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January 2002 Seneta ^W Soutb F_xpanrian * Drainage and Sediment Control Ylan 1 Page 6 <br />4.0 PONDS <br />All ponds are designed to effectively treat the peak mnoff produced from the 10-year, 24-hour storm <br />event. The ponds were designed using the SEDCAD computer program. The input parameters and <br />resul[s are shown on the SEDCAD printouts located in Appendix 1, Sediment Pond SEDCAD <br />Results, and summarized in Table 5. The location of the ponds along with pond and embankment <br />configurations for Ponds 016, 017 and 016A can be found on Drawings 13-9A, 13-8B, and 13-SC. <br />(Note: As-built drawings and stability analysis has previously been submitted for Ponds 015 <br />and 016). A minor modification of the principal spillway for existing Pond 016 has been <br />proposed in this submittal. <br />All ponds will employ a principal spillway that consists of a cmp riser (varying heights), with a cmp <br />outlet culvert. All ponds employ an emergency spillway. The emergency spillways will be trapezoidal <br />channel with 3H:1 V side slopes. The outslope of the spillways will be armored. The spillways are <br />designed to safely pass the peak discharge from the 25-year, 24-hour storm event while maintaining 1 <br />foot of freeboard. The spillways are conservatively designed assuming the water level is at the invert <br />level of the principal spillway prior to the storm event. <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 IS feet. Prior to <br />construction of the embankments all topsoil will be removed and stockp0ed. A keyway will be cut <br />down the cen[er 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 />MWH * 165 S- Union $oukvard, Suite 410 * Iokeurood, Cohrada 80228 * (970J 763-5140 <br />w:vrir~....ir,...nw.r..m/vxos/.~n,.a.~., i~sw..,r,.~r Aev 1102 <br />x..a.m ~/nz.n <br />