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1 <br /> Human Health Screening Evaluation <br /> US Can—Welty Road March 19,2012 <br /> 3.4 EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION FOR <br /> SOIL <br /> SAIC estimated potential residential exposures to COPCs in on-site soils by oral, dermal, and <br /> inhalation routes using algorithms presented in the PEA Guidance Manual. These algorithms <br /> incorporate health-protective, default exposure parameters promulgated by the DTSC and EPA <br /> that represent the reasonable maximum exposure for health hazards and health risks. <br /> SAIC also estimated cancer risks and non-cancer health hazards using the equations presented in <br /> the PEA Guidance Manual. Chronic carcinogenic impacts were calculated for combined child <br /> and adult exposure of 6 years and 24 years, respectively. Chronic non-cancer impacts were <br /> calculated for a child assuming an exposure duration of 6 years. <br /> The derivation of the equations used to estimate exposures and risks are provided as Appendix C <br /> of the PEA Guidance Manual. The exposure parameters incorporated into the screening <br /> evaluation algorithms are provided in Table 10. <br /> The Central Valley RWQCB is satisfied that the Site soil characterization dataset adequately <br /> describes site conditions; therefore, SAIC calculated the EPC for each COPC as the UCL of the <br /> mean soil concentration. SAIC used the median concentration to represent the EPC for <br /> chemicals with a detection frequency less than 4 percent, as recommended by the EPA (EPA, <br /> 2010). SAIC then calculated potential incremental lifetime cancer risks for on-site residential <br /> adult and child receptors. <br /> Potential incremental lifetime cancer risks were calculated for on-site residential adult and child <br /> receptors. SAIC estimated cancer risks as the incremental probability of an exposed individual I <br /> developing cancer over a lifetime due to exposure to a potential carcinogenic constituent(i.e., <br /> incremental lifetime cancer risk; EPA, 1989). The potential cancer health risks for each <br /> individual chemical in an exposure pathway were summed to estimate an overall cancer risk for ' <br /> each exposure pathway. Cancer risks across all evaluated exposure pathways were then summed <br /> to estimate incremental lifetime cancer risk for the individual. <br /> Likewise, SAIC calculated potential non-cancer health hazards for on-site residential child <br /> receptors. Hazards were estimated by comparing potential on-site doses to an acceptable <br /> reference-dose exposure. The calculated ratio of the estimated dose to the reference dose (the <br /> hazard quotient)was calculated for potential exposure to each COPC. The potential health <br /> hazards for each chemical in an exposure pathway were summed to estimate the total health <br /> hazard for each exposure pathway. Health hazards across all evaluated exposure pathways were <br /> then summed to estimate the total hazard index for the individual. <br /> 3.4.1 Cancer Risks from Constituents of Potential Concern in Soil <br /> SAIC calculated the oral and dermal cancer risks, and inhalation cancer risks to potential on-site <br /> residential receptors for exposure to on-site soils using the following equations: <br /> Oral and Dermal Cancer Risks for Direct Contact with Soil(PEA Guidance Manual, Figure <br /> 2.3): <br /> RiskSo;i = (SFo x Cs x 11.57E-06])+ (SFo x Cs x [1.87E-05] x ABS) <br /> Where: <br /> Risk,ij= oral and dermal cancer risks from direct soil exposure <br /> 6 <br /> SAIC <br /> I <br />