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September 2001 Off-Post Quarterly Groundwater Monitoring Report
Section 5 - Effectiveness of GAC Filter Treatment of Contaminated Groundwater
At the time of the September 2001 off-post sampling event, GAC filtration systems had already been installed at LS-6 and LS-7. As part of the quarterly monitoring event, samples were collected both PRE and POST treatment by the GAC units. Samples collected from LS-6 had one exceedance of methylene chloride (0.77 mg/L) that was above the MDL but below the RL. The MCL for methylene chloride is 5.0 mg/L. Since the LS-6 pre-GAC sample did not indicate any methylene chloride, its detection in the LS-6 post-GAC sample is considered a laboratory artifact. The post-GAC sample from LS-7 reported no detected analytes. Following installation of the GAC filtration system in RFR-10 in October 2001, post-GAC samples from RFR-10 reported no detected analytes.
In Table 5-1, Pre- and post-GAC concentrations detected in LS-6, LS-7, and RFR-10 for PCE and TCE are compared. All post-GAC samples had no detections of PCE and/or TCE. These concentrations show that groundwater processed through the GAC unit is free of VOC contamination.