7800 EVERGREEN WAY HYUNDAI Wetland Report 2025-08-05

3.2. Geology Published geologic information for the project vicinity includes the United States Geological Survey (USGS) map titled The Geologic Map of the Snohomish Quadrangle, Snohomish County, Washington (USGS 1985). Mapped soils in the immediate project vicinity consist of glacially consolidated Vashon Till deposits (glacial till). Glacial till is generally a non -sorted, non -stratified mixture of sand, gravel and siltthat has been overridden byseveral thousand feet of ice. Till typically has high shearstrength, low consolidation and low permeability characteristics in the undisturbed state. It typically develops a weathered zone of less dense till where seasonal groundwater perches on top of the relatively impermeable unweathered till and the perched groundwater occurs as seepage following the site topography. 3.3. Subsurface Soil Conditions GeoEngineers' understanding of subsurface conditions is based on the borings drilled for this project, and our review of the geologic map. Competent glacially consolidated soils consisting of glacial till were encountered at relatively shallow depths in the footprint of the proposed addition, which is consistentwith the geologic map. Materials encountered at the site generally consisted of the following: ■ Asphalt Pavement: Asphalt concrete pavementwas observed in each of the borings. Asphalt pavement was observed to range from 2 to 3 inches thick. No crushed surfacing base course (CSBC) materials were encountered below the pavement in the borings. ■ Fill: Fill was encountered below the asphalt pavement in all borings. The fill generally consists of loose to medium dense sand with silt and variable gravel content. The thickness of fill decreased in thickness from north to south and was observed to be approximately 8, 41/2 and 2 feet thick in boring B-1, B-2, and B-3, respectively. ■ Glacial Till: Glacial till deposits were encountered below the fill at depths ranging from 2 feet (boring B-3) to 8 feet (boring B-1) below existing site grades. Glacial till soils consisted of very dense silty sand to sandy silt with variable gravel. 3.4. Groundwater Conditions No groundwater was observed during drilling. However, due to the density and low permeability of the relatively unweathered glacial till deposits perched groundwater should be expected above the relatively unweathered till and to vary as a function of season, precipitation and other factors. Perched seepage zones should be expected above the relatively unweathered glacial till deposits and in permeable layers within the till deposits. Asummary ofthe geotechnical considerations is provided below. The summary is presented for introductory purposes only and should be used in conjunction with the complete recommendations presented in this report. ■ The site is bestclassified as Site Class C in accordance with the 2018International Building Code (IBC). GEOENGINEER� December6,2021 Page2 File No. 24 59-003-00