9620 19TH AVE SE Geotech Report 2024-03-28

Pacific Ridge — DRH, LLC ES-7829.01 August 26, 2021 Page 4 Geologic Hazard Areas Assessment As part of this geotechnical engineering study, the geologically hazardous areas section of the Everett Municipal Code (EMC) chapter 19 was reviewed. Per the EMC requirements, the following topics related to development plans and site conditions are addressed. Erosion Hazard Areas With respect to erosion hazard areas, section 19.04.110 of the EMC defines erosion hazards as "[t]hose areas of the city with slopes of twenty-five percent and greater in Qva and Qal geologic units; exposed slopes of greater than twenty-five percent in other geologic units; and drainage areas which receive stormwater discharge." The near surface on-site soils are generally consistent with Alderwood-urban land complex series soils (about 15 to 40 percent slopes). Based on the EMC definition, exposed slopes within the site sloped at 25 percent or greater would be considered erosion hazard areas. Best management practices in accordance with the EMC should be used for site design and development. At a minimum, silt fencing should be placed along the development envelope and soil stockpiles should be covered when not in use. Measures to control surface water during construction, such as swales, check dams, and sediment ponds, should be utilized as deemed necessary. Construction entrances should be surfaced with quarry spalls to minimize off-site tracking of silt and soil generated during site construction. Provided typical site development BMPs are incorporated into the design and construction of the proposed project, it is our opinion the erosion hazard for the project can be considered low. Landslide Hazard Areas With respect to landslide hazard areas, section 19.37.080 of the EMC defines landslide hazard areas as areas potentially subject to landslides based on a combination of geologic, topographic, and hydrologic factors. Within the city of Everett, landslide hazard areas specifically include: • Very high/severe: Slopes greater than 15 percent in the Qtb, Qw, and Qls geologic units; slopes greater than 15 percent with uncontrolled fill. • High: Slopes greater than 40 percent in all other geologic units (not Qtb, Qw, and Qls or uncontrolled fill). • Medium risk: (1) slopes less than 15 percent for Qtb, Qw, and Qls geologic units and uncontrolled fill. (2) Slopes of 25 percent to 40 percent in all other geologic units. Based on site observations and review of available topographic data, the majority of the subject site would not be classified as a landslide hazard area. However, the west-descending fill slope would classify as a very high/severe risk landslide hazard area, as defined above, based on gradients greater than 15 percent and the presence of undocumented fill; if there are records of the placement and compaction of the fill along the west-descending slope, the slope would classify as a high-risk landslide hazard area. Earth Solutions NW, LLC