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Joe Ramage, R.G. <br />Project Geologist <br />Debra Anderson <br />Operations Manager <br />LETTER REPORT — WASTE OIL TANK SITE ASSESSMENT <br />POSDEF Power Company, 2526 West Washington Street, Stockton <br />October 29, 1998 <br />Page three <br />A California Registered Geologist logged both boreholes using the Unified Soil <br />Classification System. Soil boring logs are attached. Following sampling, both <br />boreholes were abandoned with neat cement grout. The surface pavement was <br />restored using ready-mix cement. <br />Results of the Investigation <br />Soils beneath the site consisted of tank fill and imported compaction materials. At SB-1, <br />soils consisted of a loose, light brown, poorly-graded sand to a depth of approximately 4 <br />feet bgs and pea gravel from 4 to 5 feet bgs. At SB-2, soils encountered consisted of a <br />highly-compacted sandy gravel to a depth of approximately 4 feet bgs and pea gravel <br />from 4 to 5 feet bgs. Groundwater was not encountered in either boring at the total <br />drilling depth of 5 feet bgs. <br />The laboratory results from the soil sample analyses indicated 43 mg/kg of motor oil, <br />small amount of Chromium, Nickel and Zinc, that were over the detection limit. All other <br />analyses were non detect. The laboratory report is attached. <br />Conclusions and Recommendations <br />The results of this site assessment indicate that the soil in close proximity to the bottom <br />of the waste oil tank, Record ID#: TA253501, exhibit contaminants of TPH- as motor oil, <br />chromium, nickel, and zinc, all of which are below the action levels for those <br />contaminants. <br />Based on the results of the site assessment and given the structural and logistical <br />concerns associated with removing the tank, Wright recommends that the PHS/EHD <br />permit POSDEF to close-in-place the subject tank. <br />Thank you for your assistance on this project. If you have questions or need any <br />additional information, please call our Tracy office at (209) 833-0758. <br />Sincerely, <br />Wright Environmental Services, Inc. Attachments: Figure 1, <br />Location Map and <br />Picture <br />PHS/EHD Drilling <br />Permit <br />Soil Boring Logs <br />Laboratory Report