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DocuSign Envelope ID: EBE28081-13782-41342-BAD13-D8C9313687131B <br />TOXICITY REDUCTION EVALUATION — LINES OF INVESTIGATION <br />Design Basis <br />pump with the rate controlled by a pH instrument on the influent line. Continuous air stripping and <br />associated aeration rates would be controlled by variable frequency drive(s). Both the pressurized <br />granular -media filtration and the NF process are assumed to be standalone equipment skids supplied <br />with local controllers. Overall management of the process will be by a largely automated system which will <br />require operator interaction to replace reagents, adjust setpoints, and initiate maintenance cycles. <br />z.z.z woiogical Sulfate Reduction <br />The proposed BSR treatment system is a fixed/packed bed bioreactor that will use an organic carbon <br />source (food) to grow several types of bacteria that create conditions favorable to electrochemical <br />reduction of iron and sulfate with resulting sulfide formation and precipitation of metal sulfide from <br />solution. Various feed stocks are available for bacterial growth in bioreactors: organic matter, alcohol, and <br />oils. Given the temperatures and winter operation continuous feed of oils is not ideal. Alcohol si <br />considered the best possible feed stock given the relatively wide availability, cost, and freezing point <br />which allows for the system to run throughout winter without heating. Originally, it was considered that an <br />above ground (ex situ) reactor would be evaluated for this process. However, site conditions are not <br />readily amenable to the prolonged freezing cycles without management each spring. Given the intention <br />of the BSR bioreactor as a passive option, a subgrade is expected to provide more consistent and year- <br />round results and a design for this option has been developed. <br />Biological systems are inherently more sensitive to site specific factors like water quality and temperature <br />than technologies such as ion exchange (IX) and reverse osmosis (RO). This variability means issues <br />with a bioreactor at one site may be worse or non-existent at another site. These factors typically reduce <br />or enhance the bioreactor performance rather than completely eliminate treatment. Bioreactors offer <br />significantly lower operation and maintenance (O&M) costs compared to other treatment technologies, <br />and for the purposes of this cost estimate, conservative assumptions and a high degree of operational <br />flexibility were assumed to abate the risk of underperformance. These uncertainties can be better defined <br />during treatability testing, which may result in reduced bioreactor size and cost. <br />Gravity flow simplifies system operation and increases reliability while reducing operational costs. The <br />only location that allow for this is the Taylor Creek valley, which is the valley into which East Taylor Pond <br />discharges; therefore, this approach assumes regulatory approval will be granted to construct the BSR in <br />a portion of the valley. The necessary reactor volume will be understood following testing. Conceptually, <br />the area will be cleared and grubbed, but graded only to the extent required to smooth creek/valley <br />surfaces into a V or trapezoidal shape that is covered with a lower liner geomembrane, then filled with <br />uniform -sized wash rock (with minimal fines) to create the bioreactor below an impermeable liner. A <br />stormwater channel will be recreated above the liner with the treated water and stormwater flows <br />eventually merging downstream. <br />dpg \\us0321-ppfss011shared_projectsV33001407\reports\4_tre lines of investigationitre lines of investigation_20200320_ifra.docx 2.7 <br />