4920 24TH AVE W Geotech Report 2023-06-22

GeoTest Services,Inc. October 8, 2021 2405 Hillside Lane, Everett,WA Project No.21-0845 potential, landslide and seismic and hazard potential, and will improve or not adversely affect the stability of slopes;"and that the development"uses construction techniques which minimize disruption of existing topography and natural vegetation". Based on our understanding of the development, the new residences on Lots 2 and 3 will bear directly on stiff to very stiff, native soils.Tiered landscape walls (each less than 4 feet in exposed height) will be constructed to make the grade change between the southern property line and the proposed main floor elevation for the new residences. These retaining walls and associated grading activities will serve as a mitigation for landslide hazards. Robust subsurface drainage measures should also be planned to intercept perched groundwater and divert it around and away from the planned structures. A cut-off or perimeter drain is another mitigation that should be considered. No signs of severe instability evidence of ongoing large scale global instability or evidence of the initiation of large-scale global instability were observed on the existing slope at the time of our site visits and were not observed in the aerial imagery and bare earth imagery that we reviewed for this project. Thus, provided that the recommendations and mitigations in this report are followed, it is GeoTest's professional opinion that the construction of the proposed residences on this property will not adversely affect the overall stability of the existing slope. Erosion Hazard Areas GeoTest interprets the slope comprising the site area of the proposed development to be classified as an erosion hazard area. 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. • GeoTest recommends that appropriate silt fencing be incorporated into the construction plan for erosion control. • GeoTest recommends that on-site BMPs 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. 6