801 E CASINO RD Geotech Report 2022-10-25

Cascade High School Subsurface Exploration and Synthetic Turf Field Geotechnical Engineering Report Everett, Washington Project and Site Conditions Lodgement Till Native soils observed below existing fill and observed below natural turf and sand base where fill was not encountered generally consisted of dense to very dense silty sand with gravel. These materials are interpreted to represent lodgement till sediments. Lodgement till was deposited at the base of a continental glacier and was compacted by the weight of the overlying ice. Native lodgement till sediments are suitable for support of new turf with proper preparation. Native materials may be used in structural fill applications if specifically allowed by project plans and specifications, and if moisture conditions are adjusted such that compaction to a firm and unyielding condition at the specified level is attainable. At the time of exploration, we estimated that most of the site soils were above optimum moisture content for compaction purposes and would require drying during favorable dry site and weather conditions prior to use in compacted fill. 4.2 Laboratory Testing We selected one sample of the sand base below the surficial natural turf for mechanical grain -size analysis testing and three samples of the existing fill from exploration boring EB-4 for organic -content testing. The results of laboratory analyses completed for this study are presented in the Appendix. 4.3 Hydrology We did not observe ground water seepage in any of the exploration borings completed for this study. We anticipate that perched ground water may be encountered in existing fill and at the interface between fill and glacially consolidated soils at the time of construction. Perched seepage occurs where downward infiltration of surface water is impeded by lower permeability soils at depths. It should be noted that fluctuations in the level of the ground water may occur due to the time of the year, on- and off -site land use, and variations in the amount of rainfall. The site is underlain by existing fill and very dense, glacially consolidated sediments. The site is not suitable for use of storm water infiltration using conventional shallow infiltration strategies, in our opinion. 4.4 Published Geologic Map. Our interpretations of subsurface conditions onsite are generally consistent with a published geologic map of the area (Distribution and Description of the Geologic Units in the Everett Quadrangle, Washington, by James P. Minard, 1981). The referenced map indicates that the site vicinity is underlain by lodgement till sediments. March 20, 2017 ASSOCIATED EARTH SCIENCES, INC. DDV/pc-1700SIE001-2—Projects J20170N1JKEJWP Page 4