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May 1994 Quarterly Groundwater Monitoring Report

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 May 1994. This report presents a summary of previous groundwater monitoring and describes the May 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, and May 1994.

Monitoring actions include measurement of water levels, observation of current well conditions, and collection of grab samples by bailer or by well pump. Analysis has been performed in accordance with EPA method SW8010 for HVOs. May 1994 analytical results did not indicate the presence of HVO compounds in seven water samples (CSSA wells 1, 9, 10, 11, G, H, and I). However, PCE, TCE, and DCE concentrations were detected below respective MCLs in four well samples, i.e., wells 2, 3, 4, and 6, and were detected above MCLs in samples from wells 16 and D. The May 1994 analytical results are consistent with historical data trends.

Assessment of data from existing wells could not delineate the extent of the groundwater contamination. There are no wells east and immediately downgradient within one mile of well 16 and upgradient of Camp Bullis water supply wells. In order to delineate the plume and contaminant migration, further hydrogeologic assessment may be necessary.

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). Five wells are blocked or capped at or near ground surface and are considered abandoned. Of the fourteen 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, 6, and D). Well 5 is blocked above water level and does not contain water available for sampling. 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. The following information summarizes hydrogeologic and well information highlights from the report:

Survey data and state well numbers are shown in Table 1.

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 2 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 (ES, 1993).

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 3). Therefore, until the wells are upgraded to case off the perched zones, depths to water are considered to be approximate static water levels. A list of groundwater elevations is shown in Table 3.

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.

May 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 9 and 10 were pumped daily from approximately 9 A.M. to 3 P.M. Wells 10 and 11 contain airlines for water level measurements, but because the airlines were not working, static water levels could not be measured. Well 9 contains a PVC pipe for water level measurement. As well 9 is periodically pumped, and it is unknown how long it takes the well water level to reach static conditions, well 9 water level measurements may not represent static water levels.

Wells G, H, and I, located in the north pasture, are leased to USDA-ARC. A turbine pump is in well H. During groundwater monitoring of the CSSA water wells, the gas-powered pump at well G is temporarily moved to well I for sampling. As wells G and H were obstructed near the surface, water level measurements were not possible in these wells. Grease from the turbine pump was also observed within well H casing near the surface.

Wells 2, 3, 4, and 6 have poor surface completions. The concrete pads are broken and the well casings consist of loose metal covers. Well 5 has no cover. The pump and piping from well 16 were removed in December 1992 and remain outside of the well shed.

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 (Table 1).

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. These airlines were not working during the May 1994 monitoring. Also, there is no access for water level measurements in wells G and H.

Depths to water were measured in nine wells in May 1994 and varied from 108.02 feet below top of casing (BTOC) to 218.58 feet BTOC (Table 2). These depths to water were generally 2 to 5 feet higher than depths recorded during October 1992, with the exception of wells 16, D, and I in which depths to water were 1 to 12 feet lower than previous measurements. Calculated groundwater elevations ranged form 1,059.78 feet above mean sea level (MSL) to 1,095.51 feet MSL.

The May 1994 potentiometric map shows a southeasterly groundwater flow direction with an average gradient of 0.004 foot per foot (Figure 2). There were no substantial changes in flow direction and general gradient as compared to the October 1992 potentiometric map (Figure 1). Therefore, the majority of wells known to contain HVOs are in the north-central portion of CSSA. Wells 2, 3, 4, and D are side-gradient within 500 to 2,000 feet to the west and southwest of well 16. The only well downgradient of this area is well 1, located about 1.8 miles southeast of well 16.

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 May 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, 4, 6, 16, and D. Well 6 had not been sampled prior to May 1994, as previously there was not enough water from which to collect a sample.

In well 16, a grab sample was collected from the top of the water column at about 158 feet BTOC and a second grab sample collected near the bottom of the well at about 430 feet BTOC. The bottom sample was collected from a depth close to the previous pump intake. Analytical data from the well 16 bottom sample (rather than the top sample) are therefore compared to previous well 16 analytical data. The top sample was collected and analyzed for comparison of HVO concentrations at the top and bottom of the water column.

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, H, and I. Estimated purge volumes are shown in Table 4. 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 4.

For quality assurance/quality control (QA/QC), a trip blank sample prepared by the contracted laboratory (Chemron) was kept with the sample cooler at all times. An equipment rinsate sample was collected through the decontaminated bailer. In addition, a matrix spike sample and a matrix spike duplicate (MS/MSD) sample were collected from well 1.

