2008-12-04_PERMIT FILE - C1994082A (4)

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February 1999 Yoast [L1ine * 13-12 Drainage and Sediment Control Plan • 1 SENECA YOAST MINE DRAINAGE AND SEDIMENT CONTROL PLAN 1.0 INTRODUCTION Seneca Coal Company (SCC) proposes to develop the rem~?n;ng coal reserves south of the existing Yoast Coal Mine operations in the Sage Creek drainage. To control run-off from the new development area, SCC proposes to build three new sediment ponds (Pond 012, 013, and 014) and associated diversion ditches (Diversions 13A and 14A). A fourth pond, Pond 011A, was designed to pre-treat runoff from the reclaimed area in the Pond 011 watershed prior to the runoff leaving the mine disturbance area. A fifth pond, Pond 012A, was designed and approved in TR-36 as an alternative sediment control structure. Pond 012A will be used to assist Pond 012 to treat runoff and sediment from the Pond 012 contributing watershed. In addition, to access the south mine area, SCC will extend existing haul road B and construct new haul roads C and D. The location of the ponds and haul roads are shown on Exhibit 12-1, Operations Plan (see Tab 12). Once mining is complete, SCC will construct a series of posttn'n' ~ channels in conjunction with the reclamation plan. The postmining channels designs are included in this attachment The postrnine topography and postmine channel locations are shown on Exhibit 20-2, Po~tmining Topography Map (see Tab 20). The following is the methodology and assumptions that were used in the design of the ponds, diversion ditches, haul road ditches, culverts and postmining channels. The hydrologic, hydraulic, and sediment calculations used to model the ponds, ditches, and postmining channels were performed utilizing the SEDCAD4 computer program developed by Civil Software Design (Schwab, 1998). 2.0 HYDROLOGIC CALCULATIONS 1~ SEDCAD4 is the nest generation of hydrology and sedimentology modeling software that replaces SEDCt1D+. It is a comprehensive, computer-based model used to evaluate storm water, erosion, and sediment control management techniques. The SEDCAD4 model calculates run-off and peak flow via a numerical modeling technique based on user inputs of a design storm event (Le., rainfall volume and duration, selection of rainfall distribution, and convolution increment). Hydrographs are developed on a subwatershed basis with the input of area, time of concentration, SCS Curve Number, and the selection of 1 of 3 dimensionless double triangle unit hydrograph shapes. Calculated runoff is routed to the various structures input into the model Muskingum routing parameters are used. Inputs to the hydrology component of the SEDCAD4 computer model include: • Precipitation Distribution • Storm Duration • Retum Period/Predpitation • Hydrograph Response Shape • Drainage Basin Area • Time of Concentration • Muskingum Routing Parameters • Curve Number Input values are explained in following sections. • Montgomery Watson Mining Group * 165 S. Union Boulevarr~ Suite 460 * I.nkewoo~ Colorado 80228 * (303) 763-5140 x_37 Revised 08/08