2018-04-13_PERMIT FILE - C1981019A

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RULE 4 PERFORMANCE STANDARDS 4.05.2 Water Quality Standards and Effluent Limitations The plan for protection and control of drainage and sediment described in 2.05.6 provides that surface drainage from the disturbed area within the permit area will be passed through sedimentation control structures. All ponds will be constructed and maintained to contain or treat the volume design for a 10 - year, 24-hour precipitation event. The accumulation of sediment in the ponds will be monitored quarterly. In addition, grab samples of water, as required, will be collected from pond discharges to measure the effectiveness in meeting the applicable Colorado and Federal water quality standards. Drainage from the mining area, after treatment in sedimentation ponds, is not anticipated to exceed the effluent limitations of any federal or Colorado agency requirements. Baseline groundwater quality is discussed in Section 2.04.7. No acid mine drainage of pH equal to or less than 6.0 is expected. For further details relating to the sediment pond discharges Annual Hydrology Report. Historically, Colowyo has experienced no pH problems with water discharges sampled in the vicinity of the Colowyo operations. As reported in Section 2.04.7, all pH values of water samples taken in the vicinity of the Colowyo have ranged between 7.2 and 8.5; therefore, it is anticipated that no acid mine drainage will occur as the operations continue or expand with the Collom expansion. 4.05.3 Diversions and Conveyance of Overland Flow and Shallow Groundwater Flow and Ephemeral Streams Draining a Watershed Less than One Square Mile The drainage and sediment control plan described under Section 2.05.6 provides for temporary diversion of surface drainages within the permit area. A system of temporary ditches, as shown on the Hydrology - South Map (Map 12) and the Hydrology - North Map (Map 11), will divert runoff away from disturbed areas, and in other cases temporary ditches will be used to divert runoff from disturbed areas to sediment ponds. Specifications for all temporary diversions within the permit area are presented within Exhibit 7, Hydrology Information. Temporary diversions will be constructed to pass at a minimum the runoff from the precipitation event with a two year recurrence interval. The temporary diversions described above will have the purpose of reducing contribution of suspended solids to runoff and diverting undisturbed drainage from the mining area. The diversions will be constructed with a minimum gradient to pass the design flow and will be revegetated with grasses. If not removed by mining, upon completion of mining and at an appropriate point mandated in the Coal Regulations of the Colorado Mined Land Reclamation Board, the temporary diversions will be reclaimed as required in Section 4.05.17. 4.05.4 Stream Channel Diversions (Relocation of Streams) A permanent diversion constructed at the operation is used to divert surface runoff from the watershed upslope of the Streeter Fill as detailed in Section 2.06.2. The diversion structure was designed to pass safely the 100 -year, 24-hour precipitation runoff event. This diversion, located on the north side of Streeter Fill, is riprapped, as required, to control erosion. Design criteria for the permanent diversion structure along with engineering parameters for Streeter Fill are set forth in Exhibit 12, Experimental Practice Information. The permanent diversion structures will remain, but will not provide additional contributions of sediment load to Good Spring Creek as they are designed to safely pass the 100 -year, 24- hour precipitation runoff and are stabilized with riprap. A temporary diversion of Taylor Creek was approved, and the diversion is shown on the Existing Structures -North Map (Map 21), explained in detail in Exhibit 17, Haul Road and Facilities Modifications associated with Colowyo's Raw Water Supply Plan. Rule 4 Performance Standards 4-9 Revision Date: 8/28/17 Revision No.: TR -115