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-29- <br /> The alluvium of the Roaring Fork River consist of young stream, terrace, and <br /> outwash gravels. The thickness of these gravels range up to 100 feet. <br /> Unconsolidated colluvial and landslide deposits exist along the slopes of the <br /> ridges formed by the more resistant sandstones. The east-facing dip slopes <br /> along the Grand Hogback are naturally unstable slopes. Numerous landslides <br /> have developed on the unstable slopes, which has led to the characteristic <br /> hummocky topography. <br /> Ground Water <br /> The general area around the three mines contain five types of aquifers; <br /> alluvial , colluvial, continuous sandstone, laminar to lenticular discontinuous <br /> sandstone, and fracture aquifers. The regional movement of ground water is <br /> controlled by the geologic structures along the Grand Hogback (i .e., the folds <br /> and faults) . Local ground water movement is controlled by the vertical and <br /> lateral extent of the aquifer, and also by the type and magnitude of localized <br /> secondary porosity related to fault, fracture and joint systems. <br /> The overall regional ground water movement in the rock strata adjacent to Coal <br /> Basin Mines, North Thompson Creek Mines and the Sunlight Mine is to the west <br /> towards the axis of the Piceance Basin. Folding and faulting along the edge <br /> of the Grand Hogback interrupt ground water movement, and isolate ground water <br /> impacts. There is a high displacement fault north of the Coal Basin Mines. <br /> This fault restricts the migration of ground water from the Hunter's Point <br /> Syncline adjacent to the Coal Basin Mines and the unnamed syncline adjacent to <br /> the North Thompson Creek Mines, thus forming two separate ground water basins <br /> along the Grand Hogback. <br /> Alluvial ground water aquifers exist along the Roaring Fork River and the <br /> tributaries to the Roaring Fork. These alluvial aquifers are the most <br /> significant source of ground water put to beneficial use in the general area. <br /> The alluvial ground water also serves as the primary source of recharge water <br /> to the underlying bedrock aquifer. The alluvium is rapidly recharged by the <br /> stream and serves as a reservoir for surface water available for the recharge <br /> of bedrock aquifers and fracture aquifers. <br /> The most significant alluvial aquifers in the general area are the Roaring <br /> Fork and Crystal River alluvia. Many water supply wells are completed in <br /> these aquifers. This is due to their high-storage capacities and rapid <br /> recharge from their associated streams. Two water supply wells are completed <br /> in the Roaring Fork alluvium at the North Thompson Creek Mine load-out. These <br /> wells are pumped at a combined rate of 50 gpm in the summer and 15 gpm during <br /> the winter. The water is considered tributary water to the Roaring Fork <br /> River, and is under an augmentation plan, which permits water uses of dust <br /> suppression, 6.14 acre-feet; plant washdown, 2.88 acre-feet; sanitation, 0.02 <br /> acre-feet; and irrigation, 9.0 acre-feet, for a total of 18.04 acre-feet per <br />