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GEM SERVICES <br /> Dawson Project—Tailings Characterization Page 17 <br /> Both filtrate samples have neutral pH, low concentrations of sulfate and low concentrations of <br /> metals,with many parameters less than the detection limit. For context,the filtrate results were <br /> compared to the mine drainage and beneficiation mill discharge criteria,the groundwater quality <br /> standard and the Grape Creek water quality standard(Table 9). Both filtrate samples had metal <br /> concentrations two orders of magnitude less than the mine drainage and mill discharge criteria. <br /> Metal concentrations in both filtrates also meet the groundwater quality standard and are less than <br /> the background groundwater quality. The exception is manganese in the altered tailings filtrate <br /> sample. Manganese concentration exceeded the groundwater standard but was less than the <br /> background groundwater quality. <br /> The tailings filtrate quality was also compared to the Grape Creek water quality standard as a <br /> proxy for local ephemeral surface drainages. It is noted that Grape Creek is approximately 1.6 <br /> miles from the project site and seepage from the FTSF will not directly enter the creek. The <br /> filtrate quality generally meets the Grape Creek water quality standard. The exceptions are <br /> selenium in altered tailings filtrate(0.005 mg/L versus the standard of 0.0046 mg/L) and nickel in <br /> unaltered tailings filtrate(0.0317 mg/L versus the standard of 0.026 mg/L). Based on the <br /> foregoing,tailings filtrate quality meets the requirements for direct discharge to groundwater. <br /> 3.2 Kinetic Tests <br /> Kinetic tests were initiated for the two tailings samples to evaluate the potential metal release <br /> during the post-closure period of the mine. The humidity cell test was utilized. The tests were <br /> run for 25 weeks when results indicated steady state metal release had been achieved. <br /> Data are presented in Figures 5 and 6 below. The laboratory report is provided in Appendix C. <br /> Tailings sample leachates maintained a buffered, low metal concentration leachate quality <br /> throughout the testing period. These results are consistent with the low sulfide and metal <br /> concentrations in the sample solids as discussed in Section 3.1 above. Notable is the non- <br /> detection of many heavy metals, such as arsenic, cadmium, chromium,copper, iron,nickel, lead <br /> and zinc. <br /> Conductivity,pH and concentrations of major elements are shown in Figure 5. pH remained <br /> neutral to slightly alkaline throughout the testing period. Sulfate and calcium concentrations and <br /> conductivity showed similar release patterns, indicating sulfide oxidation occurred early in the <br /> testing program with carbonate dissolution neutralizing the released acid. Sulfate concentrations <br /> decreased to near the detection limit(altered tailings)and average 19 mg/L(unaltered tailings)as <br /> the reactive sulfide was depleted. Conductivity decreased to an average 150 µS/cm as the sulfate <br /> washed out. <br /> Also shown in Figure 5 is acidity and alkalinity. Alkalinity maintained an increasing trend <br /> throughout the testing period. Acidity concentrations remained low throughout the testing period, <br /> ODS/dds Zephyr Dewson_Tailings ChareGerizatlon_Fina(_Report,Feb.3,22,1:1 B PM Feb 2022 <br />