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r� <br /> (� <br /> Page 2 <br /> 2.0 BACKGROUND <br /> 2.1 SITE SETTING <br /> The prosect site is located in northwest Stockton,California at the southeast corner of the <br /> intersection of Grigsby Place and West Benjamin Holt Drive,approximately 240 feet west of <br /> Interstate 5, The site surrounded by a shopping center and Shell gasoline station to the north,a <br /> church and residential area to the west,a water tower, Seven-Eleven parking lot and store and <br /> residential area to the south,Interstate Highway 5 and a southbound highway on-ramp to the east. <br /> The area Consists of a mixture of commercial and residential properties. <br /> f <br /> The site was an active Exxon Retail Service Station from 1968 to 1991. Three single-walled steel <br /> underground storage tanks containing gasoline and having a capacity of 6,040 gallons, 8,040 <br /> gallons and 10,000 gallons are located in the northwest corner of the site(Figure 2). A 1,040 <br /> gallon waste oil tank is located in the southern portion of the site,south of the station <br /> house/garage. According to a report by Engineering Science,Inc. (ESI)of Berkeley,California, <br /> all underground storage tanks on the property are original (ESI, 1991). <br /> 2.2 PREVIOUS INVESTIGATIONS <br /> In March, 1991,ESI drilled three soil borings at the site and converted them into 4-inch diameter <br /> groundwater mottitor wells,MW-1,MW-2 and MW-3. Sail and groundwater samples were <br /> analyzed for total petroleum hydrocarbons(TPH-g)as gasoline and benzene, toluene,ethylbenzene <br /> and xylenes(BTEX). TPH-g were detected in a soil sample from MW-I at a depth of 11 feet at <br /> concentrations of 12 parts per million(ppm). TPH-g,ethylbenzene and xylenes were detected in a <br /> soil sample from MW-2 collected at 14 feet at concentrations of 1,500 ppm,2,000 parts per billion <br /> (ppb)and 6,000 ppb,respectively. BTEX were detected in the groundwater sample from MW-2 at <br /> concentrations of 760 ppb,40 ppb,50 ppb and 110 ppb,respectively. All other analytes were not <br /> detected. Depth to groundwater on the site was estimated by ESI to be about 13 feet below ground <br /> Vq surface. According to an ESI report of April, 1991,groundwater flow direction was estimated to <br /> be to the northeast(ESI, 1991). <br /> 3 > <br />