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December 2001 Off-Post Quarterly Groundwater Report

Section 4 - December 2001 Quarterly Monitoring Analytical Results

All concentrations of VOCs detected in samples collected from September through December 2001 are presented in Table 4.1. Full analytical results for December 2001 are presented in Appendix B. PCE, TCE, and cis-1,2-DCE concentrations are displayed for each well in Figure 4.1, Figure 4.2, and Figure 4.3, respectively, to show the lateral extent of migration of these contaminants off-post. Results from groundwater sampling are presented below. The wells are grouped by community or neighborhood for discussion of the December 2001 results. Also included in the summary tables are samples collected prior to the December 2001 quarterly monitoring event and after the September 2001 event.

The vertical extent of migration cannot be determined now due to minimal data (i.e. well completion depths) available for wells being sampled. Information that provides the depth of wells, pump depth, and other pertinent data to properly characterize the vertical extent of migration is not readily available.

The TNRCC�s confirmation samples did not show any detected contaminants of concern in the four wells they sampled. However, the results from the laboratory contracted by the TNRCC do not confirm or deny the results of CSSA sampling on the same date because the detection limits utilized by the TNRCC laboratory are higher than APPL�s detection limits. A summary of the results from the TNRCC�s sampling event are provided in Appendix D.

4.1 - Fair Oaks

In the Fair Oaks area one well was sampled. FO-J1 had detected concentrations of cis-1,2-DCE (0.3 mg/L) and methylene chloride (0.38 mg/L). Both detected constituents were above the MDL but below the RL. Methylene chloride, a common lab contaminant, was also present in the analysis method blank, indicating the likelihood that this analyte was introduced as a laboratory contaminant and is not present in the groundwater. There are no known historical uses of methylene chloride on-post.

4.2 - Hidden Springs

In the Hidden Springs subdivision two wells were sampled (HS-2 and HS-3). HS-2 had detected analytes reported for PCE (0.16 mg/L) and both wells had methylene chloride detections of 0.4 mg/L and 0.38 mg/L, respectively. Both detected constituents were above the MDL but below the RL. Methylene chloride, a common lab contaminant, was also present in the analysis method blank, indicating the likelihood that this analyte was introduced as a laboratory contaminant and is not present in the groundwater. There are no known historical uses of methylene chloride on-post. The TNRCC elected to collect split samples from wells HS-2 and HS-3 on December 19, 2001. CSSA requested and received a copy of the sampling results from the TNRCC. No contaminants were detected in the TNRCC analysis; however, their results are not directly comparable to the results obtained by CSSA due to the detection limits of the TNRCC�s contracted laboratory (STL) being higher than CSSA�s contracted laboratory (APPL). 

4.3 - I-10

Two wells were sampled in the I-10 area. I10-2 is approximately one-third of a mile southwest of the CSSA boundary and southwest of suspected source area AOC-65 and I10-4 is further up I-10 northwest of the suspected source area AOC-65. I10-2 had concentrations of PCE (0.16 mg/L), TCE (0.22 mg/L), and methylene chloride (0.21 mg/L). I10-4 had one detected analyte, PCE (0.12 mg/L). All analytes detected were above the MDL but below the RL. Methylene chloride is not a suspected groundwater contaminant at CSSA and was likely introduced as a laboratory contaminant. The TNRCC elected to collect split samples from wells I10-4 and I10-5 on December 19, 2001. CSSA requested and received a copy of the sampling results from the TNRCC. No contaminants were detected in the TNRCC analysis; however, their results do not directly correlate the results obtained by CSSA due to the detection limits of the TNRCC�s contracted laboratory (STL) being higher than CSSA�s contracted laboratory (APPL). CSSA did not sample well I10-5 during December 2001, as no access agreement was obtained from the well owner and permission to sample was denied. 

