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January 2002 Seneca 17-W South Expanaon * Drainage and Sediment Control Plan • Page 1 <br />1.0 INTRODUCTION <br />eneca Coal Com an SCC ro oses to develo anew coal reserve south of the existing Seneca II-W <br />S P y( )P P P <br />Coal Mine. In September 1998, to control run-off from the new development area, SCC proposed to <br />build three new sediment ponds, namely Ponds 015, 016, and 017. Two ponds, Pond 015 and 016 <br />have been constructed. Anew mine plan developed in 2001 has increased the disturbed area which <br />will report to Ponds 016 and 017. Therefore, Ponds 016 and 017 require design revisions. To <br />effectively treat the runoff, Pond 016 will require a second pond, Pond 016A. In addition, a <br />modification to the principal spillway of Pond 016 will be required. Pond.016 will then become atwo- <br />pond system. The Pond 017 revision will involve a raise in the embankment to effectively treat runoff <br />from the watershed. The designs for ponds 016, 016A and 017 are included in this submittal. In <br />addition, to access the new area SCC will construct three new haul roads (Haul Road I, J, and I~. The <br />designs of these haul roads and associated culverts have not been changed with this submittal. The <br />location of the proposed ponds and Roads are shown on Exhibit 13-2. <br />Once mining is complete and the area is reclaimed, SCC will construct a series of postmine channels <br />to collect surface runoff from the mine area and limit erosional instability in accordance with <br />Rule 4.05.3. The locations of the channels are shown on Exhibit 20-2. <br />The following is the methodology and assumption that went into the designs of the four ponds, haul <br />road ditches and culverts, and postmining channels. <br />The hydrologic, hydraulic, and sediment calculations used to model the Seneca II-W South area were <br />performed utilizing the SEDCAD+ and SEDCAD4 (SEDCAD) computer modeling program <br />developed by Civil Software Design. The results of the SEDCAD pond demonstrations are <br />presented in the Appendix 1, Sediment Pond SEDCAD Results and are summarized in Table 5 of <br />this attachment. Sedimentation Ponds 015, 016, 016A and 017 were analyzed according to the <br />methodologies presented in the following sections. <br />• <br />M6[VH * 165 S. Union Boulevard, Suite 410 * Lakervaorl Colorado 80228 * (303) 7G3-5140 <br />TR-59 Revised 05/07 <br />