Contaminants in Vadose Zone Environments

Wellman, Dawn M.; Freshley, Mark D.; Johnson, Timothy C.; Miracle, Ann L.

doi:10.2136/vzj2012.0159

Cited by 4 publications

(2 citation statements)

References 18 publications

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“…These solutions influence the dissolution of soil minerals and, based on field observations, elevated concentrations of Si, Fe, and K are still observed in the contaminated groundwater about 40 years after the waste infiltration (Wan et al 2004). After the disposal, uranium contamination, accumulated in the subsurface unsaturated zone (vadose zone), can serve as a continued "source" of U(VI) contamination for groundwater (Wellman et al 2012). There is a concern that elevated uranium concentrations slowly infiltrate towards the water table, creating a risk of higher U concentrations reaching the groundwater and then, with groundwater flow, entering rivers and lakes.…”

Section: Introductionmentioning

confidence: 99%

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

Katsenovich

Cardona

Lapierre

et al. 2016

Applied Geochemistry

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Remediation of uranium in the deep unsaturated zone is a challenging task, especially in the presence of oxygenated, high-carbonate alkalinity soil and pore water composition typical for arid and semi-arid environments of the western regions of the U.S. This study evaluates the effect of various pore water constituencies on changes of uranium concentrations in alkaline conditions, created in the presence of reactive gases such as NH 3 to effectively mitigate uranium contamination in the vadose zone sediments. This contaminant is a potential source for groundwater pollution through slow infiltration of soluble and highly mobile uranium species towards the water table. The objective of this research was to evaluate uranium sequestration efficiencies in the alkaline synthetic pore water solutions prepared in a broad range of Si, Al, and bicarbonate concentrations typically present in field systems of the western U.S. regions and identify solid uranium-bearing phases that result from ammonia gas treatment. In previous studies (Szecsody et al. 2012, Zhong et al. 2015), although uranium mobility was greatly decreased, solid phases could not be identified at the low uranium concentrations in fieldcontaminated sediments. The chemical composition of the synthetic pore water used in the experiments varied for silica (5 to 250 mM), Al 3+ (2.8 or 5 mM), HCO 3 ‾ (0-100 mM) and U(VI) (0.0021-0.0084 mM) in the solution mixture. Experiment results suggested that solutions with Si concentrations higher than 50 mM exhibited greater removal efficiencies of U(VI). Solutions with higher concentrations of bicarbonate also exhibited greater removal efficiencies for Si, Al, and U(VI). Overall, the silica polymerization reaction leading to the formation of Si gel correlated with the removal of U(VI), Si, and Al from the solution. If no Si polymerization was observed, there was no U removal from the supernatant solution. Speciation modeling indicated that the dominant uranium species in the presence of bicarbonate were anionic uranyl 3 carbonate complexes (UO 2 (CO 3) 2-2 and UO 2 (CO 3) 3-4) and in the absence of bicarbonate in the solution, U(VI) major species appeared as uranyl-hydroxide (UO 2 (OH) 3 ‾ and UO 2 (OH) 4-2) species. The model also predicted the formation of uranium solid phases. Uranyl carbonates as rutherfordine [UO 2 CO 3 ], cejkaite [Na 4 (UO2)(CO 3) 3 ] and hydrated uranyl silicate phases as Naboltwoodite [Na(UO 2)(SiO 4). 1.5H 2 O] were anticipated for most of the synthetic pore water compositions amended from medium (2.9mM) to high (100mM) bicarbonate concentrations.

