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7.A. - Page 212 Pete's Harbor c;ity ot Hedwood C:ity EIR Addendum October 8,2012 Page 3-49 3.8 SOILS AND GEOLOGY The relationships of the current Pete's Harbor project to the previously certified 2003 EIR soils and geology impact and mitigation conclusions are described below. Impact 11-1 Analysis: Geotechnical Hazards Associated with Project Grading. The certified 2003 EIR concluded that, based on the applicant's preliminary geotechnical investigation, the interaction of existing geotechnical conditions with the project proposed grading, dredging, and surface modifications could result in significant geotechnical impacts associated with surface settlement, seismic hazards, and/or soil erosion. The associated 2003 EIR mitigation required the project applicant to have detailed, design-level geotechnical investigations professionally prepared for each project structure. Topics addressed in the investigations would include, among others, strength parameters for foundation design, perimeter slope stability, soil corrosivity potential, and characteristics of the underlying Bay mud. All geotechnical recommendations resulting from the investigations would be subject to review and approval by an independent engineering geologist or geotechnical engineer retained by the City Engineer at applicant expense. The current Pete's Harbor project, although smaller, would still result in similar potentially significant geotechnical hazards associated with project grading and surface modifications (the current project would not include dredging). Conclusion. Modified impact and mitigation. References to dredging have been removed from the impact and mitigation because the current project would not involve dredging. Otherwise, the mitigation identified in the 2003 EIR for Impact 11-1 remains applicable to the current Pete's Harbor project and remains sufficient to reduce this impact to a less-than-significant level. Impact 11-2 Analysis: Total and Differential Settlement. The project site is located atop weak, compressible Bay mud. Both the previous project and the current project would introduce structural loads too great to be supported on conventional shallow foundations over Bay mud, potentially resulting in excessive total and differential settlements. Associated mitigation details, involving common engineered solutions for such projects atop Bay mud, would be included in the detailed, design-level geotechnical investigations required for both the previous project and the current project (see Impact 11-1 above), including analyses of all fill material. The previous Marina Shores Village project would require building foundations supported on piles driven approximately 95 feet or greater in depth (based on the depth to bedrock). However, the applicant has concluded that any piles required for the current Pete's Harbor project would be auger cast and not driven. Conclusion. Modified impact and mitigation. References to dredging, pile driving (auger cast piles could be necessary), and reconfigured marinas have been removed from the impact and mitigation because the current project would not involve these activities. Otherwise, the mitigation identified in the 2003 EIR for Impact 11-2 remains applicable to the current Pete's Harbor project and remains sufficient to reduce this impact to a less-than-significant level. Impact 11-3 Analysis: Ground Shaking/Liquefaction. Both the previous project and the current project would place new residences in a subregion that is expected to experience severe earthquake-induced ground shaking during the life of the project, potentially resulting in T:1106951Addenduml3(10695-01).doc