AgdaPkt 2014-10-20 Closed and Special Joint with SA_Revised_10_17_2014

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8.A. - Page 73 Section 4: Evaluation of Environmental Impacts susceptible to liquefaction." Regional liquefaction hazard mapping indicates that a 7.2 earthquake on the Peninsula portion of the San Andreas fault or a 7.9 event anywhere on the San Andreas fault could result in moderate to high liquefaction hazard in lowland portions of the city. High to very high liquefaction susceptibility was mapped in 1998 in the tidal flat areas of Redwood City. Given the soil types underlying Redwood City and high groundwater levels at many locations, the City will continue to require liquefaction investigations for most developments in low -level areas. The Seismic Hazards Mapping Act (SHMA) requires site - specific geotechnical investigations within the Zones of Required Investigation to identify the seismic hazard and formulate mitigation measures prior to permitting developments designed for human occupancy. Several of the proposed Opportunity Sites located along the eastern portion of the city are located in areas identified by the General Plan as having the potential for liquefaction. General Plan Public Safety Element policies require that sites with potential for seismic hazards, including liquefaction, be determined prior to development and require the evaluation for potential impacts. In addition, appropriate measures that reduce the ground- shaking and liquefaction effects of earthquakes are identified in the California Building Code, including specific provisions for seismic design of structures. The project itself does not involve new construction. All future development projects will be subject to the City's standard review process for evaluation of geologic hazards. Considering implementation of existing policies and standards, impacts associated with liquefaction or other ground failure will be less than significant. a.iv) Less than Significant Impact. Landslides are mass movements of the ground that include rock falls, relatively shallow slumping and sliding of soil, and deeper rotational or transitional movement of soil or rock. In general, landslides are abundant in areas underlain by shale and siltstone bedrock materials. A few areas with historic slides and earthflows are mapped in the southwest hills of Redwood City. In addition, the Seismic Hazard Zone map completed for a portion of east central Redwood City shows a few Zones of Required Investigation due to landslides near Woodside Road and 1 -280. As discussed previously in Sections 4.6a.i through 4.6a.iii, the proposed Housing Element does not increase any risks associated with landslides, as no land use policy changes are proposed. No changes are proposed to General Plan policies in place to protect against seismic hazards. Future housing development constructed pursuant to Housing Element policy will be subject to all applicable City, state, and local building regulations, including the California Building Code (CBC) seismic standards as approved by the City Building & Safety Division. Impacts will be Tess than significant. b) Less than Significant Impact. Erosion is the condition in which the earth's surface is worn away by the action of water and wind. The project does not propose or authorize any particular housing development, infrastructure project, or other development activity or changes to land use policy associated with General Plan. Little, if any, native topsoil is likely to occur at any of the Opportunity Sites located within the heavily urbanized areas. In addition, most of the area has historically been developed. All future development projects are subject to environmental and engineering review, including assessment and mitigation of soil erosion. During construction activities of housing proposed pursuant to Housing Element policy, there is the potential to expose surficial soils to wind and water erosion during construction activities. Wind erosion is required to be minimized through soil stabilization measures required by Bay Area Air Quality Management District (BAAQMD) Rule 403 (Fugitive Dust), such as daily watering. Additionally, General Plan programs PS -24 and PS -25 require proposed projects to undergo geotechnical analysis and commit the City to implementing and updating building codes as needed. Water erosion will be prevented through the City's standard erosion control practices required pursuant to the California Building Code and the National Pollution Discharge Elimination System (NPDES), such as silt fencing or sandbags. Impacts related to soil erosion will be Tess than significant with implementation of existing regulations and General Plan policies. 17 California Department of Conservation, California Geological Survey. Information Warehouse. <http: //www. quake. ca .qov /gmaps/VVH /requlatorymaps.htm> [July 24, 2014] 18 City of Redwood City General Plan EIR. Geology and Soils. 2010. 34 Redwood City Housing Element Initial Study