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Drainage Basin Run -off Calculations and Sump Designs <br />All ditch and sump designs are based on the 10 year 6 hour storm event of 1.6 inches, as determined <br />from the NOAA Atlas 2 Volume III Isopluvial Map. The granular nature of the sump materials will <br />allow infiltration of the water in the ground within 48 hours. This is based on existing site experience at <br />the mine As described in the Reclamation Plan, the sumps and ditches will be allowed to silt in after <br />mining is completed, therefore, all designs are considered temporary, thus the 10 year event is used in <br />sizing, with the exception of the emergency spillways, which are designed to pass the 100 year 6 hour <br />event. <br />For this reason, the sumps a principal spillway pipe and an emergency spillway of 3 feet width and 1 <br />feet depth with 2H:1 V sideslopes. The emergency spillways will be lined with 6" size durable rock over <br />a 12" thickness and will be designed to pass the 100 year 6 hour event. <br />A metal or plastic pipe of 2 -6" diameter with an accessible gate valve will be placed within 1 foot of the <br />low point of the sumps so that water can be discharged after it is settled and to allow the storage volume <br />to recover to handle subsequent storm events. When enough settling has occurred in the pond, the gate <br />valve can be opened to allow discharge within the NPDES limits of the parameter of concern, which is <br />suspended solids. <br />The sumps will be monitored monthly to identify sediment levels. If the levels approach the discharge <br />pipe elevation (one foot from the pond bottom), the sump will be cleaned out. No fine material from the <br />sump cleanouts will be deposited in an area that can migrate down the slope toward Yule Creek. <br />Any berms needed for the sumps will be no greater than 2 feet high and will be constructed of earth fill <br />that will prevent water seepage when compacted to 90% maximum dry density, which will be achieved <br />with these berms. <br />The NPDES discharge permit is being modified to contain the discharge points for all basins as well as <br />the water pumping from the South Portal, as shown on Map C -2. <br />Yule Quarry April 2012 22 <br />