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O()'l.l\:1l" Swnmary Under the No Action Alternative. there would be minimal increase in snowmaking and municipal demands. and consequently, impacts of ice fonnation on aquatic organisms would not differ markedly from existing conditions. There would be no additional impact to on-mountain streams nor to Castle Creek. but intermittent sedimentation of Marooo Creek could occur following high precipitation events or heavy snowmelt in early spring. This could negatively impact resident rainbow and cutthroat trout and macroinvenebrates. Sedimentation of Maroon Creek could also produce shon-term effects on the Roaring Fork River. It is unlikely that net annual water depletions to the Roaring Fork and Colorado rivers of 19 aae-feet would adversely impact aquatic resources. The Colorado River cutthroat (a Forest sensitive species that has been found in Marooo Creek) would be marginally impacted by water depletions from Maroon Creek. but sedimentation of Maroon Creek during spring could affect spawning and foraging. No fisheries are found in the composite on-mountain Maroon Creek and Castle Creek sub-watersheds. However. benthic macroinvertebrate communities in the CCW-BI sub-watershed could be affected if sediments arising from construction of the Steeplechase Catwalk under Alternative B flow into the stream. Water diversions from Maroon Creek would increase under this alternative to accommodate increased soowmaking on Aspen Highlands. h is anticipated that the proposed snowmaking diversion would lead to a 10-20 percent reduction in stream flow below the diversion point (possibly below the return flow from the hydropower plant). This could result in an increased frequency and duration of shelf and anchor ice formation below the offtake point. and diurnal variation in streamflow could increase as flows freeze during periods of cold overnight temperatures. The species most likely to be impacted by fall and winter diversions for snowmaking include brown and brook trout due to their fall spawning and the potentially reduced availability of spawning habitat and ice formation in side channels. The lack of pool forming features limits the amount of overwintering habitat in Maroon Creek. and fish tend to migrate down to the Roaring Fork River in the winter. while rainbow and cutthroat trout move into Maroon Creek only during spring runoff. Thus winter diversions would not impact these species. In addition. due to minimal proposed clearing and low increase in water yields under Alternative B. impacts to the fish and invertebrate populations in the Maroon and Castle creeks would be similar to the No Action Alternative. However, persistent increase in water yield that could occur would increase the likelihood of chronic erosion impacts to Maroon Creek and could increase the likelihood of persistent sediment inputs into the Roaring Fork River from Maroon Creek. A net annual depletion of 84 acre-feet for snowmaking would have little impact on aquatic resources in the river. Impacts to federally listed Colorado River fishes would be due to water depletions from Maroon Creek. Impacts and potential conservation measures are identified through a Section 7 consultation of the ESA (1993. as amended). The likelihood of Colorado cutthroat being negatively affected would increase due to the higher potential for sedimentation of Maroon Creek. Since the Steeplechase catwalk is excluded from Alternative C, invenebrate impacts in the CCW-B I would be lower than under Alternative B. However, impacts due to winter water depletion from Marooo Creek for snowmaking would be similar as under Alternative B due to the same takeout rate. but they would occur for a shorter period of time due to the lower total water requirement for the smaller area of snowmaking under A1temative C than under Alternative B. 10 addition, increased seasonal water yields would be lower than under Alternative B due to less SIlowmaking and the subsequent decrease in the likelihood of sedimentation and water yield impacts on invertebrates in Maroon and Castle creeks and the Roaring Fork River. Impacts to federally listed Colorado River fishes would be due to water depletions from Maroon Creek. Impacts and potential conservation measures are identified through a Section 7 consultation of the ESA (1993. as ameoded). The likelihood of Colorado cutthroat being negatively affected would increase only slightly relative to the No Action Alternative since the increased probability of sedimentation of Maroon Creek would likely be low. POTENTIAL MITIGATION MEASURES In order to minimize increased runoff and stream sedimentation. Forest Service BMPs for erosion control must be snictly adhered to. In additioo. an effective drainage system using BMPs must be designed and constructed. including culverting the perennial stream CCW -B I being culverted at the proposed Steeplechase Catwalk crossing and gravelling the catwalk surface in the vicinity of the crossing. Seclioll111 AqlMJlic Ruource.J 25