Laserfiche WebLink
RULE 4 PERFORMANCE STANDARDS <br />quality is discussed in Section 2.04.7. No acid mine drainage of pH equal to or less than 6.0 is <br />expected. <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 />the Hydrology - South Map (Map 12) and the Hydrology - North Map (Map 11), will divert runoff <br />away from disturbed areas, and in other cases temporary ditches will be used to divert runoff from <br />disturbed areas to sediment ponds. Specifications for all temporary diversions within the permit <br />area are presented within Exhibit 7, Hydrology Information. Temporary diversions will -be <br />constructed to pass at a minimum the runoff from the precipitation event with a two year recurrence <br />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 Fill as detailed in Section 2.06.2. The diversion structure was <br />designed to pass safely the 100 -year, 24-hour precipitation runoff event. This diversion, located <br />on the north side of Streeter Fill, is riprapped, as required, to control erosion. Design criteria for <br />the permanent diversion structure along with engineering parameters for Streeter Fill are set forth <br />in Exhibit 12, Experimental Practice Information. The permanent diversion structures will remain, <br />but will not provide additional contributions of sediment load to Good Spring Creek as they are <br />designed to safely pass the 100 -year, 24-hour precipitation runoff and are stabilized with riprap. A <br />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 />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 />Rule 4 Performance Standards 4-9 Revision Date: 5/25/18 <br />Revision No.: RN -07 <br />