Three-Dimensional Modeling of DNAPL in the Subsurface of the 216-Z-9 Trench at the Hanford Site

Oostrom, Mart; Rockhold, Mark; Thorne, Paul D.; Truex, Michael J.

doi:10.2172/15020955

Cited by 11 publications

(44 citation statements)

References 33 publications

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“…The simulations of SVE showed similar results to what has been previously reported in Oostrom et al (2004 and2006) in that the model appears to predict extraction of more CT by SVE than has been observed in the field. There are several possible reasons for the discrepancy between observed and simulated results, including uncertainties in flow rates, fluid-media properties, and disposal history (e.g., volumes, rates, and timing).…”

Section: Results Of Soil Vapor Extraction Simulationssupporting

confidence: 86%

“…The simulations results reported herein generally support the conclusions reported by Oostrom et al (2004;2006).…”

Section: Conceptual Model Implicationssupporting

confidence: 90%

“…This assessment indicates that it is likely that DNAPL CT has entered the groundwater. The simulation ix results herein and in Oostrom et al (2004;2006) show that the most likely location of significant DNAPL movement across the water table is below the 216-Z-9 site. …”

mentioning

confidence: 72%

“…Simulation results from the 216-Z-1A and 216-Z-18 modeling effort herein and from Oostrom et al (2004 and2006) were also compared to available field data. Key conclusions from this comparison are listed below.…”

Section: VIIImentioning

confidence: 99%

“…6. The phase distribution of CT changes over time due to volatilization, interaction of gas-phase CT with pore water and aqueous-phase CT with sorbed phase, DNAPL dissolution in groundwater, and the impact of soil vapor extraction.Simulation results from the 216-Z-1A and 216-Z-18 modeling effort herein and from Oostrom et al (2004 and2006) were also compared to available field data. Key conclusions from this comparison are listed below.…”

mentioning

confidence: 99%

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Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-18 Crib and 216-Z-1A Tile Field at the Hanford Site: Multifluid Flow Simulations and Conceptual Model Update

Oostrom¹,

Rockhold²,

Thorne³

et al. 2006

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Three-dimensional modeling was conducted with layered models to further develop the conceptual model of CT distribution in the vertical and lateral direction beneath the 216-Z-1A tile field and 216-Z-18 cribs and to investigate the effects of soil vapor extraction (SVE). Base case and sensitivity analysis simulations considered migration of dense, nonaqueous phase liquid (DNAPL) consisting of CT and co-disposed organics in the subsurface beneath the two disposal sites as a function of the properties and distribution of subsurface sediments and of the properties and disposal history of the waste. Simulations of CT migration were conducted using the Subsurface Transport Over Multiple Phases (STOMP) simulator.Simulation results support a conceptual model for CT distribution where CT in the DNAPL phase is expected to have migrated primarily in a vertical direction below the disposal trench. None of the simulations predicted that CT in the DNAPL phase would move across the water table below the 216-Z-18 site. Movement of CT in the DNAPL phase across the water table below the 216-Z-1A site was only predicted in simulations with smaller disposal areas and larger volumes, compared to the base case simulation, and in isotropic porous media. Because uncertainties in disposal area and volume exist, movement of CT in the DNAPL phase across the water table in the subsurface below the 216-Z-1A site should be considered as a possibility. However, even if DNAPL moved across the water table in the past, there may not currently be a DNAPL phase in the groundwater beneath the 216-Z-1A site because of dissolution. Results also show that the Hanford 1a geologic unit, located just beneath the 216-Z-1A and 216-Z18 disposal areas, retains more CT DNAPL within the vadose zone during infiltration and redistribution than other hydrologic units. During simulated SVE operations, CT in this unit remained in the subsurface while DNAPL in other layers was effectively removed. Additional characterization of the Hanford 1a unit below the two disposal sites would provide valuable information about the quantity of DNAPL phase CT remaining in the vadose zone. A significant amount of the disposed CT DNAPL may have partitioned to the vapor phase and subsequently into water and sorbed phases. As for the 216-Z-9 site, it is predicted that any continued migration of CT from the vadose zone to the groundwater is likely to occur through interaction of vapor phase CT with the groundwater and not through continued DNAPL migration. The results indicated that SVE appears to be an effective technology for vadose zone remediation, but additional effort is needed to improve simulation of the SVE process through an enhanced understanding of rate-limited volatilization. A total of 34 three-dimensional simulations have been conducted based on a layered EarthVision™ geologic model, which is an interpretation of available geologic data. These simulations consