title: Se Isotopes as Groundwater Redox Indicators: Detecting Natural Attenuation of Se at an in Situ Recovery U Mine.
abstract: One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. In this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradient wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ82SeVIof Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of -2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Furthermore, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.
authors.affiliation: Department of Earth and Planetary Science, University of California , 307 McCone Hall, Berkeley, California 94720, United States.
authors.forename: Anirban
authors.initials: A
authors.lastname: Basu
authors.affiliation: Department of Environmental Science, Policy and Management, University of California , 130 Mulford Hall, Berkeley, California 94720, United States.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Schilling
authors.affiliation: Department of Earth and Planetary Science, University of California , 307 McCone Hall, Berkeley, California 94720, United States.|Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Shaun T
authors.initials: ST
authors.lastname: Brown
authors.affiliation: Department of Geology, University of Illinois at Urbana-Champaign , 605 East Springfield Avenue, Champaign, Illinois 61820, United States.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Johnson
authors.affiliation: Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: John N
authors.initials: JN
authors.lastname: Christensen
authors.affiliation: Uranium Resources, Inc. , 6950 South Potomac Street, Suite 300, Centennial, Colorado 80112, United States.
authors.forename: Matt
authors.initials: M
authors.lastname: Hartmann
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Reimus
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Heikoop
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Giday
authors.initials: G
authors.lastname: Woldegabriel
authors.affiliation: Department of Earth and Planetary Science, University of California , 307 McCone Hall, Berkeley, California 94720, United States.|Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: DePaolo