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Geotechnical Engineering Evaluation NGA File No. 1033518 Larsen Property Garage May 8,2018 Everett,Washington Page 3 At the surface of all of our hand augers within the proposed garage location,we generally encountered 2.5 to 4.2 feet of loose to medium dense dark brown to brown, silty sand with varying amounts of roots, organics, wood debris, and iron-oxide staining, which we interpreted as undocumented fill soil and/or topsoil. Underlying the fill and topsoil in all of our hand augers,we encountered medium dense to dense, gray to gray-brown, silty:sand with varying amounts of gravel:and iron-oxide staining, which we interpreted as native glacial till soils. Hand:Augers 1 through,5 were terminated within the native glacial till soils at depths in the range.of 3.0 to 4.5 feet below the existing ground surface. Hydrogeologic Conditions We encountered slight to moderate groundwater seepage in Hand Auger 1 and Hand Auger 2 at respective depths of 2.0 and 4.5 feet below the existing ground surface. We interpret this water to be perched groundwater. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of relatively low permeability materials. Perched water does not represent a regional groundwater"table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard The 2015 International Building Code (IBC) seismic design section provides a basis for seismic design. of structures. Since medium dense or better soils were generally encountered underlying the site at depth, the site conditions best fit the IBC description for Site Class D. Table 1 below provides seismic design parameters for the site that are in conformance with the 2015, IBC, which specifies a design earthquake having a 2% probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1-2015 IBC Seismic Design Parameters Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec.(g) at 1.0 sec.(g) Response Ss Si Parameters Fa Sns SDI D 1.422 0.540 1.00 .1.500 0.948 :. 0.540 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website(2008 data)for the project latitude and longitude. NELSON GEOTECHNICAL ASSOCIATES,INC.