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Introduction <br />Drainage Channel SIIPM-1 receives runoff from smaller drainage channels <br />used to route runoff from the post-mine landscape and conveys the runoff to <br />Sediment Pond 002. The contributing watershed is approximately 2,702 acres <br />(9.22 square miles), of which approximately 1,248 acres where disturbed by <br />mining activities, and which have since been reclaimed and revegetated. <br />The reclaimed areas that drain to Channel SIIPM-1 include a small portion <br />of the "pre-law" mining area, as well as most Wadge and Wolf Creek mining <br />areas that were mined between 1980 and 1996. Channel SIIPM-1 is located in <br />NW/9, Section 2, Township 5 North, Range 87W and E/2 Section 34, Township 6 <br />North, Range 87 West (see Exhibit 13-2B, Postmining Topography and <br />Permanent Features. <br />Seneca Coal Company (SCC) proposes to leave Channel SIIPM-1 as a permanent <br />postmine feature. Consequently, SCC must demonstrate that the channel <br />meets the requirements of Rule 4.05.4 of the Colorado Mined Land <br />Reclamation Board. <br />Design Analysis <br />SCC completed a channel design evaluation in 1998 to determine the channel <br />specifications necessary to safely pass runoff from the 100-year, 29-hour <br />design storm event, and meet the requirements of Rule 9.05.4, The original <br />1998 design was for the worst case condition (i.e., that portions of the <br />contributing drainage were not revegetated). SCC updated the design in <br />2004 (as part of Technical Revision No. 36) to incorporate the actual <br />conditions (i.e., that the entire contributing disturbed area drainage has <br />been successfully revegetated). The design evaluations for both conditions <br />are presented in Appendix 7-12. The 1986 hydrologic calculations were <br />performed using the SEDCAD+ hydrologic computer model, while SEDCAD9 was <br />used for the 2009 hydrologic calculations. The postmine hydrologic <br />demonstrations are found in Appendix 7-12A, while the hydraulic <br />calculations for the permanent channel are found in Appendix 7-12B. The <br />design drawing is presented on Exhibit 7-20, Channel SIIPM-1 Profile. <br />Channel SIIPM-1 was designed to meet the following specifications: <br />• Comply with the requirements of Rule 9.05.3(1)(b) through (f) in <br />accordance with Rule 9.05.9 (1)(b). <br />'1 <br />~J <br />TR-37 1 Revised 10/OS <br />