5801 23RD DR W Geotech Report 2025-07-29

I I October 22, 2007 Project No. T-5922-1 j4.0 GEOLOGIC HAZARDS I Section 19.4.020 of the Everett Municipal Code (EMC) defines geologically hazardous areas as "areas susceptible to erosion,landslide, seismically induced soil failure,or other geological events." I4.1 Erosion Hazard Section 19.37.080(A)(3)of the EMC defines erosion hazard areas as: Ia. 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, IWashington: July 1, 1991: i. High erosion hazard areas include slopes of 25 to 40 percent in Qva and Qat geologic units; and slopes of greater than 40 percent in other(not Qva or Qal)geologic units. ii. Very high/severe erosion hazard areas include slopes of greater than 40 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, 11. 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 Ivegetation: i. Slopes of 25 to 40 percent in other(not Qva or Qal)geologic units. IThe sideslopes of the Narbeck Creek drainage ravine in the eastern portion of the site are steeper than 40 percent and are underlain predominantly by advance outwash deposits (Qva). Therefore, according to the criteria presented in item(a)(ii) above,the ravine sideslopes are considered very high/severe erosion hazards areas. iAs discussed, we observed shallow erosional features on the steep ravine slope resulting in loss of forest duff and weathered surficial soils. Erosional features such as these are not uncommon on steep native slopes, and are IP generally associated with extended periods of precipitation during the wet winter and spring months. We did not observe indications of significant active erosion in the planned development area; however, the site Isoils will be susceptible to erosion when exposed during construction. The information provided to us indicates that the planned site development will encroach no closer than 25 to the top of the steep ravine slope. Provided 1 Best Management Practices (BMPs) for erosion prevention and sedimentation control are properly implemented and maintained in the planned development area, along with temporary and permanent drainage improvements,it is our opinion that the erosion hazard at the site will be adequately mitigated. ITerra Associates, Inc. should observe the installation of all erosion and sedimentation measures at the site and make periodic visits to observe site conditions to verify the performance of the measures. The contractor should I perform daily review and maintenance of all erosion and sedimentation control measures at the site throughout construction. I Page No. 4 I