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DocuSign Envelope ID: EBE28081-13782-41342-BAD13-D8C9313687131B <br />TOXICITY REDUCTION EVALUATION — LINES OF INVESTIGATION <br />Design Basis <br />and early spring have the potential for reduced sulfate/TDS concentrations. This combination of higher <br />flows and reduced concentrations suggests that a less conservative approach can be assumed in the <br />design. The data also suggest that separating seepage flow from runoff may also decrease treatment <br />volumes. However, since these data represent a single year of measurements, the design approach is <br />conservative and is based on the Table 1 water quality and flow rate. <br />Figure 1 - Outfall 010: Flow and Sulfate Concentrations <br />S11 <br />.11 <br />J <br />1400 <br />E <br />r 1200 <br />0 <br />1000 <br />c <br />c800 <br />0 <br />U 600 <br />N <br />0 <br />400 <br />1111I1 <br />0 <br />12/1 /18 <br />1/30/19 3/31/19 5/30/19 7/29/19 9/27/19 11/26/19 1/25/20 <br />2.2 DESIGN CONCEPT <br />450 <br />400 <br />350 <br />01I1 <br />250 Q <br />200 0 <br />U_ <br />I671 <br />100 <br />50 <br />0 <br />The Elk Ridge site is considering a long-term solution to meet WET requirements for the discharge <br />associated with East Taylor Pond. The THE developed in January identified three primary technologies <br />for further evaluation: membrane separation, biological sulfate reduction (BSR), and enhanced <br />evaporation. <br />Membrane separation (or reverse osmosis) treatment of the water to reduce the TDS in the permeate by <br />85% (inferred by conductivity) was shown in the TIE testing to reduce overall toxicity (SeaCrest 2019). <br />The testing completed to date ensures that it is a viable solution for Elk Ridge. <br />BSR was identified as a technology option by initial analysis of the data gathered in the TIE report. The <br />lack of effective WET reduction by the lime softening treatment leaves three major constituents to be <br />considered: sulfate, sodium, and TDS. Sulfate accounts for nearly half of the TDS present in the <br />discharge and can be readily reduced in an anerobic BSR. This technology uses bacteria to reduce <br />sulfate in the water to sulfide which readily bonds with available iron to precipitate out of solution. The <br />dpg \\us0321-ppfss0l\shared_projectsV33001407\reports\4_tre lines of investigationitre lines of investigation_20200320_ifra.docx 2.3 <br />