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September 2002 Off-Post Quarterly Groundwater Monitoring Report

Section 3 - September 2002 Groundwater Monitoring Analytical Results

All concentrations of VOCs detected in samples collected from the September 2002 sampling event are presented in Table 3.1. Full analytical results from the September 2002 sampling event are presented in Appendix B. PCE, TCE, and cis-1,2-DCE concentration trends are illustrated for selected wells with detections near or 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. Groundwater sampling results are discussed below. Wells are grouped by community or neighborhood for discussion of past results and September 2002 results.

Twenty wells showed VOC levels above the MDL in September 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. 

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, March 2002 and September 2002.

3.1 - Fair Oaks

In September 2002, one well was sampled in the Fair Oaks area, FO-J1. No VOCs were detected in this sampling event. This was the fifth consecutive quarterly sample collected from FO-J1. It will remain on the quarterly sampling list until four consecutive quarters indicate results below the MDL.

The Fair Oaks wells FO-22 and FO-J1 were sampled in September 2001. Since no VOCs were detected in the two wells, subsequent sampling was conducted on an as-needed basis. In December 2001, FO-J1 was resampled and cis-1,2-DCE was detected at a concentration of 0.30 mg/L. Due to the detection, FO-J1 was placed on the quarterly sampling schedule for one year. Sampling of FO-J1 in March 2002, reported PCE and TCE (0.25 mg/L and 0.22 mg/L, respectively), both above the MDL but below the reporting limit (RL). Additional Fair Oaks wells, FO-8 and FO-17, were sampled in March 2002 and no VOCs were detected in either well. In June 2002, the entry point (EP), where FO-J1 water enters the Fair Oaks water distribution system, was sampled. The FO-J1 EP sample reported no detections.

3.2 - Hidden Springs

In September 2002 HS-2 reported a detection of PCE at a concentration of 0.17 mg/L. This concentration is above the MDL and below the RL. Based on this detection HS-2 will remain on the quarterly sampling schedule. 

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. HS-3 has no history of VOC detections and will be sampled on an as needed basis.

Two Hidden Springs wells, HS-2 and HS-3, were initially sampled in December 2001. At that time, HS-2 had a detection of PCE at 0.16 mg/L and HS-3 had a detection of methylene chloride at 0.38 mg/L. In addition, 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 resampled in March and June 2002 due to PCE detections. In March 2002, HS-2 had a detection of PCE at 0.21 mg/L and in June 2002 no VOCs were detected. 

3.3 - I-10

In September 2002 two wells were sampled in the I-10 area, I10-2 and I10-4. I10-2 had VOC detections for PCE, TCE, and methylene chloride at concentrations of 0.10 mg/L, 0.15 mg/L, and 0.83 mg/L, respectively. Based on these findings, I10-2 will continue to be monitored on a quarterly basis. I10-4 had no VOC detections in the sample collected in September 2002. However, the field duplicate collected at I10-4 reported methylene chloride at a concentration of 0.76 mg/L. Methylene chloride is considered a laboratory contaminant and has also been detected in this well in March 2002. This is the third consecutive sampling event with no VOCs other than methylene chloride reported. I10-4 will remain on the quarterly sampling schedule.

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. 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 slightly higher than MDLs used by the CSSA laboratory as required by our DQOs. In March 2002, wells I10-2, I10-4, and I10-7 were sampled and no VOCs were detected. 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 a quality control check that was performed in the lab. 

3.4 - Jackson Woods

In the September 2002 monitoring event JW-9, JW-14, and JW-26 were sampled. No VOCs were detected in JW-9 and JW-26. JW-9 will remain on the quarterly sampling schedule and JW-26 will be sampled on an as needed basis. JW-14 had one VOC detection of chloroform at a concentration of 0.24 mg/L. Chloroform has been consistently reported in this well since September 2001 and all results have been below the MCL of 80 mg/L. No other VOCs were detected in JW-14.