4.4 - Jackson Woods

Two wells (JW-9 and JW-14) were sampled in the Jackson Woods area west of CSSA. VOCs were reported in both of these wells. In JW-14 detected analytes were chloroform (1.83 mg/L) and methylene chloride (0.4 mg/L). Chloroform detections were above the MDL and RL but below the MCL. Methylene chloride is considered a lab contaminant, as discussed above. JW-9 reported one detected analyte, cis-1,2-DCE at a concentration of 0.33 mg/L. This detection is above the MDL but falls below the RL. 

4.5 - Leon Springs

Wells LS-1, LS-2, LS-3, LS-4, LS-5, LS-6, and LS-7 were sampled in the Leon Springs area, south of CSSA. These wells are located near the east, south, and west corners of the Leon Springs Villas subdivision (Figure 1.1). Due to increasing detections of PCE and TCE in various off-post wells, additional monthly sampling events were necessary to track the progress of the detected contaminants. Wells sampled monthly between the September and December 2001 quarterly monitoring events are discussed below in addition to the December 2001 results.

Due to the increased concentrations of PCE and TCE in wells in the vicinity of LS-2, additional sampling was done in late September, October and November to determine the concentrations of contaminants in Well LS-2. On September 27, 2001, PCE was reported at the highest concentration measured (4.6 mg/L) for this well. This is above the MDL and RL but below the MCL. Additional analytes of chloroform and TCE were reported at levels of 0.2 mg/L and 0.17 mg/L, respectively. A sample was also collected on October 4, 2001, and detected analytes were bromodichloromethane (0.31 mg/L), chloroform (0.65 mg/L), dibromochloromethane (0.22 mg/L), and PCE (3.2 mg/L). PCE and chloroform were above the MDL and RL. This result showed a notable decrease in the concentrations of PCE in LS-2. A sample was collected from LS-2 on November 14, 2001, and PCE (2.7 �g/L) and chloroform (0.15 �g/L) were detected. In the quarterly December 2001 sampling, analyses of the sample from LS-2 reported chloroform (0.1 mg/L), PCE (3.45 mg/L), and TCE (0.2 mg/L). These concentrations were below the RL and MCL for these analytes with the exception of PCE, which is above the RL but below the MCL. PCE concentrations have dropped slightly since its peak detection on September 27 (4.6 �g/L), reported in range from 2.7 �g/L to 3.5 �g/L. 

LS-3 was sampled on September 27, 2001, and concentrations of chloroform (0.13 mg/L), PCE (4.8 mg/L), and TCE (0.43 mg/L) were detected. As in Well LS-2, PCE exceeded the MDL and RL with its highest reported concentration. An additional sample was collected on October 4, 2001. Analytes detected included chloroform (0.13 mg/L), PCE (3.7 mg/L), and TCE (0.45 mg/L), all at levels above the MDL but below their respective RLs with the exception of PCE reported above the MDL and RL and just below the MCL. Well LS-3 was sampled again on November 14, 2001, and PCE was detected at 2.7 �g/L and TCE was detected at 0.80 �g/L. In the December 2001 quarterly monitoring event, results from LS-3 reported PCE at a concentration of 4.29 �g/L. The PCE concentration in LS-3 increased from its prior reported concentration of 2.7 �g/L, but remained at levels still below 4.8 �g/L measured on September 27th. Concentrations of methylene chloride (0.29 mg/L) and TCE (0.27 �g/L) were also reported in Well LS-3. The methylene chloride detection can be attributed to laboratory contamination. TCE concentrations never exceeded 1.0 �g/L. 

Due to the significantly high levels of PCE in LS-2 and LS-3 an additional sample was collected from the entry point of the distribution water supply, to determine COC concentrations following water treatment. An October 4, 2001, sample of LS-2-LS-3/entry point (EP) reported detections of acetone (2.2 mg/L), bromoform (4.5 mg/L), bromodichloromethane (6.2 mg/L), chloroform (3.1 mg/L), dibromochloromethane (9.4 mg/L), PCE (0.54 mg/L), and TCE (0.18 mg/L). All analytes were above the MDL and RL with the exception of acetone, PCE, and TCE which were above the MDL but below the RL. On November 14, 2001, an EP sample was again collected, which reported 1,2-dichloroethane (0.19 �g/L), bromodichloromethane (2.80 �g/L), bromoform (2.90 �g/L), chloroform (0.92 �g/L), dibromochloromethane (4.90 �g/L), PCE (0.83 �g/L), and TCE (0.16 �g/L). The levels for PCE, TCE, and 1,2-DCA were above the MDL but below the RL. The analytes detected in these EP samples are present in the water as a result of the Bexar Met water treatment system. These analytes are not detected in the associated method detection blanks and are not present in samples from LS-2 and LS-3 collected at the wellhead, prior to the treatment system. 

