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disturbance. Temporary diversions were designed to pass peak flows resulting from at <br />least a 10 -year, 24 -hour storm event with a minimum freeboard of 0.3 feet. <br />Permanent diversions are designed to pass the peak flows from a 100 -year, 24 -hour <br />storm event with similar freeboard requirements. A detailed discussion of diversion <br />structures is presented in Section 2.05.3 Operation Plan - Permit Area, under the <br />subtitle "Ponds Impoundments and Diversions ". In addition, detailed calculations for <br />diversion structures are presented in Exhibit 19, Drainage and Sediment Control Plan. <br />In conjunction with mine development, facility installation, and coal refuse <br />placement, Dorchester, and subsequently EFCI, graded and maintained all disturbed <br />areas to provide for effective drainage and minimize potential erosion. Where <br />appropriate, EFCI utilized localized grading measures to effectively control and <br />route drainage and minimize flow velocities. Examples would include the yard area <br />drainage system in the mine facilities area, temporary sumps and ditches in refuse <br />pile areas, and the drainage control berms utilized to isolate disturbed area <br />drainage in the Southfield loadout area. <br />Localized drainage control and grading measures were supplemented by EFCI's <br />extensive drainage and sediment control network consisting of collection ditches which <br />intercept disturbed area runoff and routed it to sedimentation ponds, the ponds <br />themselves, and associated discharge structures. The drainage and sedimentation <br />control network, described in detail in Section 2.05.3, Operation Plan - Permit Area, under <br />the subtitle "Ponds Impoundments and Diversions ", serves /served to collect and retain <br />disturbed area runoff allowing settlement of suspended solids and any necessary <br />treatment prior to release to natural drainages. Sedimentation ponds are operated <br />under applicable provisions of EFCI's NPDES discharge permits. Compliance with the <br />terms of these permits insures that downstream water quality impacts are minimized. <br />The status of the ponds at the mine site and loadout have changed since closure of the <br />mine in 2000, and subsequent reclamation activities at both sites through 2014. <br />Pond 1, Pond 2 and Pond 3 at the mine site were reclaimed during backfilling and <br />regrading of the area during 2001 through 2003. Pond 2 and Pond 3 were both water <br />treatment ponds discussed later in this section. <br />2.05.6 -18a Revised: 8/1/14 RN -06 <br />