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June 2002 Off-Post Quarterly Groundwater Monitoring Report
Section 3 - June 2002 Groundwater Monitoring Analytical Results
All concentrations of VOCs detected in samples collected from April through June 2002 are presented in Table 3.1. Full analytical results from April through June 2002 are presented in Appendix B. PCE, TCE, and cis-1,2-DCE concentration trends are illustrated for selected wells with detections above the MCL on at least three previous sampling events (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]. These figures are located after the discussion of results for each well). Results from groundwater sampling are discussed below. The wells are grouped by community or neighborhood for discussion of past groundwater monitoring and the June 2002 results.
Sixteen wells showed VOC levels above the MDL in June 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. The vertical extent of migration cannot be determined based on data (e.g., well completion depths), which is not available for wells sampled. Information providing depth of wells, pump depth, and other pertinent data to properly characterize the vertical extent of migration is not readily available from the well owners. Post-GAC confirmation samples were collected for wells LS-2, LS-3, and OFR-3 in April 2002. No other Post-GAC samples were collected during this quarterly reporting period (March-June 2002.) Appendix D is a comparison of pre- and post-GAC concentrations detected in wells LS-2/LS-3, LS-6, LS-7, OFR-3, RFR-10 and RFR-11 for PCE and TCE. All post-GAC samples had no detections of PCE and/or TCE. Past results confirm that the GAC systems are effective in reducing VOC levels to non-detectable levels in these drinking water wells.
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. There are no known historical uses of methylene chloride on-post. Additionally, methylene chloride has not been detected in the same wells consistently over time, enhancing the conclusion that methylene chloride is a laboratory artifact. The earliest detection of methylene chloride was in November 1992, with sporadic detections in September 1999, December 2001, and March 2002. No detections of methylene chloride occurred in the June 2002 event.
In June 2002, one well was sampled at the Fair Oaks area, FO-J1. Two samples, one from the wellhead and one from the entry point (EP) where FO-J1 water enters the Fair Oaks water distribution system were collected. The FO-J1 EP was sampled for the first time in June 2002 due to the F-flagged PCE detections in December 2001 and March 2002 in FO-J1. It was sampled to determine if contamination in well FO-J1 was reaching the EP; however, no VOC contamination was detected. FO-J1 had a detected concentration of PCE (0.22 mg/L) in this monitoring event. All VOCs detected in FO-J1 were above the MDL but below the reporting limit (RL).
The Fair Oaks wells FO-22 and FO-J1 were sampled in September 2001. No VOCs were detected in the two wells and they were scheduled for sampling on an as-needed basis. In the December 2001 event, FO-J1 was again sampled and cis-1,2-DCE was detected at a concentration of 0.30 mg/L. FO-J1 was then placed on the quarterly sampling schedule for one year. The next sampling event at FO-J1 in March 2002, reported PCE (0.25 mg/L), above the MDL but below the RL. Additional Fair Oaks wells, FO-8 and FO-17, were sampled in March 2002 and no VOCs were detected in either well.
Two Hidden Springs wells, HS-2 and HS-3, were initially sampled in December 2001. The TCEQ collected split samples from wells HS-2 and HS-3 at that time. Results from the laboratory contracted by the TCEQ did not confirm or conflict with results of CSSA sampling because the MDLs used by the TCEQ laboratory were higher. HS-2 was sampled in March and June 2002 due to PCE detections. HS-2 had detections of PCE at 0.16 mg/L in December 2001 and at 0.21 mg/L in March 2002. Both detections were above the MDL but below the RL. June 2002 was the third consecutive sampling event for HS-2 and no VOCs were detected.
HS-3 reported a detection of methylene chloride (0.38 mg/L), in the December 2001 event. 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. Methylene chloride was not detected in June 2002. The June 2002 event was the second consecutive sampling event for this well, and no VOCs were detected.
Well I10-2 was initially sampled in September 2001 and a concentration of 0.23 mg/L TCE was reported. I10-2 was resampled and I10-4 was sampled for the first time in December 2001. Concentrations from the December 2001 sampling event were 0.16 mg/L and 0.12 mg/L PCE, respectively. These concentrations were above the MDL but below the RL.