Due to the increasing concentration trends and concentrations exceeding the MCL for PCE in both LS-2 and LS-3 and the presence of PCE and TCE in the entry point samples, preliminary evaluation of a GAC treatment system for these public supply wells has begun. Plans have been drafted and are pending TNRCC approval. Additional information on the pending GAC treatment system installation will be provided in the next quarterly report. 

Analyses of the sample collected December 19, 2001, from Well LS-4 reported methylene chloride (0.2 mg/L) and PCE (0.23 mg/L). These levels are above the MDL but below the RL. PCE was not detected in this well in the September 2001 monitoring event, so this marked the first time PCE was detected at levels barely above the MDL. 

LS-5 was sampled on October 25, 2001, due to concerns raised by PCE concentrations detected in nearby wells LS-2 and LS-3. LS-5 had detections of PCE (0.15 mg/L) and TCE (0.27 mg/L). Both of these detections are above the MDL but below the RL. In the December 2001 monitoring event, Well LS-5 had one detected analyte of TCE at a concentration of 0.32 mg/L. This concentration is above the MDL but below the RL.

At the time of the December 2001 sampling event, GAC units had already been installed at wells LS-6 and LS-7. In order to determine current groundwater conditions at these wells, samples were collected at the wellhead before the carbon filters. To determine if the filters were operating properly, additional (post-GAC) samples were collected after filtration. The post-GAC sampling results are discussed in Section 5. On September 27, 2001, a sample was collected from LS-6 because of the increased concentrations of PCE in surrounding wells. PCE was detected at 10.0 mg/L and TCE at 0.19 mg/L. This is the highest concentration of PCE detected in LS-6. During the December 2001 quarterly monitoring LS-6 pre-GAC sampling reported PCE (1.97 mg/L) and methylene chloride (0.33 mg/L). The PCE concentration was above the MDL and RL, but below MCL. These levels were down significantly from samples collected in September 2001.

On September 27, 2001 a sample was collected from LS-7 pre-GAC, detected analytes were chloroform (0.09 mg/L), PCE (3.3 mg/L) and TCE (0.34 mg/L). All detections were above the MDL and below the RL with the exception of PCE, which exceeded the RL. In the December 2001 quarterly monitoring event, analyses of the pre-GAC sample from LS-7 reported concentrations of PCE (1.4 mg/L) and methylene chloride (0.39 mg/L). PCE concentrations were above the MDL but below the RL and MCL. As shown by the concentration trends presented in Figure 2-1, PCE reported in December 2001 decreased compared to the trend of increasing concentrations evidenced in previous sampling events. Except for the August and December 2001 sampling events, when the concentration of PCE decreased, PCE concentrations have generally increased over time in Well LS-7 while TCE concentrations have fluctuated over time. 

4.6 - Old Fredericksburg Road

Two wells located along Old Fredericksburg Road were sampled (OFR-1 and OFR-3). OFR-1 was previously sampled during the December 2001 monitoring event. Methylene chloride was detected at a concentration of 0.63 mg/L and PCE at a concentration of 0.42 mg/L. Both reported concentrations that were above the MDL and below the RL. OFR-3 was re-sampled on October 25, 2001, due to increasing concentrations of VOCs in nearby wells. PCE was detected at a concentration of 4.2 mg/L and TCE at 2.2 mg/L. Both reported concentrations were above the MDL and RL and approaching the MCL (5.0 mg/L). During the December 2001 monitoring event OFR-3 had reported levels of PCE (1.9 mg/L), TCE (2.2 mg/L), and methylene chloride (0.26 mg/L). Levels remained above the MDL and RL and below the MCL. Methylene chloride was not detected in samples collected in the September 2001 event. The detection of methylene chloride in the December 2001 event can be attributed to laboratory contamination, due to the presence of methylene chloride in the associated method blank. 

