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COBALT <br /> GEOTECHNICAL INVESTIGATION GEOSCIENCES <br /> EVERETT, WASHINGTON <br /> December 3,2019 <br /> 6.o Geologic Hazards <br /> 6.1 Erosion Hazard <br /> The Natural Resources Conservation Services(NRCS)maps for Snohomish County indicate that the site is <br /> underlain by Alderwood-Urban land complex (2 to 8 percent slopes). These soils would have a slight to <br /> severe erosion potential in a disturbed state,depending on the slope magnitude. <br /> It is our opinion that soil erosion potential at this project site can be reduced through landscaping and <br /> surface water runoff control. Typically erosion of exposed soils will be most noticeable during periods of <br /> rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt <br /> fences,hay bales,mulching,control ditches and diversion trenches. The typical wet weather season,with <br /> regard to site grading,is from October 31st to April ist. Erosion control measures should be in place before <br /> the onset of wet weather. <br /> 6.2 Seismic Hazard <br /> The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015 <br /> International Building Code(2015 IBC). A Site Class D applies to an overall profile consisting of dense to <br /> very dense soils within the upper too feet. <br /> We referenced the U.S. Geological Survey(USGS).Earthquake Hazards Program Website to obtain values <br /> for Ss,Si,Fa,and F. The USGS website includes the most updated published data on seismic conditions. <br /> The site specific seismic design parameters and adjusted maximum spectral response acceleration <br /> parameters are as follows: <br /> PGA (Peak Ground Acceleration,in percent of g) <br /> Ss 144.50%of g <br /> S, 56.0o%of g <br /> FA 1.00 <br /> Fv 1.5o <br /> Additional seismic considerations include liquefaction potential and amplification of ground motions by <br /> soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. <br /> The relatively dense soil deposits that underlie the site have a low liquefaction potential. <br /> 7.o DISCUSSION <br /> 7.1.i General <br /> The site is underlain by weathered and unweathered glacial till. The proposed residential buildings may <br /> be supported on shallow foundation systems bearing on medium dense or firmer native soils and/or <br /> structural fill placed on suitable native soils. Local overexcavation of fill and/or loose soils may be <br /> necessary below proposed foundation elements. <br /> 3 <br /> PO Box 82243 <br /> Kenmore,WA 98028 <br /> cobaltgeola grnail.com <br /> 206-331-1097 <br />