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<br />ATTACHMENT 1 <br />TECHNICAL REVISION -MINING AND RECLAMATION PERMIT <br />YANKEE GULCH SODIUM MINERALS PROJECT <br />AMERICAN SODA, L.L.P. <br />Piceance Site stormwater Retention Pond Spillway <br />The stormwater retention pond is designed to contain, at a minimum, direct <br />precipitation to the pond and runoff from the processing facility area resulting from the <br />100-year, 24-hour storm event plus the volume of the largest on-site storage tank. The <br />pond spillway is designed to accommodate the 50-year, 24-hour storm event. The <br />spillway design includes the assumption that the 50-year, 24-hour storm event would <br />occur when the pond is full. <br />The following is a summary of Kvaerner Metals, Davy Nonferrous Division design <br />calculations for the stormwater retention pond spillway. <br />Assumptions and Given Information <br />Precipitation for 50-year, 24-hour storm = 2.4 inches <br />Assumed intensity is that 80% of precipitation for the storm event occurs in 1 hour <br />I So-Ye„ = 0.80 storm/hour (2.4 in/storm) = 1.85 in/hr <br />Runoff coefficient, C = 0.85 for processing facility area, C = 1.00 for pond <br />Pond Length = 367.5 feet between centerlines of berms <br />Pond Width = 154.5 feet between centerlines of berms <br />Processing Facility Area = 348,480 ft' <br />The weir coefficient, C „ = 2.7 for abroad-crested weir <br />Head on the spillway = 0.6 feet <br />Spillwa,, Sig <br />Assumed intensity for 50-year storm, I so-Ye,~ = 1.85 in/hr <br />Q=CIA <br />= 0.85(1.85)(348,480 ft') (acre/43,560 ft') + 1.00 (1.85) (acre/43,560 fY)(154.5 ft)(367.5ft) <br />= 15 cfs <br />Weir Equation Q = Cw W H "~ <br />Where: <br />Q =spill overflow discharge, cfs <br />C w =weir coefficient <br />W =width of crest, feet <br />H =head on spillway, feet <br />Summary of Kvaerner Calculations <br />Stocmwater Retention Pond Spillway <br />Technical Revision Mining and Reclamation Pemut <br />