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Geotechnical Engineering Evaluation NGA File No. 1322621 Clark Garage Slope February 4,2022 Everett,Washington Page 4 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. 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 dense glacial outwash deposits interpreted to underlie the sloping and proposed development areas on the site have a low potential for liquefaction or amplification of ground motion and generally do not meet the definition of a seismic hazard area. The competent glacial soils interpreted to form the core of the site slope are considered stable with respect to deep-seated slope failures. However, the loose surficial soils and undocumented fill may have the potential for shallow sloughing failures during seismic events. 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. Natural Resources Conservation Service (NRCS) data was reviewed. The site is mapped as Alderwood-Urban land complex, 8 to 15 percent slopes. The erosion hazard for this property is not listed. Based on our experience in the area we would anticipate erosion hazards for these soils to be low to moderate in areas were vegetation is not disturbed. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. ,the site forms a relatively level terrace on an otherwise gentle-to moderate east-facing slope but includes moderate- to steep east-facing slopes on the northeastern most corner, which descend eastward toward the neighboring properties at gradients in the range of 1 to 31 degrees (1.75 to 60 percent) as shown on Cross-Section A-A' in Figure 3.We did not observe significant evidence of past deep- seated slope instability along the subject slope during our site visit. We also did not observe any indications of seepage emitting from site slopes or recent sloughing within the upper portions of the slope. Snohomish county has mapped this site a containing slopes greater than 33 percent. Snohomish County Code (SCC) 30.91L.04 defines a landslide hazard area as follows: NELSON GEOTECHNICAL ASSOCIATES, INC.