1910 W MUKILTEO BLVD Geotech Report 2022-10-25

Geotechnical Engineering Evaluen • NGA File No. 1238721 Spencer Garage Addition February 11,2021 Everett,Washington Page 2 8. Providing recommendations for subsurface utilities and pavement subgrade preparation. 9. Providing our opinion on stormwater infiltration feasibility. 10. Providing recommendations for infiltration/bioretention system installation, if feasible. 11. Providing general recommendations for site drainage and erosion control. 12. Documenting the results of our findings,conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The site consists of a rectangular-shaped parcel covering approximately 0.45 acres. The site is occupied by a single-family residence with a detached garage and sport court to the south west. Topography within the site is generally level to gently sloping to the north. A graded, east- and north-facing slope with approximate vertical relief of 13 feet occupies the extreme southwest,corner of the.property, as shown on Cross Section A-A' in Figure 3.The slope includes a rockery supporting the base,which ranges up to 3.5 feet in exposed height. Vegetation within the site consists of grass=covered yard areas bordered by shrubs and one tree on the north side of the driveway. The site is bordered to the south and west by existing residential properties,to the north by West Mukilteo Boulevard,and to the east by Water Way. We did not observe surface water within the site during our site reconnaissance on February 4, 2021. Subsurface Conditions Geology: The geologic units for this site are shown on Geologic Map of the Everett 7.5 Minute Quadrangle, Snohomish County, Washington, by Minard, J.P. (USGS, 1985). The site is mapped as transitional beds (Qtb). Transitional beds are described as beds of gray clay, silt, and very fine to fine sand with some layers of peaty sand and gravel and may include some members of Pilchuck clay, Admiralty Clay, and Whidbey Formation. Our explorations typically encountered undocumented fill underlain by fine to,coarse silty sand with varying amounts of trace gravel which we interpreted as native transitional bed deposits. Explorations: The subsurface conditions within the site were explored on February 4, 2021 by excavating one test pit to an approximate depth of 6.5 feet below the existing ground surface using a mini-trackhoe. We also performed three hand augers to depths of approximately 5.5, 5.0, and 4.5 feet below the existing ground surface.The approximate locations of our explorations are shown on the Site Plan in Figure 2. NELSON GEOTECHNICAL ASSOCIATES, INC.