5221 23RD AVE W 2023-04-10 - Laserfiche WebLink

September 10, 2021 G-5535 Geological Assessment Letter Page 2 5221 23`d Avenue W,Everett, Washington will be covered with a newly constructed roof area. The foundations for the new deck are planned to be constructed on relatively flat topography adjacent to the residence that has been previously developed with landscaping and smaller existing wooden deck. The location of the proposed new deck and the existing conditions at the project site are illustrated in Plate 2— Proposed Site Plan. According to the City of Everett GIS records,the property and the proposed work area for the new deck are located within 200 feet of a potential landslide hazard area located in the ravine to the east. As such,the City requires a reconnaissance study and a geological assessment letter prior to issuance of the permit for the new deck. GEOLOGIC OVERVIEW According to published geologic mapping of the area,the site soils are identified as Vashon Till (Qvt) deposits from the Pleistocene era. Vashon till deposits typically consist of non-stratified mixtures of sand, silt, and gravel that were deposited beneath the sole of the Vashon glacier as it advanced southward into the Puget Sound area approximately 15,000 years ago. As a result of being consolidated by the glacial ice,these deposits are typically dense to very dense. SETTLEMENT EVALUATION We used a laser level throughout the interior of the daylight basement to evaluate the potential presence of settlement. Overall,we found that the basement floors were consistently within typical tolerance for levelness at values of 0.5-inches or less. We observed no cracks in the exterior concrete walls of the residence or the crawlspace. Based on our findings, it is our opinion that the residence has not experienced notable settlement due to the nearby critical areas mapped at the site. GEOLOGICAL ASSESSMENT AND RECOMMENDATIONS According to the City of Everett GIS maps,the above-subject property is located on relatively flat topography, and the east property line is adjacent to the top of a steep slope area that descends approximately 100 feet into an undisturbed ravine area. The upper areas of the slope are mapped as a high-susceptibility potential landslide hazard area, and the bottom contours of the slope are mapped as containing very high/severe landslide hazards. According to the GIS maps,the footprint of the proposed new deck is located 100 feet west of the high-susceptibility potential landslide hazard area, and therefore meets the criteria for requiring a geological GEO Group Northwest,Inc.