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Significant hydrogeologic units.present within the West Elk Mine property include (from top <br /> to bottom) the Mancos shale, the Mesaverde Formation (including the Rollins Sandstone, <br /> Lower Coal Member, Upper Coal Member, and the Barren Member) and the colluvium and <br /> alluvium along the drainage side slopes and valley bottoms. These hydrogeologic units are <br /> depicted on Map 9 of the permit. <br /> With the exception of the Mancos shale (which has an extremely low permeability and acts <br /> as an 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 <br /> Mesaverde Formation, locally continuous permeable sands may contain groundwater which <br /> generally is recharged from the downward percolation of meteoric waters. <br /> The most continuous sandstone aquifer of any significance in the region is the Rollins <br /> Sandstone of the Mesaverde Formation. The Lower Coal Member of the Mesaverde <br /> Formation contains the Upper and Lower Marine Sandstones which may locally produce <br /> significant quantities of water. The colluvium which overlies the Barren Member of the <br /> Mesaverde Formation Wnsists of discrete, localized units which generally follow topography. <br /> The colluvial units recharge and discharge on a seasonal basis in response to snowmelt and <br /> precipitation events. The alluvium of the North Fork consists of mixed sand, cobbles, and <br /> boulders capped by finer sands and silts. The quantity of groundwater produced from the <br /> alluvial deposits is dependent upon the thickness and extent of the deposit. <br /> Evidence shows that groundwater movement is controlled largely by fracture patterns and <br /> topography. The West Elk Mine's experience in mining the F and B Seams indicates that <br /> groundwater inflows are associated with fractures near the subcrop and are seasonal. As <br /> discussed in the previous section of this document, a fault system was encountered while <br /> mining in the B Seam, which produced as much as 2,500 gpm of groundwater inflow to the <br /> mine. <br /> Ground water use in the general area around the West Elk Mine is confined to shallow wells <br /> in the alluvium and Rollins Sandstone of the North Fork of the Gunnison River and its <br /> tributaries. No private, commercial, or industrial wells are presently located within the <br /> permit area. <br /> A description of the surface water system can be found in Section 2.04.7 of the permit <br /> document. Supporting information is contained in Map 34, which illustrates the drainages <br /> associated with the WEM coal lease area, Map 37, which delineates the location of all known <br /> springs on the coal lease area, and Map 36, which shows the reservoirs and irrigation ditches <br /> associated with the Minnesota Creek Basin. <br /> A description of the surface water occurrence and mining impacts on adjacent areas can be <br /> found in the "Probable Hydrologic Consequences of Mining" section of this document, and <br /> the "Cumulative Hydrologic Impact Study" document for this mine area. <br /> All of the streams draining the West Elk Mine permit area are tributaries to the North Fork <br /> of the Gunnison River. Sylvester Gulch, Lone Pine Gulch, and Gribble Gulch are ephemeral <br /> streams draining the northern portion of the lease area. Minnesota Creek and its tributaries, <br /> Horse Creek, South Prong, Lick Creek, Dry Fork, and East Fork, drain the southern portion <br /> 10 <br />