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December 2004 Off-Post Quarterly Groundwater Monitoring Report

Section 3 - December 2004 Groundwater Monitoring Analytical Results

Twenty-one wells contained VOCs at concentrations above the MDL in December 2004. Based on historical detections, the lateral extent of VOC contamination extends approximately 0.5 mile beyond the south and west boundaries of CSSA to well I10‑7 to the west and LS‑4 to the south. Information such as well depth, pump depth, and other pertinent data necessary to properly characterize the vertical extent of migration, is not readily available from most well owners. For the purposes of this report, the concentrations of PCE, TCE, and cis-1,2-DCE are the only VOCs shown in Section 3.1 through 3.7, as these are the most common COCs detected. Other VOCs, if detected, are reported in the text and in Appendix B.

Off-post wells are grouped by community or neighborhood for the following discussion of the December 2004 results. Concentrations of VOCs detected in December 2004 are presented in Table 3.1. Full analytical results from the December 2004 sampling event are presented in Appendix B. PCE, TCE, and cis-1,2-DCE concentration trends are illustrated in Figure 3.1 for wells LS‑2, LS‑3, LS‑6, LS‑7, OFR‑3, RFR‑10, and RFR‑11. These wells were selected for display because they have had detections of PCE and TCE that approach and/or exceed MCLs. Figure 3.1 also includes precipitation data from the CS‑MW16‑LGR weather station and the AOC‑65 weather station. These figures are presented prior to the discussion of December 2004 groundwater sampling results for each neighborhood. Appendix C is a comparison of pre- and post-GAC PCE and TCE concentrations.

Further discussion of the quarterly groundwater monitoring program conducted from June 2001 to September 2004 is available in previous quarterly reports, located in Volume 5, Groundwater of the CSSA Environmental Encyclopedia.

One problem was identified during data verification performed on the December 2004 CSSA off-post data. Well RFR-13 was sampled for the first time this quarter on December 16, 2004 and analyzed originally on December 29, 2004. The surrogate Toluene‑D8 recovered below the 75% lower control limit at 72.0%. The sample was re-analyzed on January 3, 2005, four days outside of hold time. The surrogate recovery for Toluene‑D8 was again low at 60.5%. The failure is most likely due to sample matrix effects. These results were rejected and an additional sample was collected on January 11, 2005. Further discussion of the sample results are presented in Section 3.7.

Methylene chloride has been periodically detected in on- and off-post samples since 1992. However, because methylene chloride was also detected in associated quality control samples, it was concluded the analyte was introduced as a laboratory contaminant and was not present in the groundwater. In addition, there are no known historical uses of methylene chloride on-post, and methylene chloride has not been detected in the same wells consistently over time, supporting the conclusion that methylene chloride is present because of laboratory procedures. The earliest detection of methylene chloride was in November 1992, with sporadic detections in September 1999, December 2001, March 2002, and September 2002. Three detections of methylene chloride reported in March 2003 were flagged with a �B� flag, as the concentration of methylene chloride was above the RL in the method blank. Methylene chloride was not detected in the June 2003, September 2003, December 2003, March 2004, or June 2004 sampling events. In September 2004 methylene chloride was detected in two wells, one detection was particularly high prompting further investigation. An additional sample was collected to verify the anomalous results. In December 2004 methylene chloride was detected in one sample (OFR-2) along with its field duplicate, the results were rejected due to the fact that the parent sample and field duplicated were not run back to back. There was a non-compliant instrument continuing calibration verification injection which affected the field duplicate, but not the parent sample. These data were �R� flagged.

Chloroform has been detected on-and off-post since 1992. Chloroform is regulated by the EPA as a total trihalomethane (TTM) with a combined MCL of 80 ppb for all TTMs detected. No detections of chloroform and other TTMs have been above the combined MCL. These compounds are regulated as byproducts related to drinking water disinfection. Chloroform detections in well JW-14 are related to the well owner adding bleach to the drinking water well for disinfection. In December 2004 the TTMs in well RFR-13 were approaching the combined MCL of 80 ppb. The well owner was contacted and an additional sample was collected. The confirmation sample results indicated the combined TTM concentration increased but remained below the MCL. According to the well owner the well was treated with household bleach for disinfection purposes after well installation. The well owner was informed of the laboratory results and the TCEQ guidance fact sheet for the public on well disinfection was delivered to the well owner.

