4320 THOMSON AVE 2023-08-10 - Laserfiche WebLink

GeoTest Services, Inc. 4320 Thomson Avenue, Everett, WA April 12, 2019 Project No.19-0050 behave during a large earthquake. Mitigation is intended to make the risk posed by the slope that is present on site less and it should not be interpreted that mitigation is representative of completely eliminating any and all risk that might be present on the site. It is assumed that the property owner is aware of the slope that is present on the site and that the owner has been adequately informed and is accepting of the risks associated with slope property development. It is GTS's opinion that the construction of the proposed residence will not adversely affect the stability of the existing slope, if the recommendations in this report are followed. Erosion Hazards Based on the Everett Municipal Code, the slope on the west portion of the property is considered to be an Erosion Hazard due to slopes between 25 and 40 percent in the Advance Outwash (Qva) geologic unit. Accordingly, the following recommendations are intended to prevent excessive erosion from occurring: • All clearing and grading activities for future residence construction will need to incorporate Best Management Practices (BMPs) for erosion control in compliance with current City of Everett codes and standards. • GTS recommends that appropriate silt fencing be incorporated into the construction plan for erosion control. • GTS recommends that onsite BMP's be implemented during construction. Areas of native vegetation left in place, could also be enhanced by adding additional native plant species and/or other vegetation enhancements. • Removal of vegetation and trees without proper mitigation may increase the risk of failure for the surficial soils during periods of wet weather. Planting additional brush and vegetation within the subject site and in areas disturbed by excavation activities will help maintain near surface slope stability by providing a stable root base within the near surface soils. • Yard waste should not be dumped onto the top or face of existing or developed site slopes. Yard waste can retain water and cause slope instability. • Proper drainage controls have a significant effect on erosion. All surface water and any collected drainage water upslope should be directed around the proposed development. All collected stormwater should be directed to an appropriate collection system. • All areas disturbed by construction practices should be vegetated or otherwise protected to limit the potential for erosion as soon as practical during and after construction. Areas requiring immediate protection from the effects of erosion should be covered with either plastic, mulch or erosion control 7