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For these reasons, American Soda believes that the requirement for running a gamma log at <br />production levels of 85,000 tons and 150,000 tons should be eliminated. The gamma logs run at the time <br />of well construction and retirement can reasonably be accomplished since scaling is not an issue at <br />construction and is less of an issue after pulling the tubing at well retirement. If it appears that <br />subsidence has occurred, the Director would require additional studies to determine the extent of any <br />subsidence and to develop a corrective action plan. The Director may also require changes in the <br />operating plan for new cavities, such as a larger pillar between individual cavities. The subsidence <br />monitoring plan (dated August 2004) has been revised to reflect this change. <br />Proposed Modifications for Subsidence Monitoring: <br />• Replace Revision 4 of the Subsidence Monitoring Plan, dated December 23,1999, with the <br />revised Subsidence Monitoring Plan, dated August 2004 (Appendix J ) <br />• Part II, A, 3, Cavity Development, 2nd Paragraph is proposed to be changed as follows: <br />Current lan~ua~e: <br />The applicant has prepared the Subsidence Monitoring Plan dated April, 1999, which was' submitted to <br />the BLM, Colorado Division of Minerals and Geology (CDMG) and the EPA. The 4th revision of this <br />plan, dated December 23, 1999, is incorporated into this Permit as Appendix I. As provided in this plan, <br />the permittee must establish surface monitoring monuments on the initia125 wells in addition to the grid <br />of land surface monuments. The subsurface monitoring plan includes the installation of coaxial cable in <br />solution mining well bores for use of Time Domain Reflectometry (TDR), which is technology used to <br />detect differential movement close to the top of the cavity and above. If subsurface movement occurs, <br />the coaxial cable will break or stretch. The location of the change in coaxial cable properties will be <br />determined by use of a cable tester. Borehole geophysical logs will also be run periodically to <br />substantiate the TDR monitoring results, and corrective action implemented if necessary. The shape of <br />the cavity is, of course, an important element that affects subsidence. For that reason, the permittee is <br />required to undertake studies and evaluate techniques for assessing cavity shape. Depending on the <br />results of these studies, American Soda may be required to establish additional monitoring wells to better <br />track cavity influence on the pillars. <br />Proposed language: <br />The applicant has prepared the Subsidence Monitoring Plan dated August 2004, which was <br />submitted to the BLM, Colorado Division of Minerals and Geology (CDMG) and the EPA. This <br />plan is incorporated into this Permit as Appendix J. As provided in this plan, the permittee shall <br />establish surface monitoring monuments on well casings and well pads in addition to establishing <br />land surface monuments at certain section and quarter section corners. The subsurface <br />monitoring plan includes the test installation of coaxial cable in solution mining we1120-12 bore for <br />use of Time Domain Reflectometry (TDR), to detect differential movement close to the top of the <br />cavity and above. If subsurface movement occurs, the coaxial cable will break or stretch. The <br />location of the change in coaxial cable properties will be determined by use of a cable tester. <br />Borehole geophysical logs will be run twice for each well in service during the life of a well: (1) <br />following initial drilling of the well and (2) after retirement of the well. Corrective action will be <br />implemented if necessary. The Director may also require changes in the operating plan for new <br />FINAL Addendum to SOB For Modification No. 9, UIC Area Permit No. C030858-00000 Page 4 0}'29 <br />