2015-10-06_PERMIT FILE - C1981019A (3)

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RULE 4 PERFORMANCE STANDARDS In addition to the mining, reclamation, and treatment methods described and referenced in this section, further protection of the hydrologic balance will be established by an on-going plan for monitoring potential changes in surface water quality and quantity and alluvial groundwater quality. This monitoring plan is described under Section 4.05.13 and the monitoring locations are graphically shown on Map l OB. 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 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. A demonstration of the effectiveness of sediment control structures to be constructed around several topsoil stockpiles planned outside of primary sediment control may be found under Exhibit 7, Item 23, Part D. 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 10 -year, 24-hour precipitation event. 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 alluvial 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 Annual Reports from 1983 through the present. 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 6.8 and 8.8; therefore, it is anticipated that no acid mine drainage will occur as the operations move to the Collom permit expansion area. 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 the Erosion and Sedimentation Control Plan (Exhibit 7, Item 23, Part E) and Map 41B will provide for temporary diversion of surface drainages within the permit area, as needed for mine operations. 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 a two- 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 will be constructed with a minimum gradient to pass the design flow. 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. Any topsoil stockpile areas that may be constructed outside the confines of engineered sediment control structures will be required to have a perimeter ditch and berm constructed around the entire footprint of the stockpile sufficient to capture and retain any rainwater/snowmelt that may be generated from the stockpile area to preclude loss and/or contamination of the topsoil resource. A demonstration of the Collom — Rule 4, Page 5 Revision Date: 9/28/11 Revision No.: PR -03