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RULE 4 PERFORMANCE STANDARDS <br />highwall openings. Should toxic forming or acid forming water discharges be encountered, the <br />opening exhibiting the discharge will be backfilled within 72 hours of completion. <br />Colowyo will backfill each highwall miner entrance hole within 30 days following coal <br />extraction. All highwall miner entrance holes will be further buried by pit backfill during the <br />normal backfill sequence for the pits to remain in compliance with Rules 4.05.1 and 4.05.2. <br />Ground water hydrologic regimes will be re-established in the backfilled pits with no anticipated <br />detrimental effects from the highwall miner holes. <br />4.23.9 Division shall prohibit Auger (Highwall Mining) Mining <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, <br />buildings, or other surface facilities. <br />4.23.10 Backfill and Grading Requirements <br />Highwall mining will be conducted in accordance with the backfilling and grading requirements <br />of 4.14. <br />4.23.11 Highwall Shall be Eliminated <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 <br />be adequately covered by pit backfilling in conformance with the permitted PMT and <br />reclamation plan. No remnant highwalls will be left at conclusion of the reclamation activities <br />and no spoil material will be place on any outslopes. <br />4.24 Operations in Alluvial Valley Floors <br />The field investigation described in Section 2.04.7 and 2.06.8 resulted in no identification of <br />alluvial valley floors in the general area which would be adversely affected by mining <br />operations; therefore, no special performance standards for operations in the alluvial valley <br />floors are applicable to this mining permit application, and no protection or remedial measures <br />are proposed for compliance to this Section. <br />4.25 Operations on Prime Farmlands <br />Since a negative determination of prime farmland was arrived at using the eligibility <br />requirements established for prime farmland under Section 2.04.12, these performance standards <br />do not apply to the permit application. <br />Rule 4 Performance Standards 4-89 Revision Date: 4/2/18 <br />Revision No.: RN -07 <br />