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COCl in these key wells have reached the WQOs or, as predicted by an analysis of the <br /> first-order decay equations, will reach them within 21 years. The few exceptions are <br /> discussed below. <br /> • MW-14: TPHg concentrations are fairly stable at this location. However,confidence <br /> in the TPHg trend in this well is low due to possible interference of TCE and PCE. <br /> • VEW-4: Benzene levels dropped two orders of magnitude during dual-phase <br /> extraction (DPE) from 10,000 µg/L to 680 Rg/L. Post-remediation benzene levels <br /> have remained fairly stable;however,the overall trend for this well is declining. <br /> 4.0 REMEDIATION SUMMARY <br /> Summaries of the remedial activities performed at the site and their effectiveness are <br /> presented below,along with the other considered remedial approaches. <br /> DPE PILOT TEST <br /> The pilot test conducted during January 2006 recovered approximately 200 pounds of <br /> vapor-phase TPHg, 2.3 pounds of benzene, and 0.095 pounds of MTBE over a 4-day <br /> period of time. Over the same period,the pilot test recovered approximately 3.5 pounds <br /> of dissolved-phase TPHg,0.12 pounds of benzene,and 0.002 pounds of MTBE. This test <br /> occurred when the depth to groundwater was 38 to 40 feet below grade (fbg). Depth to <br /> groundwater is now approximately 6 feet higher across the site. <br /> SOIL VAPOR EXTRACTION(SVEI SYSTEM <br /> CRA operated a temporary SVE system from July 26, 2006 until November 2, 2006 at <br /> which time the system was shut off to facilitate installation of the DPE system. The <br /> temporary system extracted from well VEW-7, which is screened from 27.5 to 42.5 fbg. <br /> This well was selected as the extraction well for temporary operations based on soil <br /> analytical data collected during well installations. The SVE system removed a total of <br /> 676 pounds TPHg,3.88 pounds benzene,and 1.97 pounds MTBE. <br /> 3 CONESTOGA-ROVERS&ASSOCIATES <br /> 240880(29) <br />