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139 South Center Street, Stockton, California January 25, 1993 <br />Chevron U.S.A. Products Company Page 2 <br />2.0 BACKGROUND <br />The site has been in operation as a retail gasoline service station since 1969. In April 1990, the <br />original tanks were removed and replaced with three 10,000-galion, and one 1,000 -gallon double-wall <br />fiberglass tanks. The original tanks that were removed consisted of two 10,000 -gallon unleaded <br />gasoline, one 5,000 -gallon leaded gasoline, and one 1,000 -gallon used -oil tank. All four tanks were <br />constructed of single-wall steel. At the time of removal, soil samples were collected and analyzed <br />for gasoline constituents. The analytical results revealed elevated concentrations of petroleum <br />hydrocarbons in the gasoline and used -oil tank pits, and the pump island areas. <br />On February 14 and 15, 1991, as a result of these preliminary findings, Groundwater Technology <br />drilled and sampled four on-site soil borings, and installed 2 -inch -diameter groundwater monitoring <br />wells within each boring (MW -1 through MW -4). Soil samples analyzed from the four borings did not <br />contain detactable concentrations of petroleum hydrocarbons. Dissolved petroleum hydrocarbons <br />were detected in MW -1 and MW -2. <br />A quarterly groundwater monitoring and sampling program has been maintained at the site since <br />March, 1991. Detailed discussions of the well installation were documented in Groundwater <br />Technology's report dated April 1991, Site Assessment Report, Chevron Service_ Station No.- 9-0557, <br />139 South Center, Stockton, California. Groundwater monitoring and sampling reports are also <br />prepared quarterly to document groundwater conditions beneath the site. <br />GROUNDWATER <br />TECHNOLOGY <br />