2024-06-25_PERMIT FILE - C1980007A (4)

Home Browse Search

West Elk Mine 2.05-124 Rev. 06/05- PR10, 03/06- PR10, 05/06- PR10, 11/060- TR107, 04/07- TR108, 09/07- PR12, 02/08- PR12; 11/10- MR372; 10/20- MR-452; 12/20- TR149; 12/21- TR150, 1/24-TR152 overall increase in wetlands and creation of habitat that would benefit waterfowl and other wildlife. If subsidence in the area of wetlands creates a change in the gradient that would result in a lowering of wetland water table, modifications to the stream channel to stabilize the water table may be necessary. The mitigation efforts may include the construction of rock dams or weirs that would act as impediments to stream flow and result in the re-establishment of the wetland water table levels. The Best Currently Available Technology will be used to restore the water levels of the wetlands if necessary and only implemented after obtaining approval(s). Additional mitigation of mining impacts may be necessary if loss or diversion of flow or a significant change in the stream profile will significantly impact vegetation. Efforts will be made to re-establish riparian vegetation in areas negatively impacted by changes in flow locations. These re-establishment efforts may include, but not be limited to, planting of new seedlings or reseeding with appropriate species. The appropriate permits and approvals of plant or seed mixes will be obtained prior to performing mitigation activities. It is anticipated that little or no impacts to wildlife and domestic livestock uses, and their respective habitat will occur as a consequence of mining-induced subsidence within the permit area. In the unlikely event that subsidence effects adversely impact wildlife or domestic livestock uses associated mitigation measures will focus on returned disturbed areas to a capability and land use(s) which existed prior to mining. These mitigation measures may include, but not be limited to, repairs of surface cracks that are deemed dangerous to humans, wildlife, or livestock. The repairs of the cracks may include backfilling with available native soils, gravels, concrete block, etc. Livestock fences damaged by mining related activities will be repaired as soon as possible. In 2007, MCC worked with the Minnesota Ditch and Reservoir Company to obtain the appropriate permits and approvals, and implemented a preventative measures construction project to modify and improve the Monument Dam. These dam modifications (completed in January 2008) were consistent with the reservoir company’s existing Forest-issued Special-Use Permit. The objective of this project was to prevent damage to the dam/reservoir from the potential of mining-induced microseismicity, strengthen the dam against damage due to naturally occurring seismicity, and control damage due to past and future periodic movement of the landslide located on the left (south) abutment of the dam. Exhibit 72, Prevention Measures, contains the general design of the measures implemented that now allow the dam to reach a static safety factor of 1.5 and safely withstand any mine-induced microseismic event. The plans included the construction on the downstream face of the dam of a sand chimney drain covered by stability berm. Additionally, a buttress constructed of erosion resistant fill was placed at the toe of the dam. The purpose of the berm and buttress is to increase the stability of the dam fill itself and to impede further movement of the landslide located in the left abutment. Other preventative measures to increase dam and landslide stability included the slip-lining of the existing outlet conduit with HDPE pipe to eliminate the possibility of further damage to the existing cast iron pipe, replacement of the inlet structure to outlet conduit to eliminate leakage around the existing structure, and construction of dewatering trench to further stabilize a portion of the landslide. MCC in addressing 2.05.6(6)(f)(iv)(A-D), will complete preventative measures on Monument Dam (Exhibit 76) and may do one or more of the following: replace, repair, and otherwise