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-27- <br />ground water and quality of surface water. The applicant states that <br />this poor water quality is due to alluvial yround water flow over the <br />Mancos Shale. However, alluvial water quality analyses of the Coal Creek <br />alluvial yround water show water qualities favorably comparing to the <br />surface water qualities. This, in spite of the fact that there are <br />greater exposures of Mancos Shale in the Coal Creek Drainage Basin. <br />Continued monitoring of the alluvial ground water at both mine sites and <br />analysis of this data should aid in verifying the actual source of the <br />water quality degradation. <br />The water used at the loadout site is pumped from wells completed in the <br />Roaring Fork alluvium. The withdrawal of this yround water is small and <br />covered under a plan of augmentation. Thus, there will be a minimal <br />impact to the quantity of alluvial ground water. <br />Impacts will be minimal to the quality of ground water within the Roaring <br />Fork alluvium at the loadout site. The water exposed to the coal will be <br />either consumed through evaporation and adsorbed on the coal, or be <br />contained in a Tined pond. Any minimal infiltration of degraded water <br />will be quickly diluted by the ground water in the highly transmissive <br />Roaring Fork alluvium. <br />Probable Hydrologic Consequences of the North Thompson Creek Mines - <br />Surface Water <br />One of the potential impacts associated with most mining operations is <br />increased sediment loads to receiving streams. This would be caused by <br />surface disturbance which increases soil loss. Unnatural sediment loads <br />to receiving streams could be detrimental in the following ways: <br />1. Fish reproduction, growth rate, and life span could be reduced. <br />2. Stream temperature could be increased. <br />3. Stream channel capacity could be reduced. <br />4. Drainage structures and downstream irrigation systems could be <br />clogged. <br />5. Alluvial water tables could be raised. <br />6. Floodplains could be altered. <br />7. Sediment may carry toxic substances that could change water <br />quality. <br />To minimize the potential impacts of sediment loads at this mine, the <br />operator has constructed a sediment control system (see Section XU of <br />this document). This system will treat all mine discharges and surface <br />disturbed runoff such that total suspended solids and/or settleable <br />solids will be reduced to levels of 7D my/1 and 0.5 rng/1, respectively. <br />The contribution of sediment by this operation, even without treatment, <br />would be small. The surface disturbed area at the mine area is 522 <br />acres, or 0.~6 of the North Thompson Creek drainage. The cumulative peak <br />discharge of all ponds at the mine for the 10-year event (assuming <br />coincident hydrograph peaks} is 0.9 cfs, compared with a 409 cfs flaw in <br />North Thompson Creek. For the mine to increase the suspended solids <br />content of North Thompson Creek by 45 mg/1 (the NPDES Standard), it can <br />be calculated, at the present discharge rates, that the pond discharge <br />would have to have a TSS concentration of 20,490 mg/1. This level of <br />sediment concentration is far above any levels recorded at the mine. <br />