3003 W CASINO RD BLDG 40-23 Geotech Report 2025-01-22

2.2. Laboratory Testing Soil samples were obtained during drilling and were taken to GeoEngineers' laboratory for further evaluation. Selected samples were tested for the determination of grain size distribution (sieve analysis), and moisture content. A description of the laboratory testing and the test results are presented in Appendix B. In addition to the explorations completed as part of this evaluation, we reviewed several exploration logs from previous site evaluations for HBL Positions 1 through 4, original boring 16 by Dames & Moore in 1966, and the original site grading and fill plan of the factory area. The previous exploration logs are presented in Appendix C. The Puget Sound basin is a region of Quaternary (last 3 million years) sediments that range in thickness between 800 and 2,400 feet. Bedrock exposures are present on the basin margins to the east and west in the Cascade and Olympic Mountains, respectively. The basin area has been repeatedly overridden by Pleistocene (between 11,000 and 3 million years ago) continental glacial ice depositing till, glacial sand and gravel, and glacially formed lake clay and silt. The repeated glacial action has resulted in numerous north -south trending ridges with intervening valleys filled with post -glacial alluvium and/or marine deposits (Galster, 1989). The most recent glacial cycle of sediment deposits is referred to as the Vashon Drift, occurring between 13,500 and 15,000 years ago. Geologic maps of the Boeing Everett Facility indicate surficial soils to consist primarily of glacial till of the Vashon Drift (James P. Minard,1982) and modified land (fill), which is consistent with previous explorations and our experience. Glacial till in the Everett area typically mantles hills, ridges, and slopes and varies in thickness from about 10 to 60 feet. A deep ravine is present in the north area of the facility that previously extended south within the 40-56 Building. More gentle sloping ground was present at the main factory building prior to development. A zone of weathered till typically overlies the dense glacial till to depths of 3 to 10 feet. This weathered zone is somewhat drained, whereas the unweathered till is a barrier to vertical drainage. Water percolating into the weathered till will usually pond and migrate laterally between the weathered and unweathered layers. The weathered layer is absent in many areas of the main factory because of historic grading and site cuts that exposed the very dense glacial till prior to development. In general, the cuts exposing the very dense glacial till were completed in the west portion of the main factory and fill was required in the east. Subsurface soils encountered in the borings are consistent with the geologic mapping. The boring explorations encountered weathered glacial till overlying unweathered dense to very dense glacial till. GEoENGtNEER June 1a, 2022 Page 2 File tic. 0120-294-02