2008-03-21_GENERAL DOCUMENTS - C1980007 (3)

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wetlands are found in drainage channels, although there are small, isolated wetlands on the hillsides where springs and seeps occasionally emerge as a result of landslides/sumps. 2. Probable Hydrologic Consequences Section 2.05.6(3) of the permit application contains the applicant's prediction of the probable hydrologic consequences from mining and reclamation activities at the West Elk Mine. During the first two permit terms, the operator mined the F Seam. During the third through fifth permit terms, MCC mined the B Seam exclusively. Activity in these seams involve longwall mining methods, with very little or no activity in the F Seam. During the current permit term, MCC will be conducting development and longwall mining in the B-seam and the E-seam. The Probable Hydrologic Consequences section of the permit is divided into two main subsections: Groundwater Effects and Surface Water Effects. a. Ground Water Effects During mining at the West Elk Mine, ground water seeps into the underground workings from rock exposed in the workings. Inflow into the workings was estimated to be a total of 166 acre-feet in 2004. Excess accumulations of this water are pumped out of the workings into Sylvester Gulch through a permitted discharge outfall. After mining is completed, pumping will cease, the portals will be sealed, and the underground workings will flood with the water seeping into the workings. The operator estimates it will take between 200 to 800 years for the workings to fully flood. The water that seeps into the workings will saturate the gob (waste rock) in the downdip end of the workings and minerals will be dissolved from the gob, creating a gob leachate. This leachate can be expected to be alkaline and have TDS between 1,000 and 5,000 mg/1 (for comparison, North Fork alluvial water probably has TDS greater than 1,500 mg/1, based on monitoring at the now abandoned Bear No. 1 Mine.) As the downdip end of the West Elk Mine workings fill with gob leachate, this leachate will exert a hydraulic head on the downdip walls of the workings and the leachate may seep into the cleat porosity and fault porosity that is in the coal seams exposed in the workings. This leachate could flow downdip, parallel to bedding, through the coal seams and discharge from the coal seams into the alluvium of the North Fork of the Gunnison where the coal seams subcrop underneath the alluvium. This seepage would form a plume of gob leachate in the alluvium that would extend downgradient from the Sylvester Gulch/North Fork confluence 33