Techniques for assessing the performance of in situ bioreduction and immobilization of metals and radionuclides in contaminated subsurface environments Page: 4 of 21
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In these systems, the soil and bedrock matrix (secondary sources) have been exposed to migrating
contaminants for many decades, and thus account for a significant inventory of the total waste. A
significant limitation in defining remediation needs of the secondary sources results from an insufficient
understanding of the transport processes that control contaminant migration. Because of this, the
historical remedial approach at many DOE facilities has been to target "hot spots". Stabilization,
diversion, and containment of contaminants within the primary source areas have been the major
emphasis. Techniques such as barriers, grouting, vitrification and local-scale capping (Fig. 3) have been
used on high-risk exit pathways (e.g. preferential flow zones, seeps).
Constructing-a cap over
waste trenches at
ORNL
Figure 3: Recent capping activities on the Oak Ridge Reservation in an effort to impede infiltrating
storm water from entering subsurface waste trenches.
The treatment of contamination in the soil and rock matrix has historically not been emphasized
in most remedial endeavors. Three primary reasons are that (1) no feasible removal or immobilization
technologies for large volumes of contaminated subsurface saprolite, bedrock, or groundwater are
available, (2) remedial costs are often prohibitive, and (3) lacking knowledge on the risk posed by
secondary sources. Although huge contaminant inventories reside in the secondary source domain, their
low permeability significantly influences and slows contaminant mass-transfer to high-risk pathways.
Many contaminated sites have resorted to capping (Fig. 3) which typically does not completely
immobilize contaminants in humid regimes due lateral flowing water and seasonal groundwater
fluctuations. For this reason, the Department of Energy (DOE) has invested significant funding into basic
science that seeks to understand how subsurface microorganisms can be effectively stimulated to
immobilize metals and radionuclides in situ.
Efforts to immobilize toxic metals and radionuclides in situ using bioremediation
In April of 2000, DOE awarded Oak Ridge National Laboratory with a project to establish a field
research center where investigators could obtain samples and conduct in situ studies that would lead to
new insights into the bioremediation of metals and radionuclides and related contaminant fate and
transport processes (http://www.esd.ornl.gov/nabirfrc/). They chose the former S-3 ponds at the Y-123
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Jardine, P. M.; Watson, D. B.; Blake, D. A.; Beard, L. P.; Brooks, S. C.; Carley, J. M. et al. Techniques for assessing the performance of in situ bioreduction and immobilization of metals and radionuclides in contaminated subsurface environments, article, November 14, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc788344/m1/4/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.