10901 27TH AVE SE Geotech Report 2025-07-29

I 1 Subsurface Exploration, Geologic Hazards, and Proposed James Monroe Elementary School Replacement Revised Geotechnical Engineering Report Everett, Washington Geologic Hazards and Mitigations ' II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on 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 Existing slopes on the northwest, southeast, and southwest parts of the site appear to have been created at least in part by previous site grading. Our explorations suggest that these slopes are composed primarily of dense lodgement till sediments. In light of the geometry and subsurface conditions of the existing site slopes, the site appears to have a low risk of substantial slope ' failures. No quantitative slope stability analysis was completed as part of this study, and none is warranted, in our opinion. The existing site slopes do not meet the City of Everett definition for Landslide Hazard Areas as defined in Everett Municipal Code Title 19, Chapter 37.080. 1 6.0 SEISMIC HAZARDS AND MITIGATIONS ' The following discussion is a general assessment of seismic hazards that is intended to be useful to the District in terms of understanding seismic issues, and to the structural engineer for structural design. In our opinion, the site does not include areas that meet the City of Everett definition for Seismic/Liquefaction Hazard Areas as defined in Everett Municipal Code Title 19, Chapter 37.080. ' Earthquakes occur regularly in the Puget Lowland. The majority of these events are small, and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 2001, 6.8-magnitude event; and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this region during recorded • history and was centered in the Olympia area. Evaluation of earthquake return rates indicates ' that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact_the proposed ' project is discussed below. 1 ' October 5, 2009 ASSOCIATED EARTH SCIENCES, INC. BWG/Id-KE090312A3-Projects1200903121KE1WP Page 6