20A - AA FIRST ST BRIDGE REPLACEMENT PROJECT

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LSA ASSOCIATES, INC. INITIAL STUDY/MITIGATED NEGATIVE DECLARATION JULY 2010 FIRST STREET BRIDGE REPLACEMENT PROJECT CITY OF SANTA ANA standards. Project impacts related to seismic ground shaking would be less than significant and no mitigation is required. 3. Seismic-related ground failure, including liquefaction? Less than significant impact. According to the California Geological Survey Seismic Hazard Zonation Program,' the project area is in a potential liquefaction zone. The City of Santa Ana General Plan also shows that the project site is located in the area of high to very high liquefaction zone. Because the proposed bridge is located over Santa Ana River and extends 300 ft west and east from the bridge the liquefaction potential is a function of the alluvial soil characteristics on site. The bridge construction and First Street widening will be consistent with the City's Building Code and the California Standard Building Code. Therefore, the project construction is not expected to create additional potential liquefaction risk. The potential risk associated with the new bridge construction and street widening may actually decrease the potential for seismic-related failure because the proposed bridge would comply with existing seismic design criteria. Due to compliance with modern building practices, project impacts related to liquefaction would be less than significant and no mitigation is required. 4. Landslides? No impact. According to the California Geological Survey Seismic Hazard Zonation Program, project site is not located in the earthquake induced landslide zone. The site is already developed and the replacement of the bridge and street widening will not create additional structures that could expose people to landslides, mudslides, or elevated erosion on or off site. No impacts are anticipated, and no mitigation is required. B. Would the project result in substantial soil erosion or the loss of topsoil? Less than significant impact with mitigation. During construction activities, soil would be exposed and there would be an increased potential for soil erosion compared to existing conditions. Construction would occur in an already built-out area, which was previously graded and compacted. Construction activities would result in minor excavation occurring mostly in the channelized Santa Ana River and are not anticipated to expose substantial areas of soil to additional erosion impacts. The disturbed soil area during construction of the proposed project would be approximately 0.33 ac. Erosion impacts would be minimized through implementation of Erosion and Sediment Control Best Management Practices (BMPs). As specified in Mitigation Measure WQ-1, presented later in Section VIII, Hydrology and Water Quality, an Erosion Control Plan would be prepared for the proposed project and would specify the specific BMPs, such as sand bags, to be implemented during construction. The Erosion Control Plan would ensure the implementation and maintenance of BMPs to reduce or eliminate sediment in storm water. With implementation of Erosion and Sediment Control BMPs, as specified in Mitigation Measure WQ-1, impacts related to soil erosion during construction would be reduced to below a level of significance. ' California Division of Land Resource Protection, http://www.conservation.ca.gov/cgs/shzp/, 2007-08-10. 07/25/10 «PADMJ070l\MND\4.0 Environmental Analysis.doc» 4-16 20A-67