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February 1999 Yoart Mine * 13-12 Drainage and Sediment Cantrnl Plan • 1 <br />SENECA YOAST MINE <br />DRAINAGE AND SEDIMENT CONTROL PLAN <br />1.0 INTRODUCTION <br />Seneca Coal Company (SCC) proposes to develop the remaini a coal reserves south of the existing Yoast Coal Mine <br />operations in the Sage Creek drainage. To control run-off from the new development area, SCC proposes to build <br />three new sediment ponds (Pond 012, 013, and 014) and associated ditches (Ditch 13A and 14A). A fourth pond, <br />Pond O12A, was designed for TR 36. Pond 012A will be used to assist Pond 012 to treat runoff' and sediment <br />from a portion of the South Mine mine area. In addition, to access the new area, SCC will extend existing haul <br />road B and construct new haul roads C and D. The design of the haul road ditches are included in this attachment <br />The location of the proposed ponds, ditches and the haul roads are shown on Exhibit 12-1, Operations Plan. <br />Once mining is complete, SCC will construct a series of post mining channels in conjunction with the reclamation <br />plan. The reclaimed topography and channel locations are shown on Exhibit 20-2, Postmining Topography Map <br />(Tab 20). The designs of the post mining channels are included in this attaclunent <br />The following is the methodology and assumptions that were used in the designs of the ponds, ditches, haul road <br />ditches and culverts and post mining channels. <br />The hydrologic, hydraulic, and sediment calculations used to model the ponds, ditches, and post mining channels were <br />performed utilizing the SEDCAD4 computer modeling program developed by Civil Software Design (Civil Software <br />Design, 1998) and were analyzed according to the following methodologies. <br />2.0 HYDROLOGIC CALCULATIONS <br />SEDCAD4 is the next generation of hydrology and sedimentology modeling software that replaces SEDCAD+. It is <br />a comprehensive, computer-based model used to evaluate storm water, erosion, and sediment control management <br />techniques. The SEDCAD4 model calculates run-off and peak flow via a numerical modeling technique based on <br />user inputs of a design storm event (Le., rainfall volume and duration, selection of rainfall distribution, and convolution <br />increment). Hydrographs are developed on a subwatershed basis with the input of area, time of concentration, SCS <br />Curve Number, and the selection of 1 of 3 dimensionless double triangle unit hydrograph shapes. Calculated runoff is <br />routed to the various structures input into the model Muskingum routing parameters are used. <br />Inputs to the hydrology component of the SEDCAD4 computer model include: <br />• Precipitation Distribution <br />• Storm Duration <br />• Retum Period/Precipitation <br />• Hydrograph Response Shape <br />• Drainage Basin Area <br />• Time of Concentration <br />• Muskingum Routing Parameters <br />• Curve Number <br />• <br />Input values are explained in following sections. <br />2.1 PRECIPITATION DISTRIBUTION <br />A precipitation distribution is input to model the run-off hydrograph. SEDCAD4 allows the user to <br />Montgomery Watran Mining Group * 165 S. Union Boulevard, Suite 460 * Inkewood, Colorado 80228 * (303) 763-5140 <br />TR-36 Revised 08/07 <br />