1415 BROADWAY CM HEATING 2023-09-25

Geotechnical Engineering Evaluation NGA File No. 1213420 CM Heating Additions January 8,2021 Everett,Washington Page 3 Stratigraphy across the site was generally consistent. At the surface of each of our exploration, we encountered approximately 2.3 to 3.3 feet of dark brown to brown silty fine to medium sand with gravel and iron oxide,with various organic debris in a loose to medium dense condition that we interpreted as undocumented fill soils. Underlying the fill soils, we generally encountered gray, compact, silty fine to coarse sand and gravel, which we interpreted as native glacial till soils. Our explorations terminated within the native glacial soils at depths between 3.5 and 4.7 feet below the existing ground surface. Hydrogeologic Conditions We did not encounter groundwater seepage in any of our explorations on December 4, 2020. However, we did note the presence of iron oxidation in the upper soil horizons. We interpret any water encountered within the site 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 The 2018 International Building Code (IBC) seismic design section provides a basis for seismic design of structures.Since medium dense/medium stiff or better glacial soils were 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 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 Sl Parameters(g) Fa Fv Sos SD1 • D 1.273 0.484 1.000 1.516 0.849 0.489 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.