title: Potential aquifer vulnerability in regions down-gradient from uranium in situ recovery (ISR) sites.
abstract: Sandstone-hosted roll-front uranium ore deposits originate when U(VI) dissolved in groundwater is reduced and precipitated as insoluble U(IV) minerals. Groundwater redox geochemistry, aqueous complexation, and solute migration are important in leaching uranium from source rocks and transporting it in low concentrations to a chemical redox interface where it is deposited in an ore zone typically containing the uranium minerals uraninite, pitchblende, and/or coffinite; various iron sulfides; native selenium; clays; and calcite. In situ recovery (ISR) of uranium ores is a process of contacting the uranium mineral deposit with leaching and oxidizing (lixiviant) fluids via injection of the lixiviant into wells drilled into the subsurface aquifer that hosts uranium ore, while other extraction wells pump the dissolved uranium after dissolution of the uranium minerals. Environmental concerns during and after ISR include water quality degradation from: 1) potential excursions of leaching solutions away from the injection zone into down-gradient, underlying, or overlying aquifers; 2) potential migration of uranium and its decay products (e.g., Ra, Rn, Pb); and, 3) potential mobilization and migration of redox-sensitive trace metals (e.g., Fe, Mn, Mo, Se, V), metalloids (e.g., As), and anions (e.g., sulfate). This review describes the geochemical processes that control roll-front uranium transport and fate in groundwater systems, identifies potential aquifer vulnerabilities to ISR operations, identifies data gaps in mitigating these vulnerabilities, and discusses the hydrogeological characterization involved in developing a monitoring program.
authors: Department of Geosciences, 210 Petrie Hall, Auburn University, AL 36849, United States.
authors: James A
authors: JA
authors: Saunders
authors: CSS-Dynamac, 10301 Democracy Lane Suite 300, Fairfax, VA 22030, United States.
authors: Bruce E
authors: BE
authors: Pivetz
authors: Environmental Solutions and Services, Battelle, 1300 Clay St., Suite 600, Oakland, CA 94612, United States.
authors: Nathan
authors: N
authors: Voorhies
authors: U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, 919 Kerr Research Dr., Ada, OK 74820, United States. Electronic address: wilkin.rick@epa.gov.
authors: Richard T
authors: RT
authors: Wilkin
mesh_terms: D055593:Geological Phenomena; D060587:Groundwater / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry; D008906:Mining / Q000379:methods*; D014501:Uranium / Q000737:chemistry; D014875:Water Pollutants, Radioactive / Q000737:chemistry
chemical_list: D008903:Minerals; D014875:Water Pollutants, Radioactive; D014501:Uranium
keywords: Groundwater monitoring; Hydrogeology; In situ leaching; Roll-front deposits; Trace metal mobilization; Uranium fate and transport; Uranium geochemistry