1023 100TH ST SW Geotech Report 2022-10-25

COBALT GEOTECHNICAL INVESTIGATION " -.,," GEOSCIENCES EVERETT, WASHINGTON December 3,2019 The soils encountered were logged in the field and are described in accordance with the Unified Soil Classification System(USCS). A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil samples, classified the encountered soils, kept a detailed log of the explorations, and observed and recorded pertinent site features. The results of the sampling are presented on the exploration logs enclosed in Appendix C. 5.0 Soil and Groundwater Conditions 5.1.1 Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north-south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved, with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non-glacial sediments consisting of interbedded gravel,sand,silt,till,and peat lenses. The Geologic Map of Washington — Northwest Quadrant, indicates that the site is underlain by Vashon Glacial Till. Vashon Glacial Till is typically characterized by an unsorted, non-stratified mixture of clay, silt, sand, gravel, cobbles and boulders in variable quantities. These materials are typically dense and relatively impermeable. The poor sorting reflects the mixing of the materials as these sediments were overridden and incorporated by the glacial ice. Explorations The test pits encountered 6 inches of topsoil and vegetation underlain by approximately i to 1.5 feet of loose to medium dense, silty-fine to medium grained sand with gravel (Weathered Glacial Till). These materials were underlain by dense to very dense, silty-fine to medium grained sand with gravel (Glacial Till),which continued to the termination depth of these explorations. Fill should be expected to be present around the existing residence and possibly elsewhere in the yard areas. 5.1.2 Groundwater Groundwater was not encountered in any of the explorations. There is a chance that perched groundwater may be encountered during late winter and early spring months. We anticipate that groundwater would be perched between fill or weathered till and underlying unweathered glacial till, likely within 5 feet of the ground surface. Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. 2 PO Box 82243 Kenmore,WA 98028 cobaltgeo0gmai Lconi 206-331-1097