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Section: Introductionmentioning

confidence: 99%

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

Katsenovich

Cardona

Lapierre

et al. 2016

Applied Geochemistry

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“…Bioremediation has been found to be a more reliable, lower cost, and less intrusive method than other conventional treatments (Yadav and Hassanizadeh, 2011), especially for the unsaturated zone (Das and Chandran, 2011). Enhanced bioremediation can accelerate the natural processes by which bacteria either degrade the gasoline constituents as a carbon source into less complex byproducts or complete oxidation or mineralization to CO 2 and H 2 O by providing electron acceptors and nutrients and increasing moisture (Wellman et al, 2012). Typically, for BTEX, aerobic degradation is the most rapid and complete process and is hence preferred in engineered bioremediation (Yadav and Hassanizadeh, 2011).…”

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confidence: 99%

In Situ Bioremediation of a Gasoline‐Contaminated Vadose Zone: Implications from Direct Observations

Moshkovich

Ronen

Gelman

et al. 2018

Vadose Zone Journal

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In situ bioremediation of a contaminated vadose zone requires implementing hydraulic and chemical conditions that stimulate the development of indigenous bacteria capable of degrading contaminants in the subsurface. We investigated enhanced biostimulation of a gasoline-contaminated deep vadose zone through nutrient-and O 2 -amended water infiltration. A vadose zone monitoring system (VMS) provided real-time observations of the treatment process's effect on hydrocarbon attenuation. The VMS data included continuous measurements of variations in water content, concentrations and isotopic compositions of methyl tert-butyl ether and benzene, toluene, ethylbenzene, and xylene in pore-water and gas phases, and concentrations of O 2 and CO 2 in the vadose zone gas phase. Real-time observations from the unsaturated zone enabled interactive adjustment of the remediation strategy and improved biostimulation conditions for biodegradation of the target compounds. In the course of three infiltration events that included infiltration of an O 2 -and nutrient-enriched water solution, a significant reduction in contaminant mass was observed across the unsaturated zone.Abbreviations: BTEX, benzene, toluene, ethylbenzene, and xylene; CSIA, compound-specific isotope analysis; MTBE, methyl tert-butyl ether; NAPL, nonaqueous-phase liquid; VMS, vadose zone monitoring system; VOC, volatile organic compound.Vadose zone pollution by contaminants originating from gasoline is a widespread problem due to frequently occurring surface spills and leaks from underground gasoline storage tanks. When released into the subsurface, nonaqueous-phase liquids (NAPLs) migrate downward through the unsaturated zone, sometimes reaching the groundwater (Moran et al., 2005). Volatile organic compound (VOC) fractions of the gasoline, such as benzene, toluene, ethylbenzene, and xylene (BTEX) and methyl tert-butyl ether (MTBE), are potentially toxic or carcinogenic and can seriously affect water quality (Varjani et al., 2017).Demands to remediate polluted sites highlight the need to develop a variety of treatment techniques with minimal cost and without causing further environmental disturbance (Jørgensen, 2007). Bioremediation has been found to be a more reliable, lower cost, and less intrusive method than other conventional treatments (Yadav and Hassanizadeh, 2011), especially for the unsaturated zone (Das and Chandran, 2011). Enhanced bioremediation can accelerate the natural processes by which bacteria either degrade the gasoline constituents as a carbon source into less complex byproducts or complete oxidation or mineralization to CO 2 and H 2 O by providing electron acceptors and nutrients and increasing moisture (Wellman et al., 2012). Typically, for BTEX, aerobic degradation is the most rapid and complete process and is hence preferred in engineered bioremediation (Yadav and Hassanizadeh, 2011). Bioventing, infiltration, and O 2 -releasing compounds are the most common ways to deliver O 2 to the unsaturated zone (Machackova et al., 2012;Suthersan et al....

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Assessment of calcium addition on the removal of U(VI) in the alkaline conditions created by NH3 gas

Katsenovich

Cardona

Szecsody

et al. 2018

Applied Geochemistry

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Contaminants in Vadose Zone Environments

Cited by 4 publications

References 18 publications

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

In Situ Bioremediation of a Gasoline‐Contaminated Vadose Zone: Implications from Direct Observations

Assessment of calcium addition on the removal of U(VI) in the alkaline conditions created by NH3 gas

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