5228 EAST DR Geotech Report 2022-10-25

COBALT GEOTECHNICAL INVESTIGATIO1/4.4 N G E O S C I E N C E S EVERETT,WASHINGTON December 5, 2019 ii. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment or bedrock;and iii. Springs,groundwater seepage,or saturated soils. d. Any area which has shown movement during the Holocene epoch(from ten thousand years ago to the present)or which is underlain or covered by mass wastage debris of that epoch. e. Any area potentially unstable as a result of rapid stream incision,stream bank erosion or undercutting by wave action. f. Areas of historic failures, including areas of unstable, old and recent landslides or landslide debris within a head scarp, and areas exhibiting geomorphological features indicative of past slope failure, such as hummocky ground,slumps,earthflows,mudflows,etc. 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. 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. B. Protective Requirements. 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 iq;i8 of the International Building Code (IBC), or as the IBC is updated and amended. It is our opinion that the proposed locations of the residences are suitable. They are currently set back at least 4o feet from the top of the steep slope areas (Figure 2). We recommend a minimum building setback of 25 feet from the top of the steep slopes. We recommend a minimum buffer of 15 feet for vegetation from the top of the slope. 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. b. The city mayrequire larger.setback buffer widths under any of the following circumstances: i. The land is susceptible to severe erosion and erosion control measures will not effectively prevent adverse impacts. ii. The area has a severe risk of slope failure or downslope stormwater drainage impacts. 4 PO Box 82243 Kenmore,WA 98028 cobaltgeo Ca gmaij,tom 206-331-m97