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September 2001 Off-Post Quarterly Groundwater Monitoring Report
Section 4 - September 2001 Quarterly Monitoring Analytical Results
All detected concentrations of VOCs reported in September 2001 are presented in Table 4.1. Full analytical results for September 2001 are presented in Appendix B. PCE and TCE concentrations are displayed for each well in Figure 4.1 and Figure 4.2, 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 September 2001 results.
The vertical extent of migration cannot be determined now due to minimal data (i.e. well completion depths) available for wells being sampled. There is not adequate information that provides the depth of wells, pump depth, and other pertinent data to properly characterize the vertical extent of migration.
No analytes were detected in DOM-2; the only well sampled near the Dominion subdivision.
In the Fair Oaks area two wells were sampled. FO-22 and FO-J1 had no detected analytes reported.
One well was sampled in the I-10 area approximately one-third of a mile southwest of the CSSA boundary. TCE was detected in I10-2 at a concentration of 0.23 mg/L. This level is above the MDL but below the RL and MCL.
Five wells (JW-6, JW-9, JW-12, JW-13, and JW-14) were sampled in the Jackson Woods area west of CSSA. Low-levels of VOCs were reported in one of these five wells. Bromodichloromethane (0.47 mg/L), chloroform (7.9 mg/L), dibromochloromethane (0.1 mg/L), and PCE (0.12 mg/L) were all detected in JW-14. With the exception of chloroform, all detected constituents were above the MDL but below the RL and MCL. Detected chloroform concentrations exceeded the RL but were below the MCL in JW-14 (Figure 1.1). There were no detected VOC analytes reported at wells JW-12, JW‑13, JW-6, or JW-9.
Wells LS-1, LS-2, LS-3, LS-4, 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).
Analyses of the sample from LS-1 reported detections of chloroform, PCE, and TCE at concentrations of 0.2 mg/L, 0.47 mg/L, and 0.37 mg/L, respectively. All concentrations were below the laboratory RL and MCL.
Analyses of the sample from LS-2 reported PCE at 4.60 �g/L, an increase from the PCE concentration of 1.40 �g/L detected one month previously. Additional sampling to monitor the increasing trend of PCE concentrations was performed in October and November 2001 and will be reported in the next quarterly report. Well LS-2 also had detected chloroform and TCE concentrations of 0.20 �g/L and 0.17 �g/L, respectively. These concentrations were below the RL and MCL for these analytes. Analyses of the sample from LS-3 reported PCE at a concentration of 4.80 �g/L. As in Well LS-2, the PCE concentration is LS-3 also increased from its prior reported concentration of 1.20 �g/L. Concentrations of chloroform (0.13 �g/L) and TCE (0.43 �g/L) were also reported in Well LS-3. Due to the increasing concentration trends for PCE in both LS-2 and LS-3, preliminary evaluation of installation of a GAC treatment system has begun. Additional information on the pending GAC treatment system installation will be provided in the next quarterly report.
Analyses of the sample from Well LS-4 reported no analytes detected.
At the time of the September 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. In the LS-6 pre-GAC samples PCE (6.7 mg/L), chloroform (0.1 mg/L) and TCE (0.35 mg/L) were identified. Chloroform and TCE exceeded MDLs but were below the RLs, while the PCE concentration was above the MDL, RL, and MCL.
Analyses of the pre-GAC sample from LS-7 reported concentrations of PCE (4.5 mg/L) and TCE (0.81 mg/L). TCE concentrations were above the MDL but below the RL and MCL. PCE concentrations exceeded the MDL and RL but were slightly below the MCL of 5.0 mg/L. As shown by the concentration trends presented in Figure 2.1, concentrations of PCE reported in September 2001 matched the trend of increasing concentrations evidenced in the past. Except for the August 2001 sampling event, when the concentration of PCE decreased (1.10 mg/L) PCE concentrations have generally increased over time in Well LS-7 while TCE concentrations have both increased and decreased over time.
Five wells (RFR-6, RFR-7, RFR-8, RFR-9, and RFR-10) were sampled in the Ralph Fair Road area west of CSSA. VOCs were detected in only one well, RFR-10. PCE and TCE were reported at concentrations exceeding their MCLs, 14 mg/L and 7.5 mg/L, respectively. RFR-10 exceeded the MDL at a concentration of 0.42 mg/L for cis-1,2-DCE. Due to the exceedance of the MCLs, bottled water was supplied to the residents using RFR-10 and GAC filtration systems were installed in October 2001. Post-GAC filtration samples for RFR-10 collected in October 2001 were non-detect for VOCs.