[Home]

[Report Table of Contents] [Next Section]

December 2002 Off-Post Quarterly Groundwater Monitoring Report

Section 3 - Groundwater Monitoring Analytical Results

Overview of December 2002 Event

Seventeen wells contained VOCs at concentrations above the MDL in December 2002. Based on currently available data, the lateral extent of VOC contamination extends approximately 0.5 miles beyond the south and west boundaries of CSSA to well I10-4 to the west and LS-4 to the south. The vertical extent of migration cannot be determined because information regarding well completion depths is not available for wells sampled. Information providing depth of wells, pump depth, and other pertinent data necessary to properly characterize the vertical extent of migration is not readily available from the well owners.

Off-post wells are grouped by community or neighborhood for the discussion of historical results and the December 2002 results. Concentrations for VOCs detected in December 2002 are presented in Table 3.1. Full analytical results from the December 2002 sampling event are presented in Appendix B. PCE, TCE, and cis-1,2-dichloroethene (cis-1,2-DCE) concentration trends are illustrated for wells with detections of PCE and TCE that approach or exceed the MCL (Figure 3.1 [LS-2], Figure 3.2 [LS-3], Figure 3.3 [LS‑6], Figure 3.4 [LS-7], Figure 3.5 [OFR-3], Figure 3.6 [RFR-10], and Figure 3.7 [RFR‑11]).

Figures 3.1 to 3.7 also include precipitation data from the Well CS-MW16-LGR weather station, for evaluation of the affects of rainfall on concentrations. These figures are presented after the discussion of December 2002 groundwater sampling results for each neighborhood presented below. A table summarizing detections of COCs for wells in each neighborhood is included in the Historical Results sections below. Appendix C presents the off-post field logbook notes for the December 2002 event. Appendix D is a comparison of pre- and post-GAC concentrations detected in wells for PCE and TCE. No detections of PCE and/or TCE above the RL have occurred in the post-GAC samples collected. Further discussion of the off-post quarterly monitoring program conducted from September 2001 through December 2002 is available in the Annual Groundwater Monitoring Report, (Parsons, 2003, currently draft), located in Volume 5, Groundwater of the CSSA Environmental Encyclopedia.

Methylene chloride has been reported on- and off-post since 1992. However, each time methylene chloride was detected in a sample, it was also present in associated quality control samples, indicating a high likelihood that this 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 due to 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.

3.1 - Fair Oaks

December 2002 Results

In December 2002, two wells were sampled in the Fair Oaks area, FO-J1 and FO-22. No VOCs were detected in either well in this sampling event. This was the sixth consecutive quarterly sample collected from FO-J1 and the second sample collected from FO-22 since September 2001. FO-J1 will remain on the quarterly sampling schedule for upcoming events. After a minimum of one year, the sampling frequency will be reviewed and possibly decreased in accordance with the off-post monitoring plan.

Historical Results

Wells in the Fair Oaks area were first sampled in September 2001. Historical PCE, TCE, and cis-1,2-DCE results for all wells sampled in the Fair Oaks area include:

3.2 - Hidden Springs Estates

December 2002 Results

In December 2002, HS-2 was the only well sampled in Hidden Springs Estates. This well had a detection of PCE at a concentration of 0.22 mg/L. This concentration was above the MDL, but below the RL. Based on this detection, HS-2 will remain on the quarterly sampling schedule, in accordance with the Plan for the groundwater investigation.

Historical Results

Wells in Hidden Springs Estates were first included in CSSA�s groundwater monitoring program in December 2001. TCEQ collected split samples during the first sampling event in this area. Historical PCE, TCE, and cis-1,2-DCE results for Hidden Springs area wells include:

Methylene chloride was also detected in HS-3 in December 2001. In March 2002 methylene chloride was also present in the analysis method blank, indicating the likelihood that this analyte is a laboratory contaminant and is not present in the groundwater.

