2010-04-20_REVISION - M1977300 (9)

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Environmental Protection Plan, Schwartzwalder Mine 15-4 -• a number of individual rectangular and/or irregularly-shaped basins (cells) connected in series and surrounded by berms of earth, clay, rock, concrete or other materials. They are often associated with a variety of ancillaries (e.g., ditching, pumps, control structures, bays) to form a constructed wetlands treatment system. Engineered wetlands have been successfully employed within Colorado (Walton-Day, 1993; Owen and Otten, 1995) and elsewhere (Groudev, et al., 2009) to immobilize uranium and other dissolved metals associated with mining activities. Uranium minerals are nearly insoluble under reducing conditions; therefore, the reductive precipitation of uranium minerals is regarded as a major and sustainable treatment mechanism (Schoner, et al., 2007). Wetlands constructed in alpine locations (6,000-10,000 feet above sea level) are particularly effective at removing uranium from solution via binding with plant rhizomes and roots and with the organic carbon substrate within the wetlands (Owen and Otten, 1995). Several conditions that contribute to the long-term success of alpine treatment wetlands for uranium: • climatic conditions that allow for wetland development; • growing season for wetland plants; • ongoing groundwater source to the wetlands that maintain saturated and reducing conditions; and • specific alpine wetland plant and fungus species. The Schwartzwalder Mine site possesses these conditions and other characteristics expected to enable construction of strategically designed wetlands: • Recharge of the shallow alluvial fill by Ralston Creek; and • Surface expression of groundwater at several locations within the shallow alluvial fill. • The conceptual model of this wetlands approach is to provide a permanent, low-maintenance, reducing aquatic environment that will capture and immobilize uranium and molybdenum, minimize unnecessary destruction of existing habitats and potentially increase ecological diversity and improve overall environmental conditions at the site. The preliminary design includes three wetland treatment cells (Figure 15-1) to manage hydrologic flows through the site, capture metals from groundwater, and significantly reduce inputs to Ralston Creek. The design includes an upper and middle wetlands, each approximately 2-acres in size connected by an equalizing culvert. A third, smaller (0.3-acre) wetland may be located at the site boundary to capture the southern- most end of the groundwater in the alluvial fill to treat this water prior to the groundwater entering Ralston Creek. The outside boundaries of the wetlands would be cut and contoured to fit the existing topography and enhance the aesthetics of the existing landscape as is feasible. Surface areas outside the wetland footprints would be contoured to keep surface wager away from Ralston Creek, directing it towards one or all of the three wetlands areas. The wetland floors would be excavated flat and level, and would be designed to ensure that a local groundwater gradient is maintained toward the wetlands. The wetlands would be designed to ensure adequate residence time for groundwater that enters the wetland to undergo geochemical processes which reduce and precipitate uranium from solution and allow it to bind with organic matter, significantly reducing the potential for migration and bioavailability. Wetland plants would be selected specifically to promote capture and sequestration of uranium and molybdenum and to support the creation of additional, sustainable habitats. Based on climatic conditions of alpine locations, the fluctuation of growth in plants allows for binding surfaces and mechanisms to be continually generated such that sorption sites do not become saturated. Monitoring would be performed for • up to 10 years to demonstrate that the wetlands are functioning as designed and that releases of constituents of concern to Ralston Creek are successfully reduced to acceptable levels. 4109C.100419 WhetTtoneAssociates