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2002 Senera IIIY/ Sontb F_ayanrian * Drainage mlASediment Control Plan <br />1.0 INTRODUCTION <br />Seneca Coal Company (SCC) proposes to develop a new coal reserve south of the existing Seneca II-W <br />Coal 1~Iine. 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, Pohd 015 and 016 <br />have been constructed. Anew mine plan developed in 2001 has increased the disturbed area <br />which will report to Ponds 016 and 017. Therefore, Ponds 016 and 017 require design revisions. <br />To effectively treat the runoff, Pond 016 will requite 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 <br />a two-pond system. The Pond 017 revision will involve a raise in the embankment to <br />effectively treat runoff from the watershed. The designs for ponds 016, 016A and 017 are <br />included in this submittal. In addition, to access the new area SCC will construct three new haul <br />roads (Haul Road I, ], and I~. The designs of these haul roads and associated culverts has not been <br />changed with this submittal. The location of the proposed ponds and Roads are shown on Exhibit 13- <br />2A. <br />Once mining is complete and the area is reclaimed, SCC will constmct 4 new post-mining channels. <br />The locations of the channels are shown on Exhibit 20-2A. <br />The following is the methodology and assumption that went into the designs of the three ponds, haul <br />road ditches and culverts, and post mining channels. <br />The hydrologic, hydtauflc, and sediment calculations used to model the Seneca II-W South <br />area were performed utilizing the SEDCAD+ and SEDCAD4 (SEDCAD) computer modeling <br />program developed by Civil Software Design. The results of the SEDCAD analyses are presented <br />in the attached calculation exhibit and are summarized in Table 5 of this report. Sedimentation Ponds <br />015, 016, O16A and 017 were analyzed according to the following methodologies. <br />MWH * 165 S. Union Boulevard, Suite 410 * Lakewood, Colorado 80228 * (970J 763-5140 <br />Y':YWLSnra/femsllV'f..ed/PRO)/MeMniUSdmd.//A+. Rev 1/02 <br />Roved l/!13 rzl <br />