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The oil separator will be cleaned out as required. The oil separator will be fitted with two <br />manholes for easy access to the oil trapping baffle. A cleanout pipe is also provided for cleaning <br />the 6-inch line between the oil sepazator and the Stormwater retention pond. <br />Stormwater Retention Pond <br />The Stormwater retention pond is the last structure in the series of Stormwater management facilities <br />proposed for the train loadout facility. All Stormwater runoff from the paved containment azea and <br />` facility washwater passing through the sediment trap and oil separator will drain to the Stormwater <br />retention pond. Stormwater runoff from the portion of the paved containment azea downgradient of <br />the sediment trap will also drain to the Stormwater retention pond. The Stormwater retention pond <br />layout and design details aze shown on Drawings 1 and 3 in Appendix A. <br />The Stormwater retention pond is sized to contain the volume of washwater that will accumulate <br />from a.week of average washdown activity (approximately 2500 cubic feet) and the Stormwater <br />runoff from the paved containment azea resulting from a 25-year, 24-hour storm event <br />(approximately 3000 cubic feet). The weekly washdown water volume was estimated from the <br />washwater flowmeter records provided by West Elk Mine. The volume of Stormwater runoff was <br />estimated using methodology presented in Soil Conservation Service Technical Release 55, <br />Urban Hydrology for Small Watersheds, 1986. (The hydrology and sizing calculations aze <br />included in Appendices B and C, respectively.) <br />As shown on Drawings 1 and 3, the Stormwater retention pond is designed with two spillways. <br />A gated spillway will be located on the south wall of the retention pond. The south spillway will _ <br />~---- <br />provide controlled releases from the pond as planned by West Elk personnel. Dischazges from <br />the -south spillway will gravity-flow through a pipe to an existing Colorado Department of <br />Transportation Stormwater inlet located southwest of the train loadout facility along Highway <br />133. An emergency spillway will be located on the west wall of the retention pond. The west <br />.--- <br />spillway will provide controlled releases from the pond doting storm events larger than the 25-yeaz, <br />~J <br />West Elk Mine Train Loadoaf Environmental Improvemena; Shepherd Miller, Ine <br />p~.~~ ~-ao~~eow~~,~on.ao~ 5 July 1997 <br />