330 ELM ST VIEW RIDGE ESTATES 2022-04-04

a Geotechnical Engineering Evaluation NGA File No. 1085419 View Ridge Estates 330 Building Settlement March 22,2019 Everett,Washington Page 4 to medium sand with silt and gravel, which we interpreted as native outwash soils. Hand Augers 3 and 4 terminated at respective depths of 4.5 and 3.0 feet below the existing ground surface. Hydrogeologic Conditions We encountered varying degrees of groundwater seepage zones within our borings and hand auger explorations at depths in the range of 3.0 to 25.0 feet below the existing ground surface. We interpret the groundwater observed as 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 We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project. Since competent glacial soils are inferred to underlie the site at depth,the site conditions best fit the IBC description for Site Class D. The following Table 1 provides seismic design parameters for the site that are in conformance with the 2018 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 —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 1.391 0.528 1.000 1.500 0.927 0.528 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program P p q off' Interpolated Probabilistic Ground Motion website(2008 data)for the project latitude and longitude. 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. ein NELSON GEOTECHNICAL ASSOCIATES, INC.