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A raw water pipeline system that supplies the town of Palisade, runs along Cottonwood Creek to the <br />confluence of Rapid Creek. Damage to the pipeline was to be avoided by leaving pillars beneath the <br />pipeline route to assure additional stability. A second pipeline conveys raw water along Rapid Creek <br />from collection points southeast of the permit area. Any pipeline damage will be mitigated by the <br />operator should it occur. See page 224, Exhibits 29, 30 and 46 of the permit for further information. A <br />24 -inch concrete water line overlies portions of the permit area and is owned and maintained by the Ute <br />Water Conservancy District. On February 28, 1990, this water line broke roughly 200 feet east of the <br />North Fan Portal. The break was detected immediately and Ute Water Conservancy was able to shut <br />down the line. The water was directed down the drainage channel at the North Decline area, and some <br />water flowed to sediment pond 7 (now reclaimed). <br />The application contains an extensive analysis of the stability of pillars proposed to prevent subsidence <br />beneath the major drainages potentially affected by subsidence. The application also contains <br />predictions of maximum subsidence expected to occur if pillar failure follows cessation of mining in the <br />potentially affected areas. Each of these analyses is prepared in accordance with the state -of -the -art of <br />subsidence prediction. See Appendices 20 -1 through 20 -4 for subsidence predictions and pillar design <br />analyses. <br />The demonstration of proposed pillar stability, including calculations of pillar factors of safety using a <br />conservative method developed by A.H. Wilson, is included within this submittal. Pillars and main <br />corridors which have 80 feet by 80 feet dimension are proposed and demonstrated to exceed factors of <br />safety of 2.92 under maximum anticipated overburden loadings. The life -of -mine plan for the <br />Cottonwood lease area indicates that mains were located to directly underlie significant portions of the <br />two potentially affected creeks and the associated alluvial aquifers and raw water collection pipelines. In <br />addition, several significant portions of the Cottonwood Creek channel is underlain by proposed room <br />and pillar panel sections. In these areas, retreat mining is proposed to result in relatively conservative <br />slabbed pillars, which have been demonstrated to have a safety factor in excess of 1.34. In the North <br />Portal mining area, a safety factor of 5.27 was calculated for the maximum load over pillars to be <br />retained beneath Coal Creek and Jerry Creek. <br />A subsidence event that occurred during the initial permit review was monitored and analyzed within the <br />second and third east panels of the Roadside Mine, immediately adjoining the Cottonwood lease on the <br />north side. This recorded and analyzed event has demonstrated that the design characteristics utilized in <br />completing the proposed plan for subsidence control have functioned as projected within the area of the <br />second and third east panels of the Roadside mine. With Division approval of Technical Revision No. <br />03, the monitoring plan on the second and third east panels was dropped. The operator had also installed <br />subsidence monuments along the Ute water pipeline. Monitoring of this pipeline was also dropped with <br />Division approval of Technical Revision No. 08. Both areas of subsidence monitoring have retained <br />their monuments for future use if necessary. Monitoring of the south mains occurred until 1985, a year <br />preceding a temporary cessation that lasted until April 310, 1989. <br />In conjunction with Permit Renewal No. 3, the Division found that the past subsidence monument survey <br />monitoring had been sufficient to establish subsidence trends in the Roadside South Portals mining area. <br />Because the geology, overburden thickness and coal seam extraction height remain the same as in <br />previous mining areas that were monitored, similar effects are predicted to occur, should mining resume. <br />Visual monitoring conducted twice yearly by the operator through 1998, had confirmed this projection. <br />49 <br />