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Geotechnical Engineering Evaluation and Engineering Geologic Assessment - REVISED NGA File No. 1300621 Sharp Residential Remodel October 12, 2021 Everett, Washington Page 4 Hydrogeologic Conditions Groundwater seepage was not encountered in our explorations. If groundwater were to be encountered during construction, we would interpret it to be perched water. Perched water conditions may occur on the site during periods of wet weather. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of underlying, less permeable 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 water to fluctuate seasonally. Erosion Hazard The City of Everett designates erosion hazards based on maps published in 2006 based on a methodology from 1991. The site is not mapped as an 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. The Soil Survey of Snohomish County Area, Washington, by the Natural Resources Conservation Service (NRCS), classifies the site as Alderwood gravelly sandy loam, 15 to 30 percent slopes. The erosion hazard rating for the mapped soils is not listed. Based on our experience in the area and our observations in the field, it is our opinion that the site would have a slight erosion hazard for areas where the soils are exposed. It is our opinion that the erosion hazard for site soils should be low in areas where vegetation is not disturbed. Landslide Hazard The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The City of Everett designates Landslide Hazard Areas in the Everett Municipal Code (EMC) Section 19.37.080 (A) (1). Although maps published in 2006 by the City suggest a 'medium' landslide hazard based on a 1991 inventory, the site does not include steep slopes greater than 25 percent, and is not characterized by the customary definition of the 'Transitional Beds' with shallower slopes greater than 15 percent. Furthermore, the site does not appear to show evidence of movement during the Holocene epoch, is not potentially unstable due to rapid stream incision, is not a historic failure, does not have vertical relief of greater than 15 feet, and is not at risk of landslide due to presently -understood seismic or erosion hazards. In our opinion, the site itself contains no steep slopes or landslide hazards. NELSON GEOTECHNICAL ASSOCIATES, INC.