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• RUN-OFF.WK3 <br />APPENDIX 4-B, VOLUME III <br />North Thompson Creek Mine Site Ditches <br />Ditches D-7, D-6, D-2A, D-2 B, D-11, D-12 & D-4 <br />The following calculation is presented to determine the <br />appropriate size of the borrow ditches along county <br />road #108 and ditches located on the No. 1 Mine Site. <br />Flow from east as shown on drawing D-4-8. <br />Ditch D-7, as shown on drawing D-4-8, is located immediately <br />above the refuse pile. It will be desgined to handle the flow <br />flow from the 100-year event. <br />The drainage areas are presented on Map D-4-7. Areas 3A, 3B <br />and 4 comprise the extent of the drainage area immediately <br />above the refuse pile. <br />The lower segement of the ditch, D-6, will be designed to <br />handle the l0-year event. Ditch D-6 will be designed based <br />on the flow generated by areas 3A, 3B, 4, 5A, 5B and 1/2 of <br />area 6. <br />Flow from the west as shown on drawing D-4-7. <br />• Ditch D-2A, as shown on drawing D-4-7, will be designed to <br />handle the 10 year event. This ditch will be desgined based on <br />the flow generated by area 10. Ditch D-2 B, as shown on drawing <br />D-4-7, will also be designed to handle the 10 year event. Ditch <br />D-2B will be designed based on the flow generated by areas 7 <br />and 1/2 of area 6 and the flow from ditch D-2A. <br />Area 11 was previously broken out separately becuase it <br />represented the disturbed No. 3 Mine area. Since the No. 3 <br />. Mine is reclaimed, areas 10 & 11 were conbined into a single <br />area 10. <br />The flow from areas 8 & 9 discharge into an 18" CMP (CMP C-2) <br />located in reclaimed pond P-1. Ditch D-11 conveys the flow to <br />the 18" CMP. <br />Flow from the east and the west meet in reclaimed pond P-4 <br />where the flow is passed under the county road by a 48" <br />culvert (CMP C-6). <br />STORM EVENTS <br />10 YEAR 24 HOUR EVENT <br />100 YEAR 24 HOUR EVENT <br />1.8 INCHES <br />2.4 INCHES <br />The run-off calculations presented below are calculated based <br />on the manual - Procedures for Determining Peak Flows in <br />Colorado - published by the Soil Conservation Service, March <br />• 1984. The run-off values are calculated with the computer <br />program Storm ver. 6.21. <br />4-B:4 October 1994 <br />