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XII. Subsidence Control <br />A Subsidence Survey, Subsidence Monitoring, and Subsidence Control Plan <br />were prepared by Rocky Mountain Geotechnical (RMG) for Dorchester Coal in <br />1983, which is still utilized by the Operator of the Southfield Mine, EFCI. The <br />RMG subsidence data are contained in Exhibit 23, "Subsidence Information" of <br />the permit application. <br />The applicant previously proposed a subsidence control plan in <br />accordance with Rule 2.05.6(6) and has committed to adopt all measures <br />in order to reduce the likelihood of subsidence, prevent material damage, <br />or mitigate the effects. The Division previously approved the plan. The <br />plan is outlined in Section 2.05.6, pages 63-66 of the permit application. <br />(4.20.1(2) and 4.20.3(1)) <br />2. The applicant previously proposed and has implemented a subsidence- <br />monitoring program, in accordance with Rule 2.05.6(6)(c), designed to <br />determine the commencement and magnitude of subsidence movements. <br />Map 17, "Mine Plan Map", depicts the locations of monuments that have <br />been installed and structures that are monitored within the permit and <br />adjacent area. The results of the monitoring program are submitted to the <br />Division semi-annually. The monitoring program is designed to extend for <br />a time, beyond cessation of mining in any area, consistent with the need <br />for verification of the subsidence prediction. The monitoring plan details <br />can be found on pages 2.05.6-59 through 63 of the permit application. <br />An initial study conducted for the mine predicted probable maximum <br />subsidence depths of 1.46 to 3.22 feet. From 1984-1994, subsidence due <br />to the mining operation was 0.03 to 2.19 feet. Since these depths are <br />within the projected occurrences, the Division approved the applicant's <br />request to reduce the monitoring frequency of some subsidence <br />monuments from quarterly to semi-annually. Semi-annual monitoring is <br />performed for the Newlin Creek streambed. The Florence water line and <br />Thompson Ranch structures are monitored quarterly. <br />Based on a review of semi-annual subsidence reports, the Division <br />requested that the minimum angle of draw be increased to 25-29 degrees, <br />based on data from the reports. This was incorporated into Stipulation 21 <br />from the 1991 Mid-term Review. <br />In a letter received from EFCI, dated January 17, 1994, the response to <br />the stipulation was to revise Map 17 to reflect an angle of draw at 29 <br />degrees and to adjust the permit boundary to reflect the same. Technical <br />Revision No. 18, received 15 June 1994 and approved 23 June 1995, <br />addressed the revised angle of draw, incidental boundary changes, Map <br />revisions and lease right-of-entry provisions. With the submittal of TR18, <br />this stipulation has been terminated. <br />Page 33 of 36