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i <br /> Subsurjace Expbration, Geobgic Hawrd, md <br /> i I Sno-lsle Skills Crntt�Addition PreGminary Geotethnical Engineering Report <br /> E�erett, Washingron Project and Site Condidons <br /> ILodgement Tr!! <br /> I Lodgement till was encountered neaz the surface and extended to the full depths of our <br /> exploration borings. The lodgement till generally consisted of inedium dense to very dense <br /> gravelly silry sand. Scattered cobbles were encountered during drilling and often occur in ail <br /> I deposits. T6e lodgement till was deposited at the base of the Vashon-age glacial ice sheet and <br /> was subsequently ovettidden by several thousand feet of ice. Consequendy, these macerials <br /> � are dense to very dense, possess high-suength, low-compressibility charactetistics, aad aze <br /> reladvely impermeable. The nearly impermeable nature of the till makes t6e near-surface till <br /> soils generally unsuitable for storm water infiluation. The upper portions of the lodgement till <br /> I were generally weat6ered and less dense, oxidized brown, and siltier than the lower, <br /> unweathered portions of the deposit. The lodgement till is suitable for d'uect support of <br /> foundations and pavement sections, although these soils are susceptible to disturbance when <br /> Iwet due to t6e elevated silt contents. <br /> 4.2 Literature Review <br /> � We reviewed geologic data for the site baaed on the United States Geological Swvey (USGS) <br /> I Preliminary Surficial Geologic Map of the Mukilteo and Everett Quadrangles, Snohomish <br /> County, Washington, by Smith, dated 1976. This map indicates that the near-surface <br /> sediments in the site viciniry consist of Vashon-age lodgement d1L Associated Earth Sciences, <br /> 1 Inc.'s (AESI's) geologic findings aze in general agreement with those of the USGS. <br /> 4.3 Hydrolof;y <br /> IGround water seepage was encountered in exploration boring EB-2 at approximauly 5.5 feet <br /> and in exploration boring EB-4 at approximately 6 feet below the surface. The ground water <br /> encountered in the borings is indicative of a perched ground water condition. Perched ground <br /> I water occurs when surface water infiltraus down through relatively permeable soils, such as <br /> the fill or the weaffiered portions of the lodgement till, and becomes .:apped or "perched" atop <br /> I a compazatively unpermeable soil horizon, such as the dense to very dense unweathered <br /> lodgement till. It should be noted that fluctuations in the level of the ground waur may occur <br /> I due to the time of the yeaz, on- and off-site usage, such as irrigation, and vaziations in rainfall. <br /> The quantiry and duration of flow from excavations made into zones of perc6ed ground water <br /> I will vary depending on season, topograp6y, and soil grain size. Based on the encountered <br /> subsurface conditions and the lack of wide-spread ground water, dewatering activities will <br /> likely not be requ'ved for trenching or subsurface ezcavations. <br /> IBased on our preliminary evaluation, storm water infiltration is not feasible on t6is siu due to <br /> the presence of dense to very dense, relatively impermeable lodgement cill at or near the <br /> � ground surface. <br /> June 11. 2008 ASSOClA7ED EARTH SClENCEpS�.,l,NC. <br /> I EG/Id-EFA�D2l3A5-Projtnt1�131EEIWP `�C� � <br /> � <br />