2022-11-07_REVISION - C1981041 (2)

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transmission line across a portion of the permit area, within a portion of the South Portals mine area which had at one time been approved for future undermining. The operator committed within the permit application to develop a subsidence survey or control and mitigation plan, upon resumption of mining via the South Portal. The plan will be approved by TGTC, and will be in place prior to mining within the subsidence angle of draw of the gas line. An agreement between PCC and TGTC is included as Appendix 20-9, in Volume 6 of the permit application. The agreement includes the provision that the operator would notify TGTC six months prior to undermining of the gas transmission line. Because no further mining is proposed or approved, this provision is no longer applicable. Subsidence issues identified in association with PR-02,included updates to the"Man- made Features Map" to include the 345KV Rifle-San Juan transmission line, a house and shop building, and an area of"occasionally irrigated pastureland", all within the South Portal mining area. The house and pastureland are on previously undermined areas; the powerline has not been undermined (August 2003). Updated subsidence impact projections were provided in response to Division requests. Projected worst case impact to the occasionally irrigated pastureland is localized dewatering of ponds or ditches due to subsidence cracks, which the operator has committed to repairing if they develop. Foundation floor cracking to the dwelling foundation and shop floor as a result of differential settling were projected worst case impacts for these structures, which were constructed over a previously mined out area. Worst case impacts to the power line were projected to be minor tilting of transmission towers which could be repaired by shimming under the legs or replacing deformed members, which the operator indicated could be done without disruption of service. Mining beneath the powerline was to be limited to development mining with no secondary extraction, resulting in an extraction rate of 49%. No definitive statement from the powerline owners documenting that potential worst case subsidence damage to the powerline could be repaired without disruption of service was ever submitted. However, South Portal mining operations ceased in 1997, prior to extension of workings to within the subsidence angle of draw associated with the powerline. No further mining within the permit area is proposed or approved. The South Mine Portals were sealed in 2000, and portal entries out-by the seals were backfilled in 2007. The possibility of resumption of mining under Permit C-81-041 is essentially nil, and would at minimum require approval of a major permit revision. Stipulation No. 22,previously attached to the permit,had required the operator to submit specific written documentation from the powerline owners prior to mining within the subsidence angle of draw associated with the powerline. Due to the fact that coal extraction operations have ceased and the portals have been sealed and backfilled,the Division finds that Stipulation No. 22 is no longer necessary or applicable, and the stipulation was removed with RN-5 approval. The Division finds the subsidence control plan, as presented by Powderhorn Coal Company within the permit application document, to be in compliance with the subsidence-related regulations of Rules 2.05.6(6) and 4.20. 59