1815 HOLBROOK AVE Geotech Report 2025-03-06

June 9,2022 Page 4 of 15 Geotechnical Evaluation The areas highlighted in yellow are present within the eastern portion of the property. These include areas with slope magnitudes in excess of 4o percent and appear to be underlain by Vashon Advance Outwash. We did not observe evidence of historic or recent landslide activity or severe erosion on the subject or adjacent properties. 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. (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. In general, the erosion potential at the site varies from low to very high depending on the slope magnitudes. Severe erosion potentials generally include areas with slopes of is percent or more in outwash soils. The eastern portion of the site would have a very high erosion potential; however,typical erosion control measures and proper grading should adequately manage erosion during construction. Proper final grading and surfacing should result in a decrease in the erosion potential in these areas. 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. a. If the geological assessment recommends setback buffers that are less than the standard buffers that would result from application of Chapter 19.18 of the IBC, the specific rationale and basis for the reduced buffers shall be clearly articulated in the geological assessment. www.cobaltgeo.com (206)331-1097