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Human Health Screening Evaluation Former Vernalis Pump Station September 2,2010 SAIC-Benham estimated cancer risks and non-cancer health hazards using the equations presented in the PEA Guidance Manual. Chronic carcinogenic impacts were calculated for combined child and adult exposures of 6 years and 24 years, respectively (combined exposure duration of 30 years), and chronic non-cancer impacts were calculated for a child assuming an exposure duration of 6 years. The derivation of the equations used to estimate exposures and risks are presented in the PEA Guidance Manual. The exposure parameters incorporated into the screening evaluation algorithms are provided in Table 9 of this HHSE. The Central Valley RWQCB is satisfied that the site soil characterization dataset adequately describes site conditions; therefore, SAIC-Benham calculated EPCs as the UCL of the mean soil concentration for the COPCs. With the exception of naphthalene as described in section 3.1, SAIC-Benham used the median concentration was used to represent the EPC for chemicals with a detection frequency less than 4 percent, as recommended by the EPA (2009). Potential incremental lifetime cancer risks were calculated for on-site residential adult and child receptors. The UCL of the mean soil concentrations (Table 6)was used to estimate exposures and subsequent risks and hazards. SAIC-Benham estimated cancer risks as the incremental probability of an exposed individual developing cancer over a lifetime as a result of exposure to a potential carcinogenic constituent (i.e., incremental lifetime cancer risk; EPA, 1989). SAIC-Benham summed the potential cancer health risks for each individual chemical in an exposure pathway to estimate an overall cancer risk for each exposure pathway, and then summed cancer risks across all evaluated exposure pathways to estimate incremental lifetime cancer risk for the individual. Likewise, SAIC-Benham calculated potential future non-cancer health hazards for on-site residential child receptors. Hazards were estimated by comparing potential estimated on-site doses to an acceptable reference-dose exposure. The calculated ratio of the estimated dose to the reference dose (the hazard quotient)was calculated for potential exposure to each COPC. SAIC- Benham summed the potential health hazards for each chemical in an exposure pathway to estimate the total health hazard for each exposure pathway, and then summed health hazards across all evaluated exposure pathways to estimate the total hazard index for the individual. In accordance with the National Contingency Plan, SAIC-Benham used an incremental lifetime cancer risk of 1E-06 as a point of departure, and an excess cancer risk equal to or below this threshold was considered to be insignificant. The lead regulatory agency will make risk- management decisions on a site-specific basis if the excess cancer risk is within the acceptable range (between 1E-04 and 1E-06). A hazard index of 1 or less is considered to be an acceptable health hazard level for non-cancer health effects. If the regulatory criteria are exceeded based on the screening evaluation, this evaluation will identify the chemical and exposure pathways contributing to the elevated risks or hazards. These can be more precisely assessed in a site- specific, refined health-risk assessment, if warranted. 6 � The Benham Companies,LLC A Wholly Owned Subsidiary From&mxe to Solanoss