Geochemical Characterization of Chromate Contamination in the 100 Area Vadose Zone at the Hanford Site - Part 2

Qafoku, Nikolla P.; Dresel, P. Evan; McKinley, James P.; Ilton, Eugene S.; Um, Wooyong; Resch, Charles T.; Kukkadapu, Ravi; Petersen, Scott W.

doi:10.2172/1004807

Cited by 3 publications

(3 citation statements)

References 18 publications

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“…Thus, leaching tends to be less efficient under unsaturated conditions as only the grain surfaces of larger pores are in contact with infiltrating water. This is a similar conclusion to those found in previous studies for leaching of Cr (Qafoku et al 2011) and uranium (Szecsody et al 2012a, 2012b).…”

Section: Resultssupporting

confidence: 93%

“…These experiments consisted of infiltration of AGW or other liquid amendments into a 9.5‐ to 10‐feet (2.9‐ to 3.3‐m) high by 1‐inch inner diameter column filled with Cr‐contaminated and uncontaminated Hanford formation sediments (Figure S1). Characterization studies have shown that at field scale, Cr contamination typically occurs at a specific depth interval and the remainder of the 80‐ to 100‐feet‐deep vadose zone is not Cr contaminated (Qafoku et al 2011). To approximate these conditions, the lowest 1.0 foot of the sediment column was packed with Cr‐contaminated sediment and the remaining 8.5 to 9 feet of the column was filled with uncontaminated sediment.…”

Section: Methodsmentioning

confidence: 99%

“…Significant aqueous Cr removal has been also reported when highly basic saline waste fluids interact with the sediments (Qafoku et al 2003). The mineral dissolution that occurs under either acidic or alkaline conditions may have triggered the release of Fe(II) from the Fe(II)-bearing minerals, which subsequently reduces aqueous Cr(VI) (Qafoku et al 2003(Qafoku et al , 2010(Qafoku et al , 2011. Other studies have shown that under acidic conditions, Fe(II) in phyllosilicates (Szecsody et al 2013) and Fe oxides (Dong et al 2003) can also reduce aqueous Cr(VI).…”

Section: Introductionmentioning

confidence: 99%

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Vadose Zone Soil Flushing for Chromium Remediation: A Laboratory Investigation to Support Field‐scale Application

Szecsody¹,

Emerson²,

Lawter³

et al. 2023

Groundwater Monitoring Rem

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Cr(VI) flushing from the vadose zone to the groundwater (with subsequent Cr(VI) removal in groundwater by pump‐and‐treat system) is a promising remedial technique that has recently been used at field scale. This laboratory study was conducted to provide the technical basis to design a field soil flushing strategy. The objectives were to (1) quantify the relationship between sediment Cr(VI) and Cr(III) mass and release rates and subsequent Cr(VI) leaching; (2) investigate different methodologies to maximize Cr(VI) leaching, and (3) investigate methods to minimize leaching of remaining residual Cr. Characterization of Cr‐contaminated sediments (Hanford Site, WA) exhibited Cr(VI) showed that leach rates that were correlated to different Cr surface phases. Sediments with low leachable Cr(VI) (<2 μg/g) leached Cr rapidly, so slow infiltration of water in a single pulse was sufficient to leach most Cr. In contrast, sediments with high Cr (2 to 200 μg/g) released some Cr(VI) quickly but 10 to 50% Cr(VI) slowly (tens to hundreds of hours). Efficient unsaturated leaching of these sediments required a different infiltration strategy that includes: multiple slow leach pulses with time between flushing cycles; the use of a surfactant to increase Cr leaching from low‐permeability zones, and the use of a reductant (Na‐dithionite or Ca‐polysulfide) in the final leach water was highly effective at decreasing residual Cr leaching. This study clearly demonstrated that the methodology of basing laboratory Cr flushing on parameters such as Cr release mass and rates could be used to improve the efficiency of soil flushing at field scale.

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Section: Resultssupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Vadose Zone Soil Flushing for Chromium Remediation: A Laboratory Investigation to Support Field‐scale Application

Szecsody¹,

Emerson²,

Lawter³

et al. 2023

Groundwater Monitoring Rem

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Silicon concentration and pH controls over competitive or simultaneous incorporation of iodate and chromate into calcium carbonate phases

Katsenovich

Gort

Gudavalli

et al. 2021

Applied Geochemistry

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Foam Transport in Porous Media - A Review

Zhang¹,

Freedman²,

Zhong³

2009

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Executive SummaryAmendment solutions with or without surfactants have been used to remove contaminants from soil. However, they have drawbacks in that amendment solutions often mobilize the plume, and its movement is controlled by gravity and preferential flow paths. Foam is an emulsion-like, two-phase system in which gas cells are dispersed in a liquid and separated by thin liquid films called lamellae. The potential advantages of using foams in sub-surface remediation include providing better control on the volume of fluids injected, uniformity of contact, and the ability to contain the migration of contaminant-laden liquids. It is expected that foam can serve as a carrier of amendments for vadose zone remediation, e.g., at the Hanford Site. As part of the U.S. Department of Energy's EM-20 program, a numerical simulation capability will be added to the Subsurface Transport Over Multiple Phases (STOMP) flow simulator. The primary purpose of this document is to review the modeling approaches of foam transport in porous media. However, as an aid to understanding the simulation approaches, some experiments under unsaturated conditions and the processes of foam transport are also reviewed.Foam may be formed when the surfactant concentration is above the critical micelle concentration. There are two main types of foams -ball foam (microfoam) and polyhedral foam. The characteristics of bulk foam are described by properties such as foam quality, texture, stability, density, surface tension, disjoining pressure, etc. Foam has been used to flush contaminants such as metals, organics, and nonaqueous phase liquids from unsaturated soil. Ball foam, or colloidal gas aphrons, reportedly have been used for soil flushing in contaminated site remediation and was found to be more efficient than surfactant solutions on the basis of weight of contaminant removed per gram of surfactant. Experiments also indicate that the polyhedral foam can be used to enhance soil remediation.The transport of foam in porous media is complicated in that the number of lamellae present governs flow characteristics such as viscosity, relative permeability, fluid distribution, and interactions between fluids. Hence, foam is a non-Newtonian fluid. During transport, foam destruction and formation occur. The net result of the two processes determines the foam texture (i.e., bubble density). Some of the foam may be trapped during transport. According to the impacts of the aqueous and gas flow rates, foam flow generally has two regimes -weak and strong foam. There is also a minimum pressure gradient to initiate foam flow and a critical capillary for foam to be sustained. Similar to other fluids, the transport of foam is described by Darcy's law with the exception that the foam viscosity is variable.Three major approaches to modeling foam transport in porous media are the empirical, semi-empirical, and mechanistic methods. Mechanistic approaches can be complete in principle but may be difficult for obtaining reliable parameters, whereas empirical and semi-emp...

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Geochemical Characterization of Chromate Contamination in the 100 Area Vadose Zone at the Hanford Site - Part 2

Cited by 3 publications

References 18 publications

Vadose Zone Soil Flushing for Chromium Remediation: A Laboratory Investigation to Support Field‐scale Application

Vadose Zone Soil Flushing for Chromium Remediation: A Laboratory Investigation to Support Field‐scale Application

Silicon concentration and pH controls over competitive or simultaneous incorporation of iodate and chromate into calcium carbonate phases

Foam Transport in Porous Media - A Review

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