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2.4 Surface Water Monitoring Reports <br /> The end of the "water year" is September 30th. The surface water monitoring reports are <br /> submitted annually and generally nine months after the end of the water year. This report is <br /> submitted to the BLM in the NS annual report. Pursuant to BLM stipulations, NS will notify the <br /> Authorized Officer within 10 days of the occurrence of any significant changes to the hydrologic <br /> system. <br /> 3 Subsidence Monitoring Plan <br /> The Natural Soda LLC subsidence monitoring plan includes both surface and subsurface <br /> monitoring of potential vertical ground movement on the NS Lease. Subsidence monitoring will <br /> be performed throughout the commercial operating life of the solution mining operations and <br /> for a period of three years following cessation of mining activities. Results of the subsidence <br /> monitoring (both surface and subsurface) will be checked periodically as needed, to verify and <br /> calibrate numerical models used in the design of the well-field layout. Surface subsidence <br /> monitoring will be conducted by establishing permanent surveying monument locations. <br /> Subsurface monitoring will be conducted by periodic borehole geophysical logging of the well <br /> bores and strata overlying the cavities produced by the solution mining activities. <br /> Pursuant to BLM and EPA stipulations, NS will perform the following activities. <br /> • Survey for surface subsidence on a biennial basis. <br /> • Pursue appropriate methods to determine solution mining interval configurations. <br /> • Determine extent of subsidence when noted. <br /> • Attempt to determine impacts on USDW aquifers from caving or subsurface subsidence. <br /> Prior to implementation, the revisions and updates to the plan will be submitted to the <br /> appropriate agencies for review and approval. <br /> 3.1 Subsurface Subsidence Monitoring <br /> The purpose of the subsurface subsidence monitoring is to ascertain movement of strata <br /> overlying the solution-mined intervals. Borehole geophysical techniques will be employed for <br /> determination of potential subsurface movement of the overlying strata. In pre-existing <br /> solution mining areas south of the plant (Figure 6) (historical Area B, a moniker system no <br /> longer utilized by NS) and south and east of the plant (historical Area P1), Time Domain <br /> Reflectometry (TDR) was employed. Currently, NS monitors the 4A-5M (Area P1) TDR location <br /> on a monthly basis. In addition, an independent third party monitors the location on a <br /> quarterly basis. This method of subsidence monitoring has proved to be unreliable and not as <br /> robust as was originally expected. Some of the cables have been compromised by the <br /> infiltration of water. Due to this unreliability, and the propensity for failure, TDR methodology <br /> will not be used by NS to address subsurface monitoring issues in future mining areas. <br /> Daub&Associates, Inc. Page 12 Natural Soda LLC 2022 EMP <br />