2011-11-02_REVISION - M1986002 - Laserfiche WebLink

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Desert Shrub (Poor) 88 D 24.869 Desert Shrub (Poor) 88 D 24.193 CN (weighted): 88.0 Total Area: 118.839 Acre 2. Runoff Return Period: 100 -Year Rainfall, P: 2.60 in Runoff, Q: 1.4674 in Runoff Volume: 14.5325 Acre -Ft Project: Eastern Pond Runoff By: B. Langenfeld Date: 10/28/11 Location: Craig Ranch Pit Checked: Date: Present 1. Runoff Curve Number (CN) Cover description CN Soil Group Area(Acre) Desert Shrub (Poor) 88 D 22.927 Desert Shrub (Poor) 88 D 17.362 CN (weighted) : Total Area: 88.0 40.289 Acre 2. Runoff Return Period: 100 -Year Rainfall, P: 2.60 in Runoff, Q: 1.4674 in Runoff Volume: 4.9268 Acre -Ft The sediment ponds have sufficient capacity to contain all of the 100 -year 24 -hr event runoff in their mined out volume. The Western pond will be five feet deep over an area of 4.18 acres for a capacity of 20.9 ac -ft, while only 14.53 acre -ft will be required. The Eastern pond will be one foot deep over an area of 12.03 acres for a capacity of 12.03 ac -ft, while only 4.93 acre -ft will be required. This gives a combined capacity of 32.93 ac -ft, well in excess of what is needed. Both ponds will be totally incised. These ponds will be left in place after reclamation to fill with sediment that is produced by the reclaimed land. The water that enters the pond will evaporate and infiltrate. Additionally, a topsoil island will be built in the west sediment pond. Collection ditches will be constructed along the south side of the stormwater basins. These will ensure that water flowing across the site during mining ends up in the sediment ponds. These collection ditches will be constructed by building gravel berms along the downhill side of the slope, and allowing the water to flow along the berm to the sediment pond. The berms will be Craig Ranch Pit, March 2011 G -2