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COLORADO LEGACY LAND SCHWARTZWALDER MINE Operation of the 60-hp pump and the dewatering/treatment of the mine pool will continue to physically stabilize the water elevation in the mine pool below the regulatory limit. During the time in which the WTP is not in operation,the mine pool will be allowed to naturally recover as shown in Figure E-3.Projections based on historical mine pool elevation trends and calculations of mine recharge rates show that each year the WPT can be shut down for at least a 6-month period with little risk of exceeding the regulatory limit.The basis for a shut down of at least 6-months is provided in the following section. Maintaining the mine pool elevation below the regulatory limit(150-feet below the Steve Level)has established a hydraulic gradient inward toward the mine pool and away from Ralston Creek.A summary of the observed quarterly groundwater elevations in bedrock wells MW-13,MW-15 and MW-18 with respect to the mine pool elevation is presented in Table E-2.MW-13 is the upgradient deep groundwater well.MW-15 was installed east of the Schwartzwalder Mine, targeting the Schwartz Trend geologic transition zone, and was installed at a location that was downgradient of the mine area relative to pre-mining static water levels.MW-18 as installed in the valley floor targeting the Illinois Fault in the area near where the Illinois Fault is adjacent to Ralston Creek.These data are used to calculate the hydraulic gradient between each well and the mine pool. Negative gradients indicate an inward gradient of groundwater around the mine as measured by the transducer(which is installed within the mine pool and measured in Shaft 2).Depending on the elevation of the mine pool,which since 2018 it was below the regulatory limit,the gradient from each well ranged from 0.014 to 0.304 feet per foot. This validates that the regulatory limit is set at an appropriate depth to protect Ralston Creek and the potential for groundwater to migrate along the recognized permeable features that intersect the mine. The strongest gradient(0.304 ft/ft)was observed in MW-13 during the fourth quarter of 2021,when the mine pool was dewatered to its deepest elevation.The data also indicate an anisotropic capture zone from pumping the mine pool. A bedrock groundwater contour map is shown on Figure E-4 that illustrates the capture zone associated with the mine pool. The lateral extent of mine pool workings is shown as the red-shaded area. Groundwater elevation data from the second quarter 2020 are shown next to wells MW-13, MW-15, and MW-18. These monitoring well data,which are conservative,are provided in Table E-2 and used on Figure E-4. In the second quarter of 2020 the mine pool elevation ranged from —158 - 178 feet below the Steve Level (Table E-2). CLL has further dewatered the mine pool to greater than 345 feet below the Steve Level.Additional discussion of this figure and the physical stabilization of the mine pool is provided in Appendix 3. E.5.1.1. Physical Stabilization of the Mine Pool Conclusion The changes in mine pool elevation during the non-pumping recovery period are historically steady and consistent. On the basis of historical refill trends,once the mine pool is dewatered at the end of the operating season,the natural groundwater recharge will take at least six to and up to eight months before the mine pool approaches the regulatory limit. Historical mine pool elevations are shown in conjunction with mine pool projections in Figure E-3. The projections made for the natural refill in the spring of 2022 in Figure E-3 are based on previous recovery trends through the same elevations in the mine.The green point at 6,432 feet above mean sea level(ft amsl)represents the projected plant start-up day,when the mine pool is estimated to still be at a conservative 20 ft below the regulatory limit. On the basis of empirical data collected, the physical stabilization of the mine pool has been achieved for the last four consecutive years (i.e., since fall of 2017) by this approximately 6-month seasonal pumping. On the basis of(i) calculations developed from the empirical AUGUST 2022 18 AMENDMENT 6