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RULE 4 PERFORMANCE STANDARDS <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 /> 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 /> 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 /> 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 /> 4.05.4 Stream Channel Diversions (Relocation of Streams) <br /> A permanent diversion constructed at the operation is used to divert surface runoff from the <br /> watershed upslope of the Streeter Pond. The diversion structure was designed to pass safely the <br /> 100-year, 24-hour precipitation runoff event. This diversion, is riprapped, as required, to control <br /> erosion, and the design criteria is provided in Exh. 7-14E in Volume 2C. The permanent diversion <br /> structures will remain, but will not provide additional contributions of sediment load to Good <br /> Spring Creek as they are designed to safely pass the 100-year,24-hour precipitation runoff and are <br /> stabilized with riprap. A temporary diversion of Taylor Creek was approved as a Technical <br /> Revision on November 19, 1984. The diversion is shown on the Existing Structures-North Map <br /> (Map 21), explained in detail in Exhibit 17, Haul Road and Facilities Modifications associated <br /> with Colowyo's Raw Water Supply Plan. <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 /> None of the proposed diversions will drain into underground mines. <br /> Rule 4 Performance Standards 4-9 Revision Date: 12/20/19 <br /> Revision No.: TR-135 <br />