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O1 March 1999 AGE-NC Project No. 95-0103 Page 6 of 8 where: M = cumulative mass recovered (kg) C = soil-vapor concentration (kg/m3) Q = extraction flow rate (m3/hr) t = operational period, in hours The operational time over the last quarter was estimated to be 90 days. The mass of hydrocarbons removed was based on laboratory analyses of soil-vapor sample collected and analyzed. The mass of extracted hydrocarbons was calculated for the period using the hydrocarbon concentrations determined from the influent vapor samples collected and the average air flow rate. An estimated total of 1.2 gallons of hydrocarbons quantified as gasoline were removed from the site. The mass calculations are attached in Appendix D. 4.0. DISCUSSIONICONCLUSIONS Based upon data collected from the site and the ongoing monitoring during site remediation, AGE r.. concludes: • The relative ground water elevations at the site increased 0.02 feet over the last quarter. The map of ground water contours indicates a depression in the area of well MW-1. • Monitoring wells MW-1, MW-2, MW-3, and MW-4 had ground water approximately four feet above the top of the screened interval, potentially reducing the effectiveness of the ground water monitoring wells to characterize the dissolved-phase hydrocarbon plume. • The greatest concentrations of petroleum hydrocarbons as gasoline were detected in samples collected from well MW-3 west of the site. Hydrocarbons were detected at lesser concentrations in wells MW-1, MW-4 and VE-6. The highest concentration of benzene was detected in the sample collected from monitoring well MW-4. • Detectable concentrations of hydrocarbons were not present in the samples collected from the off-site wells MW-2, MW-5 and MW-6 and MW-7. • A reduction of the dissolved-phase hydrocarbon plume concentrations on the site has occurred. A minor increase of the dissolved hydrocarbon as gasoline concentrations has occurred at the location of well MW-3, and a reduction of contaminant concentrations has "- occurred in monitoring well MW-5. • The current concentration of benzene in well MW-1 is 0.14 % of the initial and highest -- concentration of benzene detected in the monitoring well. Advanced GeoEnvironmental,Inc.