Assessing the Potential for Biorestoration of Uranium In Situ Recovery Sites (NUREG/CR-7167)

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Publication Information

Manuscript Completed: September 2013
Date Published: June 2014

Prepared by:
S. B. Yabusaki¹, Y. Fang¹, S. R. Waichler¹, C. C. Fuller²,
K. Akstin², P. E. Long³, and M. Fuhrmann⁴

¹Pacific Northwest National Laboratory
²U.S. Geological Survey
³Lawrence Berkeley National Laboratory
⁴U.S. Nuclear Regulatory Commission

Mark Fuhrmann, NRC Project Manager

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

In situ bioremediation (ISB) may be a more effective alternative for the restoration of uranium in situ recovery (ISR) sites than current methods. ISB involves the stimulation of indigenous microorganisms that catalyze the immobilization of targeted contaminants. Many of the post-operational contaminants found at ISR sites (e.g., uranium, vanadium, selenium, molybdenum) are in oxidized, soluble forms. This is a result of the ISR process in which oxidizing solutions are injected into the subsurface to liberate uranium from its solid matrix. In this case, ISB would be directed at the chemical reduction of these contaminants to their immobile forms. While the technique has the potential for more effective restoration, shorter restoration periods, and lower cost, it is an unproven technology that relies on the stability of uranium and other metals that are left in place. Consequently, there is a need to better understand the behavior of the uranium in the bioremediated system during and after the restoration. Licensees have been conducting studies into the effectiveness of ISB, therefore an independent examination, such as that documented in this report, is important for anticipated regulatory decisionmaking regarding its acceptability.

This report is the third in a series of technical NUREG/CRs that are intended to provide background and evaluation of uranium ISB technology. The purpose of this report is to assess the potential effectiveness of ISB for uranium ISR sites, identify performance issues, and guide future implementation and monitoring. To address the limitations of the current knowledge base of field-scale ISB uranium behavior, the approach in this document is to augment the available geological, hydrological, and chemical data from existing ISR sites with 1) laboratory studies of biologically mediated removal of uranium from solution using sediment taken from a leached out uranium ore body, 2) previous studies of uranium ISB in shallow, alluvial aquifers, and 3) coupled process modeling of hypothetical field-scale ISR restoration including: coupled flow, transport, and biogeochemical processes. The models are intended to help integrate and scale up the predicted effects from the laboratory to the field. The experimental and modeling studies presented here suggest that biostimulation of indigenous bacterial populations can be effective in lowering aqueous concentrations of uranium at ISR sites to acceptable levels.