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-17- • • VII. Cumulative Hydrologic Impacts (cont'd) The disposal of coal processing waste in the Cameo and North Declines is not planned to occur until after cessation of mining. This disposal will be accomplished in a manner that mitigates any effects on the surface and ground water systems. (See Section VI of this document). The Cameo coal processing waste pile is underlain by a series of rock drains. Rny leachate would enter the sediment control pond. However, the Roadside waste pile directly overlies Colorado River alluvium, therefore, leachate will have an effect on the Colorado River. The effects of leachate from the Roadside coal processing waste pile on water quantity and quality will be negligible. Using worst case conditions, where all precipitation enters the waste pile, an average of 0.01 cfs would enter the Colorado River. Based on chemical analysis of the coal processing waste, this leachate would have a total dissolved solids (TDS) level of 875 mg/1. Even at the lowest recorded flow with the lowest recorded TDS level, the leaching effect would raise the TDS level in the Colorado River by Zess than O.OI~. All surface runoff from disturbed areas will be contained by sediment ponds. This water will be released following a 24-hour settling time and any discharge will meet effluent standards. It is difficult to quantify the effects on water quality, since t3iere has been no sediment pond discharge to date. However, the effect on water quality should be minimal following dilution in the Colorado River. Surface water monitoring will determine if the effects are minimal, as expected. The amount of surface runoff water reaching the Colorado River will be slightly lower than pre-mining conditions because of dead storage below the maximum sediment storage level in the sediment ponds. This effect should be negligible, since the amount lost would be, at worst case, 0.070 of the daily average flow of the Colorado Rives. With removal and reclamation of the sediment control system, runoff should return to normal conditions. The effect of releasing sediment-deficient waters from the sediment ponds should be minimal. Any downcutting should be limited to the point of discharge and immediately downstream. The gradient from the sediment pond is relatively flat, thus erosive velocities should not be attained. A technical assessment of the effects of undermining Rapid and Cottonwood Creeks was completed by the Division. The analysis shows that in the absence of subsidence or flow through naturalfiactures changes in flow would be insignificant, and there would be no material damage to downstream users. The applicant will be mining beneath the stream valleys according to a limited extraction plan. There- fore, possible subsidence effects should be avoided. The possibility of flow through natural fractures is difficult to predict. Major fractures such as a fault would normally be identified duri`rlg resource evaluation, and none has been identified by the applicant. Minor fracture (jointing) is ubiquitous in sedimentary rocks. How- ever, joints may be open or closed to the passage of water. Their effect cannot be accurately predicted, but can be monitored. It is therefore appropriate to monitor the stream-alluvial aquifer system during mining and reclamation, and to identify the appropriate mitigations that would be undertaken should monitoring identify an undesired effect.