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Washwater and Stormwater Management <br />The facility washwater and stormwater runoff from the paved containment area will be conveyed <br />by gravity flow to a series of stormwater management structures. These management structures are <br />shown on Drawing 1 in Appendix A and include a sediment trap, oil separator and stormwater <br />retention pond. <br />Sediment Trap <br />The sediment trap is designed to remove sediment from facility washwater and stormwater runoff <br />draining to the trap. The layout of the sediment trap and design details are shown on Drawings 1 <br />and 3 in Appendix A. Washwater will be collected and piped to the sediment trap through a trench <br />drain to be located below the loadout facility and south of the railroad track located adjacent to the <br />facility. The washwater will be conveyed from the trench drain to the sediment trap through a <br />buried pipe. (The trench drain and pipe layout are shown on Drawing 1 in Appendix A. The trench <br />drain will also function as part of the hydraulic oil spill containment system discussed later in this <br />report.) Stormwater runoff from the paved containment area upgradient of the sediment trap will be <br />directed to the sediment trap through site grading. <br />During facility washdown operations, washwater will. discharge from the sediment trap to the oil <br />separator through a pipe connecting these facilities. (The walls of the sediment trap have been <br />configured to direct any oil that may be floating on the water surface toward the inlet pipe to the <br />oil separator.) The sediment trap is designed to contain 20 cubic yards of sediment below the <br />invert of the inlet pipe to the oil separator. (Sizing calculations for the sediment trap are included <br />in Appendix C.) Approximately 20 cubic yards of sediment is currently removed quarterly from <br />the existing sediment pond <br />During larger storm events, water entering the sediment trap will also discharge through an <br />emergepW,,5pillway. The emergency spillway will be located along the northwest wall of the <br />R <br />• <br />West Elk Mine Train Loadout Environmental Improvements Shepherd Mitter, Inc. <br />pAl 1-407\reponaepon.doc 3 - July 1997 (Revised April 1998)