4735 GLENHAVEN DR Geotech Report 2022-10-25

< • S Geotechnical Engineering Evaluation NGA File No. 1113119 Dutton Foundation Stabilization and Slope Evaluation July 3,2019 Everett,Washington Page 3 j\ \ Explorations:The subsurface conditions within the site were explored with three hand auger explorations in the vicinity of the exterior of the settling addition. The approximate locations of our explorations are shown on the Schematic Site Plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc. (NGA) was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. The soils were visually classified in general accordance with the Unified Soil Classification System presented in figure 3. The logs of our explorations are attached to this letter and presented as Figure 4. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions,the logs should be reviewed. At the surface of Hand Auger One, located on the ravine side of the settling addition, we encountered approximately 7.5 feet of surficial silt with fine to medium sand and coarse sand in a very loose to loose condition, which we interpreted as surficial undocumented fill soils. Probing this layer with a 6-foot, 1/2- inch steel probe rod yielded penetrations of 1-2 feet. Underlying this fill, approximately 1.2 feet of additional organic-rich buried topsoils were encountered in a loose to medium dense condition. At depth, we encountered gray silty fine to medium sand with gravel in a dense or better condition, which we interpreted as native bearing glacial soils. In Hand Auger Two, near the main residence basement foundation,we encountered 0.5 feet of compost and topsoil underlain by brown to orange brown silty fine to medium sand, which we interpreted as weathered native glacial soils. In Hand Auger Three, adjacent to where the settling addition connects to the main residence, we encountered approximately 4.8 feet of surficial undocumented fill soils and buried topsoils, with brown gray silty fine to medium sand with gravel at depth in a medium dense or better condition,which we interpreted as native glacial soils. Hand Augers 1 through 3 were terminated within native glacial till soils at depths in the range of 1.9 to 7.5 feet below the existing surface. Hydrogeologic Conditions Groundwater seepage was not encountered in any of our explorations.If we had encountered groundwater seepage, we would interpret this water to be perched water. Perched water occurs when surface water infiltrates through less dense, more petineable soils, and accumulates on top of a relatively low permeability material. Perched water does not represent a 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.