ARCHIVED REPORTS_HUMAN HEALTH SCREENING EVALUATION 2012

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Human Health Screening Evaluation US Can—Welty Road March 19,2012 risk to a potential resident across all exposure routes. SAIC then summed the non-cancer health hazards for soil exposure pathways (oral/dermal and inhalation exposures)with the non-cancer hazard for the vapor-intrusion exposure pathway(inhalation of VOCs in groundwater)to estimate the hazard to a potential resident across all exposure routes. SAIC used an incremental lifetime cancer risk of 1E-06 as a point of departure in accordance with the National Contingency Plan; and an excess cancer risk equal to or below this threshold was considered to be insignificant. If an excess cancer risk is within the acceptable range between 1E-04 and 1E-06, the agency reviewing this HHSE will make risk management decisions on a site-specific basis. For non-cancer hazard indices, a hazard index of 1 or less 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 cancer risks or non-cancer hazards,which can be more precisely assessed in a site-specific refined health risk assessment if warranted. 4.1 CANCER RISKS SAIC estimated potential cancer risks from possible oral, dermal, and inhalation exposures to on- site soils. The risk for individual COPCs are provided in Tables 11 and 12. The aggregate risks for oral, dermal, and inhalation cancer risks from exposure to on-site soils and groundwater are provided in Table 13. The risk for individual COPCs and the summation of inhalation risks for the vapor intrusion to indoor air exposure pathway are provided in Table 22. SAIC estimated total cancer risk to a potential resident from oral, dermal, and inhalation exposures to on-site soils and subsurface vapor intrusion to be 2E-06. This level of risk is at the lower end of the risk management range of 1E-06 to 1 E-04 established by Cal/EPA and EPA. 4.2 NON-CANCER HEALTH HAZARDS I SAIC estimated non-cancer health hazards for potential oral, dermal, and inhalation exposures to on-site soils. The risk for individual COPCs for these routes are provided in Tables 14 and 15. The aggregate non-cancer hazards for oral, dermal, and inhalation exposure to on-site soil are I provided in Table 16. The hazards for individual COPCs and the summation of hazards for the vapor intrusion to indoor air exposure pathway are provided in Table 23. SAIC estimated the total non-cancer hazard from oral, dermal, and inhalation exposures to on- ' site soil and inhalation exposure to on-site groundwater to be 0.02. This level of hazard is far less than a hazard index of 1, and therefore indicates an acceptable non-cancer health hazard for exposures to on-site soils and groundwater for a potential resident. 5. UNCERTAINTIES Uncertainties were inherent to the human health cancer risk and non-cancer health hazard evaluation performed during this HHSE. Site-specific conditions that contribute most significantly to the uncertainty of the risk and hazard estimates are identified and discussed below. SAIC conducted three site characterization studies with the oversight of the Central Valley RWQCB. Data of adequate analytical quality(e.g., low detection limits) were used to support 12 i SAIE t