PCE concentrations in Well LS-7 decreased from 4.5 mg/L during the September 2001 event to 1.40 mg/L during the December 2001 event.  The TCE concentration in LS-7 remained below the RL at 0.81 mg/L in September 2001 and decreased to non-detect in December 2001.  Prior to the December 2001 sampling, CSSA received a rain event, which could relate to the decrease in PCE and TCE concentrations.  Decreasing PCE levels for the December 2001 sampling event were also noted in LS-2, LS-5, and LS-6. 

Well RFR-10 had PCE concentrations of 14.0 mg/L and TCE concentrations of 7.5 mg/L, both of which are above the MCL, in September 2001.  CSSA immediately responded in accordance with the Plan by supplying bottled water and evaluating RFR-10 for a GAC filter treatment system.  The GAC filtration treatment system was installed in October 2001 after additional sample results showed an increase of PCE to a concentration of 19.0 mg/L and TCE to 8.7 mg/L.  In December 2001, concentrations of PCE decreased to 9.02 mg/L and TCE decreased to 5.85 mg/L. 

In October 2001, well RFR-11 had PCE concentrations of 16.0 mg/L and TCE concentrations of 0.35 mg/L.  PCE concentrations were above the MCL (5.0 mg/L) and TCE concentrations were reported below the RL.  CSSA immediately responded in accordance with the Plan by supplying bottled water and evaluating RFR-11 for a GAC filter treatment system.  The GAC filtration treatment system was installed on October 16, 2001, after additional sample results showed an increase of PCE to a concentration of 16.73 mg/L and TCE to 0.58 mg/L.  In December 2001, concentrations of PCE decreased to 12.44 mg/L and TCE was not detected. 

Wells LS-2 and LS-3 are in the preliminary stages of installation of a GAC filtration treatment system.  This is due to the periodic increases of PCE concentrations, which are approaching the MCL. 

Wells RFR-9, HS-3, and JW-14 did not have any VOC concentrations detected above the MDL.  These wells should be re-evaluated for possible sampling depending on the needs of the groundwater investigation and project DQOs.  Most of these wells should be removed from the March 2002 quarterly sampling list so that additional off-post private wells can be tested to the southwest and west of AOC-65, where the lateral extent of the contaminant plume has not been sufficiently delineated. 

Wells HS-2, I10-2, I10-4, LS-1, LS-4, LS-5, OFR-1, RFR-12, FO-J1, JW-9, and LS-2-LS-3/EP had low concentrations of PCE and/or TCE above the MDL, but below the RL and less than 90 percent of the laboratory MCL.   These wells should be retained for future quarterly sampling events, including the March 2002 quarterly sampling event. 

Wells OFR-3, RFR-10, RFR-11, LS-2, LS-3, LS-6, and LS-7 had detections above 80% of the MCL for PCE and/or TCE.  Some of these wells have GAC systems in place and others may have GAC systems installed in the future.  Groundwater will continue to be sampled and monitored on a monthly basis for these wells without GAC units and on a quarterly basis for wells with GAC units installed, until they meet our DQO requirements.

Parsons recommends preparing justification for removing methylene chloride from the approved short list of VOCs to be analyzed.