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l <br /> . Former Beacon Station 494 October 8, 1996 <br /> Stockton, California Appendix B Closure Report <br /> November 1993 Remediation activities at the site were initiated by AMV in November <br /> 1993 AMV had reported that the natural groundwater flow direction prior to remediation <br /> activities at the site was westerly After initiating groundwater pumping, the flow direction <br /> was channeled toward the pumping well (MW-3), located in the center of the site <br /> Groundwater had been discharged to the City of Stockton sanitary sewer under a Municipal <br /> Utilities Department Regional Wastewater Control Permit dated August 21, 1993 The <br /> vapor-extraction system (VES) operated under San Joaquin Unified Air Pollution Control <br /> District Permit to Operate No N-116-2-0 <br /> April 1995 Horizon begin performing operation and maintenance of the remediation <br /> system and quarterly groundwater monitoring at the site <br /> June 1995 Horizon drilled four soil borings (CB-1 through CB-4) to evaluate the <br /> effectiveness of the soil vapor extraction system in removing hydrocarbons from the soil <br /> underlying the site Laboratory results of soil samples collected from these borings <br /> indicated no detectable concentrations of benzene from the samples tested TPHg was <br /> detected at concentrations ranging from 1 I to 320 mg/Kg The locations of soil borings CB- <br /> 1 through CB-4 are depicted on Figure 2 The analytical results are compiled on Table I of <br /> the August 8, 1995 Assessment Report included within Appendix B <br /> Also in June, the VES was shut down because low levels of hydrocarbons were being <br /> extracted from the subsurface At the time of shut-down of the VES, approximately 13,400 <br /> pounds (lbs ) of TPHg and 212 lbs of benzene were calculated as having been removed <br /> from the subsurface by the VES Benzene influent was below laboratory detection limits at <br /> the time of shut down The Table of Vapor Extraction Data compiled after Horizon began <br /> monitoring the system is included in Appendix D along with some previous charts compiled <br /> by AMV <br /> i <br /> 1494 APB 5 HORIZON ENVIRONMENTAL INC <br />