5001 23RD AVE W Geotech Report 2022-10-25

detailed seismic slope stability or seismic hazards evaluation. Our scope of services only included very limited or preliminary geologic hazards evaluation. SUBSURFACE CONDITIONS Soil classification and identification is based on commonly accepted methods employed in the practice of geotechnical engineering. In some cases, the stratigraphic boundaries shown on Boring Logs represents transitions between soil types rather than distinct lithological boundaries. It should be recognized that subsurface conditions often vary both with depth and laterally between individual boring locations. The following is a summary of the subsurface conditions encountered at the site: Lacustrine Deposit: The site is generally underlain by very soft to medium stiff mixtures of silts and clays (CL, ML) extending to depths of 5-10 feet below existing grades. Below 5 feet, soil consistencies are generally stiff to very stiff. Sand-silt-gravel Mixtures: The site is generally underlain by dense mixtures of sands, silt, and gravel with some cobble(SM, GM)extending to a maximum explored depth of about 20 feet below ground surface (BGS) where refusal to exploration was encountered due to the presence of mostly likely cobbles/gravels and dense relative densities. Our review of available geologic literature (USGS) and water well logs (Department of Ecology, WA) indicated that the glacial till deposit extends to a few tens of feet below the ground surface at the site. See Figure 3 for specific geologic descriptions. Groundwater: Perched or groundwater table was not encountered during explorations, however, very moist soil conditions or orange mottling were encountered below a depth of 5-9 feet indicating that perched groundwater conditions are possible at these depths during heavy rains or during wet season. This observation may not be indicative of other times or at locations other than the site. Some variations in the groundwater level may be experienced in the future. The magnitude of the variation will largely depend upon the duration and intensity of precipitation, temperature and the surface and subsurface drainage characteristics of the surrounding area. GEOLOGIC HAZARDS EVALUATION Based upon the results of our site exploration, engineering analysis, and literature review of following documents, we evaluated geologic hazards at the site. • Washington Division of Geology and Earth Resources, Open File Reports • U.S. Geological Survey Maps Project No: 0314-WA19 August 07,2019 Page No:3 of 12