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-39- <br />Minnesota Creek, Lick Creek, South Prong. and Horse Creek. Subsidence effects <br />could be significant along these stream courses. However, WECC fias proposed a <br />mining plan of limited extraction in the Minnesota Creek drainage, and future <br />mining will occur only under Lick Creek. <br />Streamflow may be diminished by a reduction in spring discharges. Decreases <br />in spring baseflow to streams would be caused by irKerception of ground water <br />sources by subsidence features. The intercepted water would remain within the <br />North Fork of the Gunnison drainage basin, but the location of surface <br />contributions could be altered. Three mines in the CHIS area monitor springs <br />and seeps for possible subsidence impacts from mining--Hawk's Nest, the <br />Mt. Gunnison No. 1 Mine, and Orchard Ya11ey. Hawk's Nest recorded no changes <br />in flow while they were operating and currently they do not monitor flow while <br />they are in temporary cessation. <br />WECC has stated that there are over 100 springs on or near the local lease <br />area. Of the 100 springs, 23 are decreed springs and only one of these occurs <br />in the Life of mine permit area (Minnesota Creek Watershed). WECC currently <br />monitors 18 springs. Of the monitored springs. only three (G-14, J-10, and <br />G-31) are directly associated with sandstone outcrops. Springs G-1, G-2, and <br />possibly G-26{a) issue from the F seam. Twerrty-six (26) springs are <br />associated with colluvial deposits. <br />A worst case spring impact analysis of the Mt. Gunnison No. 1 life-of~nine <br />• area was performed, It included all springs issuing from the F seam all from <br />locations that are undermined where the overburden cover is less than 300 feet <br />and all springs in the vicinity of major fracture zones that are undermined <br />where overburden cover is less than 500 feet. Springs located Del ow the F <br />seam outside major fracture zones are not expected to be affected by mining <br />because the fine clay at the base of the F seam would severely restrict <br />hydrologic communication with the units below the F seam. <br />The Mt. Gunnison permit application indicates that springs contribute <br />11 percent of the flow in Lower Dry Fork, 4 percent of the flow in Lick Creek, <br />12.6 percent of the flow in South Prong, and 0.9 percent of the flow in Horse <br />Creek (Table 12), WECC projects a worst case spring de ptetion of 256 gpm <br />(0.55 acre feet) for the Dry Fork of Minnesota Creek and 59 gpm (0.13 acre <br />feet) for Lick Creek, Excluding the Sylvester Gulch data, springs could <br />contribute 6,2 percent of the stream flow for the Mt. Gunnison life-of arsine <br />area during the dry part of the year. Ina worst-case scenario, where all of <br />the springs dry up, 6.2 percent of the low flow runoff could be lost. In <br />reality, it is probable that not all the springs would be affected and, <br />therefore, reduction of surface flow, although significant, would be less than <br />the worst-case scenario. <br />Nevertheless, WECC has modified their general mine plan, pending the results <br />of future monitoring, and prepared an augmentation plan. Coal quality <br />considerations caused WECC to eliminate any mining below Horse Creek and South <br />Prong. This will ensure no hydrologic impacts to those streams. <br />• Additionally, until subsidence data is obtained, WECC has redesigned the mine <br />plan to exclude most mining beneath Dry Fork and Lick Creek. Instead of the <br />previous plan to utilize 50d extraction beneath the stream areas, WECC will <br />