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Title: Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/ 235U data

In this paper, we conducted a detailed investigation of U isotopes in conjunction with a broad geochemical investigation during field-scale biostimulation and desorption experiments. This investigation was carried out in the uranium-contaminated alluvial aquifer of the Rifle field research site. In this well-characterized setting, a more comprehensive understanding of U isotope geochemistry is possible. Our results indicate that U isotope fractionation is consistently observed across multiple experiments at the Rifle site. Microbially-mediated reduction is suggested to account for most or all of the observed fractionation as abiotic reduction has been demonstrated to impart much smaller, often near-zero, isotopic fractionation or isotopic fractionation in the opposite direction. Data from some time intervals are consistent with a simple model for transport and U(VI) reduction, where the fractionation factor (ε = +0.65‰ to +0.85‰) is consistent with experimental studies. However, during other time intervals the observed patterns in our data indicate the importance of other processes in governing U concentrations and 238U/ 235U ratios. For instance, we demonstrate that departures from Rayleigh behavior in groundwater systems arise from the presence of adsorbed species. We also show that isotope data are sensitive to the onset of oxidation after biostimulation ends, even in the casemore » where reduction continues to remove contaminant uranium downstream. Finally, our study and the described conceptual model support the use of 238U/ 235U ratios as a tool for evaluating the efficacy of biostimulation and potentially other remedial strategies employed at Rifle and other uranium-contaminated sites.« less
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [3]
  1. Oregon State Univ., Corvallis, OR (United States). College of Earth, Ocean, and Atmospheric Sciences
  2. Univ. of Illinois, Champaign, IL (United States). Dept. of Geology
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
Publication Date:
Grant/Contract Number:
AC02-05CH11231; SC0006755
Type:
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 187; Journal ID: ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical Society
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of Illinois at Urbana-Champaign, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; uranium isotopes; isotope fractionation; uranium reduction; MC-ICP-MS; bioremediation
OSTI Identifier:
1471020
Alternate Identifier(s):
OSTI ID: 1328472

Shiel, A. E., Johnson, T. M., Lundstrom, C. C., Laubach, P. G., Long, P. E., and Williams, K. H.. Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/235U data. United States: N. p., Web. doi:10.1016/j.gca.2016.05.020.
Shiel, A. E., Johnson, T. M., Lundstrom, C. C., Laubach, P. G., Long, P. E., & Williams, K. H.. Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/235U data. United States. doi:10.1016/j.gca.2016.05.020.
Shiel, A. E., Johnson, T. M., Lundstrom, C. C., Laubach, P. G., Long, P. E., and Williams, K. H.. 2016. "Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/235U data". United States. doi:10.1016/j.gca.2016.05.020. https://www.osti.gov/servlets/purl/1471020.
@article{osti_1471020,
title = {Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/235U data},
author = {Shiel, A. E. and Johnson, T. M. and Lundstrom, C. C. and Laubach, P. G. and Long, P. E. and Williams, K. H.},
abstractNote = {In this paper, we conducted a detailed investigation of U isotopes in conjunction with a broad geochemical investigation during field-scale biostimulation and desorption experiments. This investigation was carried out in the uranium-contaminated alluvial aquifer of the Rifle field research site. In this well-characterized setting, a more comprehensive understanding of U isotope geochemistry is possible. Our results indicate that U isotope fractionation is consistently observed across multiple experiments at the Rifle site. Microbially-mediated reduction is suggested to account for most or all of the observed fractionation as abiotic reduction has been demonstrated to impart much smaller, often near-zero, isotopic fractionation or isotopic fractionation in the opposite direction. Data from some time intervals are consistent with a simple model for transport and U(VI) reduction, where the fractionation factor (ε = +0.65‰ to +0.85‰) is consistent with experimental studies. However, during other time intervals the observed patterns in our data indicate the importance of other processes in governing U concentrations and 238U/235U ratios. For instance, we demonstrate that departures from Rayleigh behavior in groundwater systems arise from the presence of adsorbed species. We also show that isotope data are sensitive to the onset of oxidation after biostimulation ends, even in the case where reduction continues to remove contaminant uranium downstream. Finally, our study and the described conceptual model support the use of 238U/235U ratios as a tool for evaluating the efficacy of biostimulation and potentially other remedial strategies employed at Rifle and other uranium-contaminated sites.},
doi = {10.1016/j.gca.2016.05.020},
journal = {Geochimica et Cosmochimica Acta},
number = ,
volume = 187,
place = {United States},
year = {2016},
month = {5}
}