Laserfiche WebLink
C <br />2.05.3(4) Ponds, Impoundments and Diversions • <br />A review of materia]s submitted on sediment pond design has raised a <br />number of questions and concerns which need to be addressed. The <br />permit renewal application should include revisions or additional <br />information concerning the following: <br />The inflow hydrographs for Ponds 003 and 004 adequateT.y describe <br />the runoff generated from the 10-year, 24-hour storm. However, <br />these ponds are filled with water to the principal spillway <br />elevation from pit pumpage, spoil aquifer inflow, local alluvial <br />ground water, or other unidentified upslope sources. The ponds <br />were not designed to provide sufficient storage for both standing <br />water and the design storm runoff volumes as indicated below: <br />Volume Pond 003 Pond 004 <br />ac-ft ac-ft <br />10-year, 24-hour storm runoff 3.39 9.17 <br />Principal to emergency spillway 2.86 8.38 <br />The actual volume required depends on the maximum head achieved <br />during the runoff while the pond is dewatering. The pond is <br />required to provide a minimum of 24 hours detention time. The <br />application provides an outflow hydrograph for Pond 004 but it is <br />apparent that insufficient detention time results from rapid <br />dewatering through the 36" spillway. <br /> <br />In order to meet the requirements for sedimentation ponds • <br />(4.05.6), the application needs to be revised to demonstrate . <br />24-hour detention of one-half of the storm runoff volume. This <br />requirement may require modification of the existing pond <br />configurations. <br />RESPONSE: <br />The designs of Sedimentation Pond #003 and #004 have been revised in <br />accordance with CMLRB's regulation 4.05.6. In addition, Peabody Coal <br />Company has demonstrated adequate detention time in order to meet the <br />requirement of regulation 4.05.2. <br />2.05.3(41 Ponds. Imooundments and Diversions <br />The information supplied for Pond 002 does not allow for a review <br />of detention time requirements as pond storage above the standing <br />water elevation is not specified. The long and narrow shape of <br />the pond might justify that a plug-flow model of sediment <br />deposition occurs within the pond. The application should be <br />revised to include a discussion which demonstrates that a <br />variance for sedimentation pond design requirements are <br />appropriate for Pond 002, or demonstrate 24 hour detention based <br />L <br />on the current as-built or a redesigned configuration. • <br />Revised 8/27/86 <br />