202 ALDER ST Geotech Report 2025-07-30

Limited Geotechnical Engineering Study View Ridge Elementary School Portable Classroom Installation Everett, Washington and Downspout Infiltration Feasibility organics (rootlets). The fill was observed extending to approximately 4 feet below the ground surface in EB-8 and EB-9 and approximately 3 feet below the ground surface in EB-10. Existing fill is not suitable for structural support without remedial preparation as described in the "Site Preparation"section of this letter-report. The existing fill should be removed or re-worked and compacted from below planned building areas. Excavated existing fill is suitable for reuse in structural fill applications provided it is free of excessive organic material and other deleterious material and is allowed by project plans and specifications. Vashon Advance Outwash Below the existing fill, all of the explorations in the current project area encountered medium dense grading to very dense, moist, brown to gray, sand with occasional thin layers of silty to very silty fine sand interpreted as Vashon advance outwash. 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 textural stratification, including stringers consisting of silt and/or silty sand as observed in the upper portion of the native sediments recovered from our borings. This type of stratification can limit the effectiveness of advance outwash as an infiltration receptor. Hydrology No groundwater was encountered during our current phase of exploration to depths of approximately 21 feet below the ground surface, or approximately elevation 359-361. Groundwater is expected to be present at depth within the Vashon advance outwash as an unconfined local aquifer. Shallow perched water may be present within siltier zones in the fill or above the silty interbeds or stringers encountered in the Vashon advance outwash. During our previous study (referenced above),groundwater levels were measured monthly from September 2010 to April 2011 in monitoring well EB-1/MW-1. The water levels ranged from approximately 37 to 39-1/2 feet below ground surface, or approximately elevation 343-1/2 to 346 feet. Groundwater conditions, including depth and duration and quantity of seepage, should be expected to vary seasonally, and in response to changes in precipitation, soil grain-size distribution, topography, on- and off-site land usage, and other factors. July 12,2023 ASSOCIATED EARTH SCIENCES,INC. ecr/!d-20100255E004-002 Page 5