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~~~ ESPEY, HUSTON L ASSOCIATES, INC. <br />The haul road shall have an asphalt surface from Sta. 0+00 to Sta. 3+00. <br />This will help prevent the tracking of mud onto the State Highway, and mill reduce <br />maintenance costs in this area by eliminating the "washboazd" surface which is <br />common to gravel roads where trucks frequently stop and start. The remainder of <br />the road shall be surfaced with a compacted crushed rock material The entire <br />length of the gravel road shall be treated with calcium chloride or similar dust <br />controlling agent, as necessary. <br />A Type 3 guard rail shall be installed along the east side of the road <br />where it traverses along the top of an existing eazthen dam. The guard rail will run <br />between Sta. 11+00 and Sta. 17+00. <br />3.5.1.2 Hydrology for Haul Road Crossing at Sta. 31+50 <br />• The hydrology for the design of culverts passing under the Northern <br />No. 1 (FF-Seam) haul road was obtained from Merrick and Company's Drainage <br />Facilities and Sediment Control Plan dated April 27, 1979• A 10-year 24-hour <br />design storm is used in accordance with OSM Requirements for access haul roads. <br />At the upstream end of the disturbed area of the mine site the peak flow <br />was 289 cfs at a time of 12.1 hours into the storm. The peak flow generated by <br />local drainage basins and diverted around the site is 24 cfs at a time of 11.9 hours. <br />At 12.1 hours this flow is 10 cfs. The sum of the flows at 12.1 hours results in a <br />peak flow of 299 cfs at the downstream end of the mine site. This flow was used as <br />the total design flow for two reasons: (1) The flow length from here to the crossing <br />is 1,400 feet and some additional lagging and damping of the peak occur due to time <br />of travel and channel storage. This would result in a reduction of the peak flow at <br />the crossing; (2) This reduction would be paztially offset by additional flows <br />generated along this channel section. These flows would be very small in <br />comparison to the peak flow in the channel and also have a much earlier time to <br />• peak. <br />C-45 <br />