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x <br /> _ a <br /> ' 42 January 199$ <br /> AGE-NC-95-0103 <br /> Page 6 of 7 <br /> `4.0. DISCUSSION/CONCLUSIONS <br /> Based upon data collected from the site and the on-going monitoring during site remediation, AGE <br /> ' concludes the following <br /> - - The ground water flow has returned to the typical westerly flow direction over the last <br /> quarter The hydraulic gradient was similar to that determined for previous quarters <br /> • The ground water monitoring wells'-slotted intervals were generally effective to characterize <br /> ' the dissolved-phase hydrocarbon plume The screened interval of monitoring well MW-I had <br /> ground water near or above the top of the screened interval, but was lowered to the screened <br /> interval of the well during purging <br /> • The greatest concentrations of petroleum hydrocarbons were detected in samples collected <br /> from well MW-4 east of the former gasoline USTs location and north of the former waste <br /> ' oil tank Hydrocarbons were also detected at lesser concentrations in wells MW-1, MW-3 <br /> and MW-5 Detectable concentrations hydrocarbons were not present in the samples <br /> collected from the off-site wells MW-2 and MW-6 <br /> A reduction of the dissolved-phase hydrocarbon plume concentrations in the central portion <br /> -of the site has occurred since the initiation of the remediation system, but a slight to <br /> moderate increase of concentrations has occurred in two down-gradient wells, MW-3 and <br /> MW-5 <br /> • The area showing the greatest reduction of dissolved hydrocarbon concentrations roughly <br /> - - coincides with the area of highest dissolved oxygen concentration (MW-1) Intermediate <br /> reductions of dissolved hydrocarbon concentrations coincide with intermediate dissolved <br /> oxygen concentrations (MW-4) Increased dissolved hydrocarbons concentrations coincided <br /> with minimal dissolved oxygen concentrations (MW-3 and MW-5) These relationships <br /> demonstrate the effectiveness of the IAS portion of the remediation system <br /> • Dunng seventy-five days of operation of the SVE system during this quarter, an estimated <br /> 73 gallons of gasoline were removed from the site Since initiation of the SVE system an <br /> estimated 316 gallons of gasoline have been removed <br /> 1 The SVE system has removed the mayor portion of the hydrocarbons from the vadose soil <br /> zone in the SVE system's area of influence Soil contamination probably remains in saturated <br /> soil in the core portion of the dissolved hydrocarbon plume <br /> • -BTE&X compounds in extracted soil gas have been reduced to concentrations below the <br /> -detection limits of the soil vapor analytical method <br /> r r r <br /> _ Advanced CeoEnVlronmental,Inc <br />