3.1 - Fair Oaks

December 2004 Results:

Two wells (FO-J1 and FO-22) in the Fair Oaks area were sampled in December 2004. FO-J1 reported PCE at a concentration of 0.18 �g/L, TCE at 0.22 �g/L, and cis-1,2-DCE at 0.37 �g/L, all below the RL. The September 2004 FO-J1 sampling event reported a detection of PCE at 0.17 �g/L. A sample was not collected from well FO-J1 in June 2004 due to an electrical malfunction. PCE was detected in FO-J1 at a concentration of 0.36 �g/L, above the MDL but below the RL, in March 2004.

Well FO-22 had no VOC detections in the December 2004 sampling event. Well FO-22 was not sampled previously in 2004.

Results Summary:

Wells in the Fair Oaks area were first sampled in September 2001. Through December 2004 thirteen quarterly samples were collected from FO-J1. PCE levels have ranged from non-detects to 0.36 �g/L (December 2004). FO-J1 will remain on the quarterly sampling schedule for upcoming events. Well FO-22 has been sampled yearly since September 2001 and will remain on an annual sampling schedule or be sampled as needed in accordance with DQOs. Results for PCE, TCE, and cis-1,2-DCE from wells sampled in the Fair Oaks area during the 2004 sampling events are provided in the following table:

3.2 - Hidden Springs Estates

December 2004 Results:

In December 2004, Hidden Springs Estates well HS-2 was sampled. PCE was detected at a concentration of 0.19 �g/L. In September 2004, well HS-2 had a detection of PCE at a concentration of 0.23 �g/L. HS-2 has no VOC detections in June 2004. However, this well did have detections of PCE and toluene at concentrations of 0.14 mg/L and 1.0 mg/L, respectively, in March 2004. These concentrations were above the MDL, but below the RL. Based on these detections, HS-2 will remain on the quarterly sampling schedule in accordance with the project DQOs.

Results Summary:

Wells in Hidden Springs Estates were first included in CSSA�s groundwater monitoring program in December 2001. Over the history of the sampling at well HS-2, PCE levels have ranged from 0.11 to 0.23 �g/L. Results for PCE, TCE, and cis-1,2-DCE from the Hidden Springs area wells sampled in the 2004 sampling events are provided below:

3.3 - Interstate I-10 Area

December 2004 Results:

Four wells in the I-10 area were sampled in December 2004 (I10-2, I10-4, I10-5, and I10-7). PCE was detected in wells I10-2 and I10-4 at concentrations of 0.11 �g/L and 0.12 �g/L, respectively. Wells I10-5 and I10-7 reported no VOC detections. In September 2004 well I10‑2 had a VOC detection of PCE (0.11 mg/L), below the RL. The field duplicate reported similar results with the addition of methlyene chloride, a suspected laboratory contaminant. Well I10-4 also reported a PCE detection of 0.15 �g/L in September 2004. In March 2004 well I10-4 reported its maximum detected PCE concentration of 2.22 mg/L. Based on these detections, I10-2 and I10-4 will remain on the quarterly sampling schedule. Wells I10-5 and I10-7 will remain on a yearly sampling schedule, in accordance with the Plan.

Results Summary:

Wells in the I-10 area were first included in CSSA�s groundwater monitoring program in September 2001. PCE levels in I10-2 have ranged from 0.06 to 0.16 �g/L, and in I10-4 from 0.06 to 2.22 �g/L. Results for PCE, TCE, and cis-1,2-DCE from I-10 area wells sampled during the 2004 sampling events are provided in the following table: 

3.4 - Jackson Woods

December 2004 Results:

In December 2004, eight Jackson Woods Subdivision wells (JW‑7, JW‑8, JW‑9, JW‑14, JW‑26, JW‑28, JW‑29, and JW‑30) were sampled. Five of the eight wells sampled, JW‑7, JW‑8, JW‑14, JW‑28 and JW‑30, had detections of contaminants of concern below the applicable MCLs. Wells JW‑9, JW‑26, and JW‑29 had no VOC detections. Wells JW‑7, JW‑8, JW‑9, JW‑14, JW‑28, and JW‑30 will continue to be monitored on a quarterly basis because of previous detections. Well JW‑29 had no detections the last five quarters but will remain on the quarterly sampling schedule due to its proximity to impacted wells. Well JW‑26 has had four consecutive samples with no detections and can be dropped from quarterly sampling to yearly sampling in accordance with the Plan.

