6801 SEAWAY BLVD Geotech Report 2025-08-19

Seaway Commercial Center Subsurface Exploration, Geologic Hazard, 7007 Seaway Boulevard and Geotechnical Engineering Evaluation Everett, Washington Project and Site Conditions literature.The sediments encountered in our explorations generally consisted of native glacially consolidated sediments. The following section presents more detailed subsurface information organized from the shallowest (youngest) to the deepest (oldest) sediment types. Copies of the exploration logs are included in Appendices A and B. 4.1 Stratigraphv Forest Duff/Topsoil A surficial layer of forest duff over organic-rich topsoil was encountered in all explorations and ranged from about 6 inches to 3 feet thick across the site. Topsoil is not considered suitable for foundation support or use as structural fill. Vashon Ice-Contact Deposits Directly below the forest duff/topsoil in exploration pit EP-4, we encountered sediments consisting of medium dense, tan and light brown silty fine sand grading to sandy silt with trace gravel to a depth of about 6 feet. These sediments were interpreted to be representative of ice-contact deposits. Ice-contact deposits consist of sediments deposited in contact with glacial ice by meltwater on, under, within, or marginal to the glacier. Vashon Lodgement Till Sediments encountered directly below the surficial topsoil (and directly below the ice-contact deposits in EP-4) generally consisted of dense to very dense, unsorted, gray, silty sand with some to trace gravel. We interpret these sediments to be representative of Vashon lodgement till. This unit typically included a loose to medium dense oxidized weathered zone just below the topsoil, ranging from 1 to 3 feet in thickness. The Vashon lodgement till was deposited directly from basal, debris-laden glacial ice during the Vashon Stade of the Fraser Glaciation, approximately 12,500 to 15,000 years ago. The high relative density characteristic of the Vashon lodgement till is due to its consolidation by the massive weight of the glacial ice from which it was deposited. Lodgement till typically contains a significant fine-grained fraction and is highly sensitive to moisture during placement in structural fill applications. At each of the eight exploration pit locations, the till extended beyond the maximum depths explored of approximately 5 to 10 feet. At the location of boring EB-1, the lodgement till extended to the full depth of the boring, approximately 51 feet. 4.2 Geologic Map Review Review of the regional geologic map of the area, titled Geologic Map of the Everett 7.5 Minute Quadrangle, Snohomish County, Washington, by J.P. Minard (1985) indicates that the area of December 17,2021 ASSOCIATED EARTH SCIENCES,INC. PEL/Id-20200319E001-002 Page 4