Reso PC16-23 PC 0116 Reso CEQA - Sandpiper

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Section 4.0—EnWronmental Setting and Discussion ofhnpacts 4.6.1.2 On Site Geologic Conditions Soils and Topography The project site is located on land reclaimed from the San Francisco Bay. The site is flat and consists of five to eight feet of engineered fill soils placed on the native bay mud materials. The fill soils that blanket the site have a relatively low expansion potential. Soil borings and cone penetration tests (CPTs) completed at the project site encountered groundwater at depths ranging from 4.5 to seven feet below the ground surface (bgs). This places the groundwater level at sea level, which is expected for areas located adjacent to San Francisco Bay, The locations of the soil borings and the CPTs completed at the project site are shown in Figure 4.6-1. 4.6.1.3 Seismicity and Seismic Hazards The San Francisco Bay Area is one of the most seismically active regions in the US. An earthquake of moderate to high magnitude generated within the San Francisco Bay region could cause considerable ground shaking at the project site. The degree of shaking is dependent on the magnitude of the event, the distance to its zone of rupture, and local geologic conditions. The three major faults in the region are the San Andreas Fault, Hayward Fault, and Calaveras Fault, which are located approximately 10 miles southwest, 20 miles northeast, and 32 miles northeast of the project site, respectively. The smaller Monte -Vista Shannon and San Gregorio faults are also located near the project site, approximately nine miles southeast and 22 miles southwest of the site, respectively. The project site is not Iocated within an Alquist-Priolo Earthquake Fault Zone. 14 Liquefaction Liquefaction is the result of seismic activity and is characterized as the transformation of loose, water -saturated soils from a solid state to a liquid state after ground shaking. Liquefaction can result in differential settlement and/or lateral spreading. There are many variables that contribute to liquefaction, including the age of the soil, soil type, soil cohesion, soil density, and ground water level. The project site is located in an area designated by the Association of Bay Area Governments (ABAG) as having a moderate potential for liquefaction. Soil borings and CPTs completed at the project site did not encounter soils that are highly susceptible to liquefaction. The only potentially liquefiable soil layer was encountered at a depth of 48 feet in CPT -1. Based on the liquefaction analysis that was prepared for the site, the potential for liquefaction at the site is low. Differential Settlement Differential settlement is the unequal settlement of material that causes a gradual, uneven downward movement of a structure's foundation. Differential settlement can be induced by liquefaction. Because the potential for liquefaction at the project site is low, the potential for liquefaction -induced is Association of Bay Area Governments. "Resilience Program: San Mateo County Earthquake Hazard." Accessed April 19, 2016. Available at: httn://resilience.abae.ca.sov/earthouakes/sanmateo/. City of Redwood City 39 Initial Study/Mitigated Negative Declaration Sandpiper Elementary School Facilities Expansion November 2016