Conceptual Model of Uranium in the Vadose Zone for Acidic and Alkaline Wastes Discharged at the Hanford Site Central Plateau

Truex, Michael J.; Szecsody, James E.; Qafoku, Nikolla P.; Serne, R. Jeffrey

doi:10.2172/1170495

Cited by 6 publications

(10 citation statements)

References 54 publications

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“…The waste disposal chemistry can be important because the presence of co-contaminants can affect subsurface and remediation biogeochemistry. In addition, acidic or basic conditions in the disposed fluid can lead to neutralization reactions affecting contaminant fate and transport in the vadose zone, thereby influencing the contaminant flux to groundwater (Truex et al 2014). Table 6 lists the co-contaminants for the major iodine disposal sites.…”

Section: Inputsmentioning

confidence: 99%

Conceptual Model of Iodine Behavior in the Subsurface at the Hanford Site

Truex

Lee

Johnson

et al. 2015

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DOC Dissolved organic carbon DOE U.S. Department of Energy DPMAS Direct-polarization magic-angle spinning DWS Drinking water standard EXAFS Extended X-ray absorption fine structure spectra Eh Oxidation/reduction potential Stored in single-shell and double-shell tanks Discharged to liquid disposal sites (e.g., cribs and trenches) Released to the atmosphere during fuel reprocessing operations Captured by off-gas absorbent devices (silver reactors) at chemical separations facilities (PUREX, B-Plant, T-Plant, and REDOX)

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Section: Inputsmentioning

confidence: 99%

Conceptual Model of Iodine Behavior in the Subsurface at the Hanford Site

Truex

Lee

Johnson

et al. 2015

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“…The volume of liquid disposal is another important parameter that provides the primary driving force for initial distribution of contaminants in the subsurface, with large volumes generally leading to more extensive migration and in some cases, current breakthrough observed in the groundwater. The waste disposal chemistry (i.e., acidic, basic, elemental composition) is the third important factor controlling interactions of waste fluids and sediment minerals, ultimately affecting contaminant fate and transport in the vadose zone, and influencing the contaminant flux to groundwater (Truex et al 2014). Additional information about this component of the iodine CM at Hanford has been included in the previously published CM reports (e.g., Truex et al 2017a).…”

Section: Inputsmentioning

confidence: 99%

Conceptual Model of Subsurface Processes for Iodine at the Hanford Site

Qafoku

Bagwell

Lawter

et al. 2018

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death and lysis. These solid-phase interactions are relevant with respect to attenuating iodine transport and need to be considered with respect to fate and transport and remediation. • The gas phase is also relevant to the overall iodine cycle. In particular, microbial reactions that create methyl-iodine compounds are a mechanism of volatilization. This type of reaction can occur in Hanford sediments, so it should be considered as part of the potential fate for subsurface iodine. Current studies focused on groundwater conditions, but volatilization in the vadose zone during and after waste disposal is another potential ramification of these gas-phase iodine species. Volatilization is, therefore, another attenuation mechanism related to the fate and transport of iodine in the subsurface. For iodate in the vadose zone or groundwater, transport is attenuated by sorption and co-precipitation with calcite (and other calcium carbonate polymorphs such as aragonite) and iron oxides (e.g., ferrihydrite). These solid-phase interactions are not a permanent sequestration and iodate may be released back into the aqueous phase via desorption and/or dissolution. The solubility of iodate bearing calcite is similar to that of pure calcite. Ferrihydrite has been previously shown to have a high affinity for iodate adsorption. Data showed that iodate transport was significantly retarded in ferrihydrite-amended sediment, whereas iodide and organo-I species showed little adsorption to ferrihydrite. Organo-I complexes are present in the Hanford subsurface, predominantly in the aqueous phase. While the organo-I complexation structures in the 200-UP-1 site at Hanford could not be confidently identified, the results suggested that these compounds exist at Hanford. The differences in organic matter composition indicated that pore water samples have a higher abundance of aromatic compounds that are a better target for iodine complexation. Volatilization of iodine occurred in Hanford sediments. Iodomethane was produced by all of the sediment samples examined and was positively correlated with 129 I concentrations in sediment cores. Moreover, its production rate was insensitive to nutrient supplements. This result reflects a nominal capacity of Hanford subsurface sediments to volatilize iodine without additional perturbation of the subsurface system. The fate of iodomethane in the aquifer or the extent to which this process may have impacted iodine in the vadose zone during and after waste disposal have not been quantified. However, this transformation mechanism should be considered when interpreting potential pathways for iodine in the subsurface.

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“…The estimation of current contaminant distribution needs to include an assessment of transport and attenuation effects from biogeochemical reactions and/or physical/chemical interaction with sediments. For instance, neutralization of acidic or alkaline waste discharged to the vadose zone can dissolve sediment components with subsequent re-precipitation that can coat or bind some contaminants and render them functionally immobile (i.e., only released to the pore water with slow dissolution of lowsolubility precipitates that would occur over a very long timeframe) (e.g., Truex et al 2014a;Szecsody et al 2013).…”

Section: Contaminant Distribution Assessmentmentioning

confidence: 99%

“…Thus, an analysis to determine the appropriate transport parameters in the context of the disposed fluid properties is needed. Information to support this analysis, with emphasis on uranium contamination, is provided by Truex et al (2014a) and Szecsody et al (2013). 6.4…”

Section: High Ionic Strength Waste Fluidsmentioning

confidence: 99%