2008-05-29_PERMIT FILE - C1981019A (4)

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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 fora 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. The proposed sedimentation ponds have been designed and will be constructed and maintained to effectively trap sediment from runoff resulting from precipitation events up to and including the ]0-year, 24-hour precipitation event. Drainage from the mining area, afrer 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, refer to the NPDES reports found in the 1983- through 1990 Annual Reports. 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 operations have ranged between 7.2 and 8.5; therefore, it is anticipated that no acid mine drainage will occur as the operations move to southward to South Taylor and west to Lower Wilson. . 4.05.3 Diversions and Conveyance of a Watershed Less than One Square Mile The drainage and sediment control measures described under Section 2.05.6 and presented in Erosion and Sediment Control Structures (Exhibit 7, Item 20) provides for temporary diversion of surface drainages within the permit area. A system of temporary ditches will be used to divert runoff from disturbed areas to sediment ponds. Temporary diversions will be constructed to pass at a minimum the runoff from the precipitation event with atwo-year recurrence interval. The temporary diversions drain watersheds less than one square mile in size and serve to reduce the contribution of suspended solids to runoff The diversions wilt be constructed with a minimum gradient to pass the design flow and will be stabilized with grasses or riprap. 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. • South Taylor/Lower Wilson- Rule 4, Page 5 Revision Date: 11/30/06 Revision No.: PR-OZ