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SITE HISTORY <br /> 440 West Charter Way, Stockton, California <br /> Incident No. 88870583 <br /> SAP Code 121258 <br /> Previous Investigations: During October 1988, two dispensers were removed, and soil <br /> impacted by petroleum hydrocarbons beneath the eastern dispenser was excavated to an <br /> approximate depth of 15 feet below grade (fbg). Soil collected from the bottom of the excavation <br /> contained total petroleum hydrocarbons as gasoline (TPHg) at concentrations ranging from 3 to <br /> 5,300 milligrams per kilogram (mg/Kg) and benzene at concentrations up to 31 mg/Kg. This <br /> investigation is described in the October 9, 1990 Environmental Assessment Status Report written <br /> by Groundwater Technology, Inc. (GTI)of West Sacramento, California. <br /> During May 1989, GTI drilled four vertical soil borings and one angle soil boring onsite. From <br /> May 1989 through May 1990, GTI installed seven onsite groundwater monitoring wells and four <br /> offsite monitoring wells. Maximum concentrations detected in soil from these borings were <br /> 2,500 mg/Kg TPHg and 11 mg(Kg benzene. These activities are also summarized in GTI's <br /> October 9, 1990 Environmental Assessment Status Report. <br /> During April 1992, GTI installed four soil vapor extraction)(SVE) wells and conducted an SVE <br /> pilot test. These results are described in GTI's September 16, 1992 Summary Report of Soil <br /> Vapor Extraction Test Sampling Activities. <br /> During September 1993,GTI installed five offsite groundwater monitoring wells. Soil from these <br /> borings contained TPHg at concentrations up to 3.7 mg/Kg and benzene at concentrations up to <br /> 0.23 mg/Kg. This investigation is documented in GTI's December 16, 1993 Summary Report of <br /> Drilling Activities. <br /> During June 1999, K.E. Curtis Construction Company removed one 12,000-gallon diesel and <br /> three 10,000-gallon gasoline USTs, four dispenser pumps, and their associated piping. During <br /> August 1999, the soil beneath the UST, piping, and dispensers was further overexcavated. This <br /> investigation is documented in our October 22, 1999 Underground Storage Tank Removal <br /> Report. <br /> During November 2000,Cambria Environmental Technology, Inc. (Cambria)advanced four cone <br /> penetration testing(CPT)borings to further assess the vertical and horizontal extent of petroleum <br /> hydrocarbons beneath the site. Soil from these borings contained TPHg at concentrations up to <br /> 3,150 mg/Kg and benzene at concentrations up to 14.7 mg/Kg. Groundwater from these borings <br /> contained TPHg at concentrations up to 109,000 micrograms per liter (µg/L) and benzene at <br />