1209 MADRONA AVE 2016-10-05 - Laserfiche WebLink

0 Geotechnical Engineering Evaluation • NGA File No. 870113 Packer Property March 11,2013 Retaining Walls and Steep Slope Evaluation Page 5 Everett,Washington Explorations: The subsurface conditions within the site were explored on February 1, 2013 with four hand auger explorations. The approximate locations of our explorations are shown on the Schematic Site Plan in Figure 2. A geologist from 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 hand augers. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 4. The logs of our hand augers are attached to this report and are presented as Figure 5. We present a brief summary of the subsurface conditions in the following paragraph. For detailed descriptions of the subsurface conditions,the hand auger logs should be reviewed. At the surface of all of the hand augers,we encountered approximately 0.2 to 0.3 feet of surficial topsoil. Below the topsoil in Hand Augers 1, 2, and 4, we encountered approximately 3.3 to 4.7 feet of medium dense to dense, fine to coarse sand with silt, gravel, and organics, and medium stiff sandy silt with organics that we interpreted as undocumented fill. Underlying the fill in Hand Augers 1, 2, and 4 and the topsoil in Hand Auger 3, we encountered very stiff to hard, light brown to dark gray, sandy silt and silt with sand that we interpreted as native Transitional Bed deposits. The hand augers were terminated within the native transitional bed deposits at depths in the range of 1.0 to 5.5 feet below the existing ground surface. Hydrologic Conditions Groundwater seepage was encountered in all of our explorations ranging from 0.8 feet to 5.0 feet below the existing ground surface. We also observed natural groundwater seepage emitting from the slope along the western property line, mostly from the neighboring property, within the vicinity of the block walls. We interpret all of the ground water found on this site to be a permanent perched groundwater condition. Perched water occurs when surface water infiltrates through less dense, more permeable soils, such as topsoil and the weathered horizon, and accumulates on top of a less permeable soil, such as the dense/hard glacial soils. Perched water typically does not represent a regional groundwater"table" within the upper soil horizons; however, due to the relatively large recharge area surrounding this site, it is our opinion that groundwater on this site is a chronic condition that will persist throughout the year. This is consistent with the description provided by the property owner. Perched water tends to vary spatially and NELSON GEOTECHNICAL ASSOCIATES, INC.