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October 25, 1993 <br /> 1.0 INTRODUCTION <br /> At your request, Roger F <br /> Q g oott Associates, Inc conducted a subsurface investigation of <br /> soil and groundwater contamination at the Punla Property- Center Auto Repair facility (Site) <br /> The Site is located at 1587 French Camp Turnpike in Stockton,, California (Figure I) This <br /> investigation was conducted to delineate the degree and extent of soil contamination beneath <br /> the western sidewalk, evaluate the groundwater gradient, and evaluate the degree of <br /> groundwater contamination near the former waste oil tank <br /> I A Previous Work <br /> Three underground diesel storage tanks (2-10,000 and 1-5,400-gallon) and one 515- <br /> gallon waste oil storage tank were removed from the Site on June 12, 1989, by WathalI <br /> Construction of Stockton, California Associated piping and dispensers were also removed <br /> Soil contamination was detected in the waste oil excavation pit at a depth of 12-'/z ft <br /> Analytical test results indicated a total petroleum hydrocarbon (TPH) concentration of 4,500 <br /> parts per million (ppm) in soil below the former waste oil tank Soil contamination was <br /> detected in the diesel tanks excavation pit in the western wall near the center tank area at a <br /> depth of 13 feet Analytical test results indicated a total petroleum hydrocarbon as diesel <br /> (TPHd) concentration of 650 ppm No detectable concentrations of suspected contaminants <br /> were found in samples collected from the northwestern, southwestern, and eastern portions of <br /> the diesel pit, all three piping samples, and the one eastern dispenser sample <br /> Water Works of Escalon, California prepared a Problem Assessment Report dated April <br /> 4, 1990, following an investigation of soil and groundwater contamination On November 27, <br /> 1989, soil was excavated from the waste oil tank area to a depth of 18 ft Soil contamination <br /> was detected in the pit in the southern and eastern walls only No confirmation samples were <br /> collected and the pit was evidently backfilled with clean soil Water Works then installed one <br /> groundwater monitoring well (B 1/MW 1) east of the tank area and one angle boring (ASB I) <br /> south of the tank area that was advanced beneath the existing shop building Analyses of soil <br /> samples collected from B 1/MW 1 indicated low concentrations of TPH in soil samples from <br /> depths of 15 ft (1 5 ppm), 20 ft (2 7 ppm), and 30 ft (4 1 ppm) No detectable concentrations <br /> of BTEX were detected in the soil or in the groundwater Water samples collected in February <br /> 1990 indicated a concentration of 350 ppm TPHd A concentration of 59 ppm TPHd was <br /> detected in April 1990 Analytical test results from soil samples collected from ASB I indicate <br /> the concentrations detected of TPHd, BTEX, chlorinated hydrocarbons, and semi-volatile <br /> hydrocarbons were below the laboratory method detection limits Based on these results, <br /> ROGER <br /> FMT T <br /> A SSOCIA TE ti <br />