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Streamflow reduction could develop from three separate scenarios: increased infiltration of runoff through subsidence fractures; direct stream recharge to the mine in zones of stream underminins; and loss of spring flow. Infiltration of runoff could occur on the surface -, ~ or along fractures beneath colluvial or alluvial deposits. Despite the presence of subsidence Features at several of the mine sites, this impact has not been identified by any of the monitorine programs Subsidence could reduce streamflow by directly diverting surface flow and alluvial ground water into the bedrock ground water system. Extensive mining under sveam beds developed along strong fracture zones or in areas of thin overburden could result in substantial interception of surface water by the ground water system. Information presented in the Hawk's Nest, Blue Ribbon and SomersedSanborn Creek brine permit applications indicates that mine inflows in areas underlying streams are related to the flow in streams, as evidenced by higher inflows during snowmelt and lower inflows in late fall and winter. The duration of sveam flow affects the severity of impacts and is related to sveam type. Mine inflows are not normally significant when ephemeral or intermittent sveams aze undermined and most of the sveams to be undermined in the region are ephemeral and intermittent. Flow in these streams is concentrated in periods of snowmelt and high intensity precipitation events. The stream gradients are steep and their channels contain little alluvium. Perennial sveams, however, may experience significant depletions of flow if mine workings are extended adjacent to and/or below [he level of the sveam valley (e.g., the bedrock alluvial contact). The lower sveam gradient and the thicker alluvial deposits in perennial sveam valleys favor flow retention and recharge to [he ground water systems. The West Elk Mine may undermine several perennial drainages during the life of the mine: the Dry Fork of Minnesota Creek; Lick Creek; South Prong; and Horse Creek. Subsidence effects could be significant along these sveam courses. However, MCC has proposed a mining plan of limited extraction in the Minnesota Creek drainage, and future mining will occur only under Lick Creek. Sveamflow may be diminished by a reduction in spring discharges. Decreases in spring baseflow to sveams would be paused by interception of ground water sources by subsidence features. The intercepted water would remain within the North Fork of the Gunnison drainage basin, but the location of surface contributions could be altered. Five mines in the CHIS area monitor springs and seeps for possible subsidence impacts from mining. These are the Hawk's Nest, West Elk Mine, Bowie No. 1, Bowie No. 2, and Sanborn Creek (Somerset) Mines. The monitoring programs have not documented significant impacts to springs or seeps. • MCC has stated that there are over 100 springs on or near [he local lease area. Of [he 100 springs, 23 are decreed springs and only one of these occurs in the life of mine permit area (Minnesota Creek Watershed). MCC currently monitors 18 springs. Of [he monitored springs, only three (G-14, J-10, and G-31) are directly associated with sandstone outcrops. Springs G-1, G-2, and possibly G-26(a) issue from the F seam. Twenty-six (26) springs aze associated with colluvial deposits. A worst-case spring impact analysis of the West Elk life-of-mine area was performed. It included all springs issuing from the F seam all from locations that aze undermined where the overburden cover is less than 300 fee[ and all springs in the vicinity of major fracture zones that are undermined where overburden cover is less than 500 feet. Springs located below the F seam outside major fracture zones are not expected to be affected by mining because the fine clay at the base of the F seam would severely restrict hydrologic communication with the units below the F seam. The West Elk permit application indicates that springs contribute 11 percent of [he flow in Lower Dry Fork, 4 percent of the flow in Lick Creek, 12.6 percent of the flow in South Prong, and 0.9 percent of [he flow in Horse Creek. MCC projects aworst-case spring depletion of 256 gpm (0.55 acre feet) for the Dry Fork of Minnesota Creek and 59 gpm (0.13 acre feet) for Lick Creek. Excluding the Sylvester Gulch data, springs could contribute 6.2 percent of the sveam flow for the West Elk life-of-mine area during the dry pan 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; therefore, reduction of surface flow, although significant, would be less than the worst-case scenario. Nevertheless, MCC has modified their general mine plan, pending the results of future monitoring, and has prepared an augmentation plan. Coal quality considerations caused MCC to eliminate any mining below Horse Creek and South Prong. This will ensure no hydrologic impacts to those sveams. 17