2022-01-27_PERMIT FILE - C1981019A (4)

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RULE 4 PERFORMANCE STANDARDS South Taylor/Lower Wilson – Rule 4, Page 14 Revision Date: 11/23/21 Revision No.: TR-152 procedures for working around underground mines, surface and groundwater pollution prevention procedures, reduction in fire hazards, backfilling, grading, and PMT requirements for all areas previously permitted. 4.23.2(1) Undisturbed Areas of Coal Shall Be Left in Unmined Sections As for the rules requirements [Rules 4.23.2(1)(a)-(c)] for leaving undisturbed areas of coal in unmined sections, Colowyo requests a variance from the requirements of this rule for the South Taylor Pit. Colowyo’s highly successful highwall mining methods that have been used and will be in the future in the South Taylor Pit, will maximize production and ensure no subsidence occurs. Using this particular method of highwall mining by leaving pillars and barriers allows the seams to be mined below each other and still ensures geologic stability once all seams have been mined out. Please see Exhibit 27, Item 6 and Item 7 in Volume 20 for further discussion on the geotechnical design and operational considerations implemented highwall mining the South Taylor Pit. 4.23.2(2) Abandoned or Active Underground Mine Workings No abandoned or active underground mine workings have ever existed or currently exist in any of the coal seams in the areas to be highwall mined. Highwall mining will not take place within 500 feet of any abandoned or active underground mining operation. 4.23.2(3) 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 Division 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, 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 backfill of the pit. 4.23.2(4) Prevent Pollution of Surface and Groundwater and to Reduce Fire Hazards Ground water in the pit or highwall mining holes will not be problematic since the South Taylor Pit is essentially dry (minor perched aquifers with limited seasonal flows), and is located above the 1st 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 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. Should toxic forming or acid forming water discharges be encountered, the opening exhibiting the discharge will be backfilled within 72 hours of completion. Colowyo will backfill each highwall miner entrance hole within 30 days following coal extraction. All highwall miner entrance holes will be further buried by pit backfill during the normal backfill sequence for the pit to remain in compliance with Rules 4.05.1 and 4.05.2. Ground water hydrologic regimes will be re- established in the backfilled pits with no anticipated detrimental effects from the highwall miner holes. 4.23.2(5) Holes Need Not Be Plugged All highwall miner entrance holes will be backfilled in accordance with the requirements set forth in 4.14.