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Potentially <br /> Significant <br /> Potentially Unless Less than <br /> Significant Mitigation Significant <br /> Impact Incorporated Impact No Impact <br /> • Vertical and Horizontal Preferential Pathways: If development plans include the <br /> • construction of deep foundations, the foundation of the buildings shall incorporate <br /> measures to help reduce the potential for the downward migration of contaminated <br /> groundwater. These measures shall be identified in the site-specific geotechnical <br /> investigation reports. Appropriate measures shall be implemented to reduce vapor <br /> migration through trench backfill and utility conduits. Such measures may Include <br /> placement of low-permeability backfill "plugs" at intervals on-site and where utilities . <br /> extend off current parcel boundaries. <br /> • Storm Water Pollution Controls: A storm water pollution prevention plan (SWPPP) will <br /> be required to be prepared for the site. Storm water pollution controls shall be based on <br /> best management practices (BMPs), such as those described in "Guidelines for <br /> Construction Projects" and "Erosion and Sediment Control Field Manual" published by <br /> the San Francisco Regional Water Quality Control Board. <br /> • Excavation De-Watering: Although not anticipated, if excavation de-watering Is. <br /> required,the water will be sampled and analyzed prior to pumping to evaluate discharge <br /> alternatives. The developer's environmental consultant shall collect a sample of the <br /> water for laboratory analyses for COPCs; other analyses may be required, based on the <br /> intended disposal or re-use of the water. <br /> • Additional Soil Management Protocols During Construction Activities: Soil with residual <br /> COPCs may be present on-site. Subsurface investigations planned for the Sites will <br /> determine the presence or absence of COPCs in soils. Once soils are-tested, a Site <br /> specific soil management plan (SMP)will be prepared. At the present time,there are no <br /> known chemical source areas or areas of.soil contamination on either Site. The <br /> protocols to be followed in the event that unknown areas of contamination are identified <br /> during development are described in this section. <br /> • Procedures for Discovery of Unknown Areas of Contamination: Site development <br /> activities may result in the identification of previously unknown areas or types of <br /> contamination. Unknown conditions which may trigger contingency monitoring <br /> procedures during site development include,but are not limited to,the following: <br /> o Oily,shiny,or chemical saturated soils; <br /> • o Soil with a significant chemical or hydrocarbon-like odor, or <br /> o Significantly discolored soils. 1' <br /> Upon the discovery of one of the conditions Identified above,the contractor will conduct the <br /> contingency monitoring. Contingency monitoring, If conducted, will consist of the <br /> following steps: If unknown areas of potential discolored soils are encountered, additional <br /> analyses should be conducted for the suspected constituents to assess the actual <br /> composition of the suspected contamination. A State environmental regulatory agency <br /> should be contacted for assistance in determining if additional sampling and potential <br /> mitigation is necessary. If the encountered materials are suspected to contain volatile <br /> organic chemicals,the following contingency monitoring procedures may be followed: <br /> • <br /> Conduct contingency monitoring by taking organic vapor readings using an organic vapor <br /> meter (OVM) or an organic vapor analyzer(OVA) to screen for the presence of fuel, oil, or • <br /> solvents. If the OVM/OVA indicates that an unknown area of fuel, oil, or solvents has been • <br /> detected, then a State environmental regulatory agency should be notified to determine if <br /> additional sampling is appropriate prior to continuing construction in that area. OVM or <br /> equivalent screening methods will be conducted by experienced personnel only. <br /> If an unknown area of soil contamination has been identified, and the State environmental • <br /> regulatory agency requests additional characterization,the following steps will be taken: <br /> o Soil samples will be collected from the identified area and analyzed for the likely <br /> COPC, depending on the suspected type of contamination. The sampling strategy <br /> will be discussed with a State environmental regulatory agency prior to the initiation <br /> of the sampling activities. Analytical results collected from the suspected source <br /> • will be compared to the health-based screening levels and results discussed <br /> 15 <br />