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Former Beacon Station 494 October 8, 1996 <br /> Stockton, California Appendix B Closure Report <br /> Impact Benzene was detectable In only one monitoring well (MW-3) during the last <br /> monitoring event at a concentrations of 12 ug/L (May 1996) Benzene concentrations in <br /> this well were previously reported as high as 120 ug/L In February 1993 MTBE has not <br /> been detected In groundwater at this site <br /> The soil type (silty clay) above the groundwater table appears to have restricted downward <br /> migration of gasoline hydrocarbons and allowed for successful removal of the gasoline range <br /> hydrocarbons from the soil between 15 and 45 feet The highest concentration of benzene, <br /> the most mobile gasoline constituent, detected In soil at this site was 7 0 mg/Kg at 45 feet In <br /> V W-l (December, 1992) <br /> Remediation activities were discontinued at the site due to the reduction of hydrocarbons <br /> beneath the site The VES and groundwater treatment system were no longer removing <br /> concentrations that warranted continued operation In our opinion, these remedial activities <br /> have achieved the best cleanup levels attainable by these systems and technology <br /> As previously discussed, only one industrial well exists that could have been at risk from <br /> gasoline-range hydrocarbons In the groundwater beneath the site Records indicate this well, <br /> drilled In 1943 to a total depth of 232 feet, exists greater than 250 feet east of the site <br /> However, it Is unlikely that benzene In Its present concentration could impact a deeper water <br /> bearing zone In which this well is believed to be perforated <br /> RATIONALE FOR CLOSURE <br /> The Water Quality Control Plan, Central Valley Region, Sacramento River and San Joaquin <br /> River Basins (WQCP) dated December 1994, by the California Regional Water Quality <br /> 1494 APB <br /> 12 HORIZON ENVIRONMENTAL INC <br />