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DocuSign Envelope ID: D07924E6-3D94-4398-A066-B683COBAB33E <br /> February 24,2021 <br /> Angela Aalbers,Chantell Johnson <br /> Page 3 of 12 <br /> Reference: Biological Sulfate Reduction Bench-Scale Test Results-Revision 1 <br /> column included wood chips to provide the necessary nutrients that are needed for a BSR process. Columns <br /> 2 and 3 were composed of limestone aggregate beds with iron shaving to provide iron for the ferrous sulfide <br /> precipitation. The fourth column was constructed the same as Column 1, but a bubbler was installed to <br /> oxygenate the water before discharge. The first three columns were fed in an up-flow configuration by a <br /> peristaltic pump to ensure the media substrate was fully saturated throughout the test, and the last column <br /> configured in a down-flow mode. <br /> Organic carbon sources are used to feed sulfate reducing bacteria and to enable the anaerobic metabolic <br /> process. For this bench-test, ethanol was used as the source of organic carbon. Oxidation of the organic <br /> carbon in the water provides the necessary biological conditions for electrochemical reduction of sulfate in the <br /> source water. <br /> Stantec conducted four tests with varying organic carbon concentrations added to the source water provided <br /> by Colowyo. To achieve the goal of 1,000 mg/L reduction of sulfate, 240 mg/L of ethanol is required to <br /> stoichiometrically reduce the sulfate to sulfide. The tests conducted by Stantec dosed the source water with <br /> 1X, 2X, 4X, and 8X the stoichiometric requirements, correlating to 0.125, 0.25, 0.5, and 1 gram of organic <br /> carbon (as carbon) per gram of sulfate reduction targeted. For each test, field and laboratory analytical data <br /> was collected to analyze test performance and a WET sample collected to determine toxicity of the effluent <br /> water from the 2X, 4X, and 8X tests. <br /> Conceptually, assembly of the test system was made with transparent PVC piping to allow for visual <br /> observations within the bioreaction bed itself. These columns were filled with a local source of limestone as <br /> the reaction substrate which was most representative of material that would likely be procured for a full-scale <br /> reactor. Column 1 acted as a nutrient column utilizing organic materials (in this case, wood shavings)to make <br /> available any trace nutrients needed such as phosphate and nitrate for bacterial growth. <br /> Columns 2 and 3 acted as sulfate reducing columns. These columns incorporated iron shavings to provide a <br /> binder for the excess sulfide generated by the bacterial activity. Finally, Column 4 acted as an aeration <br /> column allowing re-oxygenation of the water as well as providing gas stripping to reduce residual ethanol <br /> within the water. The entire process was maintained at roughly 40-45 °F to represent the worst-case <br /> groundwater conditions in winter. Bacterial activity decreases with declining temperature, thus the worst-case <br /> conditions allowed for determination of minimum detention time. <br /> Desic th community in mir <br /> dpg llus0321-ppfss01lshared_projects\233001407\reports\6_bench_scale_report\rpLbench_scale_report_24feb2O20_final_rl.docx <br />