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January 2002 Seneca 77-W South E.xpan.rion * Drainage and Sediment Control Plan • Page 6 <br />4.0 PONDS <br />All ponds are designed to effectively treat the peak runoff produced from the 10-year, 24-hour storm <br />event. The ponds were designed using the SEDCAD computer program. The input parameters and <br />results are presented in the SEDCAD demonstrations found in Appendix 1, Sediment Pond <br />SEDCAD Results, and summarized in Table 5. The location of the ponds along with pond and <br />embankment configurations for Ponds 016, 016A and 017 can be found on Exhibit 13-9A/-9B, 13- <br />9C, and 13-9D, respectively. (Note: As-built drawings and stability analyses have previously been <br />submitted for Ponds 015 and 016). <br />All ponds will employ a principal spillway that consists of a corrugated metal pipe (CMP) riser (of <br />varying heights), with a CMP outlet culvert. All ponds employ an emergency spillway. The emergency <br />spillways will be a trapezoidal channel with 3H:1V side slopes. The outslope of each spillway will be <br />armored. The spillways are designed to safely pass the peak discharge from the 25-year, 24-hour storm <br />event while maintaining 1-foot of freeboard. The emergency spillways are conservatively designed - <br />they assume the water level is at the invert level of the principal spillway prior to the storm event, and <br />the principal pipe is inoperable. This conservative design causes the 25-year, 24-hour runoff <br />calculation to over estimate the sediment delivery to the pond and calculate a conservative top <br />of sediment storage elevation. <br />The embankments for all ponds are less than 20 feet in height when measured from the upstream toe. <br />The embankments will be constructed with 3H:1V slopes and a top width of 15 feet. Prior to <br />construction of the embankments all topsoil will be removed and stockpiled. A keyway will be cut <br />down the center of the embankment. The embankment will be constructed in lifts not exceeding <br />twelve inches in loose thickness. Each lift will be compacted by at least one pass of the bulldozer <br />tracks over the entire lift before additional material is placed. The fill material will not contain sod, <br />large roots, other large vegetative matter, or coal waste. Placement will not occur during periods of <br />excess moisture. <br />• <br />A41i%N * 165 S. Union Boulevarc( Suite 410 * Lakewoort, Colorado 80228 * (303) 763-510 <br />TR-59 Revised 05/07 <br />