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DocuSign Envelope ID: D07924E6-3D94-4398-A066-B683COBAB33E <br /> February 24,2021 <br /> Angela Aalbers,Chantell Johnson <br /> Page 10 of 12 <br /> Reference: Biological Sulfate Reduction Bench-Scale Test Results-Revision 1 <br /> test comprises of lime softening posttreatment of the BSR effluent followed by solids settling and separate <br /> and final reduction in pH prior to WET testing. Lime softening reduces overall alkalinity which represents a <br /> fraction of the carbonate within the water the generates the calcite. Adjustment towards a neutral pH lowers <br /> the saturation level of calcite in solution. Each of these additional steps is intended to reduce the likelihood of <br /> calcite precipitation. <br /> These additional tests used the same testing apparatus for the BSR as the first set of tests. Lime softening <br /> was performed as a batch operation on the effluent water in the final test. This operation resulted in an overall <br /> decrease in alkalinity and calcium carbonate saturation in the source water, marginally decreasing the final <br /> TDS. The pH was lowered in both additional tests by GEI using hydrochloric acid ahead of starting each WET <br /> test. <br /> WET TESTING RESULTS <br /> WET was evaluated independently by GEI Consultants at the conclusion of all test conditions except the 1X <br /> carbon dose rate. The sulfate reduction was not sufficient to meet the intent of the study. Three of the initial <br /> bench scale tests were sampled for toxicity testing, including the 8X and 4X tests which were started on <br /> November 5th and subsequently the 2X test started on November 11th. To match previous evaluations, both <br /> the Cerio Dubia and the P. Promelas species were evaluated. Cerio Dubia impacts are measured using both <br /> chronic and acute toxicity whereas P. Promelas impacts were measured using chronic toxicity on a pass/fail <br /> basis. <br /> The supplemental examination tests with the pH adjustment softening were also performed on a pass/fail <br /> basis for both species as a means of verifying whether calcite desaturation and/or pH modifications would <br /> lead to satisfactory results. <br /> Overall, the test results showed that the biological approach to sulfate reduction is insufficient for lowering <br /> toxicity to appropriate levels. The C. Dubia chronic toxicity results show a 60% survival rate using the water <br /> from the 8X test and no survival with the 2X and 4X waters. Impacts to reproduction rates in the C. Dubia are <br /> between the 40-60% dilution in each test, while final full concentration in each test shows complete inhibition. <br /> Survivability of the P. Promelas shows a trend of 95% survivability in the 2X test with decreasing survival with <br /> increasing sulfate reduction in the 4X (72.5%) and 8X (75%) tests. Statistical analysis of the additional test <br /> was not performed due to the pass/fail approach. Neither of the two supplemental tests (pH adjustment and <br /> softening), conducted on a pass/fail basis, showed the necessary performance to effectively reduce toxicity. <br /> Ultimately, these tests show that the test effluent water still has negative impacts on reproduction and lethality <br /> of the aquatic species. Given these results, further analysis and treatment of the mine water collected for this <br /> test is required. Table 10 outlines the remaining water constituents of concern with relation to the TDS <br /> factors identified as the major toxicant in the SeaCrest Group TIE. <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 />