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Human Health Screening Evaluation <br /> US Can—Welty Road March 19,2012 <br /> exposure. The calculated ratio of the potential estimated dose to the reference dose(the hazard <br /> quotient)was calculated for potential exposure to each COPC. The potential health hazards for <br /> each chemical were summed to estimate the total health hazard for the receptor. <br /> 3.5.1 Cancer Risks from Subsurface Vapor Intrusion <br /> SAIC calculated the inhalation cancer risks to potential residential receptors from subsurface <br /> vapor intrusion using the screening-level model for groundwater. Potential cancer risks were <br /> estimated for the following carcinogenic and volatile BTEX and PAH COPCs: <br /> • Benzene <br /> • Ethylbenzene <br /> • Benzo(b)fluoranthene <br /> • Chrysene <br /> • Methylnapthalenes <br /> • Naphthalene <br /> The estimated inhalation cancer risk for each individual COPC was then summed for inhalation <br /> exposures. The inhalation cancer risk results for potential exposures to indoor vapor intrusion <br /> are provided in Table 22. <br /> 3.5.2 Non-Cancer Hazards from Subsurface Vapor Intrusion <br /> SAIC calculated the inhalation hazard to potential residential receptors from subsurface vapor <br /> intrusion using the screening-level model for on-site groundwater. Potential inhalation hazards <br /> were estimated for the following volatile BTEX and PAH COPCs: <br /> ' • Benzene <br /> • Ethylbenzene <br /> ' • Total Xylenes <br /> • Acenaphthene <br /> • Fluorene <br /> ' • Methylnaphthalenes <br /> • Naphthalene <br /> • Pyrene <br /> 1 The estimated inhalation health hazard for each individual COPC was then summed for <br /> inhalation exposures. The inhalation health hazard results for potential exposures to indoor <br /> vapor intrusion are provided in Table 23. <br /> 4. HUMAN HEALTH SCREENING EVALUATION RESULTS <br /> SAIC performed this HHSE at the direction of the Central Valley RWQCB to estimate <br /> residential risks and hazards under current site conditions. This HHSE was developed using <br /> health-protective, conservative reasonable maximum exposure assumptions,using risk and <br /> ' hazard algorithms developed by the DTSC and promulgated in the PEA Guidance Manual for <br /> COPCs in soil, and the Screening-Level Model for Groundwater Contamination for COPCs in <br /> groundwater. <br /> SAIC summed the cancer risks for on-site soil exposure pathways (oral/dermal and inhalation <br /> exposures)with the risks for the vapor-intrusion exposure pathway to estimate the total cancer <br /> 11 <br /> SAIC <br /> 1 <br />