2007-06-29_PERMIT FILE - C1981022A (2)

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Saziar- 2.05.3 erosion or instability. Pond maintenance includes timely repair of any erosion or damage, cleanout of • discharge structures and removal of excess sediment accumulations. Pond construction practices and ongoing maintenance have limited any need for supplemental embankment protection. Generally, sediment levek are monitored by visual inspettion and pond cleanout is scheduled before sediment levels reach the invert of the primary spillway inlet. Sedimentation ponds will remain in place during the initial portion of the reclamation liability period and will be removed, unless previously approved as permanent structures. Removal and reclamation of associated disturbance areas will occur following DMG approval of Phase II Bond Release or the drainage restoration demonstration under Rule 4.05.2 (2). Pond reclaznation will involve drairtirtg any acctunulated water, removal of outlet structures, backfilling the ponds, grading the associated disturbance areas, replacement of soil material, and revegetation. Stream Channel Diversions -The orily stream channel diversion required in conjunction with mining and related activities haz been temporary culverting of the lower and middle portions of Elk Creek through part of the Elk Creek Mme surface facilities area and the Elk Creek support facilities area. In conjunction with the historic Somerset Mme mining activities, U.S. Steel placed approximately 800 feet of 9-foot diameter culvert in the Elk Creek drainage channel and backfilled over the culvert to create a level faciliues area near the mouth of Elk Creek Canyon. OMI has subsequently extended this culvert another 650 feet to accommodate progressive mine expansion activities. The culvert has been sized, bedded, placed, and backfilled to azsure it's long-term stability. The Elk Creek culvert u designed to safely pass the peak flows resulting from a 100-year, 24-hour storm event and u permitted tinder applicable provisions of Nationwide Permit 26 by the U.S. Army Corps of Engineers (Permit No. 199675449). OMI will culvert two additional segmenzs totaling an additional 1,600 feet under C10E Permit No. 199975232 in the middle portion of Elk Creek in order to establish the portal area, haul road, and facilities pads for the Elk Cmek Mme. • Additional culvert installation will be scheduled, if reasonably feasible, during a low flow period to mmimnP potential water quality impacu. Scream flows will be diverted around the construcuon disturbance by either a temporary ditch or pipeline and silt fence, straw bales, or other appropriate temporary control measures will be used to nunim'vx additional sediment contributions to the stream Ckt completion of active operations for the associated disturbance areas, most of the Elk Creek culvert will be removed (except for that associated with the Elk Creek road crossings) and the associated stream channel reestablished. Two sections of the Ells Creek culvert will remain in place az permanent road crossings in conjunction with the postminirtg land use as shown on the Facilities Postmining Topography Map, (Map 2.05-M6). The Elk Creek culvert sections are designed to safely pass the peak flows from a 100-year, 24-hour storm event with significant excess culvert capacity (approximately 320 percent). Design information for the Elk Creek culvert is provided in Exhibit 2.05-E3, Drainage and Sediment Control Plan, and the culvert location and design configuration is illustrated by the Drainage and Sediment Control Plan Map, (Map 2.05-M4). Clean Water Diversions - Clean water diversions have been established for most of the mine disturbance areas to intercept and divert nutoff from undisturbed upgradient areaz around the ntirtirtg disturbance. The purpose of these diversions is to route natural runoff around disturbance areaz to avoid potential contamination or additional sediment contributions and to minimi>e the volume of drainage passing across disturbance areas which must be intercepted and handled by the mine drainage and sediment control systems. Clean water diversions are designed to minimize erosion and additional sediment contributions and to • safely pass design flows while maintaining adequate freeboard. Where design flow velocities would resin[ in excessive erosive fortes, adequate channel protection is provided to prevent erosion and down-cutting. Clean water diversions are identified and associated design calculations for both the diversion ditches and any associated culverts are provided in Exhibit 2.05-E3. Diversion locations and configuration are shown on the Drainage and Sediment Control Plan Map, (Map 2,05-M4). PR04 2.05-36 Revised May 2001