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RULE 4 PERFORMANCE STANDARDS <br /> <br />Rule 4 Performance Standards 4-55 Revision Date: 12/14/22 <br /> Revision No.: MR-245 <br />from which to work from to mine the successively higher (in the geologic column) coal seam. <br />Hence successful highwall mining is in part dependent upon timely and successful <br />contemporaneous reclamation of the pits. <br /> <br />4.23.8 Prevent Pollution of Surface and Groundwater and to Reduce Fire Hazards <br /> <br />Ground water in the pit or highwall mining holes will not be problematic being that the Colowyo <br />pits are essentially dry (minor perched aquifers with limited seasonal flows) and are located above <br />the first regional aquifer (Trout Creek) by a substantial distance. Ground water flow regimes and <br />the negligible impact that Colowyo’s surface mining activities have on ground water as a result of <br />mining these target coal seams/rock interburdens are detailed extensively in Permit Section <br />2.04.7(1). From this extensive body of data and from experiences to date with mining activities, <br />no toxic forming or acid forming water discharge is anticipated from any of the highwall openings. <br />Should toxic forming or acid forming water discharges be encountered, the opening exhibiting the <br />discharge will be backfilled within 72 hours of completion. <br /> <br />Colowyo will backfill each highwall miner entrance hole within 30 days following coal extraction. <br />All highwall miner entrance holes will be further buried by pit backfill during the normal backfill <br />sequence for the pits to remain in compliance with Rules 4.05.1 and 4.05.2. Ground water <br />hydrologic regimes will be re-established in the backfilled pits with no anticipated detrimental <br />effects from the highwall miner holes. <br /> <br />4.23.9 Division shall prohibit Auger (Highwall Mining) Mining <br /> <br />There is no probable reason to prohibit the highwall mining in light of no anticipated adverse <br />impacts to water quality, fill stability, pit backfilling, increased resource recovery, and highwall <br />mining is designed for zero subsidence to prevent disturbance or damage to powerlines, buildings, <br />or other surface facilities. <br /> <br />4.23.10 Backfill and Grading Requirements <br /> <br />Highwall mining will be conducted in accordance with the backfilling and grading requirements <br />of 4.14. <br /> <br />4.23.11 Highwall Shall be Eliminated <br /> <br />Highwall mining is proposed to occur in areas previously mined with adequate material on hand <br />to backfill the pits with proper static safety factors for stability to the approved postmining <br />topography thereby eliminating all highwalls. Any minimal spoil material generated by the <br />highwall mining operation will be buried at depth in the pit backfill. All coal seams mined will be <br />adequately covered by pit backfilling in conformance with the permitted PMT and reclamation <br />plan. No remnant highwalls will be left at conclusion of the reclamation activities and no spoil <br />material will be place on any outslopes. <br /> <br />4.24 Operations in Alluvial Valley Floors <br />