2710 14TH ST BLDG A Geotech Report 2023-12-29

of the site, while an asphalt and gravel parking lot occupies the southern portion of the site. The residential building is surrounded by lawn and landscape areas. Concrete sidewalks exist adjacent to the street and concrete paths and stairs lead to each unit. ' The residential buildings are surrounded by lawn and landscape areas on each site. Concrete sidewalks exist adjacent to the streets and concrete paths and/or stairs lead to each unit. Small and large deciduous ' trees are scattered around the residential units on each site. Underground utilities consisting of power, gas, water and sewer lines are located throughout the area. Overhead power and telephone lines exist along Poplar Street, 14th Street, Larch Street and Fir Street. The layout of existing site features is shown on ' Figure 2. The conceptual buildings located on Site 1 and other site improvements are shown on Figure 3. 3.2. Geology I Published geologic information for the project vicinity includes two United States Geological Survey (USGS) maps; one map is of the Everett 7.5 - Minute Quadrangle, Snohomish County, Washington and the other ' map is of the Marysville Quadrangle, Snohomish County, Washington (USGS 1985). The typical geologic soil profile (youngest to oldest) in the project vicinity is glacial till overlying advance outwash deposits. Mapped soils in the immediate project vicinity consist of glacially consolidated Vashon Till deposits (glacial I till). Advance outwash deposits are mapped along the eastern perimeter of the site along Pine Street. Glacial till is generally a non -sorted, non -stratified mixture of sand, gravel and silt that has been overridden ' by several thousand feet of ice. It typically has high shear strength, low consolidation and low permeability characteristics in the undisturbed state. It typically develops a "weathered" zone where seasonal groundwater perches on top of the relatively impermeable unweathered till and the perched groundwater ' occurs as seepage following the site topography. Advance outwash deposits are mostly clean, gray, pebbly sand with increasing amounts of gravel higher in the section deposited by meltwater flowingfrom the advancingfront of the Vashon glacier. This unittypically has high shear strength, low consolidation and moderate permeability characteristics in the undisturbed state. ' 3.3. Subsurface Conditions 3.3.LSoil Conditions ' Fill and glacial till deposits were encountered below existing grades in the test pits completed at Sites 1 and 3, while glaciolacustrine deposits were encountered in test pits on the northern part of Site 2. Our I observations included the following. 3.3.1.1. Asphalt Pavement/Gravel/Sod: ' Approximately 1 inch of crushed gravel underlain by 3 inches of asphalt concrete pavement were observed in test pit TP-17 that was completed in the parking area at the south end of Site 3. All other test pits were completed in grass/lawn areas. The average depth of the sod/topsoil associated with the grass areas was I 3 to 4 inches, 3 inches, and 4 inches at Sites 1, 2, and 3, respectively. 3.3.1.2. Fill/Weathered Glacial Till Soils ' Fill and/or weathered glacial till generally consisting of medium dense silty fine to medium sand with occasional gravel and various amounts of organic matter was encountered below existing grades in the test pits. Localized areas of cleaner sands were observed in TP-2, TP-11, and TP-14. A silty gravel with sand was I GEOENGINEERsr/,� October30,2019 Page3 ' File No 21288-002 00