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• The most recent data indicate that the mine pool is still filling, albeit at a <br />very slow rate that has become asymptotic. With the mine pool currently <br />still in a state of recovery, it is logical to assume that there is still a slight <br />cone of depression and hydraulic gradient toward the mine pool. If that is <br />the case, then the predicted 2.06 gpm contribution from the mine pool to <br />Ralston Creek via the Schwartz Trend may not reflect long-term conditions <br />that will prevail when the gradient reestablishes itself to steady state. <br />2) The Operator must therefore comply with Rule 6.4.20(6) pertaining to designated chemicals and <br />materials handling. The Operator must describe the procedures for the disposal, <br />decommissioning, detoxification or stabilization for the toxic-forming materials in the <br />underground. Specifically describe measures to be taken to prevent any unauthorized release of <br />pollutants to the environment. Options for management of the mine pool might include: <br />a) Treat in situ to immobilize or perhaps recover the uranium. DRMS <br />calculations indicate that the mine pool may contain up to 55,000 lbs. of <br />uranium. A mitigation/management tool perhaps worth considering could be the <br />introduction of sulfate reducing bacteria into the mine pool. The equilibrium pe <br />for sulfate reduction at neutral pH is in the range of -4 to -5. According to the <br />PHREEQC chemical equilibrium/speciation software, maintaining the pool Eh at <br />around -0.3v (pe = -4.75) will precipitate Uraninite to a final uranium <br />concentration of approximately 0.776 mg/L, which was the CDP effluent limit. <br />There is an abundance of sulfate in the mine pool (>2,000 mg/L), so adding <br />sulfate reducing bacteria might drop the Eh, and allow control of uranium <br />concentrations at an acceptable level by way of Uraninite precipitation. Control <br />and/or exclusion of atmospheric oxygen would also be a requirement. This <br />option, as with any other proposed in situ treatment option, would require <br />successful bench scale testing before implementation. <br />b) Pump and Treat-Discharge. A water treatment facility could either be <br />constructed at the site or a portable unit could be mobilized. Depending on the <br />leachability of the wall rocks and the redox conditions in the mine pool, this is an <br />option that may not have to be continued in perpetuity, or could be done <br />intermittently. Long-term monitoring of the mine pool water quality will be <br />essential in determining the frequency and duration of treatment. <br />3) Because the underground workings are containing the contaminants in the mine pool water, <br />DRMS contends that the underground workings should be designated as an Environmental <br />Protection Facility and therefore subject to the provisions of Rule 6.4.20(7)(e). Operator must <br />describe any release response procedures, redundancies, and "backup" measures necessary, <br />appropriate, and economically reasonable, to control, prevent and mitigate releases of the toxic- <br />forming materials from the containment facility (i.e., the underground workings) outside the <br />permit area. <br />4) Operator must continue to monitor the water level and water quality of the mine pool on a <br />quarterly basis. The analyte list must be expanded to match the suite of analytes currently in the <br />alluvium monitoring well program.