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08 September 1999 <br /> AGE-NC Project No 95-0103 <br /> ' Page 7 of 9 <br /> ' custody forms are included in Appendix C <br /> The analytical results of current and previous monitoring well samples are summarized in Tables <br /> b and 7 The laboratory report of the current ground water sampling data(MAI sample ID Numbers <br /> 14714 through 14719), quality assurance and quality control (QA/QC) data and chain-of-custody <br /> form are included in Appendix D <br /> 34 GROUND WATER ELEVATION <br /> The ground water elevations were calculated by subtracting the depths to ground water from the <br /> ' surveyed well casing elevations (Table 1) Ground water elevation decreased approximately 0 4 feet <br /> between March and June 1999 The upper surface of the saturated zone on the site appears to have <br /> a depression on the northern portion of the property near well MW-1 Groundwater flow on the site <br /> 1 is toward MW-1 Figure 5 depicts the ground water elevation contours at the site <br /> 4.0. DISCUSSION/CONCLUSIONS <br /> ' Based on data collected at the site and monitoring during site remediation, AGE concludes <br /> • ln-sltu air sparging (IAS) and soil vapor extraction operated on the site for approximately <br /> ' eight quarters Over this period a calculated minimum of 409 gallons of gasoline have been <br /> removed A population of biodegrading micro-organisms exists on the site that promotes <br /> degradation of the hydrocarbons These organisms were not detected in the off-site sample <br /> ' analyzed (December 1998) <br /> • A reduction of hydrocarbon concentrations in soil samples collected from both on-site and <br /> ' off-site is depicted in Table 8 Benzene was not detected in any of the soil samples analyzed <br /> and in general TPH-g has been reduced while three soil sample sets had an apparent increase <br /> of TPH-g concentration Benzene concentrations in soil samples analyzed prior to <br /> ' remediation did not exceed 33 mg/kg (on-site) Benzene was not detected in soil samples <br /> collected from off site locations (Appendix E) <br /> • The relative ground water elevation at the site decreased 0 4 feet over the last quarter The <br /> map of ground water contours indicates a depression in the area of well MW-1 <br /> • Monitoring wells MW-1, MW-2, MW-3, and MW-4 had ground water approximately four <br /> feet above the top of the screened interval, potentially reducing the effectiN eness of these <br /> ground water monitoring wells to characterize the dissolved-phase hydrocarbon plume in the <br /> ' shallowest ground water <br /> 4di mated CeoEni.ronmental,Inc <br />