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Design Volume Calculations <br />Sediment Ponds #3 and #4 <br />Area (acres) <br />31.1 <br />Design Event <br />100 yr. storm <br />Design Precipitation <br />2.8 <br />Calculated S <br />Average CN <br />72 <br />3.88888888889 <br />Description <br />Porous Gravel Topsoil <br />Piles <br />Calculated Runoff Volume (Q) <br />0.6918128655 <br />Calculated Runoff Volume (acre -ft.) <br />1.79294834308 <br />Ponding Percentage <br />35 <br />Actual Runoff Volume (acre /ft.) <br />1.165416423 <br />The 31.1 ac drainage area is shown on Map C -4. The average CN of 72 is based on the majority of the <br />drainage basin being very porous gravel. The 35% ponding percentage is based on the fact that there are <br />numerous depressions and small ponds throughout the drainage area before the runoff ever reaches the <br />Ponds. <br />Ponds #3 and #4 have a surface area of 1.4 ac and 1.18 ac respectively. This is a total of 2.58 ac. Since <br />the minimum depth available at any one time is 1.5 feet above the normal water level, the ponds capacity <br />is 3.87 ac -ft, therefore, the capacity is more than adequate not even considering the volume of the <br />additional ponds downstream. <br />All disturbed areas north of the drainage area into Ponds #3 and #4 are trapped by the large berm of over <br />5.0 feet height at the western edge of the disturbed area. In addition, the gravel excavation has left most <br />of the area depressed, which will hold a capacity of well over a 1000 year event, since the <br />average depth of the land is 10 feet minimum below the berm. Willits Ponds 4, 5 and 6 are in place to <br />provide additional protection for outside edges of piles (which are primarily pre -law). These ponds and <br />ditches leading to them are shown on Map C -4. <br />Alma Place Mine 01/15 18 <br />