75B - PH ADOPT RESO FOR PR NO 15-6827

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L S A FAIRVIEW BRIDGE REPLACEMENT AND STREET IMPROVEMENTS (9TH STREET TO 16TH STREET( PROJECT INITIAL STUDY/MITIGATED NEGATIVE DECLARATION SANTA ANAL CALIFORNIA MAY 2020 not impede or redirect flood flows. This impact would be less than significant. No mitigation is required. d. In flood hazard, tsunami, or seiche zones, would the project risk release of pollutants due to project inundation? Less Than Significant with Mitigation Incorporated. Tsunami. Tsunamis are ocean waves generated by tectonic displacement of the sea floor associated with shallow earthquakes, sea floor landslides, rock falls, and exploding volcanic islands. Tsunamis can have wavelengths of up to 120 mi and travel as fast as 500 miles per hour (mph) across hundreds of miles of deep ocean. Upon reaching shallow coastal waters, the waves can reach up to 50 ft in height, causing great devastation to near -shore structures. The Project site is located approximately 9 mi from the Pacific Ocean shoreline and is not located within a tsunami inundation area. Therefore, the Project site is not subject to inundation from tsunamis, and there is no risk of release of pollutants due to inundation from tsunami. Seiche Zones. Seiching occurs when seismic ground shaking induces standing waves (seiches) inside water retention facilities (e.g., reservoirs and lakes). Such waves can cause retention structures to fail and flood downstream properties. Because there are no large lakes, reservoirs, or other water retention facilities in the vicinity of the Project site, the Project site is not at risk of inundation from seiche. Therefore, the Project site is not subject to inundation from seiche waves, and there is no risk of release of pollutants due to inundation from seiche. Flood Hazard. As identified above, the Santa Ana River within the Project area is designated Special Flood Hazard Area Zone A; such areas are subject to inundation by the 1 percent annual chance flood (100-year flood) with no base flood elevations determined. The remainder of the Project area (outside of the Santa Ana River) is designated as Other Areas of Flood Hazard Zone X; such areas have reduced flood risk due to levees. In the unlikely event of levee failure and flooding during a storm, there would be a risk of inundation and pollutant risk on the Project site. As discussed above in Response 3.10.2(a), during construction, there is a potential for chemicals, liquid products, petroleum products (such as paints, solvents, and fuels), and concrete -related waste to be spilled or leaked and transported via storm runoff into receiving waters. Each of these pollutants on its own or in combination with other pollutants can have a detrimental effect on water quality. However, as specified in Mitigation Measure HYDRO-1, the proposed Project would be required to comply with the requirements set forth by the CGP and SWPPP, which would specify BMPs to be implemented to target and reduce pollutants of concern on the Project site. In addition, as discussed above in Response 3.10.2(a), expected pollutants of concern during operation of the proposed Project include suspended solids/sediment, nutrients, heavy metals, pathogens (bacteria/viruses), pesticides, oil and grease, toxic organic compounds, and trash and debris. The pollutants of concern for the Project are metals and oil and grease. As required by Mitigation Measure HYDRO-3, a final WQMP would be prepared for the proposed Project that would require implementation of operational BMPs to reduce pollutants of concern in storm water runoff. With implementation of operational BMPs, no substantial additional sources of 3-62 7 6"6*ND\Final ISMND\Fairview Street Bridge Final ISMND.doC. (05/26/20)