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through the mine site near its center. The large gully currently in this location will be slowly filled <br />during the pit's life using naturals(rejected fines produced by the ctushing(screening process. To <br />facilitate drainage alter mining a storm water channel will be installed. The design of the channel can <br />be seen below. Ditches #3 and #4 provide isolation for 2!3 of the Northern pit. They direct water <br />flow into the same drainage as Ditch #2. Ditch #5 completes the isolation of the northern pit and <br />redirects the water to the north into another natural drainage. Ditches #6 and 7 complete the isolation <br />of the South pit Area 5 and redirect the water to into another natural drainage. <br />The pit bottom will serve as the containment basin for the operation. All water will be contained from <br />a 100-yeaz event and allowed to evaporate or seep out during a 72-hr or longer period. The drainage <br />basin azea is the entire permit azea. The precipitation of a 100-yeaz event is 3.2 inches. The isolation <br />berms surrounding the site will be 3 feet in height with 2H:1 V slopes, with a primarily flat pit floor. <br />This will provide more than sufficient storage fora 100-year event. Because the pit will contain all <br />runoff from a 100-year storm no discharge pennit is required. Berms will also be built to isolate the <br />grass lined channels which are being built in the valley fdl azeas. During construction of the valley <br />fills, an isolation berm will be built at the mouth of the each valley. This berm will prevent the <br />sediment flow from leaving the permit area. <br />4. Major Storm Water Channels <br />Two drainage channels will need to be constructed on the site due to two valleys being filled. Valley <br />Fill Area #1 watershed (29.5 acres) area is much lazger and drains a watershed twice as large as Area <br />#2(13.5 acres). For easy of design and construction both channel designs will be based on the Valley <br />Fill Area # I. <br />Valley Fi11 Area # 1 <br />The topology of the site requires that storm water from above the site will need to be diverted through <br />the permit area. This azea is 29.5 acres based on USGS maps for the drainage area. Due to a gully <br />being filled at the landowners request, the original natural drainage will be buried. The valley fill will <br />be discussed Later. This will cause storm water to flow across the main pit area during mining and after <br />reclamation in the middle of the irrigated field. If left uncontrolled storm water would readily erode <br />the valley fill material. The storm water channel will be divided into two regions: Grass Lined and <br />Grouted Rip-Rap. The channel begins at a small pond neaz the gas well formed by a road installed <br />before the current operation. This pond will serve as a sediment trap. The grass lined channel will <br />direct water along the mild slope (2%). The steeper sloped (50%) portion of the channel will be <br />grouted 12" rip-rap. Due to different channel widths a grouted 12" rip-rap funnel will be built between <br />the two sections. Below aze the calculations performed in SurvCAD to determine the channel <br />characteristics. Initially, a Time of Concentration calculations was performed to provide input for the <br />Peak Flow calculation. From the Peak Flow calculation, an erodible channel calculation was <br />performed for the grass lined channel. The grouted section did not need an erodible channel <br />calculation due to the nature of its structure. However, flow calculations were performed. Due to the <br />high velocity dischazge at the bottom of the slope, three to four D50 = 5' boulders and rip-rap will be <br />used as an energy dissipater before allowing the water to dischazge into the natural drainage. <br />Cugnini 12/03 7 <br />