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Human Health Screening Evaluation Mountain House Development Site#6 January 18,2011 incremental lifetime cancer risk; EPA, 1989). SAIC 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 the cancer risks across all evaluated exposure pathways to estimate incremental lifetime cancer risk for the individual. SAIC estimated potential non-cancer health hazards for on-site residential child receptors by comparing estimated on-site doses to an acceptable reference dose exposure. SAIC evaluated the calculated ratio of the estimated dose to the reference dose (the hazard quotient) for potential exposure to each COPC, then summed the potential health hazards for each chemical in an exposure pathway to estimate the total health hazard for each exposure pathway. SAIC subsequently summed the health hazards across all evaluated exposure pathways to estimate the total hazard index for the receptor. In accordance with the National Contingency Plan, an incremental lifetime cancer risk of 1E-06 was used as a point of departure, and an excess cancer risk equal to or below this threshold is considered to be insignificant. The agency reviewing this HHSE 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 for non-cancer hazards is considered to be an acceptable health hazard level. If the regulatory criteria are exceeded based on the screening evaluation, this evaluation identifies the chemical and the exposure pathways contributing to the elevated risks or hazards, which can be more precisely assessed in a site-specific refined health risk assessment, if warranted. 5.1 RESIDENTIAL CANCER RISKS SAIC calculated the oral and dermal cancer risks and inhalation cancer risks to potential on-site residential receptors for exposure to on-site soils using the following equations: Oral and Dermal Cancer Risks for Direct Contact with Soil (PEA Guidance Manual, Figure 2.3): Risksoii=(SFo x Cs x [1.57E-061) + (SFo x Cs x [1.87E-05] x ABS) Where: Risksoil=oral and dermal cancer risks from direct soil exposure SFo= oral cancer slope factor, (mg/kg-day)-' Cs= concentration in soil, mg/kg ABS = dermal absorption fraction, dimensionless The oral and dermal cancer risk calculations for potential exposures to on-site soils are provided in Table 8. Potential cancer risks were estimated for carcinogenic COPCs and then summed among chemicals for oral and dermal exposures. Inhalation Cancer Risks for Air(PEA Guidance Manual, Figure 2.4): Riskair= SM x Ca x 0.149 Where: Risk,,,,—inhalation cancer risk from indirect soil exposure SFi= inhalation cancer slope factor, (mg/kg-day)-' from sclence to SOIUNOF18