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Geotechnical"Engineering Evaluation NGA File No. 1033518 Larsen Property Garage May 8,2018 Everett,Washington Page 4. 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 competent glacial till soils interpreted to underlie the site at depth has a low potential for liquefaction or amplification of ground motion. The competent glacial till soils interpreted to underlie the site at depth are considered stable with respect to deep-seated slope failures. However, the loose,surficial soils and undocumented fill on and near the sloping portions of the site have the potential for shallow sloughing failures during seismic events. Such events should not affect the planned site improvements provided the foundations are designed with the depths and setback distances from the sloping areas as described in this report. Erosion Hazard The criteria used for determination of erosion hazard 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, Washington, by the Soil Conservation Service (SCS) wasreviewed to determine;the erosion hazard.of the on-site soils. The site surface soilswere classified using the SCS classification system.as Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes. These soils are listed as having a moderate hazard of water erosion. The native soils should have a low.to moderate hazard for erosion in areas that are not disturbed and where the vegetation cover is not removed. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The proposed garage is situated along the toe of a moderate slope that descends. from an existing concrete rubble retaining wall to the proposed garage area at a gradient of approximately 23 degrees (42 percent). The overall height of the slope below the concrete rubble retaining wall is approximately eight feet. We did not observe evidence of significant slope instability within the immediate vicinity of the proposed garage during our investigation,such as deep-seated landsliding. We also did not observe groundwater seepage emitting from the surface of the site slopes. However, the existing concrete rubble retaining wall above appears to be in disrepair and was likely not engineered. If this wall were to fail,it could potentially impact the existing slope stability conditions below the wall and ultimately the proposed garage. The core of the slope is inferred to consist primarily of dense or better native glacial till soils. Relatively shallow sloughing failures as well as surficial erosion are natural processes and should be expected on the site slopes during extreme weather conditions. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial undocumented fill soils on the steep slope,there NELSON GEOTECHNICAL ASSOCIATES,INC.