Well JW‑7 was initially sampled in September 2003. The December 2004 sampling event was the sixth consecutive round of sampling at JW-7. PCE and dichlorodifluoromethane were detected at concentrations of 0.39 �g/L and 0.30 �g/L, respectively. In September 2004, the initial sample results reported methylene chloride at 19.24 �g/L and dichlorodifluoromethane at 0.13 �g/L. Due to the unusually high concentration of methylene chloride an additional sample was collected on October 18, 2004. These results came back as all non-detect leading Parsons to reject the sample results as anomalous data due to laboratory contamination. PCE concentrations in this well have ranged from 0.42 to 0.65 �g/L.

Well JW‑8 reported PCE (0.14 �g/L), TCE (0.22 �g/L), and cis-1,2-DCE (0.38 �g/L) in December 2004. PCE was detected in well JW-8 at a concentration of 0.27 �g/L, below the RL, in September 2004. PCE was detected below the RL in well JW-8 for four consecutive sampling events prior to the June 2004 event. TCE and cis-1,2-DCE were never detected in this well until this event. PCE levels have ranged between 0.29 to 0.35 �g/L.

No VOCs were detected in wells JW‑9, JW‑26, and JW‑29 in the December 2004 event. PCE levels have ranged between 0.06 to 0.15 �g/L for well JW‑9.

PCE (0.10 �g/L) was detected in the JW‑14 field duplicated and chloroform (0.23 �g/L) was detected in the JW‑14 normal sample. Chloroform has been consistently detected in this well since September 2001 ranging from 0.03 to 53.45 �g/L. All chloroform results have been below the TTMs MCL of 80 mg/L. This well owner routinely disinfects his well with bleach, which results in TTM detections in the water. PCE was last detected in this well in March 2003, all PCE detections have been below the RL.

Well JW‑26 had no VOC detections in the December 2004 event. This is the fourth consecutive event with no VOC detections. This well can be dropped from the quarterly sampling schedule to the annual sampling schedule in accordance with the Plan. Historic PCE levels have ranged from 0.06 to 0.14 �g/L.

Well JW‑28 had a sixth consecutive detection of toluene at a concentration of 0.12 �g/L. No other VOCs have been detected in this well. Toluene detections have ranged from 0.12 �g/L to 0.24 �g/L.

No VOCs were detected in well JW‑29. Well JW‑29 had a PCE detection in June 2003. Although this well has had six consecutive sampling events with no VOC detections it will remain on the quarterly sampling schedule because it is near impacted wells.

JW‑30 reported detections of PCE (0.14 �g/L), TCE (0.27 �g/L), and cis1,2‑DCE (0.47 �g/L), in December 2004. No VOCs have been detected in this well since March 2004. PCE levels have ranged from 0.06 �g/L to 0.2 �g/L, all below the RL. Only one other detection of TCE and cis-1,2-DCE were reported in March 2003, both below the RL.

Wells JW‑9, JW‑26 and JW‑29 had no VOC detections in December 2004. Wells JW‑7, JW‑8, JW‑9, JW‑14, JW‑28, JW‑29, and JW‑30 will remain on the quarterly sampling schedule in accordance with the Plan.

Results Summary:

Off-post sampling was first performed in the Jackson Woods area in 1995 with sampling at JW‑30, and no VOCs were detected in this well at that time. JW‑30 was again sampled in September 1999, and methylene chloride was the only VOC detected. Additional Jackson Woods Subdivision wells have been added to the sampling list since 1995. Results for PCE, TCE, and cis‑1,2‑DCE in wells in the Jackson Woods area sampled during the 2004 sampling events are provided below:

3.5 - Leon Springs Villa

December 2004 Results:

Six wells (LS‑2, LS‑3, LS‑4, LS‑5, LS‑6, and LS‑7) in the Leon Springs Villa subdivision were sampled in December 2004. All wells had detections below the applicable MCLs.

Well LS‑1 has been taken offline by Bexar Metropolitan Water Systems due to homeowners complaints of cloudy water. LS‑1 had no VOC detections in June 2004. Well LS‑1 had detections of chloroform in eight previous events. All detections of chloroform have been below the TTMs MCL (80 mg/L). PCE and TCE have been detected consistently in this well ranging from 0.24 to 0.67 �g/L for PCE and 0.05 to 0.51 �g/L for TCE. Well LS‑1 should be removed from the quarterly sampling schedule unless the well is put back into service.

Well LS‑2 had detections of PCE and TCE at concentrations of 1.64 mg/L and 0.43 mg/L, respectively, in December 2004. The TCE concentration was above the MDL and below the RL, while the PCE concentration was above the RL and below the MCL. An evaluation of concentration trends through the December 2004 event for LS‑2 is given in Figure 3.1. PCE concentrations doubled from September to December 2002. From December 2002 to March 2004 PCE levels had been decreasing and had fallen below the RL. In June 2004 PCE levels were slightly above the RL. TCE concentrations have remained fairly stable since August 2001, with a slight increase from September to December 2002.

