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i <br /> 28 April 1998 <br /> AGE-NC-95-0103 <br /> Page 8 of 9 <br /> from well MW-4 east of the former gasoline USTs location. Hydrocarbons were also <br /> detected at lesser concentrations in wells MW-1, MW-3 and MW-5. Detectable <br /> concentrations hydrocarbons were not present in the samples collected from the off-site wells <br /> MW-2 and MW-6 and no hydrocarbons were detected in newly installed well MW-7, east <br /> of well MW-4. <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. Additionally, a <br /> reduction of hydrocarbon concentrations has occurred at the location of well MW-5. A slight <br /> decrease of hydrocarbon concentrations has occurred in the down-gradient well MW-3 <br /> during the last quarter.A portion of the observed drop of dissolved hydrocarbons may be due <br /> to ground water being approximately 5 feet above the screened intervals of MW-1 through <br /> MW-4. <br /> • DIPE was detected in water samples collected from MW-3 and MW-5, with a maximum <br /> concentration of 85 ppb in MW-5.MTBE was detected in samples collected from MW-1 and <br /> MW-4, with a maximum concentration of 55 ppb in MW-4. TBA was not detected in any <br /> ground water samples this quarter. <br /> • During operation of the SVE system during this quarter, an estimated 65 gallons of gasoline <br /> were removed from the site. Since initiation of the SVE system an estimated total of 381 <br /> gallons of gasoline have been removed. <br /> • The SVE system has removed a major portion of the hydrocarbons from the vadose soil zone <br /> in the SVE system's area of influence. Soil contamination probably remains in saturated soil <br /> a in the core portion of the dissolved hydrocarbon plume. <br /> Benzene concentrations in the extracted soil vapor has been reduced to concentrations below <br />• the detection limits of the soil vapor analytical method 8020. <br /> a <br /> 5.0. RECOMMENDATIONS <br /> ased upon data collected over the quarter at site, AGE recommends the following: <br /> � tallation of additional IAS point or wells to stimulate remediation of impacted ground <br /> aster in the area of well MW-4 and the southeastern quadrant of the remediation area. A <br /> work plan for the installation of the sparge points and costs have been approved. <br /> • Operate of the SVE system drawing vapors from the central portion of the site, which has <br /> demonstrated hydrocarbon-impacted soil vapor. The SVE should be operated for an <br /> Advanced GeoEnvironmental,Inc. <br /> 1 <br />