2008-03-21_GENERAL DOCUMENTS - C1980007 (3)

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As previously described in this document, MCC encountered a large inflow of water while mining through afault/fracture system in the B East Mains. As of the date of this findings document, MCC continues to experience mine inflow in the Sylvester Gulch area of the mine. Groundwater in the area can be expected to flow generally in a downdip (northward) direction, parallel to bedding, toward the deeper part of the Piceance Basin. Data from monitoring wells generally indicate downdip flow, although some closely spaced wells in the Barren Member have highly variable water levels. Some wells are dry, indicating no groundwater flow. Dry wells and variable water levels may result from areal variation in permeability. Generally, springs in the permit area seem to act independently of the bedrock water zones and appear to be surface features related to weathered and fractured bedrock. Flow from springs tend to be highly seasonal and discharge only during spring snow melt. Springs recharge and discharge in relatively small areas. Inflows into underground mine workings from faults and fractures located outside stream valleys generally dry up with time or flow intermittently at discrete points along the fault or fracture. Those which continue to flow have flow rates which diminish to a trickle. Such mine inflows from faults and fractures may represent the dewatering of lenticular sandstone units with limited recharge areas, or may represent flows through fracture zones extending to the surface which have narrow recharge zones on steep slopes. The large initial flow rates are much larger than what would be expected from intergranular porosity in low- permeability sandstone (Darcy-type flow), indicating flow probably is from fractures or faults. Discharge of groundwater occurs through numerous seeps and springs indentified in the life-of--mine area. The locations of these springs are shown on Map 37 and 37A, Springs and Stock Ponds. c. Surface Water The North Fork of the Gunnison River is the principal drainage in the mine area. Smaller streams in or adjacent to the life-of--mine areas are tributary to the North Fork. The North Fork has an average annual streamflow at Somerset of approximately 313,500 acre-feet per year (1962-1979). Flows in the North Fork usually peak in May or June at around 2,000 to 3,000 cfs, and generally range between 50 and 200 cfs during the rest of the year. The flow is regulated by the Paonia Reservoir on Muddy Creek five miles upstream of the town of Somerset. The reservoir became operational in 1962. Water yields during that period have ranged from a high of 601,800 acre feet per year in water year 1984, to a low of 82,270 acre feet in water year 1977. Water in the North Fork 30