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7.3.B. - Page 64 <br /> The geotechnical report (p. 6) concludes, "[SJite development is feasible from a geotechnical standpoint," with <br /> solutions focused on the following geotechnical concerns: <br /> • potential presence of highly expansive near - surface clay <br /> • relatively shallow groundwater table (with a design groundwater level of 7 % ftet below the ground surface) <br /> • potential for liquefaction and liquefaction - induced settlement to occur on -site during a moderate to major <br /> earthquake <br /> The geotechnical report recommends feasible solutions to the identified issues and concerns. The report (p. 8) <br /> clearly emphasizes that its "conclusions and recommendations should not be used to develop final plans or <br /> drawings. A detailed investigation should include additional site exploration. The Feld exploration results from the <br /> final geotechnical investigation should be used to provide conclusions and recommendations regarding the <br /> geotechnical aspects of site development. " This conclusion is consistent with both the California Building Code <br /> (CBC) and the DTPP program EIR (Chapter 16, Geology and Soils). The final geotechnical report prepared for the <br /> proposed project would be subject to City review and approval, as would subsequent detailed grading and <br /> foundation plans. Also, the City would observe on -site construction work. <br /> iii) Liquefaction is a process whereby strong ground shaking causes loose, saturated, unconsolidated sediments to <br /> lose strength and behave as a fluid. The site - specific geotechnical report prepared for the project (see item ii <br /> above) addresses liquefaction potential and concludes that the project site is subject to liquefaction. Also, the site is <br /> identified on the California Geological Survey Seismic Hazard Zones map (2006) as in an area considered <br /> susceptible to liquefaction. The result could be that, "during a major earthquake, up to about 2/3 inch of <br /> liquefaction - induced settlement will occur.... The potentially liquefiable deposits are relatively deep and relatively <br /> thin. Therefore, ... the potential for surface manifestations of the liquefaction [will] be low" (Treadwell & Rollo, p. <br /> 5). The geotechnical report recommends solutions for minimizing foundation settlement, including the drilling of <br /> piers and /or removal of very highly expansive soil and replacement with less - expansive soil. <br /> iv) There is an approximate 15-foot grade change where the project site meets City-owned property on Jefferson <br /> Avenue, near the undercrossing at the Caltrain tracks. The grade change is partly sloped and partly retained by a <br /> low retaining wall (Treadwell & Rollo, p. 2; also Plan Sheet A -0.3). No project construction would occur on this <br /> City property, but the project's potential geotechnical effects on this property shall be evaluated as part of the final <br /> geotechnical investigation. <br /> In conclusion, the Downtown Precise Plan program EIR concluded that while the DTPP area could be subject to <br /> moderate to high susceptibility to ground shaking and liquefaction, the City's routine grading and building permit <br /> regulations provide reasonable assurances that the project will incorporate the design and engineering refinements <br /> necessary to reduce the impact of DTPP facilitated development to a less - than - significant level, requiring no <br /> additional mitigation. The site - specific, final geotechnical report to be prepared for the proposed project is subject <br /> to City review and approval, consistent with the California Building Code (CBC) and the DTPP program EIR. <br /> b. The project shall be subject to Downtown Precise Plan program EIR Mitigation 16 -3, which shall be required as a <br /> condition of project approval. The mitigation requires the applicant to prepare an erosion control plan subject to <br /> City approval and consistent with the required San Mateo County Stormwater Pollution Prevention Plan (SWPPP) <br /> Best Management Practices. The plan shall be implemented during construction and would reduce the potentially <br /> significant impact on soil erosion and sedimentation to a less -than - significant level. <br /> c. No changes to geologic substructures are expected to occur as a result of project implementation. As described in <br /> item (a) above, the proposed project would comply with all local and State codes and regulations, and project <br /> design would incorporate City- approved geotechnical recommendations for site development. Therefore, this <br /> impact is considered less than significant. All grading plans are subject to City review and approval. <br /> d. The Downtown Precise Plan program EIR (p. 16 -6) determined that development within the DTPP area may be <br /> subjected to hazards from expansive soils, representing a potentially significant impact. Mitigation 16 -1 requires <br /> that the final geotechnical report required by the City Building Official include an analysis of expansive soil hazards <br /> and recommended stabilization measures. Implementation of these measures, combined with conformance with <br /> standard California Building Code (CBC) and other applicable State and local regulations (all of which would be <br /> required as conditions of approval for the project) would reduce the potential effects of expansive soils to a less - <br /> than- significant level. The preliminary geotechnical report prepared for the project (Treadwell & Rollo, p. 6) <br /> recommends solutions for expansive soils, such as deepening foundations and providing non - expansive soil below <br /> the floor slab. <br /> 2 Highly expansive soil undergoes large volume changes with changes in moisture content (Treadwell & Rollo, p. 3) <br /> 15 <br />