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1. Using a 3D grid of the watershed, the actual area and average land slope was developed. <br />2. A long flow line was drawn from the top of each watershed to the bottom of the ditch. <br />3. Using the SCS Method provided within Carlson Software or SEDCAD, the time of <br />concentration was developed for each watershed. <br />4. Using the Time of Concentration and a worst case curve number, the peak flow was also <br />developed within Carlson Software or SEDCAD using the SCS graphical method. <br />5. Using the maximum velocities stated earlier, ditch slopes, depth and bottom width <br />geometry were then calculated for the channels. <br />Designs for all culverts were done in a similar manner except that once the peak flows for the <br />culvert watersheds were calculated, the standard FHA procedures were used to properly size the <br />culvert. In order to standardize culverts, a few culvert sizes were selected for all situations <br />although, in some cases, the culvert is over designed. <br />E. Sedimentation Pond 007 <br />Other pond design details are discussed in Attachments 2.05.3(3)-4, 2.05.3(3)-5, 2.05.3(3)-6 and <br />2.05.3(3)-11. In accordance with Rule 4.05.2, New Horizon will use Pond 007 to prevent, to the <br />extent possible, additional contributions of sediment to stream flow or runoff outside the permit <br />area due to mining disturbance (see Map 2.05.3(3)-1). Attachment 2.05.3(3)-2 gives the design <br />calculations on Sediment Pond 007. Attachment 2.05.3(3)-3 gives the typical soil grain size <br />distribution information. Maps 2.05.3(3)-2-1 and 2.05.3(3)-2-2 shows the as -built design of Pond <br />007. <br />The sedimentation pond is designed, constructed, and maintained to: <br />a. Provide storage for the runoff or inflow entering the pond as a result of a 10 -year, 24- <br />hour precipitation event and to meet all applicable State and Federal regulations for all <br />effluent limitations before discharge from the permit area. The characteristics of the mine <br />site, reclamation procedures, and on site sediment control practices are also considered in <br />the design. <br />b. The sedimentation pond was designed to provide adequate sediment storage volume in <br />compliance with the DRMS regulations. <br />Section 2.05.3(3) Page 4 April 2017 (MR -104) <br />