Eagle River Inventory and Assessment (2)

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b®t~ within tie S~perfu~d site and further d®wnstr~~m~ Biological impacts associated with current zinc concentrations include: 1, reduced weights in brown trout; and 2, suppression or elimination of sensitive organisms such as the mottled sculpin and certain mayfly taxa. As a result of reductions in other sources, the majority of current zinc loading to the Eagle River occurs in the Belden segment from `unaccounted' sources, The Rock Creek drainage is the second largest contributor, A re-examination of monitoring data points to the Belden Tramway area as a major bracketed source of zinc loading. Implementation of capture/treatment or passive remediation technologies at this location could potentially result in substantial reductions in zinc concentrations and improvements in biological water quality both within and below the Eagle Mine site, However, further monitoring and evaluation are requisite to quantify the likely cost-effectiveness of additional cleanup activities in this area. Field reconnaissance upstream of the Superfund site boundary revealed additional sources of current and potential metals loading. Several historical wooden structures or `cribbings' that were used to stabilize waste rock piles are decaying and collapsing in the Belden segment. A series of cribbings readily observable from U.S. Highway 24 is of particular concern given hillslope angles, proximity to the river, and the relatively large amounts of fine waste rock material that would probably be delivered directly into the Eagle River in the event of a catastrophic failure. Analyses of waste rock for paste pH and leachable zinc indicate that ongoing degradation and potential failure of these structures represent a significant risk to the biological improvements that have been achieved in the Eagle Mine site. ES.4.8 Sedimentation Impacts Suspended sediment and turbidity from Milk, Alkalai, and Ute Creeks severely limit the Coldwater fishery of the Eagle River below Wolcott. Highly erodible soils, southerly aspects, and historic overgrazing have combined to initiate widespread geomorphic instability including incision, mass wasting of channel banks, and headward migration of channel networks. Sediment concentrations as high as 12,000 mglL have been recorded by the Bureau of Land Management (BLM) during spring runoff and impacts to the fisheries in the Eagle River have been documented by the CDOW in 1971, 1982, and 1989. These inputs of fine sediment diminish fish production by an order of magnitude and often reduce the fishing season by approximately 50%. The pervasive nature of these problems necessitates a comprehensive geomorphic assessment to identify incised channel types, gauge the relative importance of these processes and upland sources in sediment production, and establish geomorphic design criteria, Adequate reductions would likely necessitate along-term effort (one or more decades) involving grade control, detention basins, drop pipes to check headward migration of channels, `brush-beating,' and improved grazing management. In the headwaters, traction sand from Interstate 70 on Vail Pass continues to affect the Black Gore Creek watershed. The protection and recovery of water quality and aquatic habitat conditions in Black Gore Creek is a high priority for the local community. In 1997, a coalition of more than ten agencies in cooperation with local stakeholders was formed to address the problem, Since 2000, significant progress has been made and over $4 million has been invested in sediment control and cleanup in and adjacent to the I-70 corridor. Sediment basins have been constructed in nearly all highway shoulder locations vulnerable to traction sand runoff, In 2002, the Colorado Water Quality Control Commission added Black Gore Creek to the State's 303(d) list of impaired waters, requiring a Total Maximum Daily Load (TMDL) for sediment from I-70 sand and other sources. Stream monitoring efforts have been initiated to support TMDL development and track water quality conditions. Eagle River Inventory and Assessment ES-9