4730 COLBY AVE YMCA Geotech Report 2025-04-14

Subsurface Exploration, Geologic Hazard,and Snohomish County YMCA Geotechnical Engineering Report Everett, Washington Project and Site Conditions rock base course, followed by another 1-inch layer of asphalt. Existing asphalt should be removed where it is encountered within the proposed building footprint. Fill Existing fill sediments were encountered and ranged in depth from 0.5 feet to 11.5 feet below the surface. Near the proposed new YMCA building, the fill thicknesses ranged from 0.5 feet to 4.5 feet below the surface. Because they have been artificially placed, fill soils often vary in composition and have an unknown lateral extent. Additional fill soils are expected to be present onsite, particularly in the vicinity of existing structures and utilities. Existing fill soils are not suitable for foundations support and should be removed where they are encountered under new foundations. Excavated fill material may be suitable for reuse in structural fill applications if it is at a moisture content that allows compaction to the specified level for the intended use, and if all organic materials and any other deleterious materials are removed prior to use in structural fill applications. At the time of exploration, we estimate that the existing fill that we observed was at or above optimum moisture content for compaction purposes, and therefore, may require drying during favorable weather prior to compaction in structural fill applications. Vashon Lodgement Till The subject site is generally mantled by variable thicknesses of Vashon-age lodgement till. The lodgement till was observed in EP-2, EP-4, EP-6 to EP-8, IT-2 to IT-4, and MW-1. The thickness of the lodgement till ranged up to approximately 6 feet where observed. The lodgement till generally consisted of very dense, slightly moist to moist, silty fine sand with varying amounts of gravel. Lodgement till was deposited at the base of an active continental glacier and was compacted by the weight of the overlying glacial ice. Lodgement till is suitable for structural support when properly prepared. Excavated lodgement till material is suitable for use in structural fill applications if suitable moisture conditions are achieved prior to compaction, and if such reuse is specifically allowed by project plans and specifications. At the time of exploration, we estimate that most or all the lodgement till soils that we observed were above optimum moisture content for compaction purposes; and therefore, will require drying during favorable weather prior to compaction in structural fill applications. Vashon Advance Outwash The Vashon lodgement till, where observed on the site, was directly underlain by Vashon-age advance outwash. Vashon-age advance outwash deposits were encountered in all explorations, except for EP-3 and EP-5, which encountered fill soil to the total depth explored.The top of the Vashon advance outwash deposits was encountered at depths ranging from immediately below thin surficial topsoil in EP-1, to a depth of 8.5 feet where overlain by fill soils in EP-9.The Vashon advance outwash sediments were present to the total depth explored of up to February26,2018 ASSOCIATED EARTH SCIENCES,INC. AWR/ms-170671E001-2-Projects\20170671\KEIWP Page 5