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-52- The Western Slope Carbon Hawk's Nest mine, located on the north slope of the basin above Somerset, utilizes it's surface water rights and rights to mine inflow water (Appendix XIII, Volume 3 of the Hawks Nest Permit Application) to meet the water requirements for mining operations, wash plant operations and domestic use. Water rights held by Western Slope Carbon are adequate to cover the consumptive use in their mine operations .(pages 2.04-29 to -33 of the Hawks Nest Permit Application). Western Slope Carbon estimates that the Hawk's Nest mine will consume 215 acre feet of water per year, which amounts to 0.052 of the total mean flow of the North Fork of the Gunnison. For the ARCO Mt. Gunnison mine, the worst case scenario would be if the 150 acre feet per year of water used for spraying the coal and for the potable water supply were entirely removed from the basin. On the average, this would amount to approximately 12.5 acre feet of water each month. From Table 8 it appears (from column 5) that the months of August and September will be the critical tronths for removal of water from the watershed. In reality, most of the water used for potable water will be returned to the North Fork of the Gunnison River. Consequently, ARC.O's main concern will be the water lost due to spraying activities. ARCO will store water diverted from the North Fork in a storage pond adjacent to the river. The total estimated worst case depletion (150 acre feet per year) would amount to only 0.04$ of the total mean flow of the North Fork. (See materials submitted by ARCO Coal Company, December I5, 1981, in response to permit stipulation No. 7). The total estimated water consumed by all of the mines presently operating in the North Fork Drainage Basin is 556 acre feet per year, this is approximately 0.14 of the total mean flow of the river. This indicates that the total coal mining activities within the North Fork of the Gunnison Drainage Basin has a very minor impact on the quantity of water available in the Basin. The mass balance analysis examines the relationship of all inflows into the system to all outflows from the system. Table 9 provides a mass balance analysis of the basin illustrated in Figure 1. On a man annual basis, there appears to be a net increase in the change of storage. However, for the May to September time period, it appears that a deficit condition exists. Part of this is due to the Zack of good _ historical climatologic and hydrologic data records. However, even with additional data, it appears that the change in storage will still be negative for this particular time period. This is due to low precipitation from May through September. The West-Central Colorado Coal Environmental Statement was reviewed for possible comparative purposes. However, the data was not used because information was in terms of broad generalizations or theoretical, unsubstantiated predictions.