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-63- Three perennial streams cross the southern portion of the Mt. Gunnison Life-pl'~ mine area, Lick Creek, South Prong, and Horse Creek. Subsidence effects could be significant along these stream courses as well, unless the applicant undertakes to design subsidence protection plans fpr these drainages as well as DFy Pork. The Somerset mine has recently mined beneath Hubbard Creek. Inspection of the under- ground workings by staff hydrologists has shown this portion of the mine to be making significant amounts of water. At the present time it is uncertain whether or not surface flows are being depleted. Additional measures may be required as a part of permit approval to protect downstream users. The Blue Ribbon permit application estimates the annual yield in Hubbard Creek to be 29,700 acre-feet/year (8~ of the annual yield of the North Fork of the Gunnison). Much of this flow is diverted by down- stream users and does not reach the North Fork of the Gunnison. 4. Depletion of Seeps and Springs Underground mining, even in the absence of subsidence could cause flow from intermittant and perennial springs to be depleted, or even to go completely dry. The significance of this effect depends upon the use of the spring water and its contribution to flow in receiving streams. Underground mining at the Mt. Gunnison mine site has a high potential for affecting springs located in Sylvester Gulch. However, flow from these springs is already diverted into the Tony Bear Pipeline for use in the Bear Mining operation,a~d does not reach the North Fork of the Gunnison. The Mt. Gunnison permit application identifies numerous springs in or adjacent to the area to be mined. The application indicates that (2-2536) springs contribute to 11 percent of the flow in Lower Dzy Fork, 4 percent of the flow in Lick Creek, 12.6 percent of the flow in South Prong, and 0.9 percent of the flow in Horse Creek. Excluding the Sylvester Gulch data, springs could contribute 6.2 percent of the stream flow for the life-of-mine area during the dry part of the year. In a worst- case scenario, where all of the springs dry up, 6.2 percent of the low flow runoff could be lost. In reality, it is probable that not all the springs would be affected and, therefore, reduction of surface flow although significant would be less than the worst case scenario. This runoff contributed by springs is not entirely lost to the hydrologic system. It would temporarily become a part of the ground water system and would eventually reemerge to the surface. It is difficult to predict where this water would reemerge. It could reemerge downstream in the same drainage (the Minnesota Creek system), or it could reemerge along the North Fork of the Gunnison. In the latter case, the impact upon water users located along Minnesota Creek is potentially the greatest. In either case, flow below the confluence of Minnesota Creek and the North Fork of the Gunnison should not be affected.