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09/02 '00 WED 13:23 FAX 19259469968 <br /> PAGE 2 <br /> i' <br /> site-specific screening levels to determine the significance of residual <br /> constituent concentrations. <br /> Consistent with the ASTM methodology,development of site-specific, <br /> 1 <br /> risk-based screening levels for the subject properties entailed threelmajor <br /> steps,as follows: <br /> Identification of constituents of potential concern in each medium(i.e., <br /> soil and ground water). 'r ` <br /> 'r <br /> 1 • Identification of realistic exposure pathways associated with each <br /> medium. <br /> l <br /> • Development of risk-based screening levels for each medium,using <br /> ! appropriate exposure assumptions and current toxicity information <br /> from California EPA and USEPA;development of these screening <br /> levels was based on the identification of realistic exposure pathways <br /> defined in the preceding step. <br /> Each of these steps is described in the following sections. <br /> +i <br /> IDENTIFICATION OF CONSTITUENTS OF POTENTIAL CONCERN <br /> Underground storage tanks(USTs)formerly used for gasoline storage <br /> were removed from the subject properties. Following removal of the ` <br /> USTs,impacted soils were excavated and remediated, and sh�allow`ground <br /> water was extracted and treated. Details of these activities are described <br /> in the Closure Report, 1325 and 1515 West Weber Avenue, Stockton, California <br /> (herein after Closure Report;ERM, 1999). <br /> In spite of the remedial activities conducted at the subject properties,some <br /> l residual constituents remain in subsurface soils and ground water.: <br /> Specific constituents found in post-remediation samples are listed below <br /> by medium: f <br /> • Subsurface soils: benzene,toluene, ethylbenzene,and xylenes.' <br /> • Ground water: benzene,toluene,ethylbenzene,xylenes; <br /> 'methyl-tent-butyl ether(MTBE);2-methyl-2-propanol (TBA);1,2-dichl6roetlane <br /> Identification of these compounds was based on the results of the excavation <br /> confirmation sampling and post-excavation sampling described ih the Closure <br /> Report(ERM,1999). <br /> 'r <br /> f <br /> l <br /> 1 <br />