5200 EVERGREEN WAY SEPA 017 - 010 Geotech Report 2025-04-23

r S Subsurface Exploration, Geologic Hazards, and Former Brien Ford Preliminary Geotechnical Engineering Report Everett, Washington Project and Site Conditions excavation to remove contaminated soils. The maximum excavation depth will be on the order of 18 feet below the existing surface and the extent of the planned excavation will include the commercial sales building footprint, approximately half of the total building footprint, and the adjacent paved area to the south. After remediation is completed the excavation will be backfilled with structural fill and covered with a crushed rock base course and new asphalt will be placed. We understand the commercial sales building was added on to the south end of the service intake building. The interior wall that separates the service intake side from the commercial sales side will remain and will be adjacent to the planned excavation. We anticipate that the planned excavation will undermine the supporting soil prism of the foundation for this wall. In addition, the south end of the excavation will undermine the supporting soil prism for the north end foundation of the detail shop. Underpinning is currently proposed to temporarily support these foundations during the planned excavation. 3.0 SUBSURFACE EXPLORATION The subsurface exploration for this study was completed on April 28, 2017. The exploration drilling was performed by Cascade Drilling, Inc., of Woodinville, Washington, working under subcontract to Associated Earth Sciences, Inc. (AESI). The conclusions and recommendations presented in this report are based on the single exploration completed for this study. We also relied on previously completed subsurface exploration data related to our previously completed reports, referenced above. The location and depth of the exploration completed for this study was completed within site and budget constraints. 3.1 Exploration Boring The exploration boring completed for this study was achieved by advancing hollow-stem auger tools with a trailer-mounted drill rig. During the drilling process, samples were obtained at 5-foot-depth intervals. The exploration boring was continuously observed and logged by a representative from our firm. The exploration log presented in the Appendix is based on the field log, drilling action, and inspection of the samples secured. The approximate location of the exploration is shown on the "Site and Exploration Plan," Figure 2. Disturbed, but representative samples were obtained by using the Standard Penetration Test (SPT) procedure in accordance with American Society for Testing and Materials (ASTM) D-1586. This test and sampling method consists of driving a standard 2-inch, outside-diameter, split-barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded, and the number of blows required to drive the sampler the final 12 inches is known as the Standard Penetration Resistance ("N") or blow count. If a total of 50 is recorded within one 6-inch interval, the blow count is recorded as the number of blows for the corresponding number of May 16,2017 ASSOCIATED EARTH SCIENCES,INC. AWR/Id-160594V003-2-ProjecfsI20160594\KV\WP Page 2