In March 2002, wells I10-2, I10-4, and I10-7 were sampled and no VOCs were detected in any of them. The TCEQ also collected samples from well I10-5 during the December 2001 event, because access to this well was denied to CSSA. No VOCs were detected in the sample tested by TCEQ, but results do not confirm or conflict with results of CSSA sampling because MDLs used by the TCEQ laboratory were higher than MDLs used by the CSSA laboratory as required by DQOs.
In June 2002 two wells were sampled in the I-10 area, I10-2 and I10-4. I10-2 and I10-4 had no VOC detections in June 2002. I10-2 had �M� flags applied for chloromethane and 1,3,5-trimethylbenzene, due to matrix interference. Matrix interference is a flag applied in accordance with AFCEE QAPP 3.0 guidance for laboratory methods. The potential matrix effect indicated possible high-biased results in the parent sample from I10-2. Even with the possible high-bias factor, both compounds were reported as non-detect in sample I10-2, reinforcing the accuracy of the reported results. Therefore, these analytes were �M� flagged due to the quality control check that was performed in the lab.
Off-post sampling was first performed in 1995 in response to VOC contamination detected in on-post well CS-16. A Jackson Woods well, JW-30, was sampled at that time. No VOCs were detected in the well. JW-30 was sampled again in September 1999, and no VOCs except methylene chloride were detected. Based on a number of arguments discussed in Section 3.0 of this report, methylene chloride is suspected to be a laboratory artifact.
In September 2001, five Jackson Woods wells, JW-6, JW-9, JW-12, JW-13, and JW-14 were sampled. No VOCs were detected in JW-6, JW-9, JW-12 and JW-13, while JW-14 had a detection of PCE (0.12 mg/L), which was slightly greater than the MDL of 0.11 mg/L but below the RL. In December 2001 only wells JW-9 and JW-14 were sampled. JW-9 had a detection of cis-1,2-DCE (0.33 mg/L), and JW-14 reported no VOCs above the MDL. Both JW-9 and JW-14 were sampled in March 2002 with no VOCs reported in these wells. The March 2002 sampling event added a new Jackson Woods well, JW-26. Chloroform (0.11 mg/L) and methylene chloride (0.21 mg/L) were detected in this well.
In June 2002, three wells (JW-6, JW-9, and JW-14) were sampled in the Jackson Woods area. JW-6 was sampled for the second time since September 2001. Similar to the September 2001 event, no VOCs were detected in the June 2002 sampling event from this well. JW-9 was sampled for the third consecutive time due to a low level of cis-1,2-DCE in December 2001. In June 2002, JW-9 had an �M� flag for 1,3,5-trimethlybenzene because it was recovered only slightly above tolerance in associated quality control samples and was non-detect in the associated field samples. The parent sample results for the non-compliant analytes were flagged �M� per the AFCEE QAPP. No additional corrective action was necessary since each well represents a unique sample matrix.
Per the groundwater sampling frequency rationale summarized on Table 1.1, JW-14 was sampled for four consecutive events due to low levels of PCE and chloroform detected in September 2001. In June 2002, chloroform was detected at a concentration of 0.49 mg/L. The chloroform detection was above the MDL and RL but below the MCL. Chloroform has been detected in JW-14 consistently since September 2001. No other VOCs were detected in JW-14.
A well from the Leon Springs area (LS-7) was first sampled December 1999 to determine whether VOCs had migrated off-post to the southwest of CSSA. Quarterly sampling of LS-7 continued after December 1999 because VOCs were detected, though at concentrations below the MCL. In March 2000, sampling of LS-7 reported PCE and TCE at concentrations of 2.87 mg/L and 0.5 mg/L, respectively. These detections were above the RL but below the applicable MCL. By June 2001, the PCE concentration increased to 4.0 �g/L. The increase in concentrations of VOCs prompted CSSA to install a GAC treatment system on August 7, 2001. This decision was based on linear regression statistics from the December 1999 through July 2001 sampling results, indicating that an exceedance of the MCL could possibly occur by the end of calendar year 2001.
