2010-04-20_REVISION - M1977300 (9)

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Environmental Protection Plan, Schwartzwalder Mine 15-6 • As envisioned, the wetlands would also create significant natural resources at the Schwartzwalder Mine site for the benefit of Ralston Creek canyon and surrounding portions of Jefferson County. The creation of wetlands would generate an increase in natural resource content, habitat type and value, and would be consistent with other environmentally responsible remediation programs in Colorado, including wetlands mine reclamation projects within the Clear Creek Watershed (CCWF, 2007). The Colorado Wetlands Program was created in 1997, and in 2008 the Wetland Wildlife Conservation Program Strategic Plan was finalized that articulated the vision, purpose, goals, strategies and structure of the program to preserve, restore, enhance and create wetlands in Colorado. To date, the program is responsible for over 220,000 acres of wetlands and adjacent habitat. The creation of wetlands at the Schwartzwalder Mine could provide another successful example of environmentally sound remedial initiatives in Colorado. (ii) Permeable Reactive Barrier (PRB) A permeable reactive barrier (PRB) system would effectively treat groundwater in-situ with very low operation and maintenance costs. A "funnel" would be constructed to route groundwater into a "gate" containing the reactive media. Groundwater would flow under natural gradient through the gate and be stripped of uranium and molybdenum. Field demonstrations of PRBs to control radionuclide and trace element levels in groundwater from abandoned mine lands have shown that funnel-and-gate PRBs using zero valent iron have consistently removed more than 99.9 percent of uranium concentrations (Naftz, et al., 1999, 2002). A typical funnel-and- gates treatment system is comprised of impermeable; "funnel" walls installed in the ground (eg. steel sheet pile, bentonite slurry wall) which direct the groundwater to a removable caisson "gate" filled with permeable treatment material. The system relies on the natural flow of the aquifer to move the contaminated plume through the treatment "gate" and is thus entirely passive in operation and requires little or no maintenance. However, to avoid plugging and consumption of the reactive media, the system can be constructed with a removable caisson gate, so the spent reactive media may be removed and replaced periodically33 The removable caisson gate is constructed to provide a watertight seal between the "funnel" walls and the caisson "gate". Compared to conventional PRB installations, the removable gate offers lower excavation and reactive material capital costs and allows for easy replacement of the treatment material over time. Because the reactive material may have a finite lifespan of 10 - 20 years, and the need for the treatment system at the Schwartzwalder may persist far longer, a removable and replaceable treatment media is preferred. Although many different reactive media may be used, including iron oxide pellets, amorphous ferric oxyhydroxide, bone char phosphate, zeolites, and other compounds, the zero-valent iron has demonstrated the most effective removal for uranium species. ZVI is capable of reducing U(VI) to U(N) in carbonate- dominated groundwater with near-neutral pH by the following reaction: 0 2- . 2+ Fe + UO2(CO,)2 + 2 H = *UO2 [solid] + 2 HCO, + Fe The lifespan and effectiveness of the PRB is influenced by the alkalinity of groundwater, potential for precipitation and resultant pore blockage, and eventual passivation of reactive iron surfaces. Detailed sizing and engineering of the system would be required to maximize longevity of the in-situ PRB. • 33 Depending on final design, the expected life of the PRB media is 10 - 15 years. 4109C.100419 Whetstone Associates