Off-post sampling was first performed in 1995 in response to VOC contamination detected in on-post well CS-MW16-LGR. A Jackson Woods well, JW-30, was sampled and no VOCs were detected at that time. JW-30 was sampled again in September 1999, and methylene chloride was the only VOC 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. Of these wells tested, only JW-14 had a VOC detection, PCE at 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. 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. No other VOCs were detected in JW-14.

3.5 - Leon Springs

In September 2002, wells LS-1, LS-2, LS-3, LS-4, LS-5, LS-6, and LS-7 were sampled. LS-1 has had detections of PCE and TCE above the MDL but below the RL during each sampling event. For September 2002, PCE was detected at 0.30 mg/L and TCE at 0.45mg/L. LS-1 had a detection of chloroform at 0.07 mg/L, the fifth consecutive detection for chloroform in this well. All detections have been above the MDL but below the RL and below the MCL for chloroform of 80 mg/L. LS-1 will remain on the quarterly sampling schedule.

LS-2 has been regularly sampled since August 2001. In September 2002, PCE, TCE, chloroform, and bromodichloromethane were detected at concentrations of 2.62 mg/L, 0.17 mg/L, 1.32 mg/L, and 0.41 mg/L, respectively. The PCE and chloroform concentrations were above the MDL and RL but below the MCL. TCE and bromodichloromethane 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 have varied since August 2001 and increased from June to September 2002. TCE concentrations remain stable. 

LS-3 has been sampled quarterly since August 2001. Results from the September 2002 event indicated concentrations of PCE at 2.90 mg/L, TCE at 0.21 mg/L, chloroform at 0.31 mg/L, and chloromethane at 0.22 mg/L. TCE and chloromethane were above the MDL but below the RL and MCL while PCE and chloroform were above the MDL and RL but below the 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.

Post-GAC samples were collected, in September 2002, to ensure VOCs were being removed from the drinking water after GAC treatment (Appendix D). One sample was collected between the canisters (A1) at the LS-2/LS-3 GAC and a second sample was collected after the second canister (A2). A detection of chloroform was reported in the A1 sample, above the MDL but below the RL. The sample collected after both canisters indicated no VOC detections. Future post-GAC testing will be scheduled on a semi-annual basis for all GAC units in operation and after system maintenance has been conducted. The next post-GAC confirmation sample for LS-2/LS-3 will be collected during the March 2003 quarterly sampling event. 

LS-4 has been sampled since September 2001, when PCE was reported at levels below the RL but above the MDL. 1,2 DCA was detected in March 2002 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. In September 2002 PCE was detected at a concentration of 0.19 mg/L, this detection is above the MDL and below the RL. No concentration trends are provided for LS-4 because no VOCs were detected in any samples above the RL. LS-4 will remain on the quarterly sampling schedule.

LS-5 has been sampled for six consecutive quarterly events since August 2001. PCE was detected at low levels in August and October 2001, 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, and was again detected in September 2002 at a concentration of 0.63 mg/L. In September 2002, TCE was detected at 0.22 mg/L, but PCE was not detected above its MDL (1.4 mg/L). LS-5 will remain on the quarterly sampling schedule. 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 from August through June 2002.

The LS-6 pre-GAC sample reported PCE at 1.58 mg/L and TCE at 0.10 mg/L during the September 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 1.5 and 3.0 mg/L. During the September 2002 sampling event, post-GAC samples were collected to ensure that VOCs were being removed from the drinking water after treatment (Appendix D). The LS-6-A2 post-GAC sample reported a detection of 4-isopropyltoluene at a concentration above the MDL but below the RL of 0.6 mg/L. This detection is slightly above the MDL of 0.05 mg/L. Future post-GAC testing will be scheduled on a semi-annual basis for all operational GAC units after maintenance or every six months. The next post-GAC confirmation samples will be collected in March 2003. 

