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3.1.1 Borehole Geophysics <br /> Subsurface Subsidence Monitoring Wells (SSMWs) will be utilized to collect borehole <br /> geophysical logs which will be run periodically. These geophysical logs will be compared to an <br /> original baseline geophysical log. A natural gamma ray (GR) and casing collar locator (CCL) log <br /> will be used to detect subsurface movement. Due to elemental differences in the chemical <br /> compositions of nahcolite and oil shale, distinct gamma ray signatures for each material can be <br /> readily identified. Changes in the nature and depth of these signatures can be used to <br /> determine the extent of subsidence. If subsurface movement is determined to exist in excess <br /> of two (2) feet, the EPA will be notified within ten (10) days of discovery with an action plan to <br /> address subsidence. Likewise, changes in the position of a casing collar as identified on a casing <br /> collar locator log can be used to monitor the extent of any subsidence, as the grouted casing <br /> string may subside or fail along with the rock strata. <br /> 3.1.2 Subsurface Monitoring Frequency,Duration,and Location <br /> Pursuant to the EPA UIC permit the following subsurface subsidence monitoring requirements <br /> are in effect. A subsurface subsidence monitor well (SSMW) shall be required for every two <br /> cavities mined. The SSMW shall be constructed and logged within 90 days after receiving <br /> authorization to inject into the first of two associated mining intervals. Periodic monitoring of <br /> these wells shall be conducted during the life of the associated mining intervals and continue <br /> until 3 years after cessation of mining from the associated mining intervals. Borehole <br /> geophysical logging will typically be conducted five times for each SSMW in service. An initial <br /> SSMW baseline log (1) will be collected during initial drilling of the SSMW well. The second log <br /> (2) will be run after a production of 50% of the planned tons of nahcolite from the first of the <br /> two solution mining intervals. The third log (3) will be collected after a production of 75% of <br /> the planned tons of nahcolite from the first of two solution mining interval. The fourth log (4) <br /> will be run after retirement of both solution mining intervals which are associated with a SSMW <br /> and the fifth log (5) will be run 3 years after cessation of mining from the associated solution <br /> mining intervals. A sample comparison of subsurface subsidence geophysical logging is <br /> presented in Figure 5. NS may submit a request for a reduction in the required number <br /> geophysical logs by providing justification with data obtained that indicates a lesser number of <br /> geophysical logs are necessary for adequate subsurface monitoring. <br /> Attempts will be made to locate the SSMW proximally above the proposed mining interval with <br /> minimal plan view offset from the proposed well bore and drill the SSMW to the base of the R-6 <br /> confining interval. With respect to longer horizontal intervals or in the case of additions to <br /> existing horizontal mining intervals, the location of the SSMW along the length of the lateral <br /> well bore will be determined to provide appropriate monitoring and the location shall be <br /> approved by the EPA. It is noted that the BLM also has an interest in the SSMW surface hole <br /> location (SHL) as it relates to cultural, paleontological, and vegetation resources. As such the <br /> final SHL location will need to mindful of these resources and approved by the BLM. <br /> Daub&Associates, Inc. Page 13 Natural Soda LLC 2022 EMP <br />