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Worst case impacts to the power line are projected to be minor tilting of transmission towers which <br />could be repaired by shimming under the legs or replacing deformed members, which the operator <br />indicates could be done without disruption of service. Mining beneath the powerline would be limited <br />to development mining with no secondary extraction, resulting in an extraction rate of 49%. As of <br />August 2003, no defmitive statement from the powerline owners documenting that potential worst <br />case subsidence damage to the powerline could be repaired without disruption of service has been <br />submitted. Mining has ceased and no further mining within the permit azea is proposed or approved. <br />Resumption of mining is unlikely, and would require approval of a major permit revision. For these <br />reasons, it is unlikely that the powerline will be undermined. The following stipulation is unlikely to <br />be triggered, but is retained as a precautionary measure. <br />Stipulation No. 22 <br />AT LEAST 120 DAYS PRIOR TO INITIATION OF COAL EXTRACTION WHICH COULD <br />POTENTIALLY CAUSE SUBSIDENCE DAMAGE TO THE 345 KV RIFLE-SAN JUAN <br />POWERLINE, THE PERMITTEE WILL SUBMIT WRITTEN STATEMENTS FROM THE <br />OWNERS OF THE POWERLINE WHICH INDICATE THAT POTENTIAL WORST CASE <br />SUBSIDENCE DAMAGE TO THE POWERLINE COULD BE REPAHtED WITHOUT <br />DISRUPTION OF SERVICE. NO MINING WHICH COULD AFFECT THE POWERLINE <br />BASED ON PROJECTED SUBSIDENCE ANGLE OF DRAW SHALL OCCUR PRIOR TO <br />DMG'S WRITTEN NOTICE OF COMPLIANCE WITH THIS STIPULATION. <br />With the acceptance of Stipulation No.22, the subsidence control plan, as presented by Powderhorn <br />Coal Company within the amended application documents, is found to be in compliance with the <br />subsidence-related regulations of Rules 2.05.6(6) and 4.20. <br />XI. Onerations on Alluvial Vallev Floors <br />The pennittee's alluvial valley floor investigations in Section 2.06.8 of Tab 21, Volume 6, of the <br />application have been reviewed for compliance. <br />There are two separate azeas where alluvial valley floors must be assessed: <br />1. The surface facilities area and adjacent areas at the Roadside North and South Portals, and <br />Unit Train Loadout; and <br />2. The Cottonwood/Rapid Creek drainages and adjacent areas which will be undermined by <br />the Roadside mine. <br />Drainages in the North Portal mining azea are characterized by steep sided canyons with deeply <br />incised channels, limited azeas of alluvial deposition, and no flood irrigated or subirrigated agriculture. <br />Headwaters for these drainages aze at relatively low elevations in the Book Cliffs, and the streams <br />exhibit intermittent or ephemeral flow regimes. Insufficient surface water availability and saline soils <br />eliminate Coal Creek, Jerry Creek and their tributaries from alluvial valley floor consideration. <br />Drainages in the bookcliffs with characteristics similaz to those in the permit azea are not typically <br />developed for irrigated agriculture (OSM, June, 1985 "Reconnaissance Maps to Assist in Identifying <br />Alluvial Valley Floors, West-Central Colorado"). <br />48 <br />