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March 2002 Off-Post Quarterly Groundwater Monitoring Report
Section 5 - Effectiveness of GAC Filter Treatment of Contaminated Groundwater
At the time of the March 2002 off-post sampling event, GAC filtration systems had been installed at LS-6, LS-7, RFR-10, and RFR-11, and GAC units were installed for LS-2, LS-3, and OFR-3 in April 2002. As part of the March quarterly monitoring event, samples were collected both pre and post treatment from the four GAC units already installed. Samples were collected post-GAC treatment to ensure the treatment systems were removing VOCs from the drinking water. Samples collected from LS-6 post-GAC had one exceedance of methylene chloride (0.3 mg/L) that was above the MDL but below the RL. Since the laboratory method blanks also reported methylene chloride, its detection in the LS-6 post-GAC sample is considered a laboratory artifact. The post-GAC samples from LS-7 and RFR-10 reported no detected analytes. The post-GAC sample collected from RFR-11 during the March 2002 sampling event reported below MCL detections of 1,2 DCA (0.13 mg/L), methylene chloride (0.52 mg/L) and toluene (0.39 mg/L). Post-GAC confirmation samples collected from LS-2/LS-3 and OFR-3 will be discussed in the next quarterly monitoring report.
In Table 5.1, pre and post-GAC concentrations detected in LS-6, LS-7, RFR-10 and RFR-11 for PCE and TCE are compared. All post-GAC samples had no detections of PCE and/or TCE. These results demonstrate that the GAC systems are effective in reducing VOC levels in these drinking water wells.