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No Further Action Required Request Report Mountain House Development Site#b September 15,2011 with the findings and conclusions presented by SAIL, and requested that an HHSE be prepared for the Site (Central Valley RWQCB, 2010). 2.5 HUMAN HEALTH SCREENING EVALUATION, 2011 SAIL evaluated risks in a residential land-use scenario from exposure to COPCs in soil at the I Site, and the potential for exposure of sensitive ecological receptors to COPCs. SAIC developed the HHSE using approaches and methodology consistent with those presented in the Preliminary Endangerment Assessment(PEA) Guidance Manual(California Environmental Protection I Agency [Cal/EPA] Department of Toxic Substances Control [DTSC], 1999). Shallow groundwater is unlikely to be used at the Site, and is minimally affected by volatile constituents associated with former OVP and TAOC operations; therefore, SAIC did not quantitatively I evaluate exposures to groundwater. SAIC conducted an ecological receptor search to identify sensitive species observed within 1 mile of the Site. SAIC estimated the cancer risk and non-cancer hazard from exposures to on-site soil using the equations and assumptions outlined in the PEA Guidance Manual under the residential exposure scenario (the most conservative exposure scenario). The evaluation of risk associated with soil exposure pathways was limited to the upper 10 feet of soil, consistent with the residential land- use scenario, and with the proposed use of the Site. SAIC quantitatively evaluated the following exposure routes: incidental ingestion of soil and dermal contact with soil, inhalation of wind- blown dust for non-volatile constituents, and inhalation of chemical vapors from soils. SAIC ' identified the COPCs during the site characterization process. All analytes detected in at least one sample collected from the upper 10 feet of soil are considered COPCs in soil. Benzene, ethylbenzene, total xylenes, and 16 PAHs are considered COPCs in soil for the Site, and were I evaluated quantitatively in the HHSE (Appendix A.8). The aggregate cancer risk for oral, dermal, and inhalation from exposures to on-site soil is 5E-06; and the aggregate non-cancer hazard for oral, dermal, and inhalation routes is 0.002. The estimates of both the cancer risk and ' non-cancer hazard indicate that the Site does not pose a health risk to potential residents. SAIC queried the California Natural Diversity Database (CNDDB), maintained by the California ' Department of Fish and Game (DFG), to search for threatened, endangered or sensitive species in the vicinity of the Site. Five occurrences of Swainson's hawk have been recorded at the edge of the 1-mile radius around the Site. The remaining species have not been observed near the 1-mile radius around the Site. This assessment indicates that a threat to sensitive ecological receptors does not appear to exist(DFG, 2010). The estimates of both the cancer risk and non-cancer hazard indicate that the Site does not pose a ' health risk to potential residents, and the CNDDB query indicated that a threat to sensitive species does not appear to exist. Therefore, no further action is required with respect to on-site soil and groundwater(SAIC, 2011). The Central Valley RWQCB concurred with the findings of ' the HHSE and requested documentation to support an NFAR closure determination (Central Valley RWQCB, 2011). ' 3. TRI-REGIONAL RECOMMENDATIONS FOR A NO FURTHER ACTION REQUIRED REQUEST REPORT Section 3.1 provides information outlined in section 6.5 of the Tri-Regional Recommendations to ' support this request for closure at this low-risk site. Section 3.2 supports a decision by the Central Valley RWQCB to issue an NFAR letter with documentation outlined in section 6.6 of 4 SAIC 1