3610 W MUKILTEO BLVD Geotech Report 2022-10-25

Geotechnical Engineering Evaluation NGA File No. 1129119 Zahler Residence Development October 14,2019 Everett,Washington Page 4 Table 1 —2018 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 F,, SDS SDI D 1.458 0.559 1.000 1.500 0.972 0.559 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. The site is located within the South Whidbey Island Fault Zone (SWIFZ): an active, shallow region of seismicity within central Puget Sound stretching from the Strait of Juan de Fuca to North Bend. Information published in 2013 by the Washington State Department of Natural Resources suggests the SWIFZ last ruptured less than 2,700 years ago, and that the fault zone can produce a M7.5 earthquake. In our opinion,the possibility of faulting ground rupture caused by this fault zone is considered low. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the medium dense or better glacial deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types,which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area,Washington,by the Natural Resources Conservation Service(NRCS) was reviewed to determine the erosion hazard of the on-site soils. The surface soils for this site were mapped as Alderwood gravelly sandy loam, 15 to 30 percent slopes. The erosion hazard for this material is listed as moderate to severe. However, this site is relatively level to gently sloping and there are no steep slopes on the property. It is our opinion that the erosion hazard for site soils should be low to moderate in areas where the site is not disturbed. NELSON GEOTECHNICAL ASSOCIATES, INC.