Evaluation of Soil Flushing for Application to the Deep Vadose Zone in the Hanford Central Plateau

Truex, Michael J.; Oostrom, Martinus; Zhang, Z. F.; Carroll, Kenneth C.; Schramke, Janet A.; Wietsma, Thomas; Tartakovsky, G.; Gordon, Kathryn A.; Last, George V

doi:10.2172/1004830

Cited by 6 publications

(6 citation statements)

References 33 publications

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“…Various factors affect the mobility and migration of metal contaminants with subsurface flushing; these include the solution's leaching characteristics, soil permeability, and contaminant concentration (Truex et al 2010;USEPA 1997a). The use of acidic washing solutions decreases soil pH and, thus, increases solubility and mobility of metal ions.…”

Section: Electrokinetic Techniquesmentioning

confidence: 99%

“…To minimize such risks, the hydrogeology of the treated site must be well understood (USEPA 1997a). Lateral water flow resulting from low permeability silt zones could increase the size of the capture zone in the groundwater, cause water to bypass contaminants, and require more time and total water volume for soil flushing (Truex et al 2010). Furthermore, the technology is relatively intrusive to the remediation areas (compared to technologies such as phytoremediation) and is yet to be demonstrated with convincing success in the field (Hinton and Veiga 2001;Kaplan et al 2002).…”

Section: Electrokinetic Techniquesmentioning

confidence: 99%

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In situ remediation technologies for mercury-contaminated soil

Gao

Pierce

et al. 2015

Environ Sci Pollut Res

111

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Mercury from anthropogenic activities is a pollutant that poses significant risks to humans and the environment. In soils, mercury remediation can be technically challenging and costly, depending on the subsurface mercury distribution, the types of mercury species, and the regulatory requirements. This paper introduces the chemistry of mercury and its implications for in situ mercury remediation, which is followed by a detailed discussion of several in situ Hg remediation technologies in terms of applicability, cost, advantages, and disadvantages. The effect of Hg speciation on remediation performance, as well as Hg transformation during different remediation processes, was detailed. Thermal desorption, electrokinetic, and soil flushing/washing treatments are removal technologies that mobilize and capture insoluble Hg species, while containment, solidification/stabilization, and vitrification immobilize Hg by converting it to less soluble forms. Two emerging technologies, phytoremediation and nanotechnology, are also discussed in this review.

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Section: Electrokinetic Techniquesmentioning

confidence: 99%

Section: Electrokinetic Techniquesmentioning

confidence: 99%

In situ remediation technologies for mercury-contaminated soil

Gao

Pierce

et al. 2015

Environ Sci Pollut Res

111

View full text Add to dashboard Cite

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“…Soil flushing can be applied to purposely accelerate movement of contaminants from the vadose zone to the groundwater where the contaminants can then be captured. 34 Flushing may be enhanced through addition of extraction solutions such as acids, chemical complexants, addition of competing ions to promote desorption, or manipulation of oxidationreduction state. 35,36 Biosurfactants, biosurfactant foam, and exopolysaccharides have been proposed for mobilization of metals in soil, but there has been limited development.…”

Section: ' Remediation Optionsmentioning

confidence: 99%

“…Soil flushing can be applied to purposely accelerate movement of contaminants from the vadose zone to the groundwater where the contaminants can then be captured . Flushing may be enhanced through addition of extraction solutions such as acids, chemical complexants, addition of competing ions to promote desorption, or manipulation of oxidation−reduction state. , Biosurfactants, biosurfactant foam, and exopolysaccharides have been proposed for mobilization of metals in soil, but there has been limited development. − Potential extractants have often been developed for other applications such as in situ mining, heap leaching, and ex-situ soil washing, and it is necessary to evaluate possible negative impacts to the environment such as mobilization of nontarget metals. ,,− Implementation of soil flushing must consider the potential for lateral spreading and possible bypass of the contaminated zone through preferential vertical flowpaths.…”

Section: Remediation Optionsmentioning

confidence: 99%

Review: Technical and Policy Challenges in Deep Vadose Zone Remediation of Metals and Radionuclides

Dresel

Wellman

Cantrell

et al. 2011

Environ. Sci. Technol.

