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Quarterly Groundwater Monitoring,Results of Verification 1 Sod Borings,and Closure Request Report Moore Petroleum, 1399 E Yosenute,Ave,Manteca,CA July 1,1996 ' Page 5 extracted soil vapors, mixed these vapors with natural gas, and then combusted these vapors in the cylinders of the engine prior to atmospheric release This system operated from April through October of 1993 at which time it was removed from the subject site In December of 1994, Apex installed another RSI unit at the subject site to finalized the soil remediation at the subject site This system was configured to extract soil vapors from either MW-1B or a horizontal pipe located within the former tank basin labeled as "HORIZ " Tlus system operated through March of 1995, at which time influent vapors decreased to the point at which the RSI system was ' replaced with an electric blower and carbon filters This system was started in July of 1995 and operated through August 1995, at which time hydrocarbon concentrations decreased to below laboratory detection limits The system was then pulsed on a monthly basis and monitored with a ' flame ionization detector(FID)until influent concentrations dropped to below instrument detection limits The system was pulsed through December of 1995, at which time influent concentrations were no longer detected with the FID Table 3 contains vapor extraction system operating data from both Aegis's and Apex's vapor extraction system operation A summaryof the mass extraction rates based on laboratory analytical is contained in Table 4 Table 4 includes extraction data compiled from Aegis's operation of the soil vapor extraction system. Vapor extraction system pulse data are contained m Tables 5A through 5E As of December 1995,the vapor extraction system has extracted approximately 211 pounds of TPH, as gasoline, and 0 80 pounds ofbenzene This figure was calculated using vapor sample analytical data collected on a ' monthly basis during the operation of the vapor extraction system. Example calculations are included in Appendix I Several times during Aegis's operation of the RSI vapor extraction system, personnel collected vacuum measurements from the monitoring wells located at the subject site while the RSI unit was operating Increased vacuum measurements were detected in all monitoring wells except ' MW-4 A comparison of this data combined with the maximum extent of soil contamination as viewed in Figure 5C indicates that the entire area of contaminates was influenced by the extraction of soil vapors from monitoring well MW-1B 1 t