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XV. Subsidence Control <br />The applicant has predicted that no material damage will result from subsidence. However, numerous <br />structures exist above the mining azea. The applicant has presented a subsidence control plan to repair <br />or mitigate damage caused by subsidence for each of the existing structures. Details regazding the <br />subsidence control plan may be found in the approved permit. A brief summary of the subsidence <br />control measures for each structure follows. <br />County Road No. 33 <br />When daily monitoring reveals that the asphalt road surface has buckled or been damaged due to <br />subsidence, TCC will temporarily repair the surface using gravel. Once subsidence monitoring <br />indicates that subsidence has ceased, a permanent asphalt overlay or patch will be applied to the <br />damaged road section. This method has successfully been employed during the mining of Longwall <br />panels 9R, 8R, 7R, 6R and SR in the Eastern Mining District. Twentymile Coal Company re-paved <br />segments of Routt County Road No. 33 in the fall of 1994, that had experienced damage due to <br />subsidence of Longwall Panels SR and 6R. <br />Southern Pacific Railroad <br />When daily monitoring indicates the track is damaged or the grade has changed, a slow speed <br />restriction will be instituted. Re-leveling and repair of the track occurred in accordance with <br />mitigation plans required by Southern Pacific Railroad. <br />Havden-Gore Pass Powerline <br />When daily monitoring reveals structural tower damage, TCC will notify power repair crews to <br />stabilize and/or repair the damage. TCC will also to notify the utility 30 days prior to undermining, <br />in addition to the Division requirement of 6 months notification of undermining. TCC <br />representatives have held discussions with the utility company and have indicated to DMG that re- <br />routingcapabilities and system redundancy will prevent end line user power loss. Ground fault <br />interruption capabilities aze also in place to prevent a downed line from remaining live if it were to <br />fall to the Bound or across County Road No. 33. TCC submitted a letter that confirms that end <br />user power would not be interrupted. This letter has been incorporated into the permit document in <br />exhibit 7D-1. The powerline was subsided without interruption or significant damage to the <br />powerline towers. Power company personnel inspected the powerline after subsidence had <br />occurred and found that deformation of the structures was within company specifications and did <br />not require Twentymile Coal Company to conduct repairs. Information regazding subsidence of the <br />Hayden-Gore powerline can be,found in the 1997 and 1998 Subsidence Reports. <br />Western Area Power Administration (WAPA)lPublic Service Companv (PSC)/Tri-State Powerlines <br />As part of PR-06, TCC is incorporating an engineering report into Exhibit 7e-7 of the permit <br />application. The report indicates the two powerlines owned by WAPA and PSC/Tri-State, which <br />overlie proposed panel 19 Right, can be subsided without interruption of power. This prediction is <br />based mainly on TCC's past success undermining powerlines without significant damage to the <br />powerlines. Also, the powerlines over panel 19 Right aze pazallel to the length of the panel. This <br />pazallel orientation will result in independent subsidence of each powerline tower, rather than the <br />simultaneous subsidence of multiple towers (or poles) as done in past undermining of powerlines by <br />TCC. The predicted worst possible consequences aze tilting and deforming of steel lattice towers. <br />23 <br />