LS-7 pre-GAC samples have been collected regularly since December 1999. This test has consistently found PCE and TCE below the MCL. In September 2002 the LS-7 pre-GAC sample reported concentrations of PCE (2.41 mg/L) and TCE (0.34 mg/L). As shown by the trends presented in Figure 3.4, PCE concentrations reported in September 2002 have declined slightly for the last two quarters; however, the overall trend shows PCE concentrations fluctuating between 1.0 and 4.6 mg/L over the 2-1/2 year monitoring period at LS-7. Also detected in the September 2002 event was chloroform (0.83 mg/L) and bromodichloromethane (0.17 mg/L). Detections of chloroform have occurred since March 2000, maximum values reported being slightly above the MDL, but well below the MCL. In the September 2002 sampling event, post-GAC samples were collected to ensure that VOCs are being removed from the drinking water following GAC treatment (Appendix D). Due to an instrument failure at APPL during analysis this sample was incompletely analyzed. LS-7-A2 was resampled the week of October 21, 2002. Preliminary results for the LS-7-A2 resampling were received at Parsons and are undergoing validation and verification. Preliminary results showed no detections of VOCs in the sample. The next post-GAC confirmation sample will be collected in March 2003. 

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. Analyses of this sample found VOCs at less than MCL levels. Because VOCs were detected, quarterly sampling of LS-7 continued after December 1999. 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 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 then. 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 low levels 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.

3.6 - Old Fredericksburg Road

OFR-1 was sampled for the first time in December 2001 and had PCE levels at 0.42 mg/L. In September 2002 OFR-1 had detected concentrations of PCE at 0.35 mg/L. The level of PCE detected in OFR-1 has remained stable, above the MDL and below the RL, each sampling event. Methylene chloride was also detected at a concentration of 1.35 mg/L in the September 2002 event. 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. The September 2002 event reported PCE concentrations at 0.20 mg/L and methylene chloride at 0.96 mg/L . This well will be monitored quarterly, in accordance with the Plan. Detected PCE levels are below its RL, and only four sampling events have been performed, so no trend analysis was prepared for this well. 

OFR-3 has been sampled on a monthly basis since October 2001 due to a concentration of 4.2 �g/L PCE. 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 April 2002, a GAC unit was installed in response to detected PCE levels 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. The September 2002 event found concentrations of PCE at 2.96 mg/L and TCE at 2.59 mg/L. An evaluation of concentration trends in well OFR-3 is given in Figure 3.5. During the September 2002 sampling event a post-GAC sample was collected to ensure the GAC unit was removing VOCs from the drinking water following installation (Appendix D). The next post-GAC confirmation sample for OFR-3 will be collected in March 2003.

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. These detections are above the MDL but below the RL and MCL. Based on Section 3.0 of this report, methylene chloride is suspected to be a laboratory artifact. 

OFR-2 was sampled during the first off-post sampling, performed in 1995. No VOCs were detected during this initial sampling event. No other wells in the Old Fredericksburg Road area were sampled until October 2001. Since then, three wells (OFR-1, OFR-2, and OFR-3) have been periodically sampled. These are the only Old Fredericksburg Road wells identified in the Offsite Well Survey Report (Parsons, 2001).

3.7 - Ralph Fair Road

In September 2002, three wells (RFR-10, RFR-11 and RFR-12) were sampled in the Ralph Fair Road area. RFR-7 and RFR-8 have been sampled in September 2001 and June 2002. 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 five consecutive events since September 2001. During the September 2002 monitoring event, RFR-10 exceeded the MCL for PCE at a level of 9.19 mg/L while TCE and cis-1,2 DCE were less than the MCL at concentrations of 4.84 mg/Land 0.33 �g/L, respectively. Concentrations of PCE peaked in October 2001 at a concentration of 20.89 mg/L. Since then, PCE concentrations have been lower, ranging from 4.50 to 9.77 mg/L (Figure 3.6). During the September 2002 sampling event, post-GAC samples were collected to ensure that VOCs were being removed from the drinking water after GAC maintenance (Appendix D). 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 March 2003. 