Results for LS‑3 included concentrations of PCE at 1.59 mg/L, TCE at 0.26 mg/L, and toluene at 0.69 mg/L. TCE and toluene were below the RL while PCE was above the RL and below the MCL. An evaluation of concentration trends through December 2004 in well LS‑3 is given in Figure 3.1. Based on previous detections, CSSA installed a combined GAC filtration system on wells LS‑2 and LS‑3 in April 2002. Wells LS‑2 and LS‑3 should continue to be sampled quarterly in the future.

In December 2004, PCE was detected at a concentration of 0.18 mg/L in LS‑4, below the RL. Well LS‑4 should continue to be sampled quarterly based on VOC detections ranging from 0.06 to 0.25 mg/L.

Well LS‑5 had a detection of TCE at a concentration of 0.19 mg/L in December 2004. Previous concentrations have all been above the MDL and below the RL and MCL for both PCE and TCE. TCE has been consistently detected in this well, at concentrations below the RL ranging from 0.16 to 0.51 �g/L. The residence supplied by LS-5 has recently been re-occupied and water production from this well will likely increase. Well LS‑5 should remain on the quarterly sampling schedule.

In December 2004, PCE and TCE were detected at concentrations of 4.23 mg/L and 0.67 mg/L, respectively, in LS‑6. PCE was above the RL but below the MCL while TCE concentrations were below the RL. An evaluation of concentration trends in LS‑6 through December 2004 is provided in Figure 3.1. Well LS‑6 is equipped with a GAC treatment system because concentrations exceeded the MCL in the past. Well LS‑6 should continue to be sampled on a quarterly schedule.

The LS‑7 sample contained concentrations of PCE (1.85 mg/L) and TCE (0.33 mg/L) during the December sampling event. TCE was below the RL, as shown by the concentration trends presented in Figure 3.1. PCE was below the MCL and above the RL. Well LS‑7 was equipped with a GAC treatment system when previous detections approached the MCL. Well LS‑7 should continue to be sampled on a quarterly schedule.

Results Summary:

Wells from the Leon Springs Villa area were first sampled in December 1999 to determine whether VOCs had migrated off-post to the south of CSSA. Based on past results for VOCs, CSSA installed GAC treatment systems at wells LS‑2/LS‑3, LS‑6, and LS‑7. In September 2004, semi-annual post‑GAC confirmation samples were collected from all Leon Springs wells equipped with GAC systems (Appendix C). The samples confirm that the GAC units are working effectively and that VOCs are reduced to concentrations below the applicable drinking water MCLs. Chloroform was detected in post-GAC samples from LS‑2/LS‑3 at concentrations below the RL and MCL in September 2002, March 2003, September 2003, March 2004, and again in September 2004. In March 2004, TCE was detected below the RL, in sample LS-2/LS‑3‑A1. In September 2004, PCE (0.59 mg/L) and TCE (0.22 mg/L) were detected in sample LS‑2/LS‑3‑A1. Sample port A1 is located between the GAC canisters. Sample port A2 is located after both carbon canisters and is a representative sample of the water being supplied to homeowners. Sample LS‑2/LS‑3‑A2 had a detection of chloroform at 0.12 mg/L, below the RL. Due to current detections a maintenance visit has been scheduled to change the carbon in the LS‑2/LS‑3 GAC unit. This carbon change out tentatively is scheduled to occur the first week of March. The next post-GAC sampling event will be conducted in March 2005.

Results for PCE, TCE, and cis-1,2-DCE in pre-GAC samples collected from the Leon Springs Villa community wells during 2004 are provided below:

3.6 - Old Fredericksburg Road Area

December 2004 Results:

Three wells (OFR‑1, OFR‑2, and OFR‑3) along Old Fredericksburg Road were sampled in December 2004. OFR‑1 and OFR‑3 had detections of VOCs.

In December 2004, PCE was detected at 0.19 mg/L, in well OFR‑1, which is below the RL. The results for OFR‑2 showed no VOCs present in the sample. The field duplicate reported the same result. However, the methylene chloride results were rejected in the sample and field duplicate. The parent sample and field duplicate were not run back to back. There was a non-compliant instrument continuing calibration verification injection which affected the field duplicate, but not the parent sample. These data were �R� flagged. Over the history of sampling at these wells, PCE has ranged from 0.29 to 0.49 �g/L in OFR-1 and 0.005 to 0.35 �g/L in OFR-2. These wells should continue to be monitored quarterly in accordance with the Plan. No trend analysis was prepared for these wells because detections have been well below the MCL.

