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Pond 013 was initially designed for the 2000 Permit Amendment. The pond was constructed in <br />is 2007. The as built report is included in attachment 2.05.3(3) -21. Due to the decision by W FC to <br />eliminate Pond 010, Ponds 011 and 013 will receive a greater drainage area. This revised <br />design of Pond 013 will demonstrate that the as built pond is sufficient to handle the revised <br />drainage area. <br />Pond 013 is a partially incised pond designed to contain the flow from a 10 year 24 hour storm <br />below the emergency spillway. the valve on the principal spillway pipe is normally held shut. <br />The principal spillway design is an 18 -24" diameter CMP or other pipe which will have a valve <br />on the entrance. This pipe will be stopped down in the inlet side to a 6" valve which will be <br />controlled by a wheel on the pond embankment. During normal conditions, the valve will be shut <br />to provide 24 hour detention time for each pond during the large events. When a large event <br />occurs, the operator will wait a minimum of 36 hours after the storm has ceased to check the <br />water still detained by the pond. An Imhoff cone will only be used to determine if the water can <br />be discharged. If an Imhoff cone shows that the water meets the effluent standard of 0.5ml <br />settleable solids per liter, the valve will be opened until the water has dissipated to the valve <br />level. It will then be shut to allow detention time for subsequent storms. Full sampling and <br />. laboratory analyses of the discharge will take place for all discharges, according to the NPDES <br />permit. <br />Pond 013 Design <br />Pond 013 must be able to hold the volume of water runoff and sediment load of the worst case <br />:scenario. In order to determine the worst case, a comparison of pre mine and post mine <br />drainage patterns, sediment load, and pit pumping is conducted. <br />,Pre Mine Calculations <br />72.4 acre drainage area (See Map 2.05.3(3) -1) <br />Pit water is pumped to Pond 011. No contribution to water volume in Pond 013. <br />Curve Number (CN) to use: From SEDCAD 4 for Windows Help menu: <br />I. Curve Numbers for Other Agricultural Land Category <br />II. Cover type: Pasture, grassland, or range -- continuous forage for grazing <br />• Revised May 2010 (PR06) Attachment 2.05.3(3) -6 -2 <br />