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December 2001 Off-Post Quarterly Groundwater Report
Section 5 - Effectiveness of GAC Filter Treatment of Contaminated Groundwater
At the time of the December 2001 off-post sampling event, GAC filtration systems had been installed at LS-6, LS-7, RFR-10, and RFR-11. As part of the quarterly monitoring event, samples were collected both PRE and POST treatment by the GAC units. Samples are collected Post GAC treatment to ensure the treatment systems are removing VOCs from the drinking water. Samples collected from LS‑6 had one exceedance of methylene chloride (0.29 mg/L) that was above the MDL but below the RL. The MCL for methylene chloride is 5.0 mg/L. Since the laboratory method blanks contained methylene chloride, its detection in the LS-6 post-GAC sample is considered a laboratory artifact. The post-GAC sample from LS-7 also reported one detection of methylene chloride at a concentration of 0.30 mg/L. The Post-GAC sample collected from RFR-10 reported methylene chloride at a concentration of 0.96 mg/L. On October 12th two additional samples were collected from the tap of the house at Well RFR-10 and the tap of the mobile home also connected to Well RFR-10. No analytes were detected. Post-GAC samples were also collected from RFR-11 on October 25, 2001, and no analytes were detected. During the December 2001 sampling event only methylene chloride, a suspected laboratory contaminant, was detected.
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 groundwater processed through the GAC unit is free of VOC contamination.