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M k <br /> PROPOSED <br /> sw FINAL REMEDIAL PLAN <br /> San Joaquin County <br /> Human Services Building Site <br /> Stockton, California <br /> I# 1.0 INTRODUCTION <br /> rte+ <br /> In response to the discovery of petroleuir hydrocarbon compound <br /> residues in the soils at the San Joaquin County Human Services <br /> Building site located at the intersection of San Joaquin Avenue <br /> and Washington street in Stockton, California (Fig-are 1) , this <br /> proposed final remedial plan has been developed to address <br /> remediation of the site. Through completion of the site investi- <br /> gation work for the site, as addressed in WESTON's Problem <br /> Assessment Report, dated February 20, 1989, it was discovered <br /> that the petroleum hydrocarbon residues are confined to a rela- <br /> tively small area located in the southeast corner of the site. <br /> 1.1 Backaround <br /> During the time period of April through May 1988, a total of nine <br /> underground fuel storage tanks were removed from the southeast <br /> corner of the site. The nine tanks were residual tanks from a <br /> gasoline service station which had been previously located at the' <br /> site. The tanks consisted of two unleaded gasoline tanks, three <br /> leaded gasoline tanks, one waste oil tank and three sand filled <br /> ' abandoned tanks. <br /> After each tank removal, the soils beneath the tank were sampled <br /> and analyzed for various analytical parameters. The analytical <br /> ».3 results for the soil samples taken from beneath some of the tanks <br /> revealed significant concentrations of total petroleum hydrocar- <br /> bons (TPH) . Additionally, concentrations of volatile compounds <br /> associated with gasoline (benzene, toluene, xylene and <br /> eth lbenzene BTX&E were found to be above San Joaquin Y ( ) ) gain County <br /> .�. Health District Acceptable Limits. <br /> In September 1988, a preliminary report covering the tank removal <br /> program and outlining the recommended scope of work necessary to <br /> develop a Problen Assessment Report was prepared. In December <br /> 1988, field activities necessary to complete the problem assess- <br /> ment were implemented. <br /> The field investigation consisted of the installation of twelve <br /> soil boreholes and three shallow groundwater monitoring wells, as <br /> shown on Figure 2. From these installations, a total of thir- <br /> ty-three soils samples and three groundwater samples were col- <br /> lected. <br /> The Problem Assessment Report, prepared on February 20, 1989 <br /> indicated the analytical results fcr these samples revealed that <br />