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12 T 2- S S <br /> lA EXECUTIVE SUMMARY <br /> This Final Problem Assessment Report and Site Closure Request is for the Stockton Terminal ! <br /> r <br /> and Eastern Railroad-site(Site) located at 1282 North Shaw Road, Stockton, San Joaquin <br /> County, California. The Prdblem Assessment Report portion of this report summarizes the <br /> results of past exploratory soil boring drilling and sampling and analysis of the nature and <br /> subsurface extent of soil and groundwater contamination at the site. <br /> Both soil and groundwater have been preciously determined to have been contaminated by total <br /> petroleum hydrocarbons as diesel fuel and related constituents from previous site assessment <br /> investigation reports. The site has been'demonstrated to have.a minor impact on local <br /> groundwater under the site by diesel and motor oil product. .Both of the soil and groundwater <br /> petroleum hydrocarbon contamination in soil and groundwater at the site is from the operation of <br /> the former 10,000 gallon underground storage tank. <br /> The underground storage tank was removed in November 1998 and a minor overexcavation of <br /> petroleum hydrocarbon contaminated soil was removed from the subsurface. The removed soil was <br /> sampled and analytical laboratory reports indicated TPH=diesel contamination was present in the soil <br /> that ranged in concentrations from 400 to 4,000 mg/kg. After the contaminated soil was sampled <br /> it was placed back into the excavation along with additional fill soil. Sheets of visqueen were <br /> placed over the former excavation in the subsurface and then covered to prevent downward <br /> migrating rainwater from leaching the-petroleum hydrocarbon compounds downward. <br /> Subsequent to the over excavation and backfill of the soil a a total of four soil borings-were drilled <br /> { <br /> and sampled in 1999. Concentrations ofTPH-d were-reported to range from 8500 to9100 mg/kg in <br /> the.upper 20 feet of the subsurface within and immediately below the former UST pit. Soil samples <br /> collected from below 20 feet bgs reportedly had concentrations of TPH-d that were below analytical <br /> method detection limits. <br /> Env ironmentakSTETARSCR09102008.wpd 1 <br /> i <br />