RFR-11 has been sampled since October 2001, for five 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 September 2002 monitoring event reported concentrations of PCE (8.44 mg/L) and TCE (0.67 mg/L). The September 2002 PCE concentration in RFR-11 shows an increasing trend to above the MCL since a peak concentration of 16.73 �g/L was detected in October 2001 (Figure 3.7). TCE levels indicate a slight decrease from the June 2002 levels of 1.52 mg/L to 0.67 mg/L in September 2002. During the June 2002 sampling event post-GAC samples were collected to ensure that VOCs were being removed from the drinking water after GAC maintenance. See Appendix D for post-GAC sample results. 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 March 2003.

During the first off-post sampling performed in 1995, 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 GAC filtration on October 9, 2001. 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). 

RFR-12 has been sampled for four events 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 detection in June 2002 at a concentration of 0.48 mg/L. In September 2002 TCE was again detected at a concentration of 0.14 mg/L. The September 2002 event reported no other VOC detections at RFR-12. RFR-12 will remain on the quarterly sampling schedule.

3.8 - Natural Attenuation Parameter Results

The results of the natural attenuation study of off-post groundwater wells are summarized in Table E.1 and E.2, within Appendix E. The natural attenuation parameters baseline study was also conducted on-post for September 2002. As part of the on-post NAP investigation, wells with no historical detections of VOCs were sampled for NAP parameters. The results for those on-post wells will indicate background NAP concentrations for un-impacted groundwater. Therefore, the off-post NAP investigation focused on those off-post wells with the highest reported historical concentrations. Twelve wells were chosen for NAP sampling off-post: HS-2, JW-9, JW-14, LS-1, LS-2, LS-3, LS-4, LS-6, LS-7, OFR-3, RFR-10 and RFR-11. 

The field analysis Hach testing yielded uniform results with no substantial geographical trend. Ferrous iron, hydrogen sulfide, manganese, nitrate, and nitrite results were either very low or non-detect. Sulfate and carbon dioxide results for off-post wells were within a consistent range, but offer little insight into possible geographical trends. Alkalinity results are consistent with historical levels in the area of CSSA (Ashworth, 1983). Direct readings during field sampling resulted in reasonably neutral pH levels and normal temperatures. Redox potential and dissolved oxygen results showed lower levels of both parameters at the southwest corner of the post (OFR-3, RFR-11), near Old Fredericksburg Rd., as well as directly south of the post (LS-1, LS-4, HS-2), in Hidden Springs Estates.

Laboratory analysis of methane and chloride yielded consistent results for all off-post wells. All of the results for chloride were above sample quantitation limits (SQL) and laboratory RL, and were consistent with average historical chloride levels for northern Bexar County (Ashworth, 1983). Methane results were above the SQL but below the RL for every well, except HS-2, which was also above the RL. The majority of VFA analysis resulted in no detects. Wells RFR-10, RFR-11, LS-1, LS-2, LS-3, LS-4, LS-6, HS-2, and JW-9 all reported VFAs above their respective SQL and RLs. The only volatile fatty acids detected for these wells were acetic, formic, and lactic acids. The dissolved hydrogen range was between .9 and 3.9 nM, with no geographical trend. 

Phospholipid fatty acid results indicated consistent results for all of the off-post wells sampled. The quantitative profile of the microbial population resulted in the majority of the microbial biomass consisting of the monoenoic (monos) PLFA structural group, found in Gram-negative bacteria, and normal saturated (Nsats), ubiquitous in both prokaryotic and eukaryotic organisms. A small total percentage of the biomass for every well consisted of eukaryotes of the polyenoic PLFA structural group, found in organisms such as fungi, protozoa, algae, higher plants, and animals. Bacterial biomass is based on PLFA specifically attributable to bacteria, and eukaryotic biomass is PLFA analogous with higher organisms. Total biomass content (Pmole/mL) is the total amount of PLFA extracted from a given sample. Comparisons of the wells� results indicate a diverse community structure. Anaerobic metal and environmental stress levels were either low or non-detect for all wells. Growth rates for all of the wells ranges from 0 to 1.71. LS-1 reported a growth value of 0, whereas JW-14 reported the higher rate of 1.71. Interpretation of the NAP results will be included in the Annual Groundwater Monitoring Report to be prepared under TO 0042. 

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