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Natural Soda LLC 2023 Project Status Report & Annual Plan of Development <br /> 23 January 2024 <br /> <br />4.4. Geotechnical Program (Geophysical Logging) <br />4.4.1. Subsurface Subsidence Geophysical Logging <br />NS conducted the EPA mandated subsurface subsidence logging in the 15H-SSMW <br />well July 2023, the analysis indicated no subsurface subsidence to the depth of 1,750. <br />The 15H-SSMW serves as the subsidence monitor well for the 15H and 16H west <br />mining intervals. <br />• NS conducted routine, EPA mandated subsurface subsidence logging in their <br />15H-SSMW well on July 14, 2023. This well serves as the SSMW for the <br />western portions of the 15H and 16H mining intervals. This SSMW log was <br />compared to the baseline SSMW log (July 9, 2016) and indicated no <br />subsurface subsidence to the log total depth of 1,750 feet measured depth <br />below ground level (MD GL). <br />• DRG & Associates, Inc. conducted routine EPA mandated Surface <br />Subsidence Monuments (SSMs) biennial surveys on June 20th, 2023. <br />Results were reported to the EPA on July 5, 2023. <br />4.4.2. Surface Subsidence Monitoring <br />A surface subsidence monument (SSM) survey of all monuments above NS’s area of <br />operations was conducted in the second quarter of 2023. Results of the 2023 SSM <br />survey are shown in Table 5 below, and survey results were reported to the EPA July <br />2023. The next planed SSM survey will be conducted in the second quarter of 2025. <br />In 2024 a new SSM will be installed above the 18H west mining interval that will be <br />drilled and completed during the spring/summer of 2024.