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Contamination in deep vadose zone environments is isolated from exposure so direct contact is not a factor in its risk to human health and the environment. Instead, movement of contamination to the groundwater creates the potential for exposure and risk to receptors. Limiting flux from contaminated vadose zone is key for protection of groundwater resources, thus the deep vadose zone is not necessarily considered a resource requiring restoration. Contaminant discharge to the groundwater must be maintained low enough by natural attenuation (e.g., adsorption processes or radioactive decay) or through remedial actions (e.g., contaminant mass reduction or mobility reduction) to meet the groundwater concentration goals. This paper reviews the major processes for deep vadose zone metal and radionuclide remediation that form the practical constraints on remedial actions. Remediation of metal and radionuclide contamination in the deep vadose zone is complicated by heterogeneous contaminant distribution and the saturation-dependent preferential flow in heterogeneous sediments. Thus, efforts to remove contaminants have generally been unsuccessful although partial removal may reduce downward flux. Contaminant mobility may be reduced through abiotic and biotic reactions or through physical encapsulation. Hydraulic controls may limit aqueous transport. Delivering amendments to the contaminated zone and verifying performance are challenges for remediation.

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“…As part of this effort, in situ vadose zone remediation approaches are being evaluated as potential options for mitigating the transport of Tc-99 and uranium from the vadose zone to the groundwater. Technologies investigated include soil desiccation (Truex et al 2012), surface infiltration barriers (Fayer et al 2010), soil flushing (Truex et al 2010a), in situ grouting (Truex et al 2010b), and geochemical manipulation (Szecsody et al 2010a(Szecsody et al , b, 2012. Previous geochemical manipulation research conducted as part of this program focused on uranium contamination using gas-phase delivery of amendments.…”

Section: Introductionmentioning

confidence: 99%

Gas-Phase Treatment of Technetium in the Vadose Zone at the Hanford Site Central Plateau

Truex

Szecsody

Zhong

et al. 2014

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Technetium-99 (Tc-99) is present in the vadose zone of the Hanford Central Plateau and is a concern with respect to the protection of groundwater. The persistence, limited natural attenuation mechanisms, and geochemical behavior of Tc-99 in oxic vadose zone environments must be considered in developing effective alternatives for remediation. This report describes a new in situ geochemical manipulation technique for decreasing Tc-99 mobility using a combination of geochemical Tc-99 reduction with hydrogen sulfide gas and induced sediment mineral dissolution with ammonia vapor, which create conditions for deposition of stable precipitates that decrease the mobility of Tc-99. Laboratory experiments were conducted to examine changes in Tc-99 mobility in vadose zone sediment samples to evaluate the effectiveness of the treatment under a variety of operational and sediment conditions. The laboratory experiments demonstrated a robust treatment approach to decrease the mobility of Tc-99 in the vadose zone at the Hanford Central Plateau using gas-phase amendments. The gas-phase Tc-99 treatment was shown to be effective for a variety of operational and site conditions, including 1) sequential and parallel addition of hydrogen sulfide and ammonia gases over a range of treatment gas concentrations, 2) Tc-99 concentrations ranging from 34 to 3800 pCi/g, 3) soil moisture contents of 1, 4, and 8 wt%, and 4) gas delivery times into the sample ranging from minutes to hours. A large fraction of Tc-99 in treated sediments was also shown be resistant to leaching in saturated soil column tests. These laboratory results suggest that the combined hydrogen sulfide and ammonia gas treatment is a viable candidate for treatment to decrease the mobility of Tc-99 in the vadose zone. The combined-gas Tc-99 treatment technique is an extension of the ammonia gas treatment for uranium. Previous efforts have examined many aspects of the ammonia treatment process, including key information needed to scale this process to field application. Much of this scale-up information is applicable to field application of the combined hydrogen sulfide and ammonia gas treatment demonstrated in this study to decrease Tc-99 mobility. The information presented herein suggests that, with moderate additional scale-up investigation, the combined-gas Tc-99 treatment could be field tested. Key scale-up elements would include evaluating the fate and transport of hydrogen sulfide gas in the subsurface in the presence of ammonia gas to support determining safe operational conditions for use of hydrogen sulfide. Some additional information on the reaction rates and processes in relation to subsurface pH conditions and Tc-99 precipitate stability and whether microbial processes interact with these reactions will also be important. For health and safety reasons, it may be important to minimize field collection of gas samples for treatment monitoring. Thus, extension of the electrical resistivity tomography monitoring previously applied for soil desiccation and researched fo...

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Evaluation of Soil Flushing for Application to the Deep Vadose Zone in the Hanford Central Plateau

Cited by 6 publications

References 33 publications

In situ remediation technologies for mercury-contaminated soil

In situ remediation technologies for mercury-contaminated soil

Review: Technical and Policy Challenges in Deep Vadose Zone Remediation of Metals and Radionuclides

Gas-Phase Treatment of Technetium in the Vadose Zone at the Hanford Site Central Plateau

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