2011-03-25_PERMIT FILE - C1981019A (2)

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system where water is allowed to discharge automatically as necessary. Colowyo will sample discharges as appropriate to remain in compliance with applicable CDPS Permit requirements. Pond dewatering through a manual headgate may be performed as necessary to lower the water level depending on operational requirements. Manual dewatering of ponds will meet applicable CDPS Permit standards. Discharge from sedimentation ponds will be controlled by energy dissipaters and flow check devices where necessary. All ponds utilize separate primary and emergency spillways with the emergency spillway located at a minimum of 1 foot above the elevation of the principal spillway. The emergency spillways are designed to pass the 25- year /24 -hour storm event in accordance with Rule 4.05.6(5). The design requirements can be found on each of the pond as -built drawings or in Exhibit 7, Item 15. All sedimentation ponds will provide a non - clogging dewatering device or conduit spillway to remove water storage from inflow. 4.05.8 Acid - forming and Toxic - forming Spoil Acid forming materials do not exist within the overburden to be removed by the mining operations. A discussion on the overburden at the Colowyo operation has been conducted as set forth in Section 2.04.6. A discussion of the overburden monitoring plan is set forth in Section 2.05. 4.05.9 Permanent and Temporary Impoundments Colowyo constructs small impoundments on reclaimed area in accordance with Section 4.05.9 of the CMLRD regulations for Coal Mining, 9/14/05. These small impoundments are essential and basic to the management of the rangeland post- mining land use of livestock grazing and wildlife habitat. The design of the impoundments provides for structures having a vertical height less than five feet from the bottom of the channel to the bottom of the spillway and impound less than two acre feet of water. As such they are exempt from Division of Water Resources, Office of State Engineer requirements. Please see Figure 2.05 -6 of the current permit for design information regarding a typical stock tank plan /profile. This design will be implemented in strategic locations of the East Pit backfilling sequence and integrated within the polygons found on Map 29 — Spoil Grading. The locations of these impoundments are shown on Map 12 - Hydrology — South and page Exh. 7- 14R -8. Timing of reclamation in the East Pit and the associated Sediment control structures is described in Exhibit 7, Item 14, Part R. Water harvesting ditches may also be used to enhance the function of the impoundments, which is consistent with practices employed on adjacent rangelands. The impoundments collect surface runoff from precipitation events and snowmelt from reclaimed areas. The impoundments do not result in the diminution of the quality or quantity of water for downstream water users. Colowyo is the holder of water rights immediately downstream. During periods of low precipitation the impoundments may be dry, which is consistent with regional practices on similar rangelands. Since the source of water is surface runoff from revegetated areas the quality of the water will meet the requirements of the intended use. The impoundments have areas of 3h:ly slopes or less to provide easy access to both livestock and wildlife. These impoundments and any associated ditches, while intended to be permanent, will be classified as temporary until the requirements of Rule 4.05.9 are met. Prior to construction, all designs are submitted to the Division. A copy of the as -built design information will be submitted after construction for inclusion into Exhibit 7, Hydrology. In addition, sedimentation ponds that are subsequently approved as part of the post- mining land use, as shown on the hydrology - South Map (Map 12), will remain as permanent impoundments after the requirements of Rule 4.05.9 have been met. All embankments, impoundments and associated structures will be revegetated if construction materials are conducive to plant growth. If not, rock or gravel will be used on the embankment. The quarterly Rule 4 Performance Standards 4.05 -6 Revision Date: 2/01/11 Revision No.: TR -87