2011-06-20_REVISION - C1981019 (6)

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RULE 4 PERFORMANCE STANDARDS Upstream diversions are proposed for portions of Little Collom X, as discussed above. Temporary diversion ditches below the disturbed area of both pits will help collect runoff from disturbed areas and route it into the sedimentation ponds. During active mining, the mining areas will aid in retaining sediment within the disturbed areas by catching water in pits, small depressions and dozer basins, etc. This captured water and sediment will not leave the mining areas. Once reclaimed, the basins will drain as they did prior to mining activities (i.e., historic drainage patterns will be re- established). All temporary diversions will be removed and reclaimed when no longer needed for sediment control in accordance with the Operations and Reclamation Plan described in 2.05.4. Channel lining rock riprap and energy dissipaters will be used when necessary. As stated above, all temporary diversion structures will be seeded and revegetated after removal. Colowyo does not anticipate that there will be any significant excess material resulting from the construction of diversion ditches. None of the proposed diversions will drain into underground mines. 4.05.6 Sedimentation Ponds The location, design parameters, and detailed sedimentation calculations of all planned sedimentation ponds are presented in Erosion and Sedimentation Control Plan (Exhibit 7, Item 23). Additional information may be found in Exhibit 7, Item 26 (Collom Pond Design Maps). The design plans and specifications for the sedimentation ponds are described in this section. All sedimentation ponds will be located as close as practical to the areas to be disturbed. Steep terrain in the upper basins precludes location of the ponds at the Collom Lite disturbance boundaries during the critical early phase of operations, necessitating down - valley locations within and downstream of the Little Collom X footprint. In later phases, in -pit ponds will be developed in Collom Lite. Other methods of sediment control will be located on the reclaimed areas; these methods include the use of contour furrowing, contour drainage ditches, chisel plowing, and revegetation. This application contains calculations used to determine runoff volumes and flow rates for the theoretical 10 -year, 25 -year, and 100 -year, 24 -hour precipitation events, as well as annual sediment volumes. The precipitation data were obtained from the NOAA Atlas 2, Volume 3 for Colorado; soil types were obtained from the Soil Conservation Service, and are shown on the soils survey map (Map 5D). The ongoing mining activities within each watershed of the permit area will create constantly changing hydrologic conditions. The design models are generally based on a static, theoretical scenario, utilizing SEDCAD 4, which considers the worst -case scenario. The worst -case scenario occurs approximately 6 months after the start of mining, when topsoil has been stripped and stockpiled for all of Little Collom X, and portions of Collom Lite, but no mining or sedimentation control installation has yet occurred in Collom Lite, and reclamation has not yet been attained for any areas. Refer to Exhibit 7, Item 23 for a delineation of the areas used for these modeling purposes as well as the maps associated with the SEDCAD runs. The 6 -month disturbance boundary indicated in Exhibit 7, Item 23 is for development of the worst -case scenario for hydrologic modeling and does not represent a definitive schedule for mining and reclamation activities. The scenario used for the sedimentation ponds corresponds to an active, disturbed operation. In terms of groundwater, Colowyo's pits have remained essentially dry. Pumping of pit water (precipitation induced surface runoff) into sedimentation ponds is not anticipated. Discharges from the ponds will remain in compliance with Colowyo's CDPS Discharge Permit. The use of flocculants in sedimentation. ponds may also be used in accordance with the provisions of the CDPS Permit. Collom — Rule 4, Page 7 Revision Date: 5/20/11 Revision No.: PR -03