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1.0 INTRODUCTION This risk assessment evaluates the potential environmental impacts and human health effects associated with the presence of petroleum hydrocarbons in soil beneath the Santa Fe Railway Company site (the site) in Stockton, California In 1985, the Santa Fe Railway Company purchased the site to develop a connection track between two perpendicular tracks Predevelopment activities included the discovery and removal of an underground vault and three underground, steel, single-walled, storage tanks (Tanks #1, #2, and #3) During the vault/tank removal, petroleum hydrocarbon-impacted soils were found beneath Tanks #1 and #2 (ERM-West 1989) The purpose of the baseline risk assessment is to assess 1) the potential for chemical migration through soil to groundwater and 2) the magnitude of any potential site-related exposures and potential health asks associated with current site conditions The approach used in this risk assessment is consistent with both State of California and Federal guidelines for performing risk assessments The guidelines include the California Environmental Protection Agency's (Cal-EPA) Scientific and Technical Standards for Hazardous Waste Sites, DRAFT (Cal-EPA, 1990) and the United States Environmental Protection Agency's (USEPA) Risk Assessment Guidance for Superfund Volume I Human Health Evaluation Manual (Part A) Interim Final (USEPA, 1989) In addition to this evaluation being consistent with regulatory risk assessment guidance, the methodologies used in this report to predict potential future impact to groundwater from petroleum hydrocarbons in soil are consistent with methodologies currently used by California regulatory agencies Specifically, the strategy and modeling used in this assessment is consistent with that used in the California Leaking Underground Fuel Tank (LUFT) Manual (California Water Resources Control Board, 1989) for setting allowable levels of petroleum hydrocarbons in soil The potential for petroleum hydrocarbons to reach groundwater beneath the site will be evaluated through the use of environmental fate and transport models. Site-specific data including soil and chemical properties are used in the model The results of the modeling will be used to evaluate whether any remediation is necessary at the site Any recommendations regarding the need for site remediation are based, in part, on the potential for petroleum hydrocarbon migration through the soil column to groundwater GW600 IMAWAFE F'Ni.Mw05 26 93 1-1 ChemRrk� 1943