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The worst case for mnoff into Pond #2 is when the operation has recently crossed the previous <br />•~ <br />L J <br />I t' <br />access road and has begun moving south. Although some runoff will be trapped in the pit, most <br />will make its way south through previous sumps and be delivered to Pond #2. This area is <br />approximately 78 acres. When the active pit is further south, more runoff will enter the pit, which <br />does not represent the worst case. Part of the azea is previously disturbed and very gravelly. The CN <br />for undisturbed azeas is 74 and disturbed gravel is 70. The approximate average for the entire <br />disturbed azea is 72. Due to a number of sediment sumps present in the basin, a ponding percent of <br />20% has been assigned. <br />The design calculations for Pond #2 aze shown below. <br />Design Volume Calculations <br />Sediment Pond #2 <br />Area (acres) 72.6 <br />Design Event 100 yr. storm <br />Design Precipitation 2.8 Calculated S <br />Average CN 72 3.88888888889 <br />Description Porous Gravel <br />Topsoil Piles <br />Calculated Runoff Volume (Q) 0.6918128655 <br />Calculated Runoff Volume (acre-ft.) 4.18546783626 <br />Ponding Percentage 20 <br />Actual Runoff Volume (acre/ft.) 3.34837426901 <br />As shown on Map C-2, Pond #2 is 1.15 acres in surface azea, therefore, its required depth is 2.9 feet <br />to hold 3.34 acre feet. It will be constructed to 3.3 feet deep and 2H:1 V sideslopes. All other ponds <br />will use similaz slopes. <br />Alma Placer 7/03 <br />14 <br />