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i of the former underground product storage tanks (Figure 3) . All soil borings were drilled to a total depth of 40 feet, except SB5 which was drilled to 43 feet below grade. Selected soil samples were analyzed for BTEx, total petroleum hydrocarbons (TPH) as gasoline, ethylene dibromide, and organic lead. Laboratory results determined that all borings contained nondetectable lead concentrations in all analyzed samples (WaterWork report dated June 1, 1990) . Only borings SB1 and SB2 contained benzene and TPS _ concentrations above their method detection limits of 0.005 mg/kg and 10 mg/kg, respectively. Boring SB1 contained 0.056 mg/kg benzene and 300 mg/kg TPH at 15 feet and nondetectable levels to total, depth. Boring SB2 contained 0.030 mg/kg benzene at 25 feet and nondetectable levels to total depth. Boring SB2 contained a TPH concentration of 10 mg/kg at 35 feet below grade and nondetectable levels at 40 feet. 4.0 HYDROGEOLOGY The soils in the vicinity of the Chevron site have been mapped by the U.S.D.A. Soil Conservation Service as Stockton clay. Stockton clay is a fine-textured, dark grey to black clay deposited by quiescent or slow moving water. Soils encountered during drilling consist primarily of lean clay to 20 feet, sands and gravel to 35 feet, and lean clay to total depth. The site is located in the Stockton East Water District. According to the San Joaquin County Flood Control and Water Conservation District, Spring 1990, the regional groundwater gradient is to the `A east - northeast (Figure 4) . The piezometric level of groundwater in the vicinity of the site has been reported to be approximately 62 feet below grade (San Joaquin County Flood Control and Water Conservation District, Spring 1990) (Figure 5) . The closest surface stream is the Mormon Slough approximately one mile to the south of the site. Groundwater was not encountered during drilling operations. U chevron u 8 A Inc. - 367 R032791 M.P 2 a—