2013-04-05_PERMIT FILE - C1981019 (10)

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RULE 2 PERMITS All ponds, regardless of size, will be examined quarterly for structural weakness, erosion and other hazardous conditions. Maintenance procedures may include mowing or cutting excessive vegetative growth to facilitate inspections and repairs keeping ditches, culverts and spillways free of debris, and removing all combustible material other than mulch and other material required for erosion control and surface stability. Sediment will be removed from all sedimentation ponds when the volume of sediment accumulates to 60% of the design sediment storage volume or when sufficient volume is not available to treat. the predicted runoff and sediment volume from a 10 -year, 24 -hour storm event.. The accumulated sediment found in the ponds will be removed and placed in existing topsoil stockpiles if the sediment meets the appropriate topsoil criteria, otherwise disposed of in the pit backfill. Sedimentation pond removal is discussed in Section 4.05. The location of all proposed sedimentation ponds and diversion structures to be constructed within the permit area are shown on the Hydrology - North Map (Map 11) and the Hydrology - South Map (Map 12). These maps also show the locations of watershed boundaries from which, along with other sources, the design criteria were established. Generally, ponds and spillways were sized and placed according to such hydrologic factors as required sediment storage volume, rate of flow and volume of flow for the appropriate storm event. Pond embankments, slopes, spillways and construction methods have been designed according to such engineering factors as structural integrity and stability, slope and surface stability; adequacy in height, size and shape to provide sufficient volume for sediment and detained water and selection of proper spillways and outlet devices, passing of design storm events and proper outflow rates. All ponds have been designed under the direction of a qualified, registered professional engineer. The purpose of the sedimentation ponds is not only to provide a final measure to prevent additional contributions of sediment outside the permit area, but also to provide a means of compliance with all applicable effluent limitations, especially with respect to total suspended solids or settleable solids, as required. The effluent quality is regulated by Section 4.05.2 and by the National Pollutant Discharge Elimination System ( NPDES) Permit. The NPDES Permit was issued by the State of Colorado Department of Health under the National Pollutant Discharge Elimination System, established as a result of the Clean Water Act (33 U.S.C. Section 1251, et. seg.). A copy of the approved NPDES Permit is found in Exhibit 7, Hydrology Information. The engineering parameters for the various sedimentation ponds are included in Exhibit 7, Hydrology Information. The engineering design parameters for the various diversion ditches are also included in Exhibit 7, Hydrology Information. Cross sections for the sedimentation ponds and the designs for the emergency and primary spillways are shown in Exhibit 7, Hydrology Information. With the construction of the Streeter Fill and the future development of the West Pit, the original drainages have been relocated as shown on the Post Mining Topography (Map 19). The details of these permanent diversions are set forth in Exhibit 12, Experimental Practice Information, and Exhibit 7, Hydrology Information. Note that for continuity the "Experimental Practice" information in the permit is left intact to provide a historical record of the Streeter Fill which is now an excess spoil fill built to meet the standards of Rule 4.09 Rule 2 Permits 2.05 -10 Revision Date: 6/11/12 Revision No.: RN -06