8407 BROADWAY SECURE SPACE STORAGE Geotech Report 2025-04-24

Zi pperGeo Broadway Everett Expansion Geoprofessional Consultants Project No. 2601.01 July 7, 2022 • Alderwood Complex-Urban Land • Hydrologic Soil Group B • Erosion Susceptibility: Low Subsurface Soil Conditions Our subsurface evaluation consisted of completing three (3) borings (B-1, B-2, and B-3) with a truck- mounted drill rig on June 2, 2022. Explorations B-1 and B-3 were completed to a depth of 25.5 feet; B-2 extended to 26.0 feet below ground surface (bgs). The explorations were laid out based on a conceptual site plan provided to us and were completed in the paved parking area of the site. The explorations' approximate locations are presented on Figure 1, the Site and Exploration Plan. We determined the exploration locations using GPS. Soils were visually described during recovery in general accordance with the Explanation of Exploration Logs provided in Appendix A. Detailed descriptive logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are presented in Appendix A. Generalized descriptions of subsurface soil conditions observed in specific areas of the site are presented below. Please refer to the exploration logs in Appendix A for a more detailed description of the conditions encountered at the exploration locations. Stratification boundaries on the boring logs represent the approximate depth of changes in soil types, although the transition between materials may have been gradual. If variations become apparent during construction, it may be necessary to reevaluate the recommendations of this report. Drilling occurred through asphalt pavement. Pavement thicknesses are about two (2) to three (3) inches over about eight (8) inches of crushed base course gravel. Subsurface soil conditions observed below the pavement generally consisted of approximately five (5) to ten (10) feet of loose to dense sand with variable silt and gravel content interpreted to be previously placed fill (Hf). Immediately below the fill material, soils consisting of very dense sand with variable silt and gravel content were observed to the completion depths of the borings.This soil material is interpreted as glacial till (Qvt) of Pleistocene age. Groundwater Conditions No groundwater was observed at the time the explorations were completed. Fluctuations in water levels will likely occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. Summary of Laboratory Testing Laboratory testing was completed on select soil samples obtained from our borings. Laboratory testing included moisture content and grain size analysis. The results of moisture content testing are shown on the boring logs. Results of remaining testing are provided in Appendix B. Moisture contents in the samples collected ranged from 6 to 14 percent with an average of about 8 percent. Grain-size(sieve)tests indicate fines contents (silt and clay size particles) ranging from about 22 to 32 percent with an average of about 26 percent in representative samples from approximately 7.5 feet to 25 feet bgs. 3