600 54TH ST SW I Geotech Report 2025-01-29

GEOTECHNICAL INVESTIGATION EVERETT,WASHINGTON March 2, 2018 Within the proposed building lots,there are local slopes with magnitudes approaching 10o percent and relief of about 10 to 15 feet. Many slope areas within the property are obscured by heavy vegetation. The site is bordered to the north,south and west by residential properties and to the east by a ravine area and Pigeon Creek. 4.o Field Investigation 4.1.1 Site Investigation Program The geotechnical field investigation program was completed on January 10,2018 and included excavating and sampling 15 test pits within the property,where accessible. Test pits were excavated with a small trackhoe and access was limited to numerous areas due to downed trees and locally steep topography. The soils encountered were logged in the field and are described in accordance with the Unified Soil Classification System(USCS). A Cobalt Geosciences field representative conducted the explorations,classified the encountered soils, kept a detailed log of each test pit,and observed and recorded pertinent site features. The results of the test pit explorations and sieve analyses are presented in Appendix C. 5.0 Soil and Groundwater Conditions 5.1.1 Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north-south trending trough that extends from southwestern British Columbia to near Eugene,Oregon. North of Olympia,Washington, this lowland is glacially carved,with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non-glacial sediments consisting of interbedded gravel,sand,silt,till,and peat lenses. The Preliminary Surficial Geologic Map of the Mukilteo and Everett Quadrangles,Snohomish County, Washington,indicates that the site is located near the contacts between Vashon Glacial Till,Esperance Sand(Vashon Advance Outwash),Whidbey Formation,and modified land. Vashon Glacial Till is typically characterized by an unsorted,non-stratified mixture of clay,silt,sand, gravel,cobbles and boulders in variable quantities. These materials are typically dense and relatively impermeable. The poor sorting reflects the mixing of the materials as these sediments were overridden and incorporated by the glacial ice. Modified land includes areas underlain by undocumented fill. In general,fill depths and characteristics vary with location and prior land use. Esperance Sand is an older term for Vashon Advance Outwash although in some areas could be considered distinct from Advance Outwash. In general,these deposits consist of fine to medium grained 2