1915 W MUKILTEO BLVD 2018-01-02 MF Import

Geotechnical Engineering Evaluation and Slide Repairs 1915 Mukilteo Boulevard July 26, 2006 NGA File No. 743206 Page 4 Both of the boring exposed loose, silty fine sand with organics extending to between two to three feet below the existing surface. We interpreted this material to be topsoil/fill. Below the topsoil, each of the borings encountered loose fine to medium sand with trace gravel and varying amounts of silt extending to between five to eight feet below the existing surface. Below the loose sand, both of the borings encountered medium dense, fine to medium sand with silt and varying amounts of gravel interbedded with silty fine sand extending to depths of approximately 17 to 18 feet. Underlying the medium dense soil, both of the explorations encountered dense to very dense fine to coarse sand with silt and gravel interbedded with silty fine sand with trace gravel. Both of the borings were terminated in dense to very dense sand at depths between 30.4 and 30.5 feet below the existing ground surface. Hand Auger 1, located at the bottom of the exposed face of the steep northern slope, encountered loose, brown, fine to medium sand with silt and gravel extending to a depth of 2.2 feet below the existing surface. Hand Auger 1 was terminated in the loose sand. Hand Auger 2, located near the toe of the slope exposed topsoil to a depth of approximately 0.8 feet. Below the topsoil, Hand Auger 2 encountered gray - brown fine to medium sand with silt, trace gravel and trace organics in a loose condition. Hand Auger 2 was terminated in the loose sand at a depth of 1.5 feet. Hand Auger 3, located below the landslide scarp exposed 0.2 feet of sod. Below the sod, Hand Auger - encountered loose topsoil extending to a depth of 2.0 feet below the existing surface. Below the topsoil, Hand Auger 3 encountered loose, gray, fine to median sand with trace roots and trace organics. Hand Auger 3 was terminated in the loose sand at a depth of 2.4 feet. Hydrologic Conditions Groundwater seepage was not encountered within any of the explorations. However, it is our opinion that a perched groundwater condition could develop on this site and daylight on the slope during wetter times of the year. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of relatively low permeability materials. The more permeable soils consist of the loose topsoil and loose upper portions of the sand soils. Lower permeability medium dense or better silty sand lenses may be present within the sand deposit, which could perch the infiltrating water. Perched water does not represent it regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. NELSON GEOTECHNICAL ASSOCIATES, INC. bl3 )