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West Elk Mine - Mine Water Control Plan Mountain Coal <br />1.0 INTRODUCTION <br />1.1 Project Description <br />This exhibit was prepared to reevaluate the mine water control plan at West Elk Mine, <br />documented in the September 1993 Mine Water Control Plan prepared by Greystone of <br />Englewood, Colorado, and subsequently revised several times from 1996 through 1999. This <br />revision presents an updated SEDCAD analysis of the mine's surface water collection and <br />treatment system, based on field inspections of the existing ditches and culverts. The analysis <br />also reflects proposed repairs, to be constructed from Fall 2008 through Summer 2009. <br />Updated site maps and drainage network diagrams are included. No changes have been made <br />to existing previously approved Small Area Exemption demonstrations, or to Pond MB-4. <br />1.2 Analysis Methods <br />The hydrologic, hydraulic, and pond sedimentation analysis was conducted using the Sediment, <br />Erosion, Discharge by Computer Aided Design (SEDCAD+), version 4, by Ms. Pamela J. <br />Schwab of Civil Software Design and Dr. Richard C. Warner, Biosystems and Agricultural <br />Engineering Department, University of Kentucky. The analysis is based on previous SEDCAD <br />demonstrations for the site, field inspections by Tetra Tech personnel, and information provided <br />by Mr. Henry Barbe and Mr. Ryan Sweetwood of Mountain Coal Company. <br />1.3 Design Criteria <br />Colorado regulations govern design criteria for surface drainage systems at coal mines. <br />Temporary ditches must be sized for the 2-year, 24-hour storm [Rule 4.05.3(2)]. Mountain Coal <br />Company (MCC) has elected to size temporary ditches for the 10-year, 24-hour storm event. A <br />freeboard of 0.3 feet is required for diversions, under Rule 4.05.3(7). Culverts and permanent <br />ditches must be sized to handle the 10-year, 24-hour storm event [Rule 4.03.2(4)]. Culverts <br />were designed assuming a projecting entrance under inlet control, and using an allowable <br />headwater to depth (HW/D) ratio of 1.5, or a lower value if necessitated by available ditch depth. <br />• <br />Tetra Tech October 2008