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8.A. - Page 38 <br />Finding: Implementation of Mitigation Measure Geology -1 would reduce impacts from <br />differential settling to a less than significant level. <br />Facts in Support of Finding: Implementation of Mitigation Measure Geology -1 would reduce <br />impacts from differential settling caused by strong ground shaking by requiring <br />implementation of the recommendations included in the geotechnical feasibility <br />documents prepared for the project to ensure the safety and stability of the <br />structures. Impact 3.5-1 and proposed mitigation are described on Draft EIR <br />pages 3.5-10 through 3.5-12, and Revised Final EIR pages 4-17 through 4-19, <br />which are hereby incorporated by reference. <br />Impact 3.5-2 <br />Impact: Excavation and backfilling for various roadway, utility, and drainage <br />improvements along Laurel Way would have the potential to result in soil creep <br />and slope instability. <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 down <br />to native soil and replaced as compacted engineered fill, unless the <br />structures are supported on drilled pier foundations, which derive support <br />from the underlying native soils and bedrock. <br />c) All drilled pier foundations shall be designed for soil creep pressures. <br />d) Permanent drainage measures shall be installed on all lots to intercept <br />surface water infiltration and migrating subsurface water and thus reduce the <br />likelihood of soils becoming wet and unstable. <br />e) Drilled pier foundations shall be used for houses on sloping lots. <br />f) Detailed foundation explorations shall be performed for each lot during the <br />design -level geotechnical investigation to collect site-specific data regarding <br />slope creep, expansive soils, and serpentinite rock. <br />g) Garage slabs on grade, driveways, walkways, sidewalks, and pavers shall <br />have sufficient reinforcement and be supported on a layer of non -expansive <br />fill. <br />h) All residences, retaining walls, and bio -retention basins shall be supported <br />on drilled, cast -in-place, straight -shaft friction piers or similar construction. <br />Consideration shall be given on a case-by-case basis to the need for extra <br />steel reinforcement of the piers and grade beams, voids beneath grade beams <br />to mitigate uplift distress to the structures, perimeter subdrains and moisture <br />22 <br />