Modern In Situ Uranium Recovery Technology Assures No Adverse Impact on Adjacent Aquifer Uses
Mark S. Pelizza
Uranium Resources, Inc., Lewisville, Texas
Water from a mineralized portion of an aquifer containing ore grade uranium is not potable and can be exempted (40 CFR 146.6) as an underground source of drinking water (USDW). The presence of uranium and its decay products of radium and radon cause that portion of the aquifer in which the uranium exists to exceed the maximum contaminant levels (“MCLs”) for such radionuclides allowable in public drinking water supplies as set forth in the U.S. Environmental Protection Agency’s (EPA’s) National Primary Drinking Water Regulations (“NPDWR”) for public water systems. As such, sites that are permitted for Class III underground injection control (UIC) activity and exempted under the provisions of the Safe Drinking Water Act (SDWA) are not USDW’s and will not serve as future sources of drinking water for a public water supply system. Therefore, when considering the relevant aquifer uses at a uranium deposit, the only reasonable use of the water in the exempted area is commercial uranium recovery.
The modern ISR method of uranium recovery in the U.S. (i.e., New Mexico, Nebraska, Texas, and Wyoming) leaves the original rock in place (in situ). This technology has various names, such as solution mining, in situ leach, in situ mining and in situ recovery. For ease of reference, this type of mining is hereinafter referred to as ISR for in situ recovery. Instead of manually excavating the rock from underground as in conventional mining and milling the ore on the surface, water wells are used, very much like those for a home. Oxygen is added to the native ground water from the orebody and that water is continuously recirculated until most of the uranium is recovered. The technology used to take the uranium out of the water is the same as that used in home water softeners. Uranium ISR is not new and has been safely used for more than thirty years, with operations in Nebraska, Texas and Wyoming. Waste from ISR uranium recovery is only a tiny fraction of that from a conventional mine, so tailings piles are not needed at the site and the required surface area for ISR facilities is far smaller than that for a conventional mining operation. ISR uranium recovery is highly regulated and monitor wells surrounding the mine site are required, ensuring protection of the surrounding aquifer. Additionally, restoration of the affected portion of the aquifer consistent with baseline conditions or federal or state concentration limits is required.
Approximately 30 commercial ISR operations and numerous pilot projects have been licensed and operated in the U.S. since the early 1970s. In all of these, some portion of the aquifer outside the mine zone is available as a USDW where engineered well field patterns, balanced well field operations and monitor wells surrounding the mine area have ensured that water quality outside the mine zone is not impacted.
Once the uranium has been recovered, the affected ground water used in ISR is treated and the quality is restored consistent with pre-mining baseline conditions, or quality of use, as appropriate to ensure that the water quality outside the mine zone will be protected after restoration is completed.
AAPG Search and Discover Article #90069©2007 GCAGS 57th Annual Convention, Corpus Christi, Texas