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Borehole geophysics logs will be run according to the monitoring schedule in <br />Section 3.4 at each well in service. A natural gamma log will be run. to provide <br />data that maybe useful in detecting subsurface movement. <br />3.3 Solution Cavity Characterization <br />In accordance with the previous subsidence plan, American Soda evaluated <br />current technologies and methods to characterize the nahcolite solution cavity and <br />presented the findings to EPA, BLM, and CDMG. Based on the findings of that <br />evaluation, American Soda used downhole seismic methods on a test cavity to <br />evaluate cavity shape and verify that the approach will work during commercial <br />mining operations. A partial displacement of cavity fluids was used to crosscheck <br />the seismic results: Results of the field testing were reported to EPA, BLM, and <br />CDMG. <br />3.4 Subsurface Monitoring Frequency and Duration <br />TDR data will be collected once per quarter to verify the integrity of the system. <br />Once installed in well 20-12, the TDR system must operate continuously and <br />remain in service for a minimum of 3 years. <br />Borehole geophysics for the purpose of subsidence evaluation will consist of a <br />natural gamma log conducted twice for each well in service during the life of a <br />well: (1) following initial drilling of the well and (2) after retirement of the well. <br />4.0 REPORTING <br />A subsidence report will be submitted to the EPA, BLM, and CDMG annually. The <br />report will contain data from surface monument measurements and TDR data. Borehole <br />geophysical data will be provided as part of the construction and closure information for <br />wells. The annual subsidence report will include a map of surface monument locations, <br />location of well 20-12 where TDR was conducted, locations of wells where borehole <br />geophysics were conducted, a list of monuments and well coordinates, and a summary of <br />pertinent observations during the reporting period. In accordance with CDMG <br />requirements, if surface subsidence is detected, it will be reported to the agencies within <br />five working days. A final summary report of TDR monitoring in well 20-12 will be <br />submitted to the agencies no later than June 1, 2008. Additional TDR monitoring maybe <br />employed if the test program proves useful. <br />5.0 MITIGATION <br />No mitigation is currently planned for surface subsidence. Measurable surface <br />subsidence is not anticipated. Even in the event of failure of several pillars between <br />FINAL: Modification No. 9, UIC Area Permit No. C030858-00000 <br />Page 45 of 46 <br />