2011-03-18_PERMIT FILE - C1981019 (3)

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• Purpose and Scope of this Exhibit 7 Item 13 Colowyo has constructed eight stock tanks in the north end of the East Pit reclamation area. Colowyo Coal Company is the surface land owner, and believes the stock tanks should remain as a permanent feature in the post mining landscape. A letter to this effect is included in Appendix C. The purpose of this evaluation is to demonstrate compliance with Rule 4.05.9(13) for permanent impoundments. Overview of Stock Tank Locations and Postmining Land Use The eight stock tanks on the post mining lands are located as shown on Figure 1 in Appendix E. In accordance with Rule 2.05.5(1)(b), the approved postmine land use for the Colowyo East Pit reclamation area is rangeland. The location of all of the existing land uses within the permit area and adjacent areas for the mining operation can be found on the Land Use Map (Map 17). The land use designations in the permit and adjacent areas are confirmed by the Moffat County Land Use Map which was prepared by the Soil Conservation Service, United States Department of Agriculture. Additional discussions of the approved postmine land use can be found in Sections 2.04.3 and 2.05.5. The stock tanks will encourage an even distribution of grazing over the reclaimed site and improve • the area for livestock and wildlife, thereby enhancing the postmine land use in the area. These eight stock tanks are intended to remain as permanent impoundments. All are small, and some are primarily below grade excavations with an embankment dam only a few feet in height. Photographs of the stock tank are provided in Appendix A. All are on ephemeral drainages in the reclaimed lands, with tributary areas limited to a small and narrow overland flow area immediately above each impoundment, generally extending uphill to the nearest watershed divide. The stock tanks are expected to hold small amounts of water in response to spring runoff and large thunderstorms, and will generally become dry or intermittent impoundments during the warmer summer months. Tributary areas for each stock tank impoundment and other dimensional details are presented in Table. 1. Overview of Applicable Hydrologic /Hydraulic and Stability Design Criteria All eight impoundments are smaller than the size and height thresholds of MSHA regulation as referenced in 2.05.3 (4) (a) (iv) and 4.05.9 (8) (a) and are therefore not subject to those design criteria. They are also smaller than the USDA TR -60 Class B and Class C classifications referred to in 2.05.3 (4) (a) (vi) and 4.05.9 (8) (a), and are therefore not subject the USDA TR -60 design criteria. With respect to Colorado State Engineer's regulations concerning dams, all of these stock tanks would classify as a • minor NPH (no public hazard) structure under that agency's regulations. As described Exh. 7 -13 -3 Revision No.: TR -89 Revision Date: 02/11/11