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<br /> <br /> <br /> <br />PR-04, Colowyo Coal Mine C1981-019 62 August 2016 <br /> <br />XVIII. Subsidence Control - Rule 4.20 <br /> <br />The Permit was found to comply with Rule 4.20. <br /> <br />Colowyo is mainly a surface coal mining operation. A small area was auger mined (see XXI <br />below). Subsidence over the auger mining was not considered a significant concern. The <br />possibility of large scale pillar failure over an area sufficient to produce surface effects was <br />considered very low (CTL/Thompson, Inc., Auger Mining Analysis, February 5, 1996). No <br />renewable resources or structures overlie the augered area, as discussed in the PAP (Rules <br />2.05.6(6) and 4.20). There is no current requirement for monitoring of subsidence by Colowyo at <br />the Colowyo Mine. <br /> <br />XIX. Coal Exploration - Rule 4.21 <br /> <br />Coal exploration outside the Permit boundary is authorized by other than this Permit, and is not <br />addressed in this finding. Coal exploration activity (resource confirmation) within the permit <br />area is found to be in compliance with applicable portions of Rule 4.21. <br /> <br />XX. Concurrent Surface and Underground Mining - Rule 4.22 <br /> <br />No concurrent surface and underground mining is planned for the Permit renewal period. <br /> <br />XXI. Auger Mining - Rule 4.23 <br /> <br />No auger mining is currently proposed in the mine plan. However, auger mining was done in <br />1993 in the Section 11 Pit. Further, highwall mining in the East Pit and West Pit has been <br />approved (PAP, pages 2.05-38a and 4.23-1) as well as in the South Taylor Pit (PAP, Rule 4, <br />pages 20 and 21). <br />XXII. Operations on Alluvial Valley Floors - Rule 4.24 <br /> <br />The Division has determined that the watersheds of Collom Gulch, Little Collom Gulch and <br />Morgan Gulch contain alluvial valley floors (AVFs). Surface coal mining and reclamation <br />operations at Colowyo, if conducted in compliance with the Permit, will preserve the essential <br />hydrologic functions of AVFs outside the permit area and will reestablish the essential <br />hydrologic functions of AVFs within the affected area, throughout the mining and reclamation <br />process (Rule 4.24.2). CCC has indicated that mining operations in the Collom area will not be <br />within the AVFs.