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<br />44 <br /> <br /> <br /> 2. Probable Hydrologic Consequences <br /> <br /> Section 2.05.6(3) of the permit application contains the applicant’s prediction <br />of the probable hydrologic consequences from mining and reclamation <br />activities at the West Elk Mine. <br /> <br />During the first two permit terms, the operator mined the F Seam. During the <br />third through fifth permit terms, MCC mined the B Seam exclusively. <br />Activity in these seams involve longwall mining methods, with very little or <br />no activity in the F Seam. During the sixth permit term the operator <br />conducted development and longwall mining in the B Seam and E Seam. <br />During the current permit term, MCC will be conducting development and <br />longwall mining in the E Seam. <br /> <br />The Probable Hydrologic Consequences section of the permit is divided into <br />two main subsections: Groundwater Effects and Surface Water Effects. <br /> <br />a. Ground Water Effects <br /> <br />During mining at the West Elk Mine, ground water seeps into the <br />underground workings from rock exposed in the workings. Inflow into <br />the workings was estimated to be a total of 166 acre-feet in 2004. Excess <br />accumulations of this water are pumped out of the workings into <br />Sylvester Gulch through a permitted discharge outfall. After mining is <br />completed, pumping will cease, the portals will be sealed, and the <br />underground workings will flood with the water seeping into the <br />workings. The operator estimates it will take between 200 to 800 years <br />for the workings to fully flood. The water that seeps into the workings <br />will saturate the gob in the down-dip end of the workings and minerals <br />will be dissolved from the gob, creating a gob leachate. This leachate <br />can be expected to be alkaline and have TDS between 1,000 and 5,000 <br />mg/l (for comparison, North Fork alluvial water probably has TDS <br />greater than 1,500 mg/l, based on monitoring at the Bear No. 1 Mine.) <br /> <br />As the down-dip end of the West Elk Mine workings fill with gob <br />leachate, this leachate will exert a hydraulic head on the downdip walls <br />of the workings and the leachate may seep into the cleat porosity and <br />fault porosity that is in the coal seams exposed in the workings. This <br />leachate could flow down-dip, parallel to bedding, through the coal <br />seams and discharge from the coal seams into the alluvium of the North <br />Fork of the Gunnison where the coal seams sub-crop underneath the <br />alluvium. This seepage would form a plume of gob leachate in the <br />alluvium that would extend downgradient from the Sylvester <br />Gulch/North Fork confluence toward Somerset. The likely maximum <br />discharge rate of gob leachate into the alluvium would be on the order of <br />100 gpm based on the maximum head that could develop in the flooded <br />workings. Such a plume would mix with and be diluted by ground water