518 51ST ST SW 2023-06-23 - Laserfiche WebLink

• • • April 6,2021 Page 3 of 7 Limited Geotechnical Evaluation 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. Site meets the criteria of item g.. 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. The site does not contain landslide hazards. There are steep slope hazards south of the property and on adjacent properties; however, these areas do not pose a threat to the subject property or project. Nor will the project affect the adjacent steep slope areas if constructed per plan and per typical engineering standards. The site is underlain by till and outwash soils. We did not observe evidence of historic or recent landslide activity or severe erosion on the subject or adjacent properties. There was no evidence of emergent groundwater,significant soil creep,or permeable soil overlying silt and clay. 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: (1) 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 15 percent or more in outwash soils. The near surface soils appear to consist of drift or till and likely have a moderate erosion potential when exposed. It should be noted that only minimal excavations around the building foundation will be required. No work will occur near the top of the slope. Therefore, the risk of soil erosion in steep slope areas is minimal. The work typically takes less than a week and all areas will be re-landscaped immediately. www.cobaltgeo.com (206)331-1097