Laserfiche WebLink
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 />~~ ~ ~ ' '., ,,I~ ?rouosed Modifications for Subsidence MonitorinE: <br />~. <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 laneuaQe: <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 maybe required to establish additional monitoring wells to <br />better track cavity influence on the pillazs. <br />Proposed laneuaae: <br />The applicant has prepared the Subsidence Monitoring Plan dated August 2004, which was <br />submitted to the BLM, Colorado Divisiou 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 <br />for use of Time Domain Reflectometry (1'DR), to detect differential movement close to the top of <br />the 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 />cavities, such as a larger pillar between individual cavities. The shape of the cavity is, of course, <br />an important element that affects subsidence. For that reason, the permittee has evaluated <br />techniques for and undertaken studies to assess cavity shape. Depending on the results of these <br />studies, American Soda may be required to establish additional monitoring wells to better track <br />cavity influence on the pillars. <br />Draft Addendum to SOB For Modification No. 9, UIC Area Permit No. CO30858-00000 Page a oj27 <br />