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Human Health Screening Evaluation <br /> Mountain House Development Site#6 January 18,2011 <br /> where appropriate. Kaplan-Meier nonparametric estimation methods were deemed most <br /> appropriate for data sets with multiple detection limits, as recommended in the User's Guide <br /> (EPA, 2010a). In addition, it may not be possible to calculate a UCL when the detection <br /> frequency is very low (less than 4 to 5 percent). In these cases, the User's Guide recommends <br /> using the sample median or sample mode as the EPC. SAIC used the sample median in this <br /> HHSE to represent the EPC for benzene and total xylenes. <br /> SAIC calculated the UCL of the mean soil concentration using all soil samples collected between <br /> 0 and 10 feet bgs. The total number of soil samples analyzed, the total number of samples with <br /> detectable concentrations, and the EPCs for all soil COPCs evaluated in this HHSE are provided <br /> in Table 4. <br /> 4. TOXICITY VALUES <br /> SAIC used toxicological information(toxicity values) to quantitatively estimate future health <br /> impacts for COPCs evaluated in this HHSE. Cancer potency factors (slope factors)were used to <br /> estimate potential cancer risks. Reference doses were used to estimate non-cancer health <br /> hazards. As presented in the PEA Manual, the hierarchy of sources for toxicity values was as <br /> follows: <br /> • California Cancer Potency Factors and Chronic Reference Exposure Levels (Cal/EPA <br /> Office of Environmental Health and Hazard Assessment [OEHHA], 2010a, 2010b); and <br /> • EPA Integrated Risk Information System(EPA, 2010b). <br /> Slope factors used in this HHSE are provided in Table 5. Non-cancer toxicity criteria(chronic <br /> reference doses)used in this HHSE are provided in Table 6. <br /> 5. EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION <br /> SAIC estimated the potential residential exposures to chemicals in on-site soils by oral, dermal, <br /> and inhalation routes using algorithms presented in the PEA Guidance Manual. These <br /> algorithms incorporate health-protective, default exposure parameters promulgated by the DTSC <br /> and EPA 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 in Appendix B <br /> of the PEA Guidance Manual. The exposure parameters incorporated into the screening <br /> evaluation algorithms are provided in Table 7 of this HHSE. <br /> SAIC calculated EPCs as the UCL of the mean soil concentration for each COPC. Potential <br /> incremental lifetime cancer risks were calculated for on-site residential adult and child receptors. <br /> It may not be possible to calculate a UCL when the detection frequency is very low (less than <br /> 4 to 5 percent). In these cases the sample median was selected as the EPC. The EPC (Table 4) <br /> was used to estimate exposures and subsequent risks and hazards. <br /> SAIC estimated cancer risks as the incremental probability of an exposed individual developing <br /> cancer over a lifetime as a result of exposure to a potential carcinogenic constituent(i.e., <br /> from SuMnoe to Solvtloas <br />