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_P7_ Cumulative Hvdroloaic lmoact The worst case impact of mining at the Eastside Mine was a predicted increase in TDS during the non-irrigation season from a baseline of 755 mg/1 to 1054 mg/1 with a flow of 0.7 cfs. The low-flow on record for the Colorado River at Glenwood Springs is 870 cfs. The mean level of TDS in the Colorado River during the 83 water year was 427 mg/1. Loading of the worst-case level of TDS in Harvey Gap into the low-flow of the Colorado River gave a rise in TDS of 0.5 mg/1. This rise is insignificant and would not affect the quality of the Colorado River. No other Significant impacts to the hydrologic balance were predicted due to mining at the Eastside Mine. No impacts to quality of the Colorado River or associated alluvium were projected from mining at Coal Ridge No. 1 Mine. Use of water for the hydraulic mining process was projected to consume 600 acre feet from the Colorado River system. This equals an average flow of 0.83 cfs. The average flow of the Colorado River during 1983 was 4,969 cfs. Therefore, the impact of the consumptive water used at the mine site is insignificant. In conclusion, based on information currently available, mining at the Eastside and Coal Ridge No. 1 operations is not projected to cumulatively impact the quality or quantity of ground water or surface water within the Colorado Basin. The assessment of the probable cumulative impacts of all anticipated coal mining in the general area of the Coal Ridge No. 1 on the hydrologic balance has been made by the Division, and the operations proposed under this application have been designed to prevent material damage to the hydrologic balance outside of the proposed permit area. Reference Tremain, Carol M. 1983. Coal Bed Methane Potential of the Piceance Basin, Colorado. Colorado Geological Survey, Department of Natural Resources, Denver, Colorado 80203. Open - File Report 82-1. X. Alluvial Valley Floors - Rules 2.06.8 and 4.24 Information on alluvial valley floors reviewed by the Division is contained in Section 5.1 of Volume I and figures 5.1-1, 5.1-2, 5.2-1, and 5.2-2 of Volume V of the application. The applicant identified unconsolidated streamlaid deposits along the Colorado River, Alkali Creek, and South Canyon Creek. South Canyon Creek is not hydrologically adjacent to the proposed mine for this permit term, therefore, it will not be considered in this alluvial valley floor (AVF) determination. Alkali Creek and the Colorado River will be discussed separately below.