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applicable design standards, operation of the Southfield sedimentation <br />ponds will effect compliance with applicable NPDES discharge effluent <br />standards as contained in Part 4.05.2. <br />All existing sedimentation ponds have been designed to provide adequate <br />storage for anticipated sediment contributions from contributing drainage <br />areas. Sediment storage calculations reflect the maximum anticipated <br />disturbance acreage for each drainage area over the mine life, In <br />addition to designing for adequate sediment storage capacity, EFCI will <br />monitor sediment levels in all sedimentation ponds, and as necessary to <br />maintain adequate storage capacity, will remove accumulated sediment and <br />dispose of it in interior portions of the permanent coal refuse stockpile. <br />Sediment removal requirements will be very limited and sediment removal <br />will not be necessary on a regular basis. If sediment removal does become <br />necessary, EFCI, in order to prevent any potential adverse impacts on coal <br />refuse stockpile stability, will remove accumulated sediment during the <br />portion of the year when sedimentation ponds are normally dry. Anticipated <br />sediment removal volumes will be minimal and should not have any <br />significant effect on refuse stockpile stability or overall volume. <br />All sedimentation ponds have been designed and constructed to retain a <br />flood routed volume equal to the runoff resulting from a ]0-year, 24-hour <br />storm event. Design calculations are presented and design methodo)ogy <br />discussed in Exhibit 19, Drainage and Sediment Control Plan. Generally, <br />with the exception of ongoing expansion of the coal refuse stockpile, <br />mining and related activities will not result in significant changes in <br />hydrologic conditions for disturbed area drainages. However, even where <br />conditions will be effected by ongoing development, pond designs are based <br />on worst-case conditions where topsoil is assumed to have been removed <br />from entire projected disturbance area. Runoff from undisturbed areas is <br />diverted around disturbance areas and was generally not considered in <br />sedimentation pond design. <br />Each pond has been designed to provide a minimum detention time of 24 <br />• hours, and longer if necessary, to meet applicable effluent limitations <br />with respect to TSS. Each pond outlet structure is sized to control pond <br />discharge rates so that adequate detention times are maintained. <br />4.05-15 <br />