2000-02-10_GENERAL DOCUMENTS - C1981041

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collection pipelines. In addition, several significant portions of the Cottonwood Creek channel is underlain by proposed room and pillar panel sections. In these areas, retreat mining is proposed to result in relatively conservative slabbed pillars, which have been demonstrated to have a safety factor in excess of 1.34. In the North Portal mining area, a safety factor of x.27 was calculatzd for the maximum load over pillars to be retained beneath Coal Creek and Jerry Creek. A subsidence event that occurred during the initial permit review was monitored and analyzed within the second and third east panels of the Roadside Mine, immediately adjoining the Cottonwood lease on the north side. This recorded and analyzed event has demonstrated that the design characteristics utilized in completing the proposed plan for subsidence control have functioned as projected within the area of the second and third east panels of the Roadside mine. With Division approval of Technical Revision No. 03, the monitoring plan on the second and third east panels was dropped. The operator had also installed subsidence monuments along the Ute water pipeline. Monitoring of this pipeline was also dropped with Division approval of Technical Revision No. 08. Both areas of subsidence monitoring have retained their monuments for future use if necessary. Monitoring of the south mains occurred until 1985, a yeaz preceding a temporary cessation that lasted until April 30, 1989. For Permit Renewal No. 3, the Division finds that the past subsidence monument survey monitoring has been sufficient to establish subsidence trends in the Roadside South Portals mining area. Because the geology, overburden thickness and coal seam extraction height remain the same as in previous mining areas that were monitored, similar eRects are predicted to occur, should mining resume. Visual monitoring conducted twice yearly by the operator through 1998, has confirmed this projection. For mining under Coal Creek and Jerry Creek in the North Portal mining area, two subsidence monitoring monuments were installed adjacent to Coal Creek and three monuments were installed adjacent to Jetty Creek, in 1997 (see Exhibit 56, Tab 18). The approved subsidence monitoring plan for the entire permit area is described beginning on page 20-8 of the permit application. Monitoring will consist of a visual surface inspection in spring and fall, to include areas to be mined within the next year, and areas mined during the past hvo years. Coal Creek and Jerry Creek monuments will be surveyed immediately prior to undermining and twice a year for two years subsequent to undermining. All monitoring results, including documentation and photographs of subsidence features and structures, will be submitted to the Division in an annual subsidence report by December 3l, of each year. Aoy new structures within the affected area not previously documented, as well as previously documented structures for which possible subsidence damage has been indicated, will be photographed and documented within the annual subsidence report. The Ute Water Conservancy installed a waterline along the south and west perimeter of the Roadside Refuse Disposal Area in the winter of 1991 /1992. Although this pile has remained stable since it was completed in 1984, care was taken to protect the pipeline should any subsidence or settling occur. The waterline consists of a six-inch PVC pipe braced inside aten-inch P.I.P. encasement pipe where it crosses the refuse pile. Should a rupture of the PVC pipe occur it would be contained in the P.I.P. pipe and directed off the pile. 45