In December 2004, OFR‑3 had detections of PCE (1.75 mg/L) and TCE (2.21 mg/L). Both concentrations were above the MDL and RL but below the MCL. In April 2002, a GAC unit was installed on OFR-3 based on PCE concentrations. An evaluation of concentration trends in well OFR-3 through December 2004 is provided in Figure 3.1. Increases in PCE and TCE occurred from February to March 2002. PCE and TCE decreased from June 2002 to September 2002 and remained stable until June 2003. The December 2003 event showed a significant increase in the PCE and TCE concentrations and both COCs exceeded their MCLs. In March 2004 concentrations decreased to below the applicable MCLs but again in June 2004 they exceeded the MCL. Well OFR‑3 should continue to be sampled on a quarterly schedule.

Results Summary:

Well OFR‑2 was first sampled in December 1995 to determine whether VOCs had migrated off-post to the west of CSSA. Every six months, post-GAC samples are collected to confirm the GAC filtration system at OFR‑3 is working. To date, no VOCs have been detected above RLs in the post-GAC samples. The next post-GAC confirmation sample for OFR‑3 will be collected in March 2005 and results for previous post-GAC sampling events are given in Appendix C. Results for PCE, TCE, and cis-1,2-DCE from Old Fredericksburg Road area wells sampled during the 2004 events are provided below:

3.7 - Ralph Fair Road Area

December 2004 Results:

In December 2004, seven wells (RFR‑3, RFR‑6, RFR‑7, RFR‑10, RFR‑11, RFR‑12, and RFR‑13) in the Ralph Fair Road area were sampled. Of the seven wells sampled, two wells, RFR‑10 and RFR‑11, had detections greater than the MCL.

Well RFR‑3 had no VOC detections. Well RFR‑3 can be removed from the quarterly sampling schedule in accordance with the Plan, this well should be sampled annually. VOCs have ranged from 0.005 to 0.12 �g/L in RFR‑3.

Wells RFR‑6 and RFR‑7 also reported no VOC detections. Both wells should remain on the annual sampling schedule.

Well RFR‑10 concentrations exceeded the MCLs for PCE at 11.7 mg/L and TCE exceeded the MCL at a concentration of 5.55 mg/L. Cis-1,2-DCE was also detected below the RL at a concentration of 0.25 mg/L. An evaluation of concentration trends through December 2004 is included in Figure 3.1. A GAC filtration system was installed on RFR‑10 when concentrations exceeded the MCL. Well RFR‑10 should continue to be sampled on a quarterly schedule.

In December 2004, RFR‑11 had detections of PCE (5.32 mg/L) and TCE (0.58 mg/L), both of which were below MCL. Based on previous results, RFR‑11 should continue to be sampled on a quarterly schedule. Over the sampling history of this well, PCE and TCE have ranged from 0.89 to 16.73 �g/L and 0.12 to 1.73 �g/L, respectively.

In December 2004, Well RFR‑12 had a detection of TCE at a concentration of 0.18 �g/L, which is below the RL. Well RFR‑12 will remain on the quarterly sampling schedule in accordance with the Plan.

Well RFR‑13 is a newly installed drinking water well. Bromodichloromethane (5.02 mg/L), chloroform (54.09 mg/L), and dibromochloromethane (1.55 mg/L) were detected in this well. These chloroform results were approaching the TTMs MCL of 80 mg/L prompting further investigation of the well. The well owner informed Parsons that the well was treated with bleach after installation for disinfection purposes. An additional sample was collected on January 11, 2005 to ensure that the levels did not exceed the TTMs MCL of 80 mg/L. Bromodichloromethane (8.74 mg/L), chloroform (64.52 mg/L), and dibromochloromethane (2.94 mg/L) were again detected in this well.

Results Summary:

Ralph Fair Road wells RFR‑3 and RFR‑8 were sampled during the first off-post sampling performed in 1995. Wells RFR‑10 and RFR‑11 required installation of GAC filtration systems in October 2001 when concentrations exceeded the MCL. Post-GAC sampling confirms that the GAC filtration systems are working effectively. See Appendix C for previous post‑GAC sampling results. The next post-GAC confirmation samples will be collected in March 2005. Results in 2004 for wells in the Ralph Fair Road area are provided below:

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