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minimum fieeboard of 0.3 feet. Permanent diversions are designed to pass <br />the peak flows from a 100 -year, 24 -hour storm event with similar <br />freeboard requirements. A detailed discussion of diversion structures is <br />presented in Section 2.05.3 Operation Plan - Permit Area, under the <br />subtitle "Ponds Impoundments and Diversions ". In addition, detailed <br />calculations for diversion structures are presented in Exhibit 19, Drainage and <br />Sediment Control Plan. <br />In conjunction with mine development, facility installation, and ongoing <br />coal refuse placement, Dorchester, and subsequently EFCI, graded and <br />maintained all disturbed areas to provide for effective drainage and <br />minimize potential erosion. Where appropriate, EFCI utilized localized <br />grading measures to effectively control and route drainage and minimize <br />flow velocities. Examples would include the yard area drainage system in the <br />mine facilities area, temporary sumps and ditches in active coal refuse <br />placement areas, and the drainage control berms utilized to isolate disturbed <br />area drainage in the Southfield loadout area. <br />Localized drainage control and grading measures were supplemented by EFCPs <br />extensive drainage and sediment control network consisting of collection <br />ditches which intercepted disturbed area runoff and routed it <br />to sedimentation ponds, the ponds themselves, and associated discharge <br />structures. The drainage and sedimentation control network, described in <br />detail in Section 2.05.3, Operation Plan - Permit Area, under the subtitle <br />"Ponds Impoundments and Diversions ", served to collect and retain <br />disturbed area runoff allowing settlement of suspended solids and any <br />necessary treatment prior to release to natural drainages. Sedimentation <br />ponds are operated under applicable provisions of EFCFs NPDES discharge <br />permits. Compliance with the terms of these permits insured that <br />downstream water quality impacts are minimized. <br />The two (2) existing sedimentation ponds in the mine area and the two <br />(2) ponds at the loadout area, along with associated collection ditches, <br />spillways, and discharge structures provide effective drainage and <br />sedimentation control for both existing and proposed future surface <br />disturbance. <br />2.05.6 -17 Revised: 8/1/14 RN -06 <br />