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r <br />Jim Herron -2- April 15, 1981 <br />4.05.4 Stream Channel Diversions <br />3) North Decline Area Diversion: The stream channel diversion shown in the <br />Sedimentation Plan Exhibit 22 is not described in the text: GEX must provide <br />sufficient information to assure compliance with all sections of Rule 4.05.4. <br />4.03.2(4)(e) Culverts and Bridges <br />4) Culvert Designs: The use of Mannings equation or Conveyance Factor methodology <br />is inappropriate for drainage culverts. These methods do not account for the <br />headloss inherent in the design. GEX must use closed conduit hydraulics to <br />design the culvert system. <br />4.05.6 Sedimentation Ponds <br />5) USLE: GEX has used C values from SCS publication Technical Note 50 Figure 7. <br />This figure is inappropriate for disturbed watersheds. Values for disturbed <br />watersheds are more likely to approximate values given in Table 5.4, page 202 <br />in Barfield and Haan (1978}1. In areas where C values change, e.g. refuse piles <br />and undisturbed rangeland, C values may be area weighted. GEX must use C <br />values in USLE calculations which are either obviously conservative or derive <br />them from applicable tables or figures. <br />6) Spillway Designs: The use of Mannings equation for sediment pond spillway <br />design is inappropriate. As the spillways for several of the ponds are drop <br />inlet CMP a stage discharge relationship for changing controls (weir, orifice, <br />pipe) must be used. (4.05.6(3)(d)). <br />7) Dewatering Devices: Several of the ponds have no means of dewatering. As <br />per Rule 4.05.6(3)(c) all ponds must have a dewatering device. <br />8) Detention Time: GEX must address the question of detention time in each of <br />their ponds in order to evaluate the likelihood of the effluent limitations <br />(4.05.2(7)) being met. <br />9) Sediment Cleanout: GEX has stated that they intend to remove accumulated <br />sediment every three (3) years. As this represents the entire sediment storage <br />volume for the ponds this maintenance schedule is unacceptable. GEX must <br />propose a more acceptable maintenance schedule. The Division would prefer a <br />maintenance schedule which calls for sediment removal when 60% of the sediment <br />storage volume is filled or before. A permanent marker placed at the approved <br />cleanout level in the ponds would assist the operator and inspection personnel <br />in providing proper maintenance. <br />10) Short Circuiting: Pond 3 at the Railroad Spur has an inlet very close to <br />the outlet spillway. GEX must either redesign the pond or provide sufficient <br />baffling to prevent short circuiting. (4.05.6(6)). <br />1C. T. Haan and B. J. Barfield, Hydrology and Sedimentology of <br />Surface Mined Lands, Lexington, Kentuc y Ink stitute fo- rT~1ining <br />and Minera Research, 1978. <br />