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

Abstract

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 wheremore » 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:

Shiel, A. E. ^[1]; Johnson, T. M. ^[2]; Lundstrom, C. C. ^[2]; Laubach, P. G. ^[2]; Long, P. E. ^[3]; Williams, K. H. ^[3]

---

+ Show Author Affiliations

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:

Fri May 20 00:00:00 EDT 2016

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1471020

Alternate Identifier(s):

OSTI ID: 1328472

Grant/Contract Number:  

AC02-05CH11231; SC0006755

Resource 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

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; uranium isotopes; isotope fractionation; uranium reduction; MC-ICP-MS; bioremediation