_GENERAL DOCUMENTS - C1981017 (283)

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-29- Unconsolidated colluvial and landslide deposits exist along the slopes of the ridges formed by the more resistant sandstones. The east-facing dip slopes along the Grand Hogback are naturally unstable slopes. Numerous landslides have developed on the unstable slopes, which has led to the characteristic hummocky topography. Ground Water The general area around the three mines contain four types of aquifers; alluvial, continuous bedrock, laminar to lenticular discontinuous bedrock, and fracture aquifers. The regional movement of ground water is controlled by the geologic structures along the Grand Hogback (i .e. , the folds and faults) . Local ground water movement is controlled by the vertical and lateral extent of the aquifer, and also by the type and magnitude of localized secondary porosity related to fault, fracture and joint systems. The overall regional ground water movement in the general area of the Coal Basin Mines, North Thompson Creek Mines and the Sunlight P'line would be towards the axis of the Piceance Basin, were it not for the folds and faults which occur along the Grand Hogback. There is a high displacement fault north of the Coal Basin Mines. This fault restricts the migration of ground water from the Hunter' s Point Syncline adjacent to the Coal Basin Mines and the unnamed syncline adjacent to the North Thompson Creek Mines, thus forming two separate ground water basins along the Grand Hogback. Alluvial ground water aquifers exist along the Roaring Fork River and the tributaries to the Roaring Fork. These alluvial aquifers are the most significant source of ground water put to beneficial use in the general area. The alluvial ground water also serves as the primary source of recharge water to the underlying bedrock aquifer. The alluvium is rapidly recharged by the stream and serves as a reservoir for surface water available for the recharge of bedrock aquifers and fracture aquifers. The most significant alluvial aquifers in the general area are the Roaring Forst and Crystal River alluvia. Many water supply wells are completed in these aquifers. This is due to their high-storage capacities and rapid recharge from their associated streams. Two water supply wells are completed in the Roaring Fork alluvium at the North Thompson Creek Mine loadout. These :yells are pumped at a combined rate of 50 gpm in the summer and 15 gpm during the winter. The water is considered tributary water to the Roaring Fork River, and is under :n augmentation plan, which permits water uses of dust suppression, 6. 14 acre-feet; plant washdown, 2.38 acre-feet; sanitation, 0.02 acre-Feet; and irrigation, 9.0 acre-feet, for a total of 18.04 acre-feet per year. The alluvium at the North Thompson Creek Mine loadout consists of medium to coarse grained sand and gravels. The aquifer' s transmissivity is 51 ,200 gpd/ft. and storativity was estimated to be 0.3. The water quality of the Roaring Fork alluvium is similar to the Roaring Fork River. Total dissolved solids (TUS) range between 280 and 500 mg/l ; and iron Fe) varies between 0 and U.U8 mg/l . The pH is neutral to sligntly alkaline, ano the water type is a calcium, magnesium-oicaroonate, sulfate.