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09/02 '00 NED 16 5s FAx 19259469968 ERMWEST WC I]019 PAGE 2 site-specific screening levels to determine the significance of residual constituent concentrations. Consistent with the ASTM methodology,development of site-specific, mk-based screening levels for the subject properties entailed three major steps,as follows: * Identification of constituents of potential concern in each medium.(i e , soil axed ground water). * Identification of realistic exposure pathways associated with each wediuxm * Development of risk-based screening levels for each medium, trying appropriate exposure asswnptiones and current toxicity information from Calitornta EPA and USEPA, development of these screerang levels was based on the identification of realistic exposure pathways deed m the preceding step Each of these steps is described in the following sections 1DENTMCAk77ON OF CONS=LENTS OF P07I 11TIAL CONCERN Underground storage tanks (LTSTs) formerly used for gasoline storage were removed from the subject properties Following removal of the CSM,impacted soils were excavated and remediated, and shallow ground water was extracted and treated Details of these activities are described in the Closure Report, 1325 and 1515 Wesi IWeberAvmw, Stockton, Cakfiornia Oherein after Closure Deport, ERM, 1999) In spite of the remedial activities conducted at the subject properties,some residual constituents remain in subsurface soils and ground water Speck constituents £ouitd in post-remediation samples are listed below by rmedium. a Subsurface soils benzene, toluene,ethylberizene, and xylenes ' ® Ground water: benzene,toluene,ethylbenzene,xylenes, methyl-terf- butyl ether(M OE);2-methyl-2 propanol(TBA),1,2-dchloroethane ' Idenhhcation of these compounds was based on the results of dic excavatton conFirmAtion samplug and post-excavahon bampling desc:nbed in the Closure Report(IKRK 1999)