4800 DOGWOOD DR Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazards, View Ridge Community Church Addition and Geotechnical Engineering Report Everett, Washington Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on review of the EMC and the geologic, slope, and ground and surface water conditions, as observed and discussed herein. The discussion will be limited to slope stability, seismic, and erosion issues. 5.0 SLOPE HAZARDS AND MITIGATIONS The site is characterized by a relatively flat topography with a steep slope area along the west side of the site underlain by loose to medium dense existing fill and native glacial soils. Based on the topographic survey provided to us, the steep slope area directly west of the proposed addition ranged between approximately 30 to 40 percent. Observations were made of the slopes during our subsurface exploration. The trunks of the observed trees on the slopes generally appeared to be straight and vertical, with no significant bowing. No tension cracks, hummocky topography, or other indications of slope instability were observed on the slopes. The existing slopes did not exhibit visual indications of slope instability or erosion. We noted seepage about 3 to 4 feet above the creek level on the slope in several areas. EMC defines a medium risk landslide hazard area as slopes with less than 15 percent for transitional beds, Whidbey Formation, landslide deposits and uncontrolled fill, or between 25 and 40 percent for other soils; when combined with springs or seeps, immature and/or no vegetation. In our opinion based on the EMC definition and our site observations the slope at the site would be classified as a medium risk landslide hazard area. 5.1 Slope Stability The topography of the site generally slopes down toward the west and southwest. Review of a topographic map of the site indicates that slope inclinations on the property range from approximately 30 to 40 percent. The height of the steep slope area ranges from approximately 8 to 18 feet. The proposed addition would be approximately 25 to 35 feet from the top of the steep slope area. During our reconnaissance of the property, no indications of historical landslide activity were observed, such as slide scarps, reversed slope benches, tension cracks, or unusually distorted tree trunks. An analysis of the static and seismic stability of the steep slope on the subject site was conducted using the computer program Slope/W 2007, version 7.23 by GeoSlope International. The program used the Morgenstern -Price method for evaluating a rotational failure. Input August 29, 2016 ASSOCIATED EARTH SCIENCES, INC. SKL11d - KE160351A2 - Projects J20160351 JKE�WP Page 5