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Privileged and Confidential-Attorney Client Communication Geosyn.tec" consultants (Skousen, et al., 2017). In addition, there is research that adding granular activated carbon (GAC)to SRBs can enhance biological performance, particularly in cold weather applications (Johir, Shanmuganathan, Vigneswaran, & Kandasamy, 2013). • Anaerobic Wetland: deep basin (>12 inches) with native wetland vegetation planted in a substrate that consists of soil, sand, and/or gravel mixed with an organic material such as peat moss or straw(Skousen, et al., 2017). They are commonly used for the formation and precipitation of metal sulfides, and metal exchange and complexation reactions (Smith, 1997). • Vertical Flow Bioreactor/Wetland: also known as successive alkalinity producing systems (SAPS) or reducing and alkalinity producing systems (RAPS). These systems typically consist of a pond with water ponded over a layer of organic substrate and then a layer of limestone (Costello, 2003). The organic substrate consumes the oxygen to produce anoxic conditions and reduces iron to prevent coating of the underlying limestone layer. Iron and manganese is then precipitated out in subsequent treatment processes. These ponds can also be designed in an upflow configuration (Skousen, et al., 2017). Through discussions with OSMI about the evaluation of the new water treatment system a few items should be noted relative to the technology evaluation: • There is an existing, naturally occurring wetland located on the Mine site that appears to be flourishing. This is a positive sign that an engineered passive water treatment system should be capable of supporting vegetative growth at the Mine. No technical evaluation of the existing wetland was conducted by Geosyntec. • Prior pilot testing of a vertical flow bioreactor at the Mine portal was successful in establishing a biological reactor that produced treated water achieving groundwater standards as required by the Colorado Department of Reclamation, Mining, and Safety. The four technologies included in the evaluation were assessed based on their treatment performance for similar mine water quality at different sites, highly variable flow conditions, cold climate for the majority of the year, and plugging and other engineering risks. Our evaluation concluded that both the aerobic and anaerobic wetland systems are viable technologies and that both of them provide valuable treatment benefits that can enhance the passive water treatment system at the Mine. As further outlined in Section 2.3, they are both included in the conceptual design established in this Work Plan. Treatability Study Work Plan 9 February 8,2018