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16 1.0 INTRODUCTION <br /> 1 This report is being submitted in response to a request by the San Joaquin County Public Health <br /> Services, Environmental Health Division (PHS/EHD) to prepare a Problem Assessment Report <br />' for the subsurface investigation at 601 South Ventura Avenue, Stockton, California (Figure 1) <br /> and to propose remediation alternatives for soils on the site which have been impacted by <br /> petroleum hydrocarbons The report provides background information and outlines a proposed <br /> Soil Contamination Workplan (SCW) for the impacted soils <br /> 1 2.4 SITE BACKGROUND <br /> 1 On March 9, 1989, two underground fuel storage tanks were removed from the site <br /> Hydrocarbon contamination was noted in soil samples collected from the east side of the tank <br />' pit excavation, however, a water sample collected from the southwest corner of the pit did not <br /> record any fuel constituents above method detection limits Laboratory results are summarized <br /> in Table 1 Due to the elevated concentrations of petroleum hydrocarbons in the soils, further <br /> investigation was required <br /> On October 25, 1989, the floor of the former tank pit was deepened from 10 to 18 feet below <br /> grade using a tracked excavator Subsequent to excavation, 12 soil samples were collected from <br /> the floor and sidewalls of the pit The samples were analyzed for benzene, toluene, <br /> Lethylbenzene, and xylenes (BTEX), total petroleum hydrocarbons as gasoline (TPHG), ethylene <br /> dibromide (EDB), 1,2-dichloroethane (EDC), and organic lead (Pb) utilizing EPA method <br /> 8240/8260 and DHS/HML 338 methods, respectively The samples were composited in a two <br /> to one manner, for a total of six composites Laboratory results are summarized in Table 2 <br /> On November 22, 1989, six composite soil samples were collected from the excavated material <br /> stockpiled on-site Laboratory results for composite samples collected from the excavated <br /> material did not indicate the presence of hydrocarbon contamination above method detection <br /> levels Hydrocarbons present in the material excavated on October 25, 1989 apparently <br /> volatilized prior to composite sampling on November 22, 1989 Based on analytical results, the <br /> former tank pit was backfilled with the excavated and remediated material <br /> rPAR 0593 FNL 1 <br /> r <br />