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Revised January, 1996 <br />• <br />The plan for protection and control of drainage and sediment described in <br />2.05.6 provides that surface drainage from the disturbed area within the <br />permit area will be passed through sedimentation control structures. All <br />ponds will be constructed and maintained to contain or treat the volume <br />design for a 10-year, 24-hour precipitation event. The accumulation of <br />sediment in the ponds will be monitored quarterl~r. In addition, grab <br />samples of water, as required, will be collected from pond discharges to <br />measure the effectiveness in meeting the applicable Colorado and Federal <br />water quality standards. <br />4.05.2 Water Ouality Standards and Effluent Limitations <br />The proposed sedimentation ponds have been designed and will be constructed <br />and maintained to effectively trap sediment from runoff resulting from <br />precipitation events up to and including the 10-year, 24-hour precipitation <br />event. <br />Drainage from the mining area, after treatment in sedimentation ponds, is <br />not anticipated to exceed the effluent limitations of any federal or <br />Colorado agency requirements. Baseline groundwater quality is discussed <br />. in Section 2.04.7. No acid mine drainage of pH equal to or less than 6.0 <br />is expected. For further details relating to the sediment pond discharges, <br />refer to the NPDES reports found in the 1983 through 1990 Annual Reports. <br />• <br />Historically, Colowyo has experienced no pH problems with water discharges <br />sampled in the vicinity of the Colowyo operations. As reported in Section <br />2.04.7, all pH values of water samples taken in the vicinity of the Colowyo <br />Operations have ranged between 7,2 and 8.5; therefore, it is anticipated <br />that no acid mine drainage will occur as the operations move southward. <br />4 O5. Diversions and Conveyance of Overland Flow and Shallow <br />Groundwater Flow and F,phemeral Streams Draining a Watershed Less Than One <br />Square Mile <br />The drainage and sediment control plan described under Section 2.05.6 <br />provides for temporary diversion of surface drainages within the permit <br />area. A system of temporary ditches, as shown on the Hydrology - South Map <br />(Map 12) and the Hydrology - North Map (Map <br />inR-3b <br />