6801 SEAWAY BLVD Geotech Report 2025-08-19

Seaway Commercial Center Subsurface Exploration, Geologic Hazard, 7007 Seaway Boulevard and Geotechnical Engineering Evaluation Everett, Washington Geologic Hazards and Mitigations 6.2 Seismically Induced Landslides Similar to the discussion in Section 5.0, it is our opinion that the potential risk of damage to the proposed distribution center by seismically induced slope failure is low during a design-level seismic event due to the lack of steep slopes at the project site and vicinity and the presence of dense to very dense glacially consolidated soils. 6.3 Liquefaction Liquefaction is a process through which unconsolidated soil loses strength as a result of vibrations, such as those which occur during a seismic event. During normal conditions, the weight of the soil is supported by both grain-to-grain contacts and by the fluid pressure within the pore spaces of the soil below the water table. Extreme vibratory shaking can disrupt the grain-to-grain contact, increase the pore water pressure, and result in a temporary decrease in soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore water pressure alone. Liquefaction can result in deformation of the sediment and settlement of overlying structures. Areas most susceptible to liquefaction include those areas underlain by non-cohesive silt and sand with low relative densities, accompanied by a shallow water table. Review of the WADNR Liquefaction Susceptibility Map of Snohomish County, Washington, by Palmer et al. (2004), indicates that liquefaction susceptibility at the project location is "Very Low to Low." In our opinion, the potential risk of damage to the proposed distribution center by liquefaction is low due to the high relative density of the underlying sediments and the absence of adverse groundwater conditions at the site. No detailed liquefaction hazard analysis was performed for this study, and none is warranted, in our opinion. 6.4 Ground Motion Structural design of proposed structures should follow 2018 IBC standards using Site Class "C" as defined in Table 20.3-1 of American Society of Civil Engineers (ASCE) 7 - Minimum Design Loads for Buildings and Other Structures. 7.0 EROSION HAZARDS AND MITIGATION The site is classified as a Low Risk Erosion Hazard Area under the Everett Municipal Code. The City of Everett's Erosion Hazard Map also identifies the site as a low risk erosion hazard area with slopes less than 25 percent. However, the sediments underlying the site generally contain significant quantities of silt and fine sand that are sensitive to erosion and disturbance when wet. Therefore, the project should follow best management practices (BMPs) to mitigate erosion hazards and potential for off-site sediment transport. December 17,2021 ASSOCIATED EARTH SCIENCES,INC. PEL/Id-20200319E001-002 Page 7