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-42- The Western Slope Carbon Hawk's Nest Mine, located on the north slope of the basin above Somerset, utilizes its surface water rights and rights to mine inflow water (Appendix XIII, Volume 3 of the Hawk's 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 Hawk's 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 mean annual yield of the North Fork of the Gunnison River. For the WECC Mt. Gunnison No. 1 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 9, it appears (from Column 5) that the months of August and September will be the critical months 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, WECC's main concern will be the water lost due to spraying activities. WECC 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 mean annual yield of the North Fork. (See materials submitted by ARCO Coal Company, December 15, 1981, in response to permit Stipulation No. 7.) U. S. Steel has not submitted an estimate of the total water consumption in the Somerset Mine. The Division, therefore, has made the assumption that water consumption at the Somerset Mine is similar to the proposed maximum water consumption in the Mt. Gunnison No: 1 Mine. This assumption is based on the proximity of the mines, the similarity in mining methods, coal handling, manpower requirements, and total annual coal production. This estimated water consumption would amount to 150 acre-feet per year, or 0.04% of the mean annual yield in the North Fork of the Gunnison River. The total estimated water consumed by all of the mines presently operating in the North Fork of the Gunnison Drainage Basin is 556 acre-feet per year. This is approximately 0.14% of the mean annual yield 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. Cumulative Impacts of the Blue Ribbon and Somerset Mines Since all anticipated mining at the Blue Ribbon Mine is within the Hubbard Creek Drainage Basin, the most significant cumulative impacts of all anticipated mining will be the combined impacts of the Blue Ribbon Mine and Somerset Mine on Hubbard Creek and on the downstream water users.