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ARCADIS <br />would have concentrated mine water brine added to the tests. These microcosms would be sampled over <br />time to evaluate uranium treatment and byproduct generation. <br />5.4 Long -term Stabilization of the Mine Pool Water Level <br />Pumping of Mine Pool <br />Overview: The available hydrogeologic and water quality data indicate that the mine pool is still strongly <br />connected to the alluvium. Even if the mine pool is treated in -situ, cessation of pumping after treatment <br />may introduce uranium into the alluvium at levels that, once mixed with water in the creek, could exceed <br />0.03 mg /L in the creek. <br />Data Adequacy: The only circumstance under which mine pool pumping could cease is if all of the <br />following conditions are met: <br />• Appropriate mitigation actions are implemented at the South Waste Rock Pile after the <br />additional characterization is conducted. <br />• The historical alluvial fill is removed as planned. <br />• Alluvial groundwater is recovered and treated as planned. <br />• The mine pool is treated in -situ and demonstrated to be treated to acceptable levels to meet and <br />sustain water quality standards. <br />• The diversion pipeline continues as a "permanent" mitigation measure to ensure that the creek <br />is protected. Otherwise, rebound of the mine pool may introduce uranium back into the alluvium <br />that could impact the creek. <br />Recommendations: Continue mine pool pumping until the conditions detailed above are met and are <br />sustainable based on established performance criteria. <br />Long -Term Stabilization of the Mine Pool <br />Overview: The Reclamation Plan states that the mine pool has reached an equilibrium elevation <br />approximately 20 feet below the Steve Level. This appears to be accurate based on the mine pool water <br />elevations, but it is more likely that the reason for the apparent equilibrium level is due to mine pool water <br />discharging or "spilling out" into the alluvium. The elevation of the mine pool is approximately 6,580 feet, <br />which is about 20 feet higher than the valley floor (approximately 6,560 feet); thus, mine pool water can <br />flow into the alluvium under natural gradient conditions through fractures and through the Illinois fault <br />zone, or through open coreholes as discussed above. This steady discharge of mine pool water into the <br />alluvium is sufficient to equal the inflow into the mine, thereby creating a near static level of the mine pool. <br />This discharge of mine pool water will continue until these pathways are cut off. Once cut off, the mine <br />pool will likely rise to the Steve Level or higher. <br />Page <br />14/16 <br />