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RULE 4 PERFORMANCE STANDARDS <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 diversion <br />of surface drainages within the permit area. A system of temporary ditches, as shown on the Hydrology - <br />South Map (Map 12) and the Hydrology - North Map (Map 11), will divert runoff away from disturbed <br />areas, and in other cases temporary ditches will be used to divert runoff from disturbed areas to sediment <br />ponds. Specifications for all temporary diversions within the permit area are presented within Exhibit 7, <br />Hydrology Information. Temporary diversions will -be constructed to pass at a minimum the runoff from <br />the precipitation event with a two year recurrence interval. <br />The temporary diversions described above will have the purpose of reducing contribution of suspended <br />solids to runoff and diverting undisturbed drainage from the mining area. The diversions will be <br />constructed with a minimum gradient to pass the design flow and will be revegetated with grasses. If not <br />removed by mining, upon completion of mining and at an appropriate point mandated in the Coal <br />Regulations of the Colorado Mined Land Reclamation Board, the temporary diversions will be reclaimed <br />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 watershed <br />upslope of the Streeter Fill as detailed in Section 2.06.2. The diversion structure was designed to pass <br />safely the 100-year, 24-hour precipitation runoff event. This diversion, located on the north side of <br />Streeter Fill, is riprapped, as required, to control erosion. Design criteria for the permanent diversion <br />structure along with engineering parameters for Streeter Fill are set forth in Exhibit 12, Experimental <br />Practice Information. The permanent diversion structures will remain, but will not provide additional <br />contributions of sediment load to Good Spring Creek as they are designed to safely pass the 100-year, 24- <br />hour precipitation runoff and are stabilized with riprap. A temporary diversion of Taylor Creek was <br />approved as a Technical Revision on November 19, 1984. The diversion is shown on the Existing <br />Structures-North Map (Map 21), explained in detail in Exhibit 17, Haul Road and Facilities Modifications <br />associated with Colowyo's Raw Water Supply Plan. <br />All temporary diversions will be removed and reclaimed when no longer needed for sediment control in <br />accordance with the Operations and Reclamation Plan described in 2.05.4. Channel lining rock riprap <br />and energy dissipaters will be used when necessary. As stated above, all temporary diversion structures <br />will be seeded and revegetated. Colowyo does not anticipate that there will be any significant excess <br />material resulting from the construction of diversion ditches. <br />None of the proposed diversions will drain into underground mines. <br />No additional diversions of intermittent or perennial streams are planned or provided for at this time. See <br />Mine Plan Map (Map 23), Hydrology South Map (Map 12) and Hydrology - North Map (Map 11). As <br />indicated on these maps, the stream channels of Goodspring Creek will be maintained in its natural <br />positions. <br />Rule 4 Performance Standards 4.05-3 Revision Date: 6/23/08 <br />Revision No.: MR-91