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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 8 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />3.3 SUBSURFACE CONDITIONS <br />HWA’s interpretations of subsurface conditions are based on the results of field explorations, our <br />review of available geologic and geotechnical data, and experience with similar geologic <br />settings. The soils encountered in HWA’s geotechnical explorations consisted of fill, bay <br />deposits, recessional outwash, and advance outwash deposits. These soil units are described <br />below in the anticipated order of deposition, from youngest to oldest. The exploration logs in <br />Appendix A and Appendix D provide more details of subsurface conditions observed at specific <br />locations and depths. HWA’s interpretation of geologic conditions within the project site are <br />presented on Figures 3A and 3B for Geologic Profile A-Aʹ and B-Bʹ, respectively. <br />Historic Fill: Fill material was encountered in each of the borings and consisted of very <br />soft to medium stiff fine-grained cohesive soils and very loose granular soil. Fresh to <br />decomposed wood was encountered in layers throughout the fill at some locations; this <br />was most prevalent in the westernmost borings overlying bay deposits. To HWA’s <br />knowledge, the placement of this fill was undocumented. The quality, thickness, and <br />extent of the fill is expected to vary spatially. <br />Bay Deposits: Bay deposits were encountered beneath the historic fill in boreholes <br />HWA-8 through HWA-11 and HWA-14P. This unit consisted of loose, silty sand and <br />gravel with shells interbedded. It ranged from approximately 40 to 60 feet thick. This <br />material appeared to consist of near-shore littoral deposits derived from wave action at <br />the bluff toe (former beach) and offshore transport of sediment. <br />Recessional Outwash: Recessional outwash soils were encountered below the fill in <br />borings HWA-1 through HWA-7, HWA-12, HWA-13, HWA-15 and HWA-16P. It was <br />also encountered below the bay deposits in borings HWA-9 through HWA-11. Boring <br />HWA-8 was terminated in these deposits. These deposits consisted of loose to medium <br />dense silty, gravelly sand. <br />Advance Outwash: Dense to very dense, silty, gravelly fine to medium sand was <br />encountered underlying recessional deposits to termination depths in all borings except in <br />boring HWA-8. <br />3.4 GROUNDWATER CONDITIONS <br />Groundwater was observed in most borings. However, the use of mud rotary drilling complicates <br />confidently observing groundwater levels during drilling. Shallow groundwater was observed <br />during drilling, ranging from 1 to 9 feet bgs. Groundwater monitoring wells were installed in <br />borings HWA-10P and HWA-13P in April 2022, in borings HWA-14P and HWA-16P in <br />October 2023, and in borings HWA-17P-24/HWA-17P-24A and HWA-18P-24 in August 2024 <br />to monitor groundwater fluctuations over time. Groundwater monitoring transducers set to