5404 S 3RD AVE 2024-03-29 - Laserfiche WebLink

Geotechnical Engineering Evaluation and Engineering Geologic Assessment - REVISED NGA File No. 1300621 Sharp Residential Remodel October 12, 2021 Everett, Washington Page 2 4. Providing our opinion on the presence of Geological Critical Areas on the site, as well as general recommendations for hazard mitigation, if applicable. 5. Providing general recommendations for drainage and erosion control. 6. Documenting the results of our findings, conclusions, and recommendations in a written geotechnical letter. SITE CONDITIONS Surface Conditions The property is rectangular in shape and covers approximately 0.16 acres in area. It is currently occupied by a single-family residence, detached garage, and detached accessory structure. The site is bordered by South 3rd Avenue to the east, neighboring residences to the north and south, and by unopened right-of- way to the west. Topographically, the site slopes gently to the east, with a short and moderate east -facing slope adjacent to South 3rd Avenue on the easternmost portion of the site. There are no steep slopes over ten feet in relief within the site. However, steep, east -facing slopes are located on downhill properties approximately 150- to 200 feet to the east of the subject site with up to 20 feet of vertical relief. No surface water was observed within the subject site on our site visit on September 16, 2021. The current site conditions are shown on the Site Plan in Figure 2. LiDAR Imagery Review We were requested to provide a review of LiDAR imagery for the vicinity of the site to give context to surrounding steep slopes and evaluate potential deep-seated stability concerns affecting the proposed development. Regional geomorphic features which may be imperceptible at ground level can be inferred remotely through aerial imagery and data. Light Detection and Ranging (LiDAR)-derived imagery shows mathematically -interpolated ground surface elevations by removing vegetation interference. In general, landslides are characterized on these images by hummocky, undulating topography and steep head scarps. Selected LiDAR imagery provided as part of a regional set of data to Snohomish County by Quantum Spatial, Inc. on September 29, 2017 was reviewed for this site. A selected portion of the image is presented as Figure 3. The site is situated on a gently -sloping terrace below steep slopes associated with Interstate 5 to the west and the Snohomish River to the east. The nearby steep slope to the east of the subject site is localized to several properties and is very diffuse, suggesting the deposition of the underlying geologic deposits may be responsible for the relief. Indicators such as hummocky terrain or steep, arcuate scarps are not present in the vicinity of the site. Therefore, the imagery does not suggest deep-seated landslides are a hazard for this property. NELSON GEOTECHNICAL ASSOCIATES, INC.