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SECTIONTHREE Technical Appxoub <br /> • The human health risk assessment will evaluate existing and potential future risk to on-site and off-site <br />■ human receptors Additionally, the assessment will evaluate potential impacts to groundwater at <br /> hypothetical groundwater wells downgra.dient of the site On-site receptors consist of occupational <br /> employees and visitors Off-site receptors will be evaluated by vicinity maps and may consist of <br /> occupational employees and residents The screening evaluation is used to identify chemicals which <br /> may pose an unacceptable risk to human health The approach to this screening follows guidance set <br /> forth by the U S EPA (1989a), State of California Office of Scientific Affairs (1993 and 1994), <br /> Calnfornva Regional Water Quality Control Board (1989), and American Society of Testing and <br /> Materials (ASTM) (1995) The following sections will discuss the proposed approach and scope of <br /> work for the screening evaluation assumptions and exposure factors as presented in this <br /> aforementioned guidance documents <br /> 3.1 HUMAN HEALTH SCREENING EVALUATION <br /> The objective of the human health screening evaluation is to quantify health risks to potentially exposed <br /> populations under future and current conditions of site use This section presents a brief description of <br /> each of the steps involved in the nsk assessment, and discusses the purpose of each step The process <br /> is consistent with the guidance provided in the Risk Assessment Guidance for Superfund, Vol I, <br /> Human Health Evaluation Manual(Part A) (U S EPA, 1989a) Each of the steps will be expanded on <br /> in the remaining sections of this Workplan <br /> The Human Health Screening Evaluation will be conducted in accordance with U S EPA and State of <br /> California guidance, and will include the following elements <br /> o Prepare a conceptual site model <br /> o Evaluate data and select chemicals of concern <br /> o Identify exposure pathways(I)resent and future scenarios) <br /> Io Identify human receptor populations <br /> o Locate exposure points and identify chemical exposure concentrations <br /> o Estimate chemical intake for all receptors <br /> o Assess toxicology of chemicals of concern <br /> o Characterize human health risks <br /> ® C%CALTRANS WNM0%WRKPLNF oom74=-ww73oown%sNn 3-1 <br />