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Simple Non-Electrostatic Model Successfully Predicts Long-Term Uranium Mobility
Published: July 06, 2017
Posted: November 21, 2017

When compared to results from a more complicated surface complexation model with electrostatic correction, the simple model performed just as well but was less computationally intensive.

Scientific Achievement
A simple non-electrostatic model was developed through a step-by-step calibration procedure to describe U (Uranium) plume behavior at the Savannah River site. This simple model was found to be more numerically-efficient than a complex mechanistic model with electrostatic correction terms in predicting long-term U behavior at the site and by extension other uranium contaminated sites.

Significance & Impact
Uranium geochemistry has been extremely challenging to describe and predict. Although complex mechanistic models have been used to describe U sorption in field settings, there is significant uncertainty in model predictions due to scarce field data and modeling assumptions concerning mineral assemblage and subsurface heterogeneity. This study demonstrates that a simpler non-electrostatic model is a powerful alternative for describing U plume evolution at the Savannah River Site (SRS) because it can describe U(VI) sorption much more accurately than a constant coefficient (Kd) approach, while being more numerically efficient than a complex model with electrostatic correction terms. This study provides valuable insight into predicting uranium plume persistence from contaminated sites using simple non-electrostatic models.

Summary
The aim of this study was to test if a simpler, semi-empirical, non-electrostatic U(VI) sorption model (NEM) could achieve the same predictive performance as a model with electrostatic correction terms in describing pH and U(VI) behavior at multiple locations within the SRS F-Area. Modeling results indicate that the simpler NEM was able to perform as well as the electrostatic surface complexation model especially in simulating uranium breakthrough tails and long-term trends. However, the model simulations differed significantly during the early basin discharge period. Model performance cannot be assessed during this early period due to a lack of field observations (e.g., initial pH of the basin water) that would better constrain the models. In this manner, modeling results highlight the importance of the range of environmental data that are typically used for calibrating the model.

Contacts
(BER PM)

David Lesmes
SC-23.1
David.Lesmes@science.doe.gov (301-903-2977)

(PI Contact)
Haruko Wainwright
Lawrence Berkeley National Laboratory
HMWainwright@lbl.gov

Funding
This material is based upon work supported as part of the ASCEM project, which is funded by the U.S. Department of Energy Environmental Management, and as part of the Genomes to Watershed Science Focus Area, which is funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, both under Award Number DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory.

Publications
Arora, B., J.A. Davis, N.F. Spycher, W. Dong, and H.M. Wainwright. 2017. “Comparison of Electrostatic and Non-Electrostatic Models for U (VI) Sorption on Aquifer Sediments” Groundwater. doi:10.1111/gwat.12551.

Topic Areas:

  • Research Area: Subsurface Biogeochemical Research
  • Mission Science: Environmental Cleanup

Division: SC-23.1 Climate and Environmental Sciences Division, BER

 

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