202 ALDER ST Geotech Report 2025-07-30 (2)

Proposed View Ridge Subsurface Exploration, Geologic Hazards, Infiltration Potential, Elementary School Replacement and Preliminary Geotechnical Engineering Report Everett, Washington Project and Site Conditions 4.1 Stratigraphy Surficial Topsoil Those exploration borings not located in paved areas generally encountered approximately 6 inches of grass and topsoil. Topsoil is not suitable for structural support, and should be stripped from structural areas. Excavated topsoil may be suitable for reuse in landscape areas. Existing Paving Existing paving was encountered at one of the boring locations. The asphalt paving was approximately 3 inches thick at the location of EB-7. Existing paving should be removed from below planned building areas. Fill Existing fill was encountered in two of our explorations to maximum depths of approximately 10 feet below the existing ground surface. Possible existing fill was encountered in two additional explorations. It should be noted that some of the existing fill appears to consist of soils derived on-site and are difficult to distinguish from intact site soils in exploration borings. Typically, such determinations are much easier in open excavations such as those that are made at the time of construction. Existing fill is not suitable for structural support without remedial preparation as described in the "Site Preparation" section of this report. Existing fill should be replaced below planned building areas, and should be re-worked under paving. Excavated existing fill material is suitable for reuse in structural fill applications if it is free of excessive organic material and other deleterious materials and is allowed by the project plans and specifications. Advance Outwash Below the surficial fill where it was present, all of the exploration borings encountered dense sand with few silt and silt stringers interpreted as Vashon advance outwash sediments. Advance outwash was deposited at the base of an advancing glacier, and was subsequently compacted by the weight of the overlying glacial ice. Advance outwash deposits typically exhibit gradational stratification, including stringers consisting of silt and/or silty sand. Such stratification has the potential to limit advance outwash sediments from performing well as an infiltration receptor. The construction of pit drains, as discussed in this report, penetrates finer strata and substantially improves the ability of advance outwash to serve as an infiltration receptor. Excavated advance outwash sediments are expected to be suitable for reuse in September 22, 2010 ASSOCIATED EARTH SCIENCES, INC. BWG/tb-KE100255r12-Prof ects120100255IKEIWP Page 4