2019-11-22_REVISION - C1981019 (2)

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RULE 4 PERFORMANCE STANDARDS 27 plus years of mining activities in the West, East, and Section 16 pits, and are so limited in thickness and extent that it is not practical to recover the remaining coal reserves by either surface or underground mining methods. At Colowyo, future surface mining will entail moving to separate, distinct, and in some cases distant pits while future underground mining will entail mining totally different seams in different locations. 4.23.5 Undisturbed Areas of Coal Shall Be Left in Unmined Sections As for the CDRMS Rules (Rules) requirement for leaving undisturbed areas of coal in unmined sections, Colowyo contends that this application of the Rules does not apply since the seams to be highwall mined are being accessed from active surface pits that by this Permit and other applicable sections of the Rules are required to be backfilled and fully reclaimed. Hence should undisturbed barrier areas of coal be left for some future access, these potential portal areas would be inaccessible for future generations because they would be buried under the pit backfill. Additionally and importantly,as discussed above, due to the many geological reasons,there is not economical coal to be recovered from"behind"the areas slated to be highwall mined. 4.23.6 Abandoned or Active Underground Mine Workings To Colowyo's knowledge, no abandoned or active underground mine workings have ever existed or currently exist in any of the coal seams in the areas proposed to be highwall mined. No highwall mining will be allowed to take place within 500 feet of any abandoned or active underground mining operation. 4.23.7 Surface Mining Activities and Highwall Mining The highwall mining shall follow the surface coal mining activities in a contemporaneous manner consistent with the applicable requirements of CDRMS Rule 4. Due to active pit progressions and sequencing of mining (in addition to meeting the Permit requirements for contemporaneous reclamation), it is required that highwall mining occurs timely if not immediately following conclusion of pit mining activities. Also,as described more fully in 2.06.9(2),the need to backfill, i.e., contemporaneously reclaim the pits, is mandatory for Colowyo in order to build the pit floor from which to work from to mine the successively higher (in the geologic column) coal seam. Hence successful highwall mining is in part dependent upon timely and successful contemporaneous reclamation of the pits. 4.23.8 Prevent Pollution of Surface and Groundwater and to Reduce Fire Hazards Ground water in the pit or highwall mining holes will not be problematic being that the Colowyo pits are essentially dry(minor perched aquifers with limited seasonal flows)and are located above the first regional aquifer(Trout Creek)by a substantial distance. Ground water flow regimes and the negligible impact that Colowyo's surface mining activities have on ground water as a result of mining these target coal seams/rock interburdens are detailed extensively in Permit Section 2.04.7(1). From this extensive body of data and from experiences to date with mining activities, no toxic forming or acid forming water discharge is anticipated from any of the highwall openings. Rule 4 Performance Standards 4-88 Revision Date: 11/18/19 Revision No.: MR-211