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 glacial ice. The advance outwash sediments encountered in our exploration boring EB-1 consisted of dense to very dense, fine- to medium-grained sand with trace amounts of silt and variable amounts of gravel. In the push-probe explorations the encountered advance outwash generally consisted of silty sands to sands with trace silt and variable amounts of gravels. The advance outwash contained faint, thin, silt interbeds recognized as lamination. The advance outwash was observed to a depth of approximately 53% feet below existing site grade in exploration EB-1. Pre-Fraser Fine-Grained Sediments Pre-Fraser fine-grained sediments were encountered in exploration EB-1 directly below the Vashon advance outwash, and extended past total depths explored. These fine-grained sediments consisted of stiff to very stiff, slightly moist bluish gray to greenish gray, massive, silt. Trace amounts of coarse sand and fine gravels were observed within the silt, and were identified as dropstones. These pre-Fraser fine-grained sediments were identified to be that of a glacial lacustrine deposit. Review of Selected Available Geologic Data Review of the regional geologic map of the area titled Geologic Map of the Everett 7.5-Minute Quadrangle, Snohomish County, Washington, by James P. Minard, 1985 indicates that the area of the project site is underlain by Vashon lodgement till. Exposures of Vashon advance outwash, which stratigraphically underlies the lodgement till, are depicted a short distance to the west. Our on-site exploration and interpretations are not consistent with the conditions depicted on the referenced published map. We recommend that project planning follow conclusions in this report and not the published map. 4.2 Hydrology A regional ground water aquifer was not encountered in our deep boring location EB-1. An increase in moisture content was observed in the outwash sediments at a depth of 55 feet, however no free ground water was observed. Perched ground water was observed within the encountered existing fill in several of our previously completed push-probe explorations. Perched ground water occurs when vertical infiltration of surface water is impeded by less-permeable soil layers, resulting in horizontal flow. The quantity and duration of perched ground water flow from an excavation will vary, depending on season, soil gradation, and adjacent topography. The observed ground water was perched on top of the siltier ice-contact deposits. Fluctuations in the level of ground water and amount of seepage may occur due to variations in rainfall, time of the year, and changes in site development. May 16,2017 ASSOCIATED EARTH SCIENCES,INC. AWR/Id-160594V003-2-ProjectsI20160594\KVIWP Page 5