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RULE 4 PERFORMANCE STANDARDS <br /> <br />Rule 4 Performance Standards 4-9 Revision Date: 4/9/25 <br /> Revision No.: MR-261 <br /> <br />Historically, Colowyo has experienced no pH problems with water discharges sampled in the <br />vicinity of the Colowyo operations. As reported in Section 2.04.7, all pH values of water samples <br />taken in the vicinity of the Colowyo Operations have ranged between 7.2 and 8.5; therefore, it is <br />anticipated that no acid mine drainage will occur as the operations continue or expand with the <br />Collom expansion. <br /> <br />4.05.3 Diversions and Conveyance of Overland Flow and Shallow Groundwater Flow and <br />Ephemeral Streams Draining a Watershed Less than One Square Mile <br /> <br />The drainage and sediment control plan described under Section 2.05.6 provides for temporary <br />diversion of surface drainages within the permit area. A system of temporary ditches, as shown on <br />Map 12, will divert runoff away from disturbed areas, and in other cases temporary ditches will be <br />used to divert runoff from disturbed areas to sediment ponds. Specifications for all temporary <br />diversions within the permit area are presented within Exhibit 7, Hydrology Information. <br />Temporary diversions will -be constructed to pass at a minimum the runoff from the precipitation <br />event with a two year recurrence interval. <br /> <br />The temporary diversions described above will have the purpose of reducing contribution of <br />suspended solids to runoff and diverting undisturbed drainage from the mining area. The <br />diversions will be constructed with a minimum gradient to pass the design flow and will be <br />revegetated with grasses. If not removed by mining, upon completion of mining and at an <br />appropriate point mandated in the Coal Regulations of the Colorado Mined Land Reclamation <br />Board, the temporary diversions will be reclaimed as required in Section 4.05.17. <br /> <br />4.05.4 Stream Channel Diversions (Relocation of Streams) <br /> <br />A temporary diversion of Taylor Creek was approved as a Technical Revision on November 19, <br />1984. The diversion is shown on the Existing Structures-North Map (Map 21), explained in detail <br />in Exhibit 17, Haul Road and Facilities Modifications associated with Colowyo’s Raw Water <br />Supply Plan. <br /> <br />All temporary diversions will be removed and reclaimed when no longer needed for sediment <br />control in accordance with the Operations and Reclamation Plan described in 2.05.4. Channel <br />lining rock riprap and energy dissipaters will be used when necessary. As stated above, all <br />temporary diversion structures will be seeded and revegetated. Colowyo does not anticipate that <br />there will be any significant excess material resulting from the construction of diversion ditches. <br /> <br />None of the proposed diversions will drain into underground mines. <br /> <br />No additional diversions of intermittent or perennial streams are planned or provided for at this <br />time. <br /> <br /> <br />