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The oil separator will be cleaned out as required. The oil separator will be fitted with two <br />--ph easy access to the oil trapping bale. A cleanout pipe is also provided for cleaning <br />the 6-inch line between the oil separator 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 area 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 area downgradient of <br />the sediment trap will also drain to the stormwater retention pond. The stormwater retention pond <br />layout and design details are 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 area resulting from a 25-year, 24-hour storm event <br />(approximately- 3D09:.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 are <br />included in Appendices B and C, respectively.) <br /> <br />As shown on Drawings 1 and 3, the stormwater retention pond is designed with two discharge <br />pipes. A gated pipe will be located on the south wall near the bottom of the retention pond. The <br />pipe will provide controlled releases from the pond as planned by West Elk personnel. An <br />emergency spillway pipe will be located on the south wall at the top of the retention pond. The <br />emergency spillway pipe will provide controlled releases from the pond during storm events larger <br />than the 25-year, 24-hour storm event. Discharges from both pipes will gravity-flow to an existing <br />Colorado Department of Transportation stormwater inlet located southwest of the train loadout <br />facility along Highway 133. <br />West Elk Mine Train Loadout Environmental Improvements Shepherd Miller, Inc <br />p:U 1-407Veport\ cport.doc 5 July 1997 (Revised April 1998)