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 May 25 and 26, 1994. The samples were transported to the analytical laboratory (Chemron, Inc.) in San Antonio on May 27, 1994. Standard chain-of-custody procedures were followed during sampling and analysis.

Analytical Results

Including the QA/QC samples, eighteen water samples were sent to Chemron for analysis by EPA method SW8010. The laboratory reports and chain-of-custody records are in Appendix A. Sample results for the trip blank and equipment rinsate were non-detect. The MS/MSD sample results showed that the spike percent recoveries were within acceptable ranges.

The EPA SW-846 list of target constituents for the SW8010 analysis does not include cis-1,2-DCE. However, the laboratory reports stated that this compound may be present in the May 1994 samples from wells 16 and D. As cis-1,2-DCE is not a target compound of SW8010 and was not part of the laboratory calibration standard, the cis-1,2-DCE results are considered to be estimates.

Analytical results to date are summarized in Table 2. HVOs were detected in samples from CSSA wells 2, 3, 4, 6, 16, and D to May 1994. However, only samples from wells 16 and D contained contaminants (PCE, TCE, and possibly cis-1,2-DCE) above their respective MCLs listed in Table 2.

PCE concentrations ranged from 0.44 ug/L in well 4 sample to 150 ug/L in the well 16 bottom sample. TCE concentrations varied from 83 ug/L in the well 16 top sample to 170 ug/L in the bottom sample. TCE was also detected at 120 ug/L in the well D sample. Trans-1,2-DCE was detected only in the well 16 sample at 1.3 ug/L, below its MCL. Cis-1,2-DCE was estimated at 75 to 150 ug/L in the well 16 top and bottom samples, respectively, and at 76 ug/L in the well D sample.

PCE was below the MCL in the sample from well 6 located at the southwest corner of CSSA (Figure 2). Because the water level was just above an obstruction in the well casing, it was not possible to collect a sample during the November 1992 preliminary evaluation. Well 6 is about 2.5 miles southwest of well 16, which is sidegradient of the general flow direction. Wells 9, 10, and 11, which are 1 to 1.4 miles southwest of well 16 and did not contain PCE, TCE, or DCE. Therefore, it is not likely that the PCE detected in well 6 is related to PCE detected in well 16. At this time, it is not known if the PCE in well 6 is from an onsite or offsite source.

The chlorination by-products bromodichloromethane, chloroform, and dibromochloromethane (listed in SDWA drinking water regulations as trihalomethanes, or THMs) were detected in the well 11 sample. According to CSSA, this well had recently been treated with chlorine. The detected levels and their cumulative level were well below the THM MCL of 100 ug/L.

Dichloromethane (methylene chloride) had been detected in samples from wells 1, 2, 10, D, G, and H during the November 1992 analysis. The laboratory reports indicated that the results were "suspected laboratory contamination." As methylene chloride is routinely used for cleaning of laboratory glassware, it is considered a common laboratory contaminant. This compound was not detected in any of the May 1994 CSSA water samples.

Data Trends

The wells that contain HVOs are generally within a small portion of CSSA and are sidegradient rather than upgradient or downgradient of well 16 (the well with the highest concentration of HVOs). Therefore, an accurate concentration contour map which depicts HVO concentrations within a monitored area is not possible at this time, as no wells exist upgradient, immediately downgradient, or sidegradient to the east and northeast. 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 as a compound is used to represent both cis- and trans-1,2-DCE, as analytical data regarding these two compounds have not been consistent. Figure 4 is a graph of the same three 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, while the DCE concentration decreased. In December 1991, the PCE and TCE concentrations decreased to less than the first concentrations detected, and the DCE concentration increased slightly. 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.

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 and May 1994. Either cis- or trans-1,2-DCE was detected only in December 1991 (the TWC would not provide the specific chemical name to CSSA), but was not detected as trans-1,2-DCE in November 1992 (cis-1,2-DCE was not part of the November 1992 SW8010 target compound list). Cis-1,2-DCE was estimated to be slightly above MCL in the well D sample during the May 1994 monitoring.

Evaluation of these graphs and other data suggests that a source of HVO compounds is near wells 16 and is periodcially flushed into the aquifer. Hydrographs of local precipitation are recommended to assess potential correlation between rainfall events and HVO concentrations in wells 16 and D.

Conclusions

Groundwater monitoring results from CSSA water wells from August 1991 through May 1994 are summarized as follows: