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March 7, 2011 <br /> Mr. Paul Thompson/Kolbear, Inc. <br /> L&A Job No. 11-001 • <br /> Page 6 <br /> dispersion over vegetated segments. Driveway may be paved with pervious pavement to allow <br /> runoff to disperse into the ground. <br /> Seismic Hazard <br /> The Puget Sound region is in an active seismic zone. The site is underlain at shallow depth by <br /> fresh very-dense fresh glacial till soils of very-high shear strength. Therefore, it is our opinion <br /> that the potential for seismic hazards, such as landslides, liquefaction, lateral soil spreading, to <br /> occur on the site should be minimal if the erosion mitigation, drainage control, site stabilization <br /> measures recommended in this report are fully implemented. The proposed residences,however, <br /> should be designed for seismic forces induced by strong earthquakes. Based on the soil <br /> conditions encountered by the test pits, it is our opinion that Seismic Use Group I and Site Class <br /> D should be used in the seismic design of the proposed residences in accordance with the 2009 <br /> International Building Code(IBC). <br /> CONCLUSION AND RECOMMENDATIONS <br /> GENERAL <br /> The site is underlain by fresh, very-dense till and dense advance outwash soils. The proposed <br /> new residences may be supported on footing foundations poured on or into these competent soils. <br /> Based on the soil data obtained from the test pits excavated on the site, infiltration trenches may <br /> be used along the common lot line of Lots 1 and 2 for these two lots where sand deposit was <br /> encountered by test pits, and surface dispersion may be used on Lot 3 for onsite disposal of roof <br /> runoff of the new residences. As most of the site is underlain by fresh till of extremely low <br /> permeability,pervious pavement should be considered for the new joint-use driveway to disperse <br /> runoff into the ground. <br /> LIU & ASSOCIATES, INC. <br />