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Drainage Basin Run -off Calculations and Sumn Desiens <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 allow <br />infiltration of the water in the ground within 48 hours. This is based on existing site experience at the <br />mine. As described in the Reclamation Plan, the sumps and ditches will be allowed to silt in after mining <br />is completed, therefore, all designs are considered temporary, thus the 10 year event is used in sizing, <br />with the exception of the emergency spillways, which are designed to pass the 100 year 6 hour event. <br />For this reason, the sumps have a principal spillway pipe and an emergency spillway of 3 feet width and <br />1 feet depth with 2H:1 V sideslopes. The emergency spillways will be lined with 6" size durable rock <br />over 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. This is the principal spillway pipe. When enough settling <br />has occurred in the pond, the gate valve can be opened to allow discharge within the NPDES limits of <br />the parameter of concern, which is 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 10 basins as well <br />as the water pumping from the South Portal, as shown on Map C -2. <br />All watershed basin areas have been calculated in CAD and are shown on Map C -2. <br />Yule Quarry January 2014 25 <br />