4600 BAKER DR Geotech Report 2025-03-03

January 12,2021 Page 4 of 7 Limited Geologic Evaluation g. Any area with a slope of forty percent or steeper and with a vertical relief of fifteen or more feet, except those manmade slopes created under the design and inspection of a geotechnical professional,or slopes composed of consolidated rock. Present in steep slope areas on site. h. Areas that are at risk of landslide due to high seismic hazard. i. Areas that are at risk of landslides or mass movement due to severe erosion hazards. 3. Erosion hazard areas: a. Those areas defined as high and very high/severe risk of erosion in the Dames and Moore Methodology for the Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett,Washington:July 1,1991,or as revised through best available science: (1) High erosion hazard areas include slopes of twenty-five to forty percent in Qva and Qal geologic units;and slopes of greater than forty percent in other(not Qva or Qal)geologic units. Present on steep slope areas in units Qtb and Qw. (2) Very high/severe erosion hazard areas include slopes of greater than forty percent in Qva and Qal geologic units. b. Those areas defined as medium risk of erosion in the Dames and Moore Methodology for the Inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, 1991, or as revised through best available science, when they contain debris and mud flows,gullying or rifling,immature vegetation,or no vegetation: (i) Slopes of twenty-five to forty percent in other(not Qva or Qal)geologic units. 4. Other areas which the city has reason to believe are geologically hazardous. The NRCS maps indicate that the site is underlain by Alderwood gravelly sandy loam (25 to 70 percent slopes). In general, the erosion potential at the site varies from low to very high depending on the slope magnitudes. The areas with slope magnitudes greater than about 25 percent have severe to very severe erosion potential when exposed. Provided proper erosion control measures are implemented until final landscaping is in place,the erosion potential can be maintained at a very low level. These include keeping all exposed soils covered when work is not taking place,providing silt fences around the low side of all work areas, and utilizing other systems as needed based on specific conditions. The area of the small addition and deck are nearly level and have an existing low'erosion potential. B. Geologically Hazardous Slope Setbacks and Slope Protection. 1. Geotechnical Assessment Requirements. Development proposals on or within two hundred feet of any area designated as or which, based on site-specific field investigation, the city has reason to believe are geologically hazardous areas shall submit a geological assessment as required by subsection F of this section. 2. The setback buffer requirement shall be based upon information contained in a geological assessment, and shall be measured on a horizontal plane from a vertical line established at the edge of the geologically hazardous area limits (both from the top and toe of slope). In the event that a specific setback buffer is not included in the recommendation of the geological assessment, the setback buffer shall be based upon the standards contained in Chapter 19.18 of the International Building Code(IBC),or as the IBC is updated and amended. www.cobaltgeo.com (206)331-1097