level (MSL) to 1,022.46 feet MSL.

The September 1994 potentiometric map shows a southerly groundwater flow direction with an average gradient of 0.009 foot per foot (Figure 2). In the southern part of CSSA, there was a change in the groundwater flow direction as compared to the May 1994 potentiometric map. In this area of the site, the September 1994 potentiometic map shows a southwesterly groundwater flow direction (Figure 2). Wells 16 and D, known to contain HVOs (PCE and TCE) are located in the north-central portion of CSSA while wells 2, 3, and 4 are located approximately 1800 feet southwest of the impacted wells.

Sampling Procedures

Water samples were collected from CSSA water wells using existing pumps or a clean Teflon bailer. Sampling procedures were similar to previous sampling procedures used by Texas state agencies. The exception is well 16, which was sampled from the pump from August 1991 through November 1992. Due to the removal of pump and piping in December 1992, well 16 was sampled with a bailer in May 1994 and September 1994.

In wells known or suspected to contain HVOs and that did not have a pump, no water was purged and a grab sample was collected in a clean Teflon bailer near the top of the water column. these wells are 2, 3, 16, and D. Well 6 was samples in May 1994, but not in September 1994. The well was plugged in September 1994 after attempts to remove its blockage failed, and only the purge water was sampled from a drum used to containerize the fluid.

At least one well volume was purged from those wells with pumps that were known not to contain HVO concentrations. Water samples were collected at the taps. These wells are 1, 9, 10, 11, G, and I. Estimated purge volumes are shown in Table 3. The purged water was discharged to nearby drainage systems.

Temperature, pH, and conductivity were measured prior to sample collection. The field water quality measurements are listed in Table 3.

For quality assurance/quality control (QA/QC), trip blank samples prepared by the contracted laboratory (Chemron) was kept with the sample coolers at all times. An equipment rinsate sample was collected through the decontaminated bailer. In addition, a duplicate sample was collected from well 2.

The water samples were collected in 40-milliliter volatile organic analyte (VOA) vials from the laboratory and placed on ice in a cooler. Sampling was performed on September 28 to October 3, 1994. The samples were picked up by the analytical laboratory (Chemron, Inc.) at CSSA on October 1 and October 3, 1994. Standard chain-of-custody procedures were followed during sampling and analysis.

Analytical Results

Including the QA/QC samples, fifteen water samples were sent to Chemron for analysis by EPA method SW8010. The laboratory reports and chain-of-custody records are in appendix A. One trip blank contained methylene chloride, a common laboratory contaminant, at a concentration of 5 ug/L. The equipment rinsate contained chloroform, a well sterilization by-product, at a concentration of 16 ug/L. The duplicate sample taken at well 2 had concentrations similar to the regular sample.

Analytical results to date are summarized in Table 1. HVOs were detected in September 1994 samples from CSSA wells 1, 2, 3, 9, 10, 11, 16, D, G, and I. However, only samples from wells 16 and D contained contaminants (PCE and TCE) above their respective MCLs listed in Table 1.

PCE concentrations were 81 ug/L in the well 16 sample and 110 ug/L in the well D sample. TCE concentrations were 81 ug/L in the well 16 sample and 130 ug/L in the well D sample. 1,1-DCE was detected only in the well 9 sample at 1.0 ug/L, below its MCL.

In May 1994, PCE was below the MCL in the sample from well 6 located at the southwest corner of CSSA (Figure 2). Well 6 was plugged after attempts to remove its blockage failed during upgrading activities in September 1994, and therefore, only the purge water was sampled. Purge water from well 6 in September 1994 was nondetect for HVOs. Well 6 is about 2.5 miles southwest of well 16. Wells 9, 10, and 11, which are 1 to 1.4 miles southwest of well 16, did not contain PCE or TCE. Therefore, the PCE detected in well 6 (May 1994) is not apparently related to the PCE contamination detected in well 16.

The chlorination by-product chloroform (Listed in SDWA drinking water regulations as a trihalomethane, or THM) was detected in samples from wells 1 and 11. According to CSSA, these wells had recently been treated with chlorine. The detected level was well below the THM MCL of 100 ug/L.

Methylene chloride was detected in samples from wells 2, 3, 10, G, and I at concentrations up to 8 ug/L. The trip blank also contained methylene chloride at a concentration of 5 ug/L. As methylene chloride is routinely used for cleaning of laboratory glassware, it is considered a common laboratory contaminant.

Data Trends

The wells that historically contain HVOs (PCE and TCE) are wells 16 and D, located within 500 feet of each other just south of burn area 2. No wells exist immediately upgradient or downgradient of these wells; and therefore, the horizontal extent of contamination is not known. Graphs of groundwater HVO concentrations over time, however, are presented to show the trends of contaminants in CSSA wells 16 and D.

Figure 3 shows a graph of PCE, TCE, and DCE concentrations in well 16 since August 1991. DCE, used in the graph to represent both cis- and trans-1,2-DCE, has been detected in well 16 (and well D) but analytical reports regarding this compound have not been consistent. Figure 4 is a graph of the same chemical constituents in well D since December 1991 (well D was not sampled in August 1991).

The well 16 graph depicts a sharp increase in PCE and TCE concentrations between August 9 and 23, 1991, when the pump was first turned off. In December 1991, the PCE and TCE concentrations decreased to less than the concentrations detected in August 1991. It is unknown if this decrease indicated the dilution of HVOs in well 16 with upgradient, clean aquifer water or a reduced downward migration of contaminants from the upper unsaturated zone due to below average rainfall. Between December 1991 and May 1994, the HVO concentrations in well 16 gradually increased. The compounds decreased by half between May and September 1994. cis-1,2-DCE was not reported by the laboratory, because it is not a target analyte of the SW8010 method.

Figure 4 shows a gradual increase of PCE and TCE concentrations over time in well D since December 1991. PCE and TCE were not detected in December 1991, but were detected in November 1992, May 1994, and September 1994. trans-1,2-DCE was detected only in December 1991, and cis-1,2-DCE was detected only in May 1994. The cause of fluctuations in the DCE levels in well D are not known.

Evaluation of these graphs and cumulative hydrogeologic data suggests that a source of HVO compounds is near wells 16 and D. The concentrations of these HVOs (PCE and TCE) have been gradually increasing since December 1991. Hydrographs of local precipitation are recommended to assess potential correlation between rainfall events and HVO concentrations in wells 16 and D.

Conclusions

Appendix A - Laboratory Reports and Chain-of-Custody Record