2022-02-09_PERMIT FILE - M2021046 (7)

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tailings and development rock samples had a carbonate neutralization to acidity production ratio greater than 4. Material with a ratio greater than 2 is considered non-potentially acid generating. Paste pH for all samples ranged from 6.9 to 9.7, indicating no net acidity is currently being produced. The FTSF leachate will be dominated by the quality of the tailings filtrate entrained in the tailings. Filtrate from altered and unaltered tailings, generated during the metallurgical testing that produced the tailings, was directly analyzed using ICP-MS. Results were compared to the EPA effluent criteria (40 CFR Part 440 Subpart J), surface water quality standard for Grape Creek (5 CCR 1002-32), groundwater quality standard (5 CCR 1002-41) and baseline groundwater quality at the site. The filtrate meets all three standards and is similar or less than the background groundwater quality, with the following exceptions: • Nickel and selenium concentrations exceed the surface water quality standard; however,they meet the groundwater quality standard and are similar to background groundwater concentrations • Manganese concentration exceeds the groundwater standard, but is similar to background groundwater concentrations • Potassium concentration is greater than background groundwater concentrations; however,there are no surface nor groundwater standards for potassium. The evolution of tailings leachate quality is currently being assessed through humidity cell testing. These tests are ongoing. To date, many metals have not been detected after the initial filtrate was flushed. Metal release from development rock was assessed using the shake flask extraction (SFE)test. SFE tests were done on all 5 development rock samples. The SFE test is similar to the Synthetic Precipitation Leaching Procedure (SPLP),the difference being the SFE test is conducted at a 3:1 water to solid ratio for 24 hours whereas the SPLP test is conducted at a 20:1 water to solid ratio for 18 hours. All other aspects of the procedures are the same. The SFE test was chosen because it produces a more concentrated solution (without hitting solubility limits)that enables detection of some elements that could otherwise be missed. This is a more conservative approach to the State of Colorado's leach test requirement. Results from the SFE tests show few detectable trace metals. Metals and metalloids detected include aluminum, antimony, arsenic, barium, copper, lead, manganese, molybdenum and uranium. All parameters met the water quality standard for Grape Creek and the groundwater quality standard. The exception is lead, where 3 of the 5 samples exceeded the water quality standard for Grape Creek. Lead concentrations ranged from <0.0005 mg/L to 0.0057 mg/L. The water quality standard for Grape Creek is 0.001 mg/L. All SFE tests produced slightly alkaline pH. No sulfate was detected. 2.7.3.2 FTSF Seepage Quality The seepage from the FTSF will comprise of filtrate introduced to the facility with the tailings, infiltration water that contacts the tailings and infiltration water that contacts the support buttresses (development rock). The contributions from development rock and tailings were combined in proportion to the tonnage of each material expected in the FTSF, utilising the 40