2013-11-05_REVISION - C1981022 (3)

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The topography of the region is characterized by steep canyons cut by the North Fork of the Gunnison River and its tributaries, with several remnant alluvial terraces above the valley of the North Fork. Proceeding downstream below Somerset, Colorado, the canyon widens. At Paonia, Colorado, the canyon has given way to a broad alluvial plain with interspersed remnant alluvial terraces. The coal to be mined is located in the Somerset Coal Field. The strata exposed in the Somerset Coal Field consist of the Mancos Shale and the coal- bearing Mesaverde Formation of Upper Cretaceous Age, and of the Ohio Creek Conglomerate, the Wasatch Formation and the Quartz Monzonite Porphyry of Early Tertiary Age. Coal is mined from the Mesaverde Formation, a 2,500 foot thick sequence of sedimentary strata overlain by the Ohio Creek Conglomerate and underlain by the Mancos Shale. The strata in the Elk Creek Mine permit area dip three to five degrees north - northeast within the permit area, but varies locally. The Mesaverde Formation contains a number of coal - bearing members. The Somerset Mine mined coal from the B -2 seam of the lower coal bearing (Bowie) member of the Mesaverde Formation. The Sanborn Creek and Sanborn Creek East additions mined the B and C seams of this member. The Elk Creek mine ramps down to the D -seam and will mine that level. The Lower Coal member ranges from 260 to 350 feet thick in the Somerset Coal Field and bears three minable coal seams. This member consists of interbedded and lenticular sandstones, siltstones and coals, and is overlain by a massive sandstone, 25 to 225 feet thick which lies directly on the C seam and marks the bottom of the upper coal member. Three categories of potential aquifers exist in the general area: alluvial deposits associated with the North Fork of the Gunnison River and its tributaries, the Rollins Sandstone, and lenticular discontinuous sandstones of the Upper Mesaverde Formation. The largest alluvial aquifers are associated with the North Fork of the Gunnison River. Smaller, more isolated alluvial aquifers are associated with several tributaries of the North Fork. The Rollins Sandstone is the only known sandstone with sufficient porosity and lateral extent to be considered a regional bedrock aquifer. The only wells in the region which are completed in this aquifer are located near the Hawk's Nest Mine along the North Fork. Localized perched bedrock aquifers exist in the discontinuous, lenticular, fine - grained sandstones of the Upper Mesaverde Formation. The amount of ground water in these sandstones is controlled by faulting and fracturing of the strata (secondary porosity) and the topography of the recharge area. No known wells are completed in the sandstones of the Upper Mesaverde Formation above the mine workings. The valley in which the towns of Paonia and Somerset are situated is semi -arid, with annual precipitation averaging about 15 inches per year. Mean annual precipitation increases with elevation, reaching over 40 inches per year near the summit of Mt. Owen. The May to September precipitation is five inches for the lowlands and 13 inches for the mountain peaks. This indicates that snowfall patterns play an important part in determining the hydrologic conditions of the area. Temperature extremes at Paonia have ranged from —28 °F in January to 100 °F during July and August. The average annual temperature is approximately 49 °F. Snowfall averages 58 inches per year.