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Mountain Coal Company Exhibit 69 <br />West Elk Mine Sylvester Gulch Facilities <br />and west edge of the benches paralleling roads or ditches. The total length of <br />guardrail for the shafts site benches is approximately 1,750 ft. <br />HydroloQy <br />North and south Clearwater diversion ditches, designed for the peak runoff from [he <br />100-year, 24-hour storm event will carry storm runoff around the site. This very <br />conservative design approach ensures surface water runoff can not enter the <br />ventilation shafts. <br />Along the north side of the site, a standard grass-lined ditch or a riprapped ditch will <br />be built adjacent to and upgradient of the access road and topsoil pile to carry clear <br />runoff from the south facing slopes and the road. The diversion ditch that will <br />extend eastward to provide Clearwater diversion for the topsoil pile will be <br />riprapped due to steeper slopes and higher flow velocity. Below the topsoil pile <br />area the ditch will be grass lined. Stormwater will flow westward in the ditch <br />paralleling the road until outfalling northward through a culvert to Sylvester Gulch. <br />Hemp or coconut fiber mats will be placed in the grass lined diversion ditch until <br />vegetation is established. The culvert outlet will be riprapped to provide erosion <br />protection. The Clearwater ditch and culvert will be sized to carry the peak flow <br />from a 100-year, 24-hour event. <br />Along the south side of the site, a combination of buried culvert and surface ditches, <br />in conjunction with an upstream surge basin will provide Clearwater diversion of <br />runoff from the upstream drainage basin and local drainage south of the shafts site. <br />The surge basin east of the shafts site is designed as a ]0 foot high riprapped <br />embankment which will route upstream flows up to the 100-year, 24-hour event <br />directly into a 48" buried culvert. Flows greater than the 100-year, 24-hour event, <br />and up to approximately the 250 year, 24-hour event will backwater behind the <br />embankment providing flow attenuation in the Clearwater culvert. In the event of <br />blockage of the trash rack at the surge basin culvert inlet, the embankment has been <br />designed for overtopping and a secondary concrete collector channel with grated top <br />plate will be installed for 50' below the embankment. This grated concrete channel <br />will also pass the 100-year, 24-hour flow into the buried Clearwater culvert, and <br />provides redundant assurance that stormwater can not inundate the shafts site. <br />Localized flows from the hillsides south of the shafts site will be captured by a <br />small grass lined surface ditch. Flows in the surface ditch will also enter the buried <br />Clearwater culvert through drop inlets spaced approximately 400' along the ditch. <br />The clear water is 48 inches in diameter from the detention pond to the first <br />manhole. The culvert then increases to 54 inches in diameter. <br />Total flows into the ditch and culvert system will be routed downslope to Sylvester <br />Gulch through buried metal culverts. Riprap energy dissipators will be installed at <br />the culvert outlet to provide erosion protection. Total length of the ditch and culvert <br />3 Nov. 1996 PR07R; Revived Mnr 7997 MR216 <br />Nevie~edJul. 1997 MR219; Revised June 2003 MR297 <br />