Microbiological, Geochemical and Hydrologic Processes Controlling Uranium Mobility: An Integrated Field-Scale Subsurface Research Challenge Site at Rifle, Colorado
Principal Investigator:
Philip E. Long
Pacific Northwest National Laboratory
Field Site Manager and co-Manager:
Richard Dayvault and Stan Morrison
SM Stoller – DOE Grand Junction Office
Co-Principal Investigators:
Jill Banfield (UC/Berkeley), Darrell Chandler (Akonni
Biosystems), Jim Davis (USGS), Bob Hettich (ORNL), Peter Jaffe (Princeton
U.), Lee Kerkhof (Rutgers U.), Ravi Kukkadapu (PNNL), Mary Lipton
(PNNL), Aaron Peacock (UTK), Nathan VerBerkmoes (ORNL), Kenneth H.
Williams (LBNL),
Steve Yabusaki (PNNL)
ABSTRACT
The U.S. Department of Energy faces the challenge
of cleaning up and/or monitoring large, dilute plumes contaminated
by metals, such as U and Cr, whose mobility and solubility change
with redox status. At the Uranium Mill Tailings Site in Rifle, CO,
field-scale experiments with acetate as the electron donor have stimulated
metal reducing bacteria to effectively remove uranium [U(VI)] from
groundwater. The shallow depth to groundwater (3-4 m), thin saturated
zone (~2.5 m), and well-defined groundwater flow system at the Rifle
site facilitated the monitoring of microbial and geochemical processes
which led to two important findings: the transition from iron reduction
to sulfate reduction significantly decreased the U(VI) bioreduction
rate, and U(VI) removal from groundwater continued for 18 months,
actually increasing after acetate amendment was terminated. Understanding
these behaviors in the context of site-specific hydrologic, geochemical,
and biological processes and conditions is critical to the design
of
optimal biostimulation strategies for prolonging
uranium bioremediation. The objective of the research proposed for the
Rifle site is to gain a comprehensive and mechanistic understanding
of the microbial factors and associated geochemistry controlling uranium
mobility so that DOE can confidently remediate uranium plumes as well
as support stewardship of uranium-contaminated
sites. Specifically, we propose to test four hypotheses
that address knowledge gaps in the following areas: 1) geochemical and
microbial controls on stimulated U(VI) bioreduction by iron-reducers,
2) U(VI) sorption under Fe-reducing conditions, 3) post-biostimulation
U(VI) stability and removal, and 4) rates of natural bioreduction of
U(VI). Hypotheses will be tested with a focused set of field and lab
experiments that use recently developed sciences of proteogenomics and
stable isotope probing to track microbial metabolic status and specific
organisms responding to acetate amendment. We will directly relate this
information to changes in Fe redox status and sulfide minerals, with
field-scale changes detected by non-invasive hydrogeophysics, including
3-D complex resistivity tomography. The approach specifically
targets new knowledge that can be translated into
scientifically defensible flow and reactive transport process models
of microbially mediated and abiotic reactions, taking a major step toward
ERSP’s long-term goal to “…incorporate coupled biological,
chemical and physical processes into decision making for environmental
remediation.”
Experimental Test Plot at the Old Rifle UMTRA site in Rifle, CO |
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| (A) Location of the proposed Rifle Field Sie in Colorado. (B) Map of the site showing estimated U(VI) concentration in groundwater as of approximately 1998 and location of existing experimental plots on the site. (C) Photograph of the site looking east. |
