1329 MADRONA AVE Geotech Report 2022-10-25

Subsurface Exploration,Geologic Hazard,and Janowicz Property Geotechnical Engineering Report Everett, Washington Geologic Hazards and Mitigations 7.0 EROSION HAZARDS AND MITIGATION The City of Everett identifies erosion hazard areas based on certain geologic, topographic, and surface conditions. Slopes of about 20 to 30 percent inclination on the property and the immature vegetation onsite meet the criteria for medium risk of erosion as defined in EMC 19.37.080.3 as follows: "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, 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." The code further defines high erosion hazard areas as "areas [that] 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." The steep slope descending to the northwest and the rail line appears to meet the criteria for very high/severe erosion hazard area due to its near-vertical inclination. The proposed residential construction may proceed without increasing the erosion hazard at the site or on the adjacent slope if appropriate mitigation measures are implemented as part of the project. Mitigative measures during construction may consist of: • Scheduling construction during the drier periods of the year. • Providing quarry spall construction access to reduce the sediment "track-out" by construction traffic. • Collecting and directing all stormwater from impermeable surfaces via tightline away from work areas and to an approved facility. Stormwater falling on pervious surfaces should be dissipated by sheet flow and not allowed to pool or form channels on the surface. No stormwater should be allowed to discharge over the steep slope. • Placing silt fences along the lower elevations of areas to be cleared or disturbed. • Protecting stockpiles by covering with plastic sheeting, using low stockpiles in flat areas, and using silt fences along the perimeter of stockpiles. • Installing sediment control devices such as interceptor swales and rock check dams. May 10,2018 ASSOCIATED EARTH SCIENCES,INC. NS/td 170649E002-2-Profects1201706491XEIWP Page 9