Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste Page: 71 of 177
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5.0 Contaminant Release Model
The primary objective of this project is to develop source release models for contaminants of concern
present in residual waste upon closure of Hanford single-shell tanks. As shown in Figure 5.1, developing
these models consists of laboratory testing to produce contaminant release data and a conceptual source
release model. After development, the release model can be incorporated into a fate and transport model
as part of a long-term risk/performance assessment for the closed tank. A previously developed release
model for residual sludge from tank C-106 assumed that the sludge was contacted with dilute water meant
to simulate rainwater that has infiltrated through the vadose zone to contact the sludge (Deutsch et al.
2005a). This section describes a new conceptual release model developed for 238U, 99Tc, Cr, and 129I for a
scenario in which the residual sludge is covered with cementitious grout, which is under consideration as
a component of the closure process.
Data collected and analyses conducted in Deutsch et al. (2005a) and in this study indicated that
contaminant release from tank C-106 residual sludge will be geochemically complex. Contaminant
release from the sludge is expected to involve mineral dissolution and precipitation, oxidation-reduction
reactions, solution phase complexation, and surface adsorption. Some of these reactions can be modeled
as equilibrium reactions whereas others will be rate controlled. Although significant insight was gained
in this study regarding the contaminant release mechanisms that will be important for tank C-106 sludge,
it was not possible to adequately characterize the phase associations of the contaminants of concern in
sufficient detail to produce a mechanistically rigorous geochemical release model. This could change
with additional work; however, in the meantime, a release model based on empirical solubilities has been
developed. The approach used is inherently conservative and will over-estimate contaminant release.
Further characterization work could allow the development of a more mechanistically rigorous geochem-
ical release model, if warranted.
Risk Assessment
Testing
Contaminant Project
Release Rate iScope
Source Release
Model
Contaminant Fate &
Transport Model
Long-Term
Risk/Performance
Assessment
Figure 5.1. Source Release Model Development for Long-Term Risk/Performance Assessments5.1
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Deutsch, William J.; Krupka, Kenneth M.; Lindberg, Michael J.; Cantrell, Kirk J.; Brown, Christopher F. & Schaef, Herbert T. Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste, report, September 1, 2006; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc887933/m1/71/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.