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1 - <br /> k%1 KLEINFELDER <br /> SAN JOAQUIN COUNTY MOTOR POOL <br /> WASTE OIL TANK CLOSURES <br /> SITE ASSESSMENT WORK PLAN ADDENDUM <br /> BACKGROUND <br /> The San Joaquin County Motor Pool is located at 444 South Wilson Way, Stockton, <br /> California. Two waste oil storage tanks (500-and 1000-gallon) were excavated and <br /> removed from the site in May 1988. Kleinfelder conducted a soil assessment in November <br /> 1989 to assess the potential presence of petroleum hydrocarbons in the soil. Results of <br /> Kleinfelder's soil assessment and previous tank excavation sampling indicated that <br /> petroleum hydrocarbons are present in the vicinity of the two tank excavations and appear <br /> to be limited to the soil in and around the bottom of the tank excavations. Concentrations <br /> of chromium and zinc were also detected in soil samples analyzed from the former waste <br /> oil tanks, which appeared to be consistent with background soil concentrations typical of <br /> the northern San Joaquin Valley. The results of the soil assessment are presented in <br /> Kleinfelder's "Soil Assessment Report, San Joaquin County Motor Pool, Stockton, <br /> California", dated December 22, 1989. <br /> Based on the results of the soil assessment, the San Joaquin County Public Health Services <br /> Environmental Health Division (SJCEHD) has requested two additional borings be drilled <br /> at the site. Total petroleum hydrocarbons were detected in the sample collected at the <br /> bottom of soil boring SB-5 (21.5 feet) at 12 mg/kg. The boring was drilled adjacent to the <br /> former 500-gallon waste oil tank. The SJCEHD requested an additional soil boring be <br /> drilled in close proximity to SB-5 to further assess the vertical extent of petroleum <br /> hydrocarbons beneath the waste oil tank excavation. <br /> Concentrations of chromium and zinc were detected in the soil samples analyzed from the <br /> former waste oil tanks. To assess if these concentrations may be the result of leakage from <br /> the tanks, the SJCEHD has requested a second boring be drilled in an area not suspected <br /> of contamination to assess the background metal concentrations in the area. A comparison <br /> of metal concentrations reported in the soil assessment to the background concentrations <br /> will allow evaluation on whether soil beneath the former tanks may have been affected by <br /> metals. <br /> SCOPE OF WORK <br /> Soil Boring <br /> One boring will be drilled adjacent to soil boring SB-5 to a depth of 50 feet to further <br /> assess the vertical extent of petroleum hydrocarbons beneath the waste oil tank excavation. <br /> The second boring will be drilled onsite in an area not suspected of contamination to <br /> provide background information on concentrations of chromium and zinc. The boring will <br /> be advanced near the California Water Service municipal water well north of the site to a <br /> depth of 10 feet. Both proposed boring locations are shown on Plate 1. <br /> The soil borings will be drilled using a truck-mounted drill rig equipped with 6- or 8-inch <br /> hollow-stem augers. During the drilling, an experienced Kleinfelder geologist will classify <br /> the subsurface soil, collect soil samples, and log the borehole. Upon completion of the soil <br /> boring and sampling, the boring will be backfilled with neat cement. <br /> F10-90-243 1 <br />