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F <br /> . Former Beacon Station 494 October 8, 1996 <br /> Stockton, California Appendix B Closure Report <br /> During vapor extraction operations, an estimated 13,401 lbs of TPHg as vapor volume was <br /> removed from the subsurface and treated as listed in the Vapor Extraction Data Table within <br /> Appendix D <br /> Based on the analytical results of the samples collected from the confirmation borings, the <br /> highest concentrations of TPHg were detected in samples collected from boring CB-2 <br /> between 35 and 45 feet (320 mg/Kg at 45 feet) We estimate that less than 400 cubic yards <br /> of soil remain in place with an average concentration of 162 mg/Kg Applying the equation <br /> above approximately 181 lbs of TPHg (29 gallons)remain in place south of the former UST <br /> cavity between 35 and 45 feet bsg Benzene was below detection limits in samples analyzed <br /> from the confirmation borings and therefore we assume has been removed to negligible <br /> amounts <br /> The latest quarterly groundwater monitoring data indicate that benzene and TPHg are only <br /> detected in MW-3 (1 2 ug/L benzene) and MW-2 (58 ug/L TPHg) Approximately 313,101 <br /> gallons of groundwater were pumped from beneath the site through MW-3 <br /> DISCUSSION <br /> Assessment activities at the site conducted between April 1992 and July 1993 indicated that <br /> gasoline-range hydrocarbons were present in limited areas of soil beneath the site In <br /> addition, the samples of groundwater monitoring revealed the presence of dissolved <br /> gasoline- range hydrocarbons in the groundwater beneath the site Soil and groundwater <br /> remediation units operated at the site appear to have significantly removed the gasoline- <br /> range hydrocarbons from the soil and groundwater beneath the site No benzene was <br /> detected in confirmation bonngs drilled within the area of confirmed gasoline hydrocarbon <br /> 1494 APB 11 HORIZON ENVIRONMENTAL INC. <br />