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DocuSign Envelope ID: EBE28081-13782-41342-BAD13-D8C9313687131B <br />TOXICITY REDUCTION EVALUATION — LINES OF INVESTIGATION <br />Summary of Analysis <br />Ethanol Usage <br />Actual ethanol usage rates will be the primary factor that affects long-term O&M costs. The actual site - <br />specific volume will be determined during both the bench and field tests, but a placeholder is required for <br />this estimate. A review of published data suggest at little as 0.67 grams of COD is required to reduce 1 <br />gram of sulfate. Other sources found that up to 2 grams COD is required to reduce 1 gram of sulfate. The <br />majority of data reviewed suggests that less than 1 gram of COD per 1 gram of sulfate is optimal; <br />therefore, 1 gram of COD has been assumed for the purposes of this cost estimate. <br />Given the COD of ethanol, this means for every 100 gpm of seep flow roughly 0.1 gpm of ethanol would <br />be required to support the required bacterial activity. Therefore, a 364 gpm seep flow rate would require <br />nearly 16,000 gallons of ethanol per month for adequate treatment. Based on the published data, the <br />potential range of ethanol feed to the system is expected to range between $200 and $600k annually. <br />aUMMAP yr ANALYSIS <br />Two viable technology options have been evaluated for WET reduction at the Elk Ridge Outfall 010: (1) <br />NF membrane separation and (2) BSR bioreactor. The evaluation includes development of conceptual <br />designs to support preliminary feasibility of implementation and identification of required equipment and <br />material quantities for cost estimating. <br />Both the capital and operation cost estimates indicate that the BSR bioreactor treatment option is <br />potentially the more cost-effective option to pursue and would result in lower environmental impacts in <br />terms of power, reagent, and equipment requirements. In terms of future mine closure and remediation, <br />the BSR bioreactor also represents an opportunity to minimize the infrastructure that remains on site over <br />the long term. <br />On the basis of schedule, historical testing of an NF membrane separation system represents an <br />advantage in terms of time to implement. In order to implement the BSR bioreactor option, additional <br />bench -scale testing and more extensive pilot testing are required to validate and optimize the design. <br />Investigative drilling is recommended ahead of the proposed tests so that the impacts of the existing <br />geology are understood, and potential system optimizations are identified. <br />dpg \\us0321-ppfss011shared_projectsV33001407\reports\4_tre lines of investigationitre lines of investigation_20200320_ifra.docx 4.17 <br />