5200 EVERGREEN WAY SEPA 017 - 010 Geotech Report 2025-04-23

Subsurface Exploration, Geologic Hazards, and Former Brien Ford Preliminary Geotechnical Engineering Report Everett, Washington Project and Site Conditions 4.1 Stratigraphy Asphalt/Concrete A surficial layer of existing asphalt was encountered at the location of EB-1. The asphalt was approximately 2 inches in thickness. In the push-probe explorations the asphalt ranged in thickness from 3 to 4 inches. Concrete slabs were also encountered in our push-probe explorations and ranged in thickness from 3 to 8 inches. Fill Fill soils (those not naturally placed) were encountered in location EB-1 directly below the surficial asphalt. The fill consisted of loose to dense, slightly moist, brownish gray with oxidation staining, fine to medium sand with variable amounts of silt and gravel, and trace amounts of wood debris. The fill material appeared to consist primarily of materials derived onsite and moved or disturbed during earlier site work. Existing fill was also encountered in 27 of the push-probe explorations below the asphalt or concrete surface and extended to approximate depths ranging from 2 to 11 feet below the surface. The fill in these explorations generally consisted of loose to dense, silty to very silty sand or sand with trace silt and varying amounts of gravel. Existing fill soils are not suitable for support of foundation underpinning elements. Uncontaminated existing fill may be reused as structural fill if allowed by project specifications and all deleterious materials are removed. Ice-Contact Deposits Ice-contact deposits were encountered in 28 of 29 direct-push probe explorations completed for the previous studies. These deposits were generally encountered underlying asphalt or concrete surfacing or underlying existing fill soils. Where encountered, these deposits extended to the depths explored of 15 feet or less or were underlain by Vashon advance outwash sediments. The ice-contact sediments generally consisted of moist to wet, fine to coarse sand, silty or very silty fine to coarse sand, sandy silt, silt with trace sand, and clay all with variable gravel content. The ice-contact deposits were not consolidated by an overriding glacier but were deposited in topographic depressions by the meltwater of the receding glacier. The ice-contact deposits were over optimum in moisture content at the time of the exploration and would require drying during favorable weather prior to compaction and potential reuse in structural fill applications. Vashon Advance Outwash Advance outwash sediments were encountered in exploration EB-1 directly below the fill soils and were also encountered underlying ice-contact sediments in several of the push-probe explorations. Advance outwash sediments were deposited in rivers and streams flowing ahead of an advancing glacier, and were subsequently compacted by the weight of the overlying May 16,2017 ASSOCIATED EARTH SCIENCES,INC. AWR/Id-160594V003-2-Projects\20160594�KVIWP Page 4