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areas will be removed to depths ranging from 6.5 to 8 feet bgs and,based on the existing data, remaining COC/COEC concentrations in soil are expected to be low relative to the remediation goals. As a result, the increased infiltration within the stormwater detention basins is unlikely to affect future groundwater conditions. The RDIP to be prepared for the Project Sierra development will identify contingency actions (e.g., soil sampling and analysis)to validate this assumption. 4.6 Basis for Proposed Remedy The proposed remedy for Site 47 is Alternative 5,Expanded Excavation with On-Site Consolidation, Existing Durable Cover, Expanded New Durable Cover, and ICs. The remedy was proposed based on an evaluation of the remedial alternatives, as described in Section 4.4, relative to the nine evaluation criteria. Alternative 5 is the most effective and viable alternative because it supports the Project Sierra development with near-term economic benefits to the region, and provides comparable performance relative to Alternative 3. Alternative 5 re-locates and manages COC/COEC- impacted soil in a manner that prevents exposure to humans and wildlife. Alternative 5 will satisfy the RAOs by installing new durable covers, repairing existing covers, maintaining the covers over time, and establishing ICs to restrict future land use and activities to minimize exposure to remaining COCs and COECs in soil. The proposed remedy allows the property to be used for commercial and industrial purposes and includes monitoring and maintenance that would be performed as long as necessary to protect human health and the environment. In accordance with California HSC Section 25356.1, Site 47 RAP includes a non-binding preliminary allocation of responsibility for the proposed remedy (Appendix E). Site 47 RAP for Soil 17 October 2023