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• plant and facilities area will be retained to eliminate the possibility of subsidence. <br />Refer to Appendix 20-1 for initial protective pillar design calculations for the Ute <br />Water Property. In the case of the Ute Water Pipeline, the worst possible <br />consequence which subsidence could have, if it occurred, would be to cause a <br />break in the welded steel pipeline. This would result in a reduction or loss of the <br />raw water supply to the treatment and storage facility until the break was repaired. <br />In the case of the city of Palisade's 6-inch and 8-inch cast iron pipelines, the worst <br />possible consequence subsidence could have, if it occurred, would be to separate <br />or fracture the cast iron pipeline. This would result in a reduction or loss of the raw <br />water supply flow to the storage tank. <br />The mine plan for the Roadside North and South Mines allows for protective pillars <br />beneath Rapid, Cottonwood, Jerry and Coal Creeks within the permit area. Pillars <br />designed to safely carry maximum loads will be retained within an area defined by a <br />. 12° angle-of-draw. Initially, a 25° angle-of-draw was used which was a <br />conservative measure since the initial maximum angle-of-draw determined from <br />actual subsidence measurements made over room-and-pillar panels at the <br />Roadside South Portals was 21 °. Information to verify this determination is <br />contained in Appendix 20-2 and Exhibit 48. Subsequent monitoring revealed <br />angles-of-draw between 7° and 9°. The use of a 12° angle-of-draw was approved <br />as TR-06 (#86-01) in 1986. <br />Most of the pillars in the Roadside South Portals that will be developed beneath the <br />creeks are main-entry support pillars which are typically 80 ft. X 80 ft. in dimension. <br />Pillars this size have a factor of safety against failure of 2.92 under maximum <br />loading at 1,500 feet, which is the maximum overburden depth below the creeks. <br />At the Roadside North Portals, most of the pillars will be room pillars 50 ft. X 50 ft. <br />in dimension. The safety factor for these pillars is 5.27 under 500 ft. of maximum <br />loading. <br />20-3 (Rev. 01/01 ) <br />