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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 9 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />collect readings at 30-minute intervals were installed in each monitoring well. Data collected <br />from April 26, 2022, to November 18, 2024, is presented on Figure 5. The transducer installed in <br />well HWA-14P malfunctioned, and a new transducer was installed in February 2024. <br />At HWA-10P, groundwater levels varied over time and ranged from approximately elevation 4.7 <br />to 10.3 feet, corresponding to a depth of 2.6 to 8.2 feet bgs. Data collected at HWA-10P shows <br />that water elevation at this location is influenced by tidal fluctuations in Puget Sound, with up to <br />2 feet of diurnal fluctuations in the well. Well HWA-17P-24 exhibited a tidal response of around <br />1 foot. Deeper zones (40 to 50 feet bgs) screened in HWA-10P and HWA-17P-24 may be under <br />partially confined conditions, while nearby wells HWA-14P and HWA-18P-24 had no tidal <br />response, particularly with HWA-18P-24 closer to the shore than HWA-17P-24. The lack of tidal <br />response in deeper screened portions of wells indicates the presence of confined and potentially <br />artesian groundwater conditions. <br />Data collected at HWA-13P indicated that groundwater in this area is essentially at or very close <br />to the well surface elevation of 16.5 feet, which indicates confined conditions within the advance <br />outwash soils at this location. <br />Monitoring well HWA-13P is screened within the advance outwash deposits from 40 to 50 feet <br />bgs. The soil samples collected at HWA-13P do not indicate the presence of a pronounced low- <br />permeability soil layer above the well screen elevation to justify presence of artesian condition in <br />this area; however, it is possible that the sampling interval at HWA-13P was not able to intercept <br />and capture a low-permeability layer in this area, or the overlying fill is acting as a confining <br />layer. Based on the artesian pressures measured at HWA-13P and high barometric efficiency, the <br />well is screened in a confined aquifer. Well HWA-13P also exhibits a low degree of response <br />(less than 1 inch) to tidal fluctuations in Puget Sound. <br />At HWA-16P, groundwater levels varied over time and ranged from approximate elevation 13.1 <br />to 14.5 feet, corresponding to a depth of 1.5 to 2.9 feet bgs. Well HWA-16P also exhibits a low <br />degree of response (less than 1 inch) to tidal fluctuations in Puget Sound. <br />Prospective contractors should be prepared to encounter and manage tidally and seasonally <br />varying groundwater conditions, with water levels ranging from 5 feet bgs to a few inches below <br />or at the ground surface. <br />The groundwater conditions depicted in the explorations are only for the specific date and <br />location reported and, therefore, are not necessarily representative of other locations and times. <br />HWA expects groundwater levels will vary depending on location, subsurface soil conditions, <br />season, tidal elevation, and the relative abundance of precipitation.