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1 <br /> SITE CLOSURE EVALUATION REPORT <br /> Beacon Station No.502 <br /> 35 Noah Cherokee Lane <br /> Lodi,California <br /> Delta Project No. D093-907 <br /> 4.0 SITE REMEDIATION <br /> Petroleum hydrocarbons have been removed from the subsurface by soil vapor extraction and excavation. <br /> The soil vapor extraction system was operated at the site in October and November 1986 utilizing an <br /> internal combustion (IQ engine for destruction of petroleum hydrocarbons. Records of the operation of <br /> the IC engine indicate that during this period approximately 280 gallons of petroleum hydrocarbons were <br /> removed from the subsurface. The soil vapor extraction system was restarted in September 1992 and <br /> operated through December 1992 using a catalytic oxidizer for destruction of petroleum hydrocarbons. <br />' Records of the operation of the catalytic oxidizer indicate that during this period approximately 84 gallons <br /> of petroleum hydrocarbons were removed from the subsurface. <br /> During removal and replacement of the underground fuel storage tanks in February 1995 approximately <br />' 1,075 cubic yards of soil were excavated and removed from the site_ Soil at the north end of the tank <br /> basin was excavated to a depth of 26 feet bsg. The extent of excavations is shown in Figure-5. <br /> The decline of concentrations of petroleum hydrocarbons in ground water to less than the laboratory <br />' limits of detection is likely due to both soil vapor extraction and biological degradation by naturally <br /> occurring microorganisms. <br /> 5.0 ASSESSMENT OF REMEDIATION EFFECTIVENESS <br />' Mass balance calculations of petroleum hydrocarbons in soil and ground water before and after site <br /> remediation have been used to evaluate the hydrocarbon removal efficiency. The calculations are <br /> presented in Enclosure A. Using very conservative assumptions, the efficiency of hydrocarbon removal <br /> from both sail and ground water is greater than 99.9 percent. The mass balance calculations indicate that <br /> it is unlikely that more than 0.008 gallons of hydrocarbons could remain in soil, and that not more than <br /> 0.0009 gallons of hydrocarbons are likely to be present in ground water. <br /> 6.0 RATIONALE FOR CLOSURE <br /> No detectable concentrations of petroleum hydrocarbons have been present in ground water samples <br /> collected from the site monitoring wells since May 1992; therefore, it would appear that concentrations <br />' RPT 139.5.15 <br />