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the wall will remain stable under maximum loading condition, (design storm event and the <br />accumulated sediment). Worksheets in Appendix C detai this analysis. The waN would be <br />. founded on compacted sediment within the basin abng a spread footing. Tha footing would <br />be keyed into the alluvium to increase shear resistance of the wall. At the side of the bssin, <br />the wall would be keyed into the exposed sandstone with an excavated keyway and dowels. <br />The dowels will be connected to steel reinforcement within the concrete welt. <br />Results show that the proposed waN is adequate to retain maximum water and soil toads. <br />Considering the railroad tracks located adjacent to the waN, as weN es Highway 133 further <br />bebw, the intern was to design a wall wFth high safety factors. The factor of safety against <br />sliding for the sediment pond wall is 3.8. Against overturmg, the safety factor is 2.8. These <br />factors of safety do not include the keyway at the sides of the basin, so the wall design wiN <br />provide the sediment pond with a conservatively designed structure. <br />4.2.5 Sadrrent Pond Dewetering <br />The sediment pond will be dewaterod using an eight-inch steal outlet pipe, placed as shown <br />on Drawing 95255.04. An eight-indt dlarrteter pips wss selected to dewstsr the pond rapidly <br />if needed and to ensuro that rt vvli not dog when used. The pips intake will be at D. 8,038.5 <br />• ft, just above maximum elevation of sediment produced by the 10-year, 24hour storms at EI. <br />6,036.3 ft. The intake should be constructed as shown in Drawing 95255-04, with a gate <br />valve upstream to prohibit the accumulation of water in the pipe, and discourage freezing and <br />thawing that may damage the gate valve. Piping after the gate valve will take discharge water <br />down to the elevation of the railroad embankment. The outlet pipe wiN discharge into the <br />railroad embankment drainage ditch and then into the existing 18-irtdt culvert bebw railroad <br />tracks. Discharge will occur at the opposite side of the railroad trades to prohibk ponding of <br />water between the sediment pond wall and the tradt embankment. <br />The existing 18-inch diameter CMP culvert was instalbd beloMi the railroad treeks to transport <br />ftowa from within the draw where the coal mine waste bank will be constructed. Sines the <br />waste bank and upland diversion wi now divert flow from the culvert, it must now only carry <br />fbws produced by the jximary and secondary sediment pond spitlwayi. The maximum flows <br />•1 <br />96260/1424.gFR Coil Mirt• W~~t~ amt Owtgn fa tl» a~n0orn QNk Mlro <br />Oetotwr 199e WESTEC, Irc. 1~ <br />