2018-09-04_GENERAL DOCUMENTS - C1980007

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40 the dilution of alluvial groundwater by North Fork River water at this well. Except for areas in the Minnesota Creek Drainage, the alluvium along the lower reaches of tributaries to the North Fork is predominantly thin and confined to discontinuous narrow bands along the stream courses. The deeply incised channels of these tributaries restrict the width of the alluvium, while the stream gradient and the presence of resistant sandstone in the stream channels limit the thickness and downstream extent of the alluvium. Occurrences of groundwater have been noted in the Mesaverde Formation based upon information obtained from drilling, experience in the mines, and from the presence of springs and seeps in the region. This information also indicates that the only potential regional bedrock aquifer in the general area is the laterally continuous Rollins Sandstone. The laterally discontinuous lenticular sandstones within the Upper Mesaverde Formation support only localized groundwater flows. The Rollins Sandstone is recharged in the vicinity of the West Elk Mine by snowmelt and rainfall on outcrops, and in subcrops beneath stream alluvium and in the channels of the North Fork and its tributaries. These recharge areas have limited areal extent due to the steep dips of outcrops and the narrowness of the stream valleys; consequently, little recharge occurs. Some recharge to the continuous units and much of the recharge to the more discontinuous, lenticular units will come directly from the percolation of snowmelt and precipitation downward through sandstone lens and along fractures. The same is true in the Jumbo Mountain area. Of 112 exploration drill holes at the West Elk Mine that were drilled prior to the mine opening, only three of the holes produced water from the F Seam at a production rate of 3 gpm or less. Three other holes in the Barren Member had rates of about 0.75 gpm. The Mesaverde Formation is cut by fractures and faults that extend vertically to the surface. The faults and fractures produce narrow bands of permeability and provide the primary ground water flow path in the areas. When faults and fractures are encountered in mines in the North Fork region, they generally produce mine inflows. The flow characteristics of each mine inflow associated with faults and fractures depend on the lateral extent and the proximity of the fault or fracture to a stream valley. All inflows from these sources are characterized by an initial surge of water which then either decreases or ceases completely with time. Locally, water flow through fractures probably occurs more rapidly, as suggested by the seasonal fluctuation in discharge rates of some springs in the mine plan area. Mine inflow studies conducted as recently as 1985