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� K) EINFELDER <br /> 1 EXECUTIVE SUM-MARY <br /> In November 1989, Kleinfelder conducted a soil assessment of two underground storage <br /> tanks (USTs) containing waste oil that were removed from the San Joaquin County Motor <br /> Pool in May 1985. Three borings were drilled around each of the two excavations. <br /> Petroleum hydrocarbons were det,.cted in only one of the six borings (B-5), which was <br /> drilled adjacent to the former 500-gallon UST. The concentrations detected decreased <br /> significantly with depth. Concentrations of chromium and zinc detected in the six borings <br /> appeared to be consistent with background soil concentrations typical of the northern San <br /> Joaquin Valley. During the investigation,ground water was encountered at a pth of 56.5 <br /> feet below the ground surface; 35 feet below the deepest petroleum hydrocarbon <br /> concentration of 12 mg/kg. <br /> Although the concentrations of TPH detected in B-5 was low, the San foaquin County <br /> Public Health Services, Environmental Health Division (SJCEYD) requested that the <br /> vertical extent of TPH migration in the vicinity of boring B-5 be further assessed. In <br /> addition, the County requested that the chromium and zinc concentrations be compared to <br /> a background sample. <br /> In August 1990,Meinfelder collected and analyzed soil samples from one boring (B-7) in <br /> the vicinity of the former 500-gallon UST(adjacent to B-5) and one background boring(13- <br /> 8) approximately 45 feet to the northeast. Total petroleum hydrocarbons we-a not <br /> detected itt samples collected and analyzed from B-7 at a depth of 16.5 and 51.5 feet. <br /> Chromium and zinc concentrations detected in the bottom sample from B 7 appear to be <br /> consistent with the background sample collected f em B-8. <br /> Based on the analytical results and Meinfelder's previous soil assessment. Kleinfelder does <br /> not recommend further assessment of petroleum hydrocarbon migration in the vicinity of <br /> the former 500-gallon UST. San Joaquin County Department of General Services should <br /> seek approval to properly backfill the former 500-gallon UST site. <br /> F13-90-60 1 <br />