In August 2001, sampling of wells LS-2, LS-3, LS-5 and LS-6 was conducted to determine whether other wells near LS-7 were impacted. The August 2001 concentrations ranged from 0.28 to 6.5 mg/L for PCE and 0.26 to 0.90 mg/L for TCE. The PCE concentration in LS-6, (6.5 mg/L) was the first measured off-post exceedance of any groundwater MCL under CSSA�s groundwater monitoring program. Based on these findings, CSSA immediately provided bottled water to residents using the LS-6 well and installed a GAC filtration system on August 15, 2001. Public water system supply wells LS-1 and LS-4 were added to the September 2001 quarterly sampling event, and all Leon Springs wells have been sampled on a quarterly basis since September 2001. In October and November 2001, a sample was collected from the EP at which water from LS-2 and LS-3 enters the distribution system. Based on increasing concentration trends in LS-2 and LS-3 and the presence of PCE and TCE above the MDL but below the RL in EP samples, installation of a GAC treatment system for LS-2 and LS-3 was completed in April 2002. All Leon Springs wells with GAC systems installed will have post GAC confirmation samples collected every 6 months. In June 2002, wells LS-1, LS-2, LS-3, LS-4, LS-5, LS-6, and LS-7 were sampled.
LS-1 had detections of PCE and TCE above the MDL but below the RL in each event sampling. For June 2002, PCE was detected at 0.40 mg/L and TCE at 0.32 mg/L. LS-1 had chloroform detected at 0.12 mg/L, the fourth consecutive detection for chloroform in this well. Because all detections have been above the MDL but below the RL, no trend analysis is given for these concentrations.
LS-2 has been regularly sampled since August 2001. In June 2002, PCE, TCE and chloroform were detected at concentrations of 2.22 mg/L, 0.31 mg/L, and 0.15 mg/L, respectively. The PCE concentration was above the MDL and RL but below the MCL. TCE and chloroform detections were above the MDL and below the RL and MCL. An evaluation of concentration trends over time for LS-2 is given in Figure 3.1. PCE concentrations varied since August 2001 and decreased from March to June 2002. TCE concentrations remain stable.
LS-3 has been sampled regularly since August 2001. Results from the June 2002 event indicated concentrations of PCE at 1.06 mg/L and TCE at 0.20 mg/L. Both analytes were above the MDL but below the RL and MCL. An evaluation of concentration trends over time in well LS-3 is given in Figure 3.2. Concentrations in LS-3 peaked at 4.8 mg/L in September 2001, and remained above the RL (1.4 mg/L) in each subsequent quarterly event until January 2002. Prior to the June 2002 sampling event, post-GAC samples were collected to ensure VOCs were being removed from the drinking water after GAC treatment. Future post-GAC testing will be scheduled on a semi-annual basis for all GAC units in operation after system maintenance has been conducted. The next post-GAC confirmation sample for LS-2/LS-3 will be collected during the September 2002 quarterly sampling event.
LS-4 has been sampled since September 2001. PCE was reported at levels below the RL but above the MDL. For the first time in March 2002, 1,2 DCA was detected at a concentration of 0.12 mg/L, which is above the MDL and below the RL. The June 2002 event reported no VOC detections from LS-4. No concentration trends are provided for LS-4 because no VOCs were detected in any samples above the RL.
LS-5 has been sampled for five consecutive events since August 2001. PCE was detected at low levels in August and October 2001, and was not detected in the other three events, while TCE was reported at low levels in every event. Methylene chloride (0.25 mg/L) was reported for the first time in March 2002, but was not detected in June 2002 or in any prior samples indicating that the March 2002 detection was a laboratory contaminant. In June 2002, TCE was detected at 0.16 mg/L, but PCE was not detected above its MDL (1.4 mg/L).
