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1.5 Historic Soil Conditions <br /> • <br /> Following the December 1986 detection of the leak in the western-most <br /> gasoline tank, ESE drilled five borings around the perimeter of the two <br /> adjacent USTs and the nearby diesel UST, and collected soil samples for <br /> analysis ESE's results, contained as an appendix 1n ACG's December 19, <br /> 1991 Problem Assessment Report, indicated petroleum hydrocarbon impact in <br /> soil to a depth of 28 feet bgs <br /> During the April 1987 UST removals, impacted soil was overexcavated to the <br /> depth of 28 feet Approximately 450 cubic yards of soil, including some 120 <br /> I cubic yards that was noted to be impacted with gasoline, was allowed to aerate <br /> and be disposed of onsite with guidance from the San Joaquin Air Pollution <br /> Control District <br /> Subsequent drilling, sampling, and analysis performed at this site indicate that <br /> the mass of remaining petroleum impact in soil is relatively negligible It <br /> appears that the overexcavat>on performed in 1987 removed most of the <br /> impacted soli in the vicinity of the USTs The few collected soil samples that <br /> did contain measurable concentrations of petroleum hydrocarbons were likely <br /> cross-contaminated by impacted groundwater at that depth and location A <br /> summary of soil sample results is contained in Table 6 Geologic cross- <br /> sections, shown 1n Figure 4 and Figure 5, illustrate petroleum hydrocarbon <br /> RIDconcentrations in soil samples <br /> May 1999 Subsurface Investigation and Groundwater Monitoring Report <br /> • The Earthgrams Company Facility <br /> 2651 South Airport Way <br /> Stockton,CaliforniaPrepared for THE EARTHGRAINS COMPANY Prepared by Philip Services Corp <br /> E U2082\121382EG1125997\05991REP DOC June 22, 1999 <br /> 4 <br />