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monitoring stations, and Map 35, which is a composite Barren Member well water level and <br />spring elevation map. <br />A description of groundwater occurrence and mining impacts on groundwater within the permit <br />and adjacent areas can be found in the "Probable Hydrologic Consequences of Mining" section of <br />this document and the "Cumulative Hydrologic Impact Study" document for the North Fork of <br />the Gunnison area. <br />There are seven categories of potential aquifers that occur in the Somerset Coal Field. These are: <br />1) the alluvial and terrace deposits associated with the North Fork of the Gunnison River; 2) the <br />localized, shallow alluvium along creeks tributary to the North Fork; 3) the discontinuous, <br />lenticular and laminar sandstones of the Mesaverde Formation; 4) the Rollins Sandstone; 5) the <br />coal seams; 6) shallow colluvial surficial deposits; and 7) fracture zones in bedrock. <br />Significant hydrogeologic units present within the West Elk Mine property include (from top to <br />bottom) the Mancos shale, the Mesaverde Formation (including the Rollins Sandstone, Lower <br />Coal Member, Upper Coal Member, and the Barren Member) and the colluvium and alluvium <br />along the drainage side slopes and valley bottoms. These hydrogeologic units are depicted on <br />Map 9 of the permit. <br />With the exception of the Mancos shale (which has an extremely low permeability and acts as an <br />aquitard), groundwater is generally localized and of limited areal extent within these <br />hydrogeologic units. The Mesaverde Formation is typically 2,500 feet thick at the mine and <br />consists of sandstone, shale, clay, and interbedded coal. Within the members of the Mesaverde <br />Formation, locally continuous permeable sands may contain groundwater which generally is <br />recharged from the downward percolation of meteoric waters. <br />The most continuous sandstone of any significance in the region is the Rollins Sandstone of the <br />Mesaverde Formation. The Lower Coal Member of the Mesaverde Formation contains the <br />Upper and Lower Marine Sandstones which may locally produce significant quantities of water. <br />The colluvium which overlies the Barren Member of the Mesaverde Formation consists of <br />discrete, localized units which generally follow topography. The colluvial units recharge and <br />discharge on a seasonal basis in response to snowmelt and precipitation events. The alluvium of <br />the North Fork consists of mixed sand, cobbles, and boulders capped by finer sands and silts. <br />The quantity of groundwater produced from the alluvial deposits is dependent upon the thickness <br />and extent of the deposit. <br />Evidence shows that groundwater movement is controlled largely by fractures and topography. <br />The West Elk Mine's experience in mining the F and B Seams indicates that groundwater inflows <br />are associated with _fractures and are seasonal. As discussed in the previous section of this <br />document, a fault system was encountered while development mining in the B Seam, which <br />produced as much as 8,000 gpm of groundwater inflow to the mine. <br />Groundwater use in the general area around the West Elk Mine is confined to shallow wells in <br />the alluvium of the North Fork of the Gunnison River and its tributaries. No private, <br />commercial, or industrial wells are presently located within or down - gradient adjacent the permit <br />10 <br />