1992-07-22_GENERAL DOCUMENTS - C1981017

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-35- As a worst case condition, with all mines and preparations plant ponds discharging simultaneously under average flow conditions, the soluble salt level of Coal Creek immediately below the last discharge point would be increased by 177 mg/l to 544 mg/l . The water below the final discharge point would have a moderate salinity hazard for irrigation use. However, by the time the water reaches the Crystal River, which is the first point of diversion of Coal Creek water. The soluble salt level would be reduced to 440 mg/l which translates to a low salinity hazard. The Coal Basin Mines characteristically discharge more water during the late spring and early summer when stream flows are the greatest. Very little water is discharged during the low flow periods. Therefore, the worst case condition would rarely be met. The maximum increase in soluble salts concentrations are short-termed, and will occur only over the life-of-mine. Upon completion of mining, there will be no discharge from the mines and upon successful revegetation, the preparations plant ponds will be removed. Thus, upon reclamation, the soluble salt content of the surface water should approximate pre-mining concentrations. The mine discharge has not had an effect on the ion balance in the stream. The baseline information indicates that the surface and ground water is dominated by calcium bicarbonate. The mine discharge waters are likewise dominated by calcium bicarbonate. One projected surface water impact of the Coal Basin mining activities is an increase in the sediment loads contributed by the road system. It is not possible to determine the actual amount of sediment contributed by the road system by directly monitoring the streams. There are numerous small undisturbed tributaries to the streams along the reaches which could be affected by the road system. In addition, the natural erosion rates vary widely throughout Coal Basin due to the wide variety of rock types. Natural erosion rates, based on suspended solids and settleable solid measurements for undisturbed drainages, frequently exceed 200 tons per acre. Much of this natural erosion rate is due to the presence of the highly erosive Mancos shale throughout Coal Basin. It is projected that additional sediment contributions from the road system will be negligible because all haul roads are gravel surfaced, ditches and culverts are continually maintained, and culvert outlets are riprapped where necessary. The mining activities will not have an adverse effect on the quantity of surface water within or outside the permit area. Mid-Continent has a water right to withdraw water from Coal Creek up to 7.48 cfs. This is the only withdrawal of water from within the permit area. Through discharging underground mine waters, the flow in Coal Creek is increased on the average of 3.75 cfs. Thus the net depletion is 3.73 cfs, which is approximately one percent of the average low flow in the Crystal River. Most of the water is used during the summer months for dust suppression. Since the average monthly flow in the summer months are greater than the mean annual flows, the Crystal River will be depleted by less than one percent during the summer. Therefore, the proposed operation will not significantly affect the quantity of surface water in the hydrologic regime outside the permit area.