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8.A. - Page 42 <br />and Revised Final EIR pages 4-17 through 4-20, which are hereby incorporated <br />by reference. <br />Impact 3.5-3 <br />Impact: Project components would have the potential to be located on expansive soil, or <br />result in subsidence or collapse from settling of loosely consolidated soils, which <br />would create substantial risks to life or property. <br />Mitigation: Mitigation Measure Geology -1: All recommendations in the TRC Lowney <br />(2007), Cornerstone Earth Group (2008), and Treadwell & Rollo (2008a and <br />2008b) geotechnical feasibility documents, included in Appendix E, shall be <br />implemented. These measures include the following: <br />a) All undocumented fills beneath pavement, driveway, or other hard- <br />scape areas shall be removed down to native soil and replaced with <br />compacted engineered fill. <br />b) All undocumented fills beneath proposed structures shall be removed <br />down to native soil and replaced as compacted engineered fill, unless <br />the structures are supported on drilled pier foundations, which derive <br />support from the underlying native soils and bedrock. <br />c) All drilled pier foundations shall be designed for soil creep <br />pressures. <br />d) Permanent drainage measures shall be installed on all lots to <br />intercept surface water infiltration and migrating subsurface water <br />and thus reduce the likelihood of soils becoming wet and unstable. <br />e) Drilled pier foundations shall be used for houses on sloping lots. <br />fl Detailed foundation explorations shall be performed for each lot <br />during the design -level geotechnical investigation to collect site- <br />specific data regarding slope creep, expansive soils, and serpentinite <br />rock. <br />g) Garage slabs on grade, driveways, walkways, sidewalks, and pavers <br />shall have sufficient reinforcement and be supported on a layer of <br />non -expansive fill. <br />h) All residences, retaining walls, and bio -retention basins shall be <br />supported on drilled, cast -in-place, straight -shaft friction piers or <br />similar construction. Consideration shall be given on a case-by-case <br />basis to the need for extra steel reinforcement of the piers and grade <br />beams, voids beneath grade beams to mitigate uplift distress to the <br />structures, perimeter subdrains and moisture barriers, and <br />construction precautions for concrete over -pours at the tops of the <br />drilled piers. <br />i M Proper detailing of construction and control joints for concrete slabs <br />shall be considered in the final design of sidewalks and patios in <br />areas of expansive soils. For example, a construction joint with rebar <br />dowels may be provided when concrete slabs on grade meet the <br />26 <br />