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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 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 />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 />The sediment storage capacity of the sedimentation pond will be periodically monitored to <br />ensure that at least one year of sediment storage is available beneath the principal spillway inlet <br />(based on the U.S.L.E. or the equivalent sediment storage of one 10 -year, 24-hour storm event <br />based on the M.U.S.L.E.). When adequate capacity is no longer available, sediment removal or <br />other corrective actions will be taken to restore adequate sediment storage capacity to the pond. <br />Section 2.05.3(3) Page 4 February 2017 (TR -78) <br />