ARCHIVED REPORTS HUMAN HEALTH SCREENING EVALUATION

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' Human Health Screening Evaluation Surland Homes-Bridle Creek February 12,2009 groundwater samples detected low concentrations of toluene, ethylbenzene, total xylenes, and several PAHs. The City of Tracy has enacted an ordinance that prohibits the installation of private water-supply wells; consequently, groundwater at the site will not be used as a drinking-water source, and groundwater exposure pathways were not evaluated further in this HHSE. 4. TOXICITY VALUES For COPCs evaluated in this HHSE, toxicological information (toxicity values) was used to quantitatively estimate potential future health impacts. Cancer potency factors (slope factors) were used to estimate potential cancer risks. Reference doses were used to estimate non-cancer health hazards. The hierarchy of sources for toxicity values as presented in the PEA Guidance Manual is as follows: • California Cancer Potency Factors and Chronic Reference Exposure Levels (Cal/EPA, 2008a, 2008b). • EPA Integrated Risk Information System (IRIS; EPA, 2008). Slope factors used in this HHSE are provided to Table 5. Non-cancer toxicity criteria (chronic reference doses) used in this HHSE are provided in Table 6. 5. EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION ' The estimation of potential residential exposures to chemicals in on-site soils by oral, dermal, and inhalation routes was performed using algorithms presented in the PEA Guidance Manual. These algorithms incorporate health protective, default exposure parameters promulgated by the DTSC and EPA that represent the Reasonable Maximum Exposure for health hazards and health risks. Cancer risks and non-cancer health hazards were also estimated using the equations presented in the PEA Guidance Manual. Chronic carcinogenic impacts were calculated for combined child and adult exposure of 6 years and 24 years, respectively. 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 provided in Appendix B of the PEA Guidance Manual. The exposure parameters incorporated into the screening evaluation algorithms are provided in Table 7. ' EPCs were calculated as the UCL of the mean soil concentration for each COPC. Potential incremental lifetime cancer risks were calculated for on-site residential adult and child receptors, and for adult construction workers. The UCL of the mean soil concentrations (see Table 4), was used to estimate exposures and subsequent risks and hazards. Cancer risks were estimated 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., 6 � :: ..AWUL.. From Science to Solutions