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-16- The Harvey Gap Drainage is tributary to the Colorado River. The total natural drainage area of this stream is approximately 5200 acres (8.1 sq.mi.). The Harvey Gap Drainage is a perennial stream with six small tributary ephemeral drainages. The nature of this drainage has been altered by construction of canals and a reservoir for irrigation. The Grass Valley Reservoir is located 600 feet upstream of the mine site on Harvey Gap Creek. This reservoir has a design storage of 5$00 acre feet. The water is impounded during high flow seasons from the headwaters of Harvey Gap and from water diverted from the headwaters of East Rifle Creek through the Grass Valley Canal. The impounded water is released from April 15 to October 15 to irrigate almost 6000 acres of land in the Silt and Rifle area. The Grass Valley Reservoir is constructed on the relatively impermeable Mancos Shale Formation. The Eastside Mine is located downstream of this reservoir, on the William Fork Formation of the Mesa Verde Group, which overlies the Mancos Shale. The rock strata dip steeply to the south and the strata are younger in age in the down gradient direction as shown in Figure 1. As shown in Figure 1. as the drainage passes through the axis of the Grand Hogback Monocline, the topography flattens as the Tertiary aged Wasatch Formation is encountered at the surface. This formation lies beneath the flood plain in the Colorado River and is in some cases overlain by as much as 100' of Quaternary alluvial deposits. The Eastside Mine will be developed in coals of the Iles and Williams Fork Formations of the Mesa Verde Group. The stratigraphy of the immediate area is shown in Figure 2. The Iles Formation intertongues with and overlies the Mancos Shale in the area. The Iles Formation is typified by marine to non-marine sandstones, siltstones, shales, and coals. The Williams Fork Formation is predominately non-marine sandstone, siltstones, mudstones, shales and coals. The five-year permit is for mining in the E-Seam of the Iles Formation. This seam is approximately 20 feet thick and dips 590 on the average to the south. Coal will be mined by continuous miner or conventional section with approximately 200,000 tons per year projected as maximum production. The life-of-mine plan includes recovery of the Wheeler seams of the Williams Fork Formation which are separated from the E-Seam by 200 feet of strata characterized as predominately marine shales. The maximum production for the life-of-mine plan is projected at 1,000,000 tans per year. Potential aquifers in the mine area are found within the Iles Formation, Williams Fork Formation, Wasatch Formation, and the Colorado River alluvium south of the permit area. The relatively permeable sandstone and coal units of the Iles and Williams fork Formations are separated by impermeable interbedded shales within the Mesa Verde. The sandstones are lenticular in nature, pinching out laterally in both directions from the mine site and are characterized as fine to medium grained, calcite cemented units.