4.7 - Ralph Fair Road

Four wells (RFR-9, RFR-10, RFR-11 and RFR-12) were sampled in the Ralph Fair Road area west of CSSA. RFR-9 had one detected analyte, methylene chloride (0.52 mg/L), which can be attributed to laboratory contamination due to the presence of methylene chloride in the associated method blank. 

On October 9, 2001, two GAC treatment systems were installed at well RFR-10 and on October 16, 2001, a GAC treatment system was installed at well RFR-11. The GAC units were installed due to the September 2001 sampling results. RFR-10 has one GAC unit dedicated to the existing residence and the second GAC unit installed for a mobile home. To determine current groundwater conditions at these wells, samples were collected at the wellhead before treatment by the GAC units. To determine if the filters were operating properly, additional (post-GAC) samples were collected after filtration through each GAC unit. Results indicate the GAC units are removing VOCs from the groundwater. The post-GAC sampling results are presented in Section 5, below. 

On October 4, 2001, samples were collected from the wellhead and tap of the house at RFR-10 and one sample was collected from the tap of the mobile home connected to the same well. The wellhead sample detected analytes of PCE (19.0 mg/L), TCE (8.7 mg/L), and cis-1,2-DCE (0.49 mg/L). The house tap had detected analytes of chloroform (0.07 mg/L), PCE (17.0 mg/L), TCE (7.5 mg/L), and cis-1,2-DCE (0.48 mg/L). The mobile home tap had detections of chloroform (0.07 mg/L), PCE (19.0 mg/L), TCE (9.4 mg/L), and cis-1,2-DCE (0.46 mg/L). PCE and TCE were reported at concentrations exceeding their MCLs at both the wellhead and taps from the mobile home and house. Based on these sampling results, bottled water was supplied to the affected residents and the GAC units were installed for RFR-10 on October 9, 2001. During the December 2001 monitoring event, RFR-10 exceeded the MDL for cis-1,2-DCE at a concentration of 0.26 mg/L. The MCL was exceeded in RFR-10 for both PCE and TCE at levels of 9.02 and 5.85 mg/L, respectively. The concentrations initially reported in the September 2001 sampling event for PCE and TCE increased during sampling in October 2001 and then decreased by the December 2001 event. Post-GAC groundwater samples were also collected, which indicate the GAC treatment system is working properly. Post GAC sample results are discussed in Section 5, below.

RFR-11 was sampled on October 4, 2001, and detected analytes were chloroform (0.14 mg/L), PCE (16.0 mg/L), and TCE (0.35 mg/L). Detected analytes were above the MDL but below the RL with the exception of PCE, reported above its MCL of 5.0 mg/L. Based on these findings, CSSA immediately provided bottled water to residents using RFR-11 and installed a GAC treatment system on October 16, 2001. An additional sample was collected on October 12, 2001, and PCE levels had increased to 16.73 mg/L and TCE increased to 0.58 mg/L. The December 2001 monitoring event reported a slight decrease in PCE levels to 12.44 mg/L, but remained well above the MCL. Methylene chloride was also detected at a level of 0.24 mg/L. Methylene chloride detections can be attributed to laboratory contamination due to the presence of methylene chloride in the associated method blank. Post GAC groundwater samples were collected to ensure the treatment system was removing contaminants from the water. Results for Post GAC samples are given in Section 5 below. 

RFR-12 was sampled during the December 2001 monitoring event. Detected analytes were TCE (0.15 mg/L), cis-1,2 DCE (0.12 mg/L), and methylene chloride (0.38 mg/L). All detected analytes were above the MDL and below the RL. The detection of TCE at a concentration of 0.15 �g/L is the same level detected previously in the sampled collected on October 30, 2001. 

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