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• • <br /> Wendy L. Cohen -2- 24 September 1993 <br /> In well boring MW-1/KJC, approximately 1,000 feet northwest of Alden Park, a soil sample <br /> contained 5,300 mg/kg oil at a depth of 6 feet and 70 mg/kg at a depth of 16 feet. Depth to ground <br /> water in MW-1/KJC is approximately 6 feet. Neither EPA-specified organic priority pollutants nor <br /> dissolved hydrocarbons were detected in the ground water sampled. <br /> On 23 September 1987, Dames & Moore (D&M) conducted a Phase H Site Assessment for Chevron <br /> to confirm the location of the buried concrete reservoir lining and to evaluate the areal extent and <br /> concentration of oil and grease under residential properties, the extent of the liquid oil beneath the <br /> concrete slab and outside the slab, and the concentration of dissolved hydrocarbons in the ground <br /> water. D&M installed 131 shallow probe borings to a depth of 9 feet to determine the distribution <br /> of oil and grease in the soil. Soils in the immediate perimeter of the buried concrete slab along the <br /> southeast edge of Alden Park contained up to 9,700 ppm oil and grease. Also, an accumulation of <br /> offy soil is present at the 2-foot depth along the west side of Forest Hills Drive. <br /> The ground water investigation included installation of 18 borings, 17 of which were completed as <br /> wells, to a maximum depth of 22 feet. The water table occurs at depths of 7.4 to 11.4 feet below <br /> the ground and has a gradient to the northwest. The two wells completed within the concrete slab <br /> and six of the wells adjacent to the slab contained liquid oil floating on the water table. According <br /> to D&M's report, low concentrations of dissolved oil and grease in wells immediately adjacent to <br /> the concrete slab, where liquid oil is present, suggest that the oil is highly insoluble in water. <br /> Ground water samples from eight monitoring wells contained dissolved oil and grease at <br /> concentrations ranging from 6 to 420 ppm. <br /> On 9 February 1988, Radian Corporation completed a Draft Preliminary Site Assessment for the <br /> Department of Health Services Toxic Substances Control Division. Radian reviewed all the work <br /> done by that time but did not perform any drilling or sampling. Radian personnel conducted a site <br /> visit and did not observe hazardous conditions that warranted implementation of interim remedial <br /> measures. In its conclusions, Radian states "Soil contamination at the Alden Park site is well- <br /> defined as a result of an extensive soil sampling effort conducted by Dames & Moore in 1987... <br /> Ground water contamination at the site has been indicated in analyses that only identify the absence <br /> or presence of total oil and grease. Because total oil and grease analysis is not applicable for the <br /> determination of relatively volatile and semi-volatile hydrocarbons, their existence in ground water <br /> is uncertain." <br /> Radian also proposed follow-up actions that should include quarterly monitoring of upgradient and <br /> downgradient wells to determine trends in contamination at the site and the effectiveness of remedial <br /> measures. Radian suggested that biannual sampling of wells could be conducted after a year if it <br /> was determined that levels of contamination in the ground water do not pose a health risk to <br /> downgradient users. <br /> On 8 September 1988, D&M completed a report entitled Liquid Hydrocarbon Recovery Evaluation, <br /> Alden Park for Chevron. Using MW-16, D&M performed preliminary tests to evaluate the <br /> feasibility of recovering the liquid oil floating on the water table using a well pumping system. The <br /> hydrocarbon yield at an average pumping rate of 0.2 gpm, without a correction for water was <br />