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I . sediment trap, as shown on Drawing 3 in Appendix A. The spillway has been sized to pass the <br />stormwater runoff resulting from up to the 100-yeaz, 24-hour storm event with a minimal <br />increase in head on the inlet pipe to the oil sepazator. (The Rational Method was used to estimate <br />peak runoff flow during a 100-year, 24-hour storm event. The hydrology calculations for peak <br />flow aze included in Appendix B.) Greater than design flows through the oil sepazator may flush <br />out oil accumulated in the separator. Stormwater dischazged through the emergency spillway <br />will drain downgradient to the stonnwater retention pond. <br />The sediment trap will require cleaning when the surface of the sediment approaches the <br />elevation of the inlet pipe to the oil separator. An access ramp at a 10% grade is provided to allow <br />a motorized loader easy access into the trap for removing sediment. During cleaning operations, <br />standing water in the sediment trap will be pumped to the stormwater retention pond. Sediments <br />removed from the trap will be placed in the lower refuse pile located at the mine. <br />Oil Separator <br />• During facility washdown operations, washwater draining to the sediment trap will dischazge <br />from the trap to the oil sepazator, the second structure in the series of washwater and stormwater <br />runoff management facilities. Design details of the oil sepazator aze shown on Drawing 3 in <br />Appendix A. Sizing calculations are included in Appendix C, and an equipment detail sheet for the <br />oil separator is included in Appendix D. <br />The 1500 gallon oil sepazator is sized to provide more than 5 minutes detention time at the <br />maximum anticipated flow rate of 150 gallons per minute. (This design flow rate is based on the <br />facility washwater flowmeter records provided by West Elk Mine.) Oil will be sepazated from the <br />water by a conventional baffling and piping system. Water will be conveyed from the oil <br />separator to the stormwater retention pond through a 6-inch pipe connecting the two facilities. <br /> <br />Wes! Elk Mine Train Loadoat Ertvirartmrrttal lmprovemertfs Shepherd Miller, Inc <br />p ~~ I.ao7vcpontrcpon.dac 4 July 1997 <br />