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 3 The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 4. The logs of our test pits are attached to this report and are presented as Figures 5 and 6. We present a brief summary of the subsurface conditions in the following paragraphs. For a detailed description of the subsurface conditions,the logs of the test pits should be reviewed. At the surface of Infiltration Pit 1 and Test Pits 1 through 5 we generally encountered approximately 2.0 to 2.6 feet of dark to light brown, silty sand with varying amounts of roots, organics, gravel,and debris in a loose to medium dense condition, which we interpreted as undocumented fill soils: Underlying the undocumented fill soils we typically encountered gray to gray-brown, silty fine sand with varying amounts of silt, gravel, and iron-oxide staining in a medium dense or better condition, which we interpreted as competent native glacial deposits. Infiltration Pit 1 and Test Pits 1 through 5 terminated at respective depths of 4.0,6.0, 8.0,7.0,9.0, and 7.0 feet below the existing ground surface. Hydrogeologic Conditions We did not encounter groundwater within our explorations. If groundwater is encountered during construction we would interpret the water to perched groundwater. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of relatively low permeability materials. The more permeable soils consist of the topsoil/weathered soils and undocumented fill. The low permeability soil consists of relatively silty glacial soils. 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 transitional bed soils are inferred to underlie 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 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. NELSON GEOTECHNICAL ASSOCIATES, INC,