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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. For all culverts, a corrugated metal pipe was used with inlet control. In order to <br />standardize culverts, a few culvert sizes were selected for all situations although, in some cases, <br />the culvert is over designed. Although New Horizon commits to maintaining the culverts in good <br />condition, we only commit to the cross-sectional area needed to pass the design peak flow, not <br />the entire area of the culvert. <br />E. Sedimentation Pond 007 <br />Other ponds 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 4.05.2 and the approved NPDES permit, New Horizon will use <br />Pond 007 to prevent, to the extent possible, additional contributions of sediment to stream flow <br />or runoff outside the permit area due to mining disturbance (see Map 2.05.3(3)-1). Attachment <br />2.05.3(3)-2 gives the design calculations on Sediment Pond 007. Attachment 2.05.3(3)-3 gives <br />the typical soil grain size distribution information. Maps 2.05.3(3)-2-1 and 2.05.3(3)-2-2 shows <br />the as -built design of Pond 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 />c. An appropriate non -clogging dewatering device will be installed to maintain a 10 -year, <br />24-hour storage volume. <br />d. Appropriate combinations of principal and emergency spillways to safely discharge the <br />runoff from a 25 -year, 24-hour precipitation or larger event, as required by the DRMS's <br />regulations, will be installed. <br />Page 2.05.3(3)-4 January 2016 (TR -70) <br />