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16 January 2001 <br /> • AGE-NC Pioject No 97-0290 <br /> Page 5 of 6 <br /> 3 4 MASS OF RECOVERED HYDROCARBONS <br /> The hydrocarbon mass (TPH-g) removed during the operating period was calculated using the <br /> following equation M = C•Q•t <br /> where M = cumulative mass recovered (kg) <br /> C = soil-vapor concentration (kg/m') <br /> Q = extraction flow rate (M3/hr) <br /> t= operational period, in hours <br /> The operational time was divided into three time eriods Mass of hydrocarbons removed was based <br /> p <br /> on analysis of soil-vapor samples The mass of extracted hydrocarbons was calculated for each time <br /> Iperiod using average hydrocarbon concentrations of influent soil-vapor samples collected and <br /> average air flow rates <br /> IApproximately 439 gallons of hydrocarbons as gasoline and BTEX were removed from the SVE <br /> network at the site over 53 days of operation The volume/mass calculations are attached in <br />' • Appendix D <br /> I3 5 IN-SITU AIR SPARGING <br /> Elevated concentrations of dissolved oxygen were detected in monitoring wells MW-1 MW-4 and <br /> MW-5, which were used as observation wells outside the IAS network on the site Dissolved oxygen <br /> concentrations in the remaining, down gradient wells showed smaller changes A small change in <br /> dissolved oxygen was observed in well MW-2 samples within the sparging well network The <br /> dissolved oxygen data for each well measured is summarized in Table 5 <br /> 40 SUMMARY AND CONCLUSIONS <br /> Based on the data collected from the site, AGE finds <br /> • Ground water was encountered in the monitoring wells at approximately 44 feet bsg and was <br /> inferred to have a southwesterly flow direction during the November 2000 monitoring event <br /> • The highest concentrations of dissolved petroleum hydrocarbons were detected in samples <br /> collected from wells MW-2 and MW-4 Concentrations of benzene have increased in well <br /> IMW-4 over the past two quarters Benzene typically leads the migration of dissolved <br /> • hydrocarbons, at the down-gradient margin of plumes Some mitigation should be performed <br /> in well MW-4, at the edge of the dissolved plume <br /> Advarrcetl CcuEnvirnnmcntal,Inc <br /> I <br />