Reso13 PC 13-09 2859 Initial Study Mitigated Negative Declaration Kensington

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Proposed Senior Assisted Living Facility PSI Project No. 575-308-2 August 3, 2011 Page 8 To assess the liquefaction potential of the site soil, the computer program LIQUEFYPRO was used. For this analysis we used the soil profile identified within Boring B-1, a groundwater level of 12 feet and a site acceleration of 0.482g (Sps/2.5, per the CBC). The results of this analysis are presented in Appendix C and indicate that the granular soils between about 23 to 27 feet and 32 to 36 feet below grade are subject to potential liquefaction upon application of the design earthquake. Due to the relative thickness of the overlying non-liquefiable soils as compared to the thickness of the potentially liquefiable soils layers, the potential for surface manifestations resulting from soil liquefaction is considered to be low. The most significant effect of the soil liquefaction is expected to be ground surface settlement resulting from volumetric strain within the liquefiable soil layers. Based on our analysis, we estimate total liquefaction-induced and differential settlements of approximately 2-'/2 and 1-'/4 inches respectively. Based on these estimated settlements, ground modification or the use of a deep foundation system is not, in our opinion, warranted. However, the structural engineer should review these settlement estimates and assess the affects on their design. Lurchinq and Shallow Ground Rupture — Evidence of active fault rupture was not observed within the explored areas of the site at the time of our subsurface exploration and no faults are mapped as crossing the site. However, due to the active seismicity of California, this possibility cannot be completely ruled out. Landslidinq - Seismically induced landsliding is not considered a hazard on, or adjacent to the project site due to the absence of significant steep slopes in the project area. Tsunamis and Seiches - Inundation by tsunamis (seismic or "tidal waves") or seiches ("tidal waves" in confined bodies of water) are not considered to be a significant threat to the subject site due to the absence of proximal large bodies of water.