1618 HOLBROOK AVE 2018-01-02 MF Import

Retaining Wall Letter Lyashuk Residence, Everett, WA January 29, 2007 NGA File No. 755806 Page 3 Explorations: We visited the site on January 15 and 22, 2007 to explore the subsurface soil and groundwater conditions with hand auger excavations in the vicinity of the planned temporary ultra block wall. The % -proximate locations of our explorations are shown on the site plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc. (NGA) excavated three test holes in the area near the south wall of the building pad excavation, examined the soils and geologic conditions encountered, collected soil samples, and maintained logs of the explorations. The soils were visually classified in general accordance with the Unified Soil Classification System, ,)resented in Figure 4. The logs of the explorations are attached to this report in Figure 5. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions, the exploration logs should be reviewed. Exploration HA -I was located at the toe of the building pad cut slope. In general, HA -I exposed medium dense, gray -brown, fine to medium sand with trace silt to the depth explored at 5.0 feet below the existing ground surface. We interpreted this material be native advance outwash sand. Explorations HA-2 and HA-3 were both located above the south wall of the building pad excavation. IBoth explorations exposed a 2.8- to 3 2-foot thick surficial layer of loose to medium dense, fine to medium sand with silt and trace organics. We interpreted this material to be weathered advance outwash. IBelow the dark brown sand, both explorations exposed medium dense/medium stiff, orange -brown to gray -brown, interbedded silty sand, sand, and silt to the depths explored at 8.0 feet. Hydrologic Conditions Groundwater seepage was encountered at depths of 7.4 and 6.5 feet below the existing ground surface in explorations I IA-2 and HA-3, respectively. It is our opinion that this water represents a perched water condition. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of underlying less permeable soils. The more permeable soils consist of clean sand and weathered soils. 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.