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toward Somerset. The likely maximum discharge rate of gob leachate <br />into the alluvium would be on the order of 100 gpm based on the <br />maximum head that could develop in the flooded workings. Such a <br />plume would mix with and be diluted by ground water in the North Fork <br />alluvium and would be attenuated where the alluvium significantly <br />widens upgradient from Somerset. North Fork alluvial ground water is <br />monitored upgradient from Somerset at the Bear 3 Mine. <br />Low permeability of bedrock units in and near the West Elk Mine <br />(Rollins Sandstone, B through F seams, and the Barren Member) will <br />prevent any significant seepage of gob leachate into these units. <br />MCC has submitted two possible plans for sealing the portals upon <br />closure of the mine. One plan calls for perpetual gravity discharge of <br />mine water to the surface through afour-inch PVC pipe that will be <br />installed in a block wall at the portal. An alternate plan (to be <br />constructed if water is toxic) is to construct water-tight seals within the <br />mine that will withstand the expected hydraulic pressures. Samples taken <br />in the adjacent Oliver Mine indicate mine waters will not be toxic. <br />Subsidence fractures that develop over mine workings have the potential <br />to dewater natural springs and wetlands in the West Elk permit area. The <br />permit application explains that the risk of such depletion is significantly <br />reduced by the overburden thickness of greater than 280 ft. and the <br />resistance to fracturing of interbedded fine-grained units that would <br />deform ductiley (bending), rather than brittley (fracturing). Monitoring <br />of springs since before the mine was developed has not detected impacts <br />from mining. This monitoring will continue. <br />The operator predicts overall ground water/surface water balance will not <br />be significantly affected if mine inflows are much greater than predicted <br />because mine inflows will ultimately be discharged back to the North <br />Fork of the Gunnison. <br />i. Refuse Material Disposal Impacts on Groundwater - <br />Lower Refuse Disposal Area -Coal mine waste will be disposed <br />in the Lower Refuse Disposal and Refuse Pile Expansion sites. <br />The lower refuse pile is permitted for permanent disposal of 1.09 <br />million cubic yards of mine development waste and sediment <br />pond cleanout material. The refuse pile expansion is designed to <br />hold 1.38 million tons of material over a life of 9.4 years. (The <br />Refuse Pile Expansion is discussed in Permit volume l OB.) <br />To date, refuse piles have not impacted the groundwater zone <br />near Sylvester Gulch. Because of the low permeability of the <br />colluvial soils and the lack of a groundwater table near the surface <br />34 <br />