2017-11-06_PERMIT FILE - C1980007

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West Elk Mine - Mine Water Control Plan Mountain Coal Company 1.0 INTRODUCTION 1.1 Project Description Exhibit 66 was prepared to update the Mine Water Control Plan at West Elk Mine to reflect the construction of a new sedimentation pond (Pond MB -5E) and associated work on ditches and culverts necessary to direct water to the new pond. Pond MB -5E will replace MB -5, and will serve the drainage areas that formerly reported to Ponds MB -1, MB -2R, and MB -5. MB -1 will be to be converted to freshwater storage (FW -2), while MB -2R will be filled and converted to a coal stockpile area, and MB -5 will be replaced by the new pond. Ponds MB -1, MB -2R, and MB - 5 are no longer part of the Mine Water Control Plan. This exhibit updates the one produced in November 2008 to reevaluate the September 1993 Mine Water Control Plan initially prepared by Greystone of Englewood, Colorado, and revised several times from 1996 through 1999. The November 2008 revision presented an updated SEDCAD+ analysis of the mine's surface water collection and treatment system, based on field inspections of the existing ditches and culverts, and also reflected proposed repairs to be constructed from Fall 2008 through Summer 2009. The analysis was based on previous analyses provided by West Elk Mine, and field confirmation of site conditions. No changes were made to existing previously approved Small Area Exemption demonstrations, or to Pond MB -4. 1.2 Analysis Methods The hydrologic, hydraulic, and pond sedimentation analysis was conducted using the Sediment, Erosion, Discharge by Computer Aided Design (SEDCAD+), version 4, by Ms. Pamela J. Schwab of Civil Software Design and Dr. Richard C. Warner, Biosystems and Agricultural Engineering Department, University of Kentucky. The analysis is based on previous SEDCAD+ demonstrations for the site, field inspections by Tetra Tech personnel, and information provided by Mr. Henry Barbe and Mr. Ryan Sweetwood of Mountain Coal Company. 1.3 Design Criteria Colorado regulations govern design criteria for surface drainage systems at coal mines. Temporary ditches must be sized for the 2 -year, 24-hour storm [Rule 4.05.3(2)]. Mountain Coal Company (MCC) has elected to size temporary ditches for the 10 -year, 24-hour storm event. A freeboard of 0.3 feet is required for diversions, under Rule 4.05.3(7). Culverts and permanent ditches must be sized to handle the 10 -year, 24-hour storm event [Rule 4.03.2(4)]. Culverts were designed assuming a projecting entrance under inlet control, and using an allowable headwater to depth (HW/D) ratio of 1.5, or a lower value if necessitated by available ditch depth. Tetra Tech October 2010