3.3 - I-10 Area

December 2002 Results

In December 2002 three wells were sampled in the I-10 area: I10-2, I10-4, and I10-5. I10-2 had VOC detections for PCE and TCE at concentrations of 0.08 mg/L and 0.12 mg/L, respectively. Based on these results, I10-2 will continue to be monitored on a quarterly basis in accordance with the plan. No VOCs were detected in I10-4 and I10-5 in December 2002. This is the fourth consecutive sampling event with no VOCs other than methylene chloride reported in well I10-4. Therefore, I10-4 may be removed from the quarterly sampling schedule in the future. I10-5 was sampled in December 2002 for the first time since the TCEQ samples in December 2001. As no detections of VOCs occurred in either sampling event I10-5 can be sampled on an as needed basis.

Historical Results

Wells in the I-10 Area were first included in CSSA�s groundwater monitoring program in September 2001. TCEQ also collected split samples from I10-4 and sampled I10-5 in December 2001. Historical PCE, TCE, and cis-1,2-DCE results for I-10 area wells include:

In March 2002, well I10-2 had �M� flags applied to results for chloromethane and 1,3,5‑trimethylbenzene, due to a quality control check that was performed in the lab. In September 2002, methylene chloride was detected in I10-2 (0.83 mg/L) and in the field duplicate collected at I10-4 (0.76 mg/L). Methylene chloride is considered to be a laboratory contaminant, as discussed in Section 3.0.

3.4 - Jackson Woods

December 2002 Results

In December 2002, five Jackson Woods wells (JW-9, JW-12, JW-13, JW-14, and JW‑26) were sampled. No VOCs were detected in JW-9, JW-12, JW-13, and JW-26, but PCE (0.16 �g/L) and chloroform (0.30 �g/L) were detected in JW-14. Chloroform has been consistently reported in this well since September 2001 and all results have been below the MCL of 80 mg/L. JW-14 will remain on the quarterly sampling schedule in accordance with project DQOs. JW-9 reported no VOC detections for the fourth consecutive sampling event and can be sampled on an as needed basis in accordance with the Plan. The well owner at JW-9 had a filtration system installed during this quarter. A post-filtration sample was collected from JW-9 and no VOCs were detected.

Historical Results

Off-post sampling was first performed in the Jackson Woods area in 1995 and no VOCs were detected in the well (JW-30) sampled at that time. JW-30 was again sampled in September 1999, and methylene chloride was the only VOC detected. In March 2002 a new Jackson Woods well, JW-26, was sampled and chloroform (0.11 mg/L) and methylene chloride (0.21 mg/L) were detected in this well. Historical PCE, TCE, and cis-1,2-DCE results for wells in the Jackson Woods community include:

In June 2002, JW-9 had an �M� flagged result for 1,3,5-trimethylbenzene because the analyte was recovered slightly above tolerance in associated quality control samples. Also in June 2002, chloroform was detected in JW-14 at a concentration of 0.49 mg/L. The chloroform detection was above the MDL and RL, but below the MCL (80 �g/L). In September 2002, chloroform was again detected in JW-14 at a concentration of 0.24 mg/L.

3.5 - Leon Springs Villa

December 2002 Results

In December 2002, seven wells (LS-1, LS-2, LS-3, LS-4, LS-5, LS-6, and LS-7) were sampled in the Leon Springs Villa subdivision. PCE was detected in LS-1 at 0.67 mg/L and TCE at 0.30 mg/L. LS-1 also had a detection of chloroform at 0.25 mg/L, the sixth consecutive detection for chloroform in this well. All detections of chloroform have been above the MDL but below the RL and below the MCL (80 mg/L) for chloroform.

LS-2 had detections of PCE, TCE, and chloroform at concentrations of 7.4 mg/L, 0.45 mg/L, and 0.09 mg/L, respectively in December 2002. The PCE concentration exceeded the MCL for the first time in LS-2. TCE and chloroform detections were above the MDL and below the RL and MCL. An evaluation of concentration trends through December 2002 for LS-2 is given in Figure 3.1. PCE concentrations varied from August 2001 to September 2002 and doubled from September to December 2002. TCE concentrations have remained stable since August 2001, with a slight increase from September to December 2002.

Results for LS-3 included concentrations of PCE at 4.42 mg/L, TCE at 0.34 mg/L, and chloroform at 0.10 mg/L. TCE and chloroform were above the MDL but below the RL and MCL while PCE was above the MDL and RL but below the MCL. An evaluation of concentration trends through December 2002 in well LS-3 is given in Figure 3.2. The PCE concentration in LS-3 was 4.8 mg/L in September 2001, and remained above the RL (1.4 mg/L) until January 2002. PCE concentrations then increased significantly from June 2002 to December 2002, increasing from 1.06 mg/L to 4.42 mg/L. Wells LS-2 and LS-3 had a combined GAC filtration system installed by CSSA in April 2002, as described in the historical results section below. LS‑2 and LS-3 should be sampled quarterly in the future.

In December 2002, PCE was detected at a concentration of 0.25 mg/L in LS-4. No concentration trends are provided for LS-4 as no VOCs have been detected above the RL in this well. LS-4 should continue to be sampled quarterly due to VOCs detected above the MDL.

LS-5 had PCE (0.12 mg/L) and TCE (0.25 mg/L) detected in this event. Both concentrations are above the MDL and below the RL and MCL. LS-5 should remain on the quarterly sampling schedule in accordance with the DQOs.

In December 2002, PCE and TCE were detected at concentrations of 6.86 mg/L and 0.40 mg/L, respectively, in LS-6. An evaluation of concentration trends in LS-6 through December 2002 is provided in Figure 3.3. Since the detection of 10.0 mg/L in September 2001, PCE concentrations decreased to between 1.5 and 3.0 mg/L from December 2001 to September 2002. The December 2002 concentration for PCE exceeded the MCL (5.0 mg/L) again at 6.86 mg/L, while TCE remained below the RL and MCL. LS-6 is equipped with a GAC treatment system due to past concentrations, and results of post-GAC sampling is discussed below. LS-6 should continue to be sampled on a quarterly schedule.

The LS-7 sample had concentrations of PCE (7.16 mg/L) and TCE (1.05 mg/L) during this event. As shown by the concentration trends presented in Figure 3.4, PCE concentrations reported in December 2002 have increased significantly since September 2001. PCE concentrations were between 1.1 mg/L and 4.6 mg/L for three years, through September 2002. From September 2002 to December 2002, PCE increased from 2.41 mg/L to 7.16 mg/L. The December 2002 PCE concentration is the first exceedance of the MCL (5.0 mg/L) in LS-7. Chloroform (0.08 mg/L) was also detected in the December 2002 event.

Historical Results

Wells from the Leon Springs Villa area were first sampled in December 1999 to determine whether VOCs had migrated off-post to the southwest of CSSA. Based on past concentrations of VOCs, CSSA installed GAC treatment systems at wells LS-2/LS-3, LS-6, and LS-7. Semi-annual post-GAC confirmation samples have been collected from all Leon Springs wells equipped with GAC systems (Appendix D). The testing has confirmed that the GACs are working effectively and that no VOCs above the RLs have been detected after filtration. However, at one well location sampled in December 2002, it was noted that the valves had been adjusted so that water bypassed the GAC system. The valves were corrected prior to sampling and they were locked to prevent future bypassing of the GAC. The next post-GAC sampling event will be conducted in March 2003.

Historical PCE, TCE, and cis-1,2-DCE results for pre-GAC samples collected for wells in the Leon Springs Villa community include:

In addition to PCE, TCE, and cis-1,2-DCE, previous detections include 1,2‑dichloroethane (1,2-DCA) detected in LS-4 in March 2002 at a concentration of 0.12 mg/L, which is above the MDL and below the RL. Methylene chloride (0.25 mg/L) was reported in LS‑5 in March 2002, and was again detected in September 2002 at a concentration of 0.63 mg/L. Detections of chloroform have occurred in LS-7 since March 2000; maximum values reported being slightly above the MDL, but well below the MCL.

3.6 - Old Fredericksburg Road Area

December 2002 Results

Three wells (OFR-1, OFR-2 and OFR-3) were sampled along Old Fredericksburg Road in December 2002. PCE was detected at 0.29 mg/L in well OFR‑1. The results for OFR-2 include PCE at a concentration of 0.12 mg/L. These wells should be monitored quarterly, in accordance with the Plan. No trend analysis was prepared for these wells because detections have not exceeded the RL or MCL.

In December 2002, OFR-3 had detections of PCE (3.48 mg/L), TCE (3.25 mg/L), cis-1,2‑DCE (0.11 mg/L), and dichlorodifluoromethane (1.16 mg/L). The concentrations were above the MDL and RL but below the MCL, except for cis-1,2-DCE which was above the MDL and below the RL and MCL. In April 2002, a GAC unit was installed on OFR-3 due to PCE concentrations above the MCL. An evaluation of concentration trends in well OFR-3 through December 2002 is provided in Figure 3.5. Increases in PCE and TCE occurred from February to March 2002. PCE and TCE decreased from June 2002 to September 2002 and both have slightly increased from September to December 2002. OFR-3 should continue to be sampled on a quarterly schedule.

Historical Results

OFR-2 was first sampled in December 1995 to determine whether VOCs had migrated off-post to the west of CSSA. Although PCE, TCE, and cis-1,2-DCE were not detected in 1995, samples collected in this area since 2001 have contained PCE concentrations of up to 12.15 μg/L, and TCE and cis-1,2-DCE have also been detected sporadically, as shown below. Based on these results a GAC system was installed on OFR-3. Every six months, post-GAC samples are collected to confirm the filtration system is working. To date, no VOCs have been detected above the RLs in any of the OFR-3 post-GAC samples. The next post-GAC confirmation sample for OFR‑3 will be collected in March 2003 and results for previous post-GAC sampling events are given in Appendix D. Historical PCE, TCE, and cis-1,2-DCE results for Old Fredericksburg Road area wells include:

Methylene chloride has been detected periodically in OFR-1 with concentrations ranging from 0.32 to 1.35 mg/L. In September 2002 methylene chloride was reported at 0.96 mg/L in OFR-2. Other analytes detected over time in OFR-3 include dichlorodifluoromethane and methylene chloride. Concentrations of these analytes have ranged from 0.28 to 1.57 mg/L and non-detect to 0.96 mg/L, respectively. As discussed in Section 3.0 of this report, methylene chloride is suspected to be a laboratory artifact.

3.7 - Ralph Fair Road Area

December 2002 Results

In December 2002, five wells (RFR-3, RFR-6, RFR-10, RFR-11, and RFR-12) were sampled in the Ralph Fair Road area. No VOCs were detected in RFR-3 and RFR-6. PCE and TCE were detected in RFR-12 at 0.08 �g/L and 0.24 �g/L, respectively. These values are below the RL, but above the MDL.

RFR-10 concentrations exceeded the MCL for PCE and TCE at 14.94 mg/L and 7.33 mg/L, while cis-1,2 DCE was less than the RL and MCL at a concentration of 0.28 mg/L. An evaluation of concentration trends through December 2002 is included in Figure 3.6. Concentrations of PCE in October 2001 were the maximum concentration reported of 20.89 mg/L. PCE concentrations decreased until March 2002. PCE concentrations rose from 4.50 to 14.94 mg/L from March 2002 to December 2002.

In December 2002, RFR-11 had concentrations of PCE (12.65 mg/L) and TCE (0.17 mg/L). PCE concentrations in RFR-11 were again above the MCL, after dropping below the MCL in June 2002. The maximum concentration, 16.73 �g/L, was detected in October 2001 (Figure 3.7). TCE levels decreased from the September 2002 levels of 0.67 mg/L to 0.17 mg/L in December 2002.

RFR-10 and RFR-11 required the installation of GAC filtration systems in October 2001 when concentrations exceeded the MCL. During the December 2002 sampling event a dripping canister was noted at the RFR-10 GAC filtration system. A fitting was tightened until dripping slowed. Regular maintenance to be conducted in March 2003 will repair any leaks. No VOCs have been detected above the RL in any post-GAC sample. See Appendix D for previous post-GAC sampling results. Future post-GAC sampling is scheduled on a semi-annual basis and the next post-GAC confirmation samples will be collected in March 2003.

Historical Results

During the first off-post sampling performed in 1995, Ralph Fair Road wells RFR-3 and RFR-8 were sampled. Other historical results for pre-GAC samples collected for wells in the Ralph Fair Road area include:

Methylene chloride has been detected in RFR-3, RFR-8 and RFR-9, below the RL but above the MDL. Based on a number of arguments discussed in Section 3.0 of this report, methylene chloride is suspected to be a laboratory artifact. Chloromethane was detected in June 2002 in RFR-12, at a concentration of 0.48 �g/L.

[Next Section]