LS-6 pre-GAC samples have been collected regularly since August 2001. PCE levels above the MCL and TCE at low levels, below the RL, were reported in August and September 2001. PCE remained below the MCL, and TCE levels remained below the RL from December 2001 to June 2002. The LS-6 pre-GAC sample reported PCE at 2.48 mg/L and TCE at 0.25 mg/L during the June 2002 event. An evaluation of concentration trends in LS-6 is given in Figure 3.3. Since peaking at 10.0 mg/L in September 2001, PCE concentrations have stabilized between 2.0 and 3.0 mg/L. Prior to the June 2002 sampling event, post-GAC samples were collected to ensure that VOCs were being removed from the drinking water after treatment, or periodically as appropriate, but future post-GAC testing will be scheduled on a semi-annual basis for all operational GAC units after maintenance. The next post-GAC confirmation sample will be collected in September 2002.
LS-7 pre-GAC samples have been collected regularly since December 1999. PCE and TCE were detected below the MCL consistently since December 1999. In June 2002 the LS-7 pre-GAC sample reported concentrations of PCE (2.68 mg/L) and TCE (0.22 mg/L). As shown by the trends presented in Figure 3.4, PCE concentrations reported in June 2002 remained relatively stable for the last two quarters; however, the overall trend shows PCE concentrations fluctuating between 1.0 and 5.0 mg/L over the 2-1/2 year monitoring period at LS‑7. The only other analyte detected in the June 2002 event was chloroform (0.13 mg/L). Inconsistent detections of chloroform have occurred since March 2000, but the level has routinely been either slightly above the MDL or non-detectable. Prior to the June 2002 sampling event, post-GAC samples were collected to ensure that VOCs are being removed from the drinking water following GAC treatment. The next post-GAC confirmation sample will be collected in September 2002 after maintenance.
During the first off-post sampling, performed in 1995, in response to VOC contamination detected in on-post well CS-16, OFR-2 was sampled. No VOCs were detected during this initial sampling event. No other wells in the Old Fredericksburg Road area were sampled until October 2001. Three wells (OFR-1, OFR-2, and OFR-3) were periodically sampled periodically since October 2001. These are the only Old Fredericksburg Road wells identified in the Offsite Well Survey Report (Parsons, 2001).
OFR-1 was sampled for the first time in December 2001 and had PCE levels at 0.42 mg/L. In June 2002 OFR-1 had detected concentrations of PCE at 0.34 mg/L, a similar concentration to the reported concentrations in December 2001 and March 2002. No other analytes were detected in June 2002. The PCE detection was above the MDL and below the RL and MCL. No concentration trend analysis was prepared for OFR-1 because detections did not exceed the RL or the MCL.
OFR-2 was sampled in March 2002 for the first time since December 1995. The March 2002 event reported a detection of PCE (0.29 mg/L). The June 2002 event reported PCE at a concentration of 0.22 mg/L. This well will be monitored quarterly, in accordance with the Plan. Detected PCE levels are below its RL, and only three sampling events were performed, so no trend analysis was prepared for this well.
OFR-3 was sampled on a monthly basis since October 2001 due to a concentration of 4.2 �g/L PCE. In April 2002, a GAC unit was installed in response to detected PCE levels in March 2002. In March 2002 OFR-3 had reported levels of PCE at 12.15 mg/L, TCE at 5.65 mg/L, and cis 1,2 DCE at 0.14 mg/L. Both PCE and TCE exceeded their respective MCLs (5.0 mg/L) in March 2002. In the June 2002 monitoring event PCE and TCE were again detected at concentrations above the MCL at 10.22 mg/L and 6.24 mg/L, respectively. An evaluation of concentration trends in well OFR-3 is given in Figure 3.5. Prior to the June 2002 sampling event a post-GAC sample was collected to ensure the GAC unit was removing VOCs from the drinking water following installation. The next post-GAC confirmation sample for OFR-3 will be collected in September 2002.
Other analytes detected over time in OFR-3 include a January 2002 detection of dichlorodifluoromethane at 0.28 mg/L. In February 2002, dichlorodifluoromethane and methylene chloride were reported at 1.43 mg/L, and 0.96 mg/L, respectively. During the March 2002 monitoring event, dichlorodifluoromethane (1.48 mg/L) and methylene chloride (0.37 mg/L) were again detected. In June 2002 dichlorodifluoromethane was detected at a concentration of 1.57 mg/L. This detection is above the MDL and RL but below its MCL. Based on a number of arguments discussed in Section 3.0 of this report, methylene chloride is suspected to be a laboratory artifact.
During the first off-post sampling performed in 1995 in response to VOC contamination detected in on-post well CS-16, Ralph Fair Road wells RFR-3 and RFR-8 were sampled. No VOCs were detected in either well. Another sampling event for these two wells in September 1999 detected no VOCs, except methylene chloride.
RFR-6, RFR-7, RFR-8, RFR-9 and RFR-10 were sampled during the first quarterly sampling event in September 2001. No VOCs were detected from any of the sampled wells except for well RFR-10. RFR-10 reported PCE at 14.0 mg/L prompting the installation of two GAC units on October 9, 2001. RFR-10 has one GAC unit dedicated to the existing residence and the second GAC unit installed for a mobile home. Eight wells in the Ralph Fair Road area were periodically sampled since September 2001 (RFR-3, RFR-6, RFR-7, RFR-8, RFR-9, RFR-10, RFR-11 and RFR-12). In June 2002, six wells (RFR-7, RFR-8, RFR-9, RFR-10, RFR-11 and RFR-12) were sampled in the Ralph Fair Road area. Results are given below.
RFR-7 and RFR-8 were sampled for the first time in June 2002 since September 2001. No VOCs were detected in September 2001 or in this follow up sampling event. RFR-9 was sampled in September and December 2001 and in the June 2002 event. The only detection in these three events was methylene chloride at 0.52 �g/L in December 2001. Based on a number of arguments discussed in Section 3.0 of this report, methylene chloride is suspected to be a laboratory artifact.
RFR-10 pre-GAC samples have been collected at four consecutive events since September 2001. During the June 2002 monitoring event, RFR-10 exceeded the MCL for PCE at a level of 9.77 mg/L. TCE was slightly less than the MCL at a concentration of 4.91 mg/L in June 2002, and cis-1,2 DCE (0.92 �g/L) was detected above the MDL but below the RL. Concentrations of PCE decreased for two consecutive events from October 2001 to March 2002 and peaked in October 2001 at a concentration of 20.89 mg/L; however, the June 2002 event showed a rebound (increase) in PCE and TCE concentrations back to December 2001 levels (Figure 3.6). Prior to the June 2002 sampling event, post-GAC samples were collected to ensure that VOCs were being removed from the drinking water after GAC maintenance, but future post-GAC testing will be scheduled on a semi-annual basis for all GAC units in operation. The next post-GAC confirmation sample will be collected in September 2002.
RFR-11 has been sampled since October 2001, for four consecutive events. On October 16, 2001, a GAC treatment system was installed at well RFR-11 because September 2001 sampling results indicated PCE at 16.0 mg/L. The June 2002 monitoring event reported concentrations of PCE (2.77 mg/L) and TCE (1.52 mg/L). The June 2002 PCE concentration in RFR-11 shows a continuation of the decreasing trend since a peak concentration of 16.73 �g/L was detected in October 2001 (Figure 3.7). TCE levels indicate a slow but steady rise in concentrations from December 2001 levels near 0.14 mg/L to 1.54 mg/L in June 2002. Prior to the June 2002 sampling event post-GAC samples were collected to ensure that VOCs were being removed from the drinking water after GAC maintenance, but future post-GAC testing will be scheduled on a semi-annual basis for all GAC units in operation. The next post-GAC confirmation sample will be collected in September 2002.
RFR-12 has been sampled three times since August 2001, with repeated detections of TCE above the MDL but below the RL ranging from 0.15 mg/L to 0.16 mg/L. Chloromethane was the only detected analyte in June 2002 at a concentration of 0.48 mg/L. The June 2002 event reported no other VOC detections at RFR-12.