4730 COLBY AVE SEPA 016 - 027 - YMCA Geotech Report 2025-04-14

October 25, 2015 YMCA - Everett L&A Job No. 15-089 Page 7 systems connected to roof downspouts and catch basins installed in paved areas. Water collected into these drain line systems should be tightlined to discharge into a storm sewer or suitable stormwater disposal facilities, such as infiltration trenches or galleries. Areas devoid of vegetation cover from construction activities should be seeded and re-vegetated. Seeded and re-vegetated areas should be covered with clear plastic sheets until vegetation is fully established. Seismic Hazard The Puget Sound region is in an active seismic zone. The site is mostly gently sloped and is underlain at shallow depth by a dense advanced outwash deposit of high shear strength. Therefore, the potential for seismic hazards, such as landslides, liquefaction, lateral soil spreading, to occur on the site should be minimal if the erosion mitigation, drainage control, site stabilization measures recommended in this report are fully implemented. The proposed multi-use building should be designed for seismic forces induced by strong earthquakes. Based on the soil conditions encountered by the test pits, it is our opinion that Seismic Use Group I and Site Class D should be used in the seismic design of the proposed residence in accordance with the 2012 International Building Code (IBC). DISCUSSION AND RECOMMENDATIONS GENERAL The multi-use building may be supported on footing foundations constructed on adequately and properly prepared subgrade soil per recommendations in the BUILDING FOUNDATION sections below. The advance outwash deposit is also of moderately high permeability and it is feasible to dispose stormwater onsite with infiltration LIU & ASSOCIATES, INC.