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Design Volume Calculations Sed Pond Fetcher Vale Pit Area (acres) 17.57 <br />Design Event 100 yr. storm <br />Design Precipitation3.4 Calculated S 2.34567901235 <br />Average CN 81 <br />Description Exposed Porous Gravel and Part Undisturbed grass <br />Calculated Runoff Volume (Q) 1.62795311299 <br />Calculated Runoff Volume (acre-ft.) 2.38359468294 <br />Ponding Percentage 5 <br />Actual Runoff Volume (acre/ft.) 2.26 <br />The pond will t>e designed to contain the 100 year runoff of 2.26 acre-feet and 0.2 ac-ft <br />for sediment buildup. This totals 2.46 acre-feet. The pond will be only incised to a depth <br />of 0.5 feet and the dam will be approximately 3,5 feet high and will have 2.OH:1 V <br />sideslopes. The pond area as shown on the Mine Plan Map is 0.8 acres, therefore the <br />average depth needed is approximately 3.0 feet. The dam will provide 3.5 feet height <br />and the 0.5 feet below ground level will be used to store sediment that enters the pond. <br />Since the sump will only excavate a depth of 0.5 feet, there is no chance that <br />groundwater will be exposed. <br />The pond will detain the water for 24 hours but will allow it to seep into the ground so <br />that the water is returned to the natural drainage. In order that the seepage occurs with <br />detention, the material used to construct the embankment will meet the following size <br />specifications: <5% minus 200 mesh, <20% minus 25 mesh, <50% minus %d', <100% <br />minus 4 inches. No fitter fabric in the dam will be used, since the dam material is sized <br />to detain sediment. The dam material will not be compacted to any large extent for two <br />reasons: 1) the strength of the gravelly material of the dam comes from internal angle of <br />friction and not cohesion, and since the angle of repose ofi the material is approximately <br />39 degrees, the slope of 2H:1 V yields an angle of 26.5 degrees. Therefore, the safety <br />factor of the dam is approximately 39!26.5 = 1.47, which is well within the factor of <br />safety to provide long term stability. Inspections will occur after major storms and when <br />113 of the pond volume contains sediment, the pond will be cleaned of sediment, which <br />will be deposited in the disturbed area. <br />As shown on Exhibit C-2, a collection ditch along the dirt road on the southwest part of <br />the permit area will be used to direct water to the sump. This ditch will be 1.5 feet deep <br />and 2:1 sideslopes. Once mining extends to this southwest corner, a lower collection <br />ditch will be installed to ensure that all disturbed water will flow to the sediment sump. <br />This ditch will have the same dimensions as the first ditch. <br />In order to provide vehicle access to the site and direct all flows from the east into the <br />sump, a mild berm of 1.5 feet height and 6H:1 V sideslopes will be used. See Exhibit C- <br />2_ <br />