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3. RISK EVALUATION AND REMEDIAL ACTION OBJECTIVES The following sections summarize the results of the human health and ecological risk assessment and identify the remedial action objectives (RAOs) for Site 47. The complete risk assessment is provided in Appendix F of the Site 47 RUFFS. 3.1 Summary of Risk Assessment A human health and ecological risk assessment was performed as part of the Site 47 RUFFS (Geosyntec, 2022). The risk assessment evaluated the exposure pathways consistent with the conceptual site model (Section 2.1; Figures IOa and IOb) and identified the following chemical constituents as COCs/COECs. Human Health COCs: arsenic and select PAHs, specifically benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, dibenzo(a,h)anthracene, and indeno(1,2,3-c,d)pyrene. Ecological COECs: arsenic and total 4,4'-dichlorodiphenyltrichloroethane (DDT) (drainage channel only). The risk assessment determined that arsenic is the primary risk-driving COC/COEC throughout Site 47 and adjacent areas. The soil background threshold value (BTV) for arsenic at RRI is 30.7 milligrams per kilogram (DTSC, 2015), which exceeds human health risk-based screening levels established by DTSC Human and Ecological Risk Office. For a future commercial/industrial worker at Site 47, the risk assessment in the Rl/FFS estimated that the incremental increase in human health risk over background is approximately 50 times higher than baseline at RRI. Additionally, PAHs were identified as COCs at the former skeet/trap range, and total DDT was identified as a COEC at the drainage channel along the southern boundary of Site 47. Table 5 summarizes the concentrations of arsenic, PAHs, and total DDT that were evaluated in the risk assessment. Figures 6 and 8 present the results of the integrated evaluation of the arsenic and PAH data collected between 1995 and 2020; each map shows the spatial distribution and magnitude of an individual COC/COEC within Site 47. For each COC/COEC, the results are presented as the magnitude of exceedance of a selected screening level (SL) for that contaminant.3 Exceedance of the SL indicates potential risks to wildlife inhabiting Site 47 and/or industrial/commercial workers who may work on the site in the future. As noted in Section 3.2, this Site 47 RAP proposes to adopt these specific SLs as remediation goals. The risk assessment identified the area within the data set boundary that warranted remedial action to reduce human health and ecological risks to acceptable levels. The area warranting remedial action is referred to as the remedial boundary and is identified in Figure 11. 3 The selected SL is the lower(more stringent)of either the human health commercial/industrial screening level or the selected"low effect"ecological screening level.Appendix F of the Site 47 RI/FFS provides additional information. Site 47 RAP for Soil 9 October 2023