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' 4 ✓ <br /> 2. BACKGROUND <br /> 2.9 SITE DESCRIPTION AND HISTORY <br /> The Site is a vacant lot situated on the southwest corner of Pacific Avenue and <br /> Walnut Avenue (Figure 1-1) in the City of Stockton, California Land use in the vicinity of <br /> the Site includes retail stores, an elementary school, and private residences The closest water- <br /> supply well was documented by Applied GeoSystems, Inc (AGS) to be 800 feet to the <br /> northeast of the Site (December 1990) The Site hes at an approximate elevation of 10 feet <br /> ' above mean sea level The topography in the vicinity is essentially flat with a gentle slope to <br /> the west toward the San Joaquin River,which is located 3 miles to the west of the Site <br /> ' AL n leased the Site in January 1947 The station was completely <br /> UNOCAL originally ary P Y <br /> ' remodeled in 1967 PHR Consultants (1992) reported that during the remodel, three <br /> previously installed 4,000-gallon underground storage tanks(USTs), two pump islands, and six <br /> dispensers were replaced with two 10,000-gallon USTs and four dispensers on two pump <br /> islands The station was demolished between February and April 1988 During station <br /> demolition, two 10,000-gallon underground gasoline tanks were removed from a common <br /> excavation along with a separate 550-gallon waste oil tank The former tank locations, along <br /> ' with the product islands and station building, are shown on Figure 1-2 <br /> ' 2 2 PREVIOUS SITE ENVIRONMENTAL ACTIVITIES <br /> ' Kleinfelder, Inc installed five soil borings (KB-1 through KB-5) at the Site in January, <br /> 1988 (Phase 1 Soil Investrgahon, Kleinfelder, March 3, 1988) These borings were installed <br /> ' around the tank complex, adjacent to the product islands, and adjacent to the waste oil tank <br /> ' Maximum concentrations of petroleum hydrocarbons were detected in samples taken from <br /> approximately 20 feet below ground surface The two samples with the highest detections, <br /> ' samples KB3 and KB5, had total petroleum hydrocarbons calculated as gasoline (TPHg) <br /> concentrations of 239 0 and 370 0 milligrams per kilogram(mg/kg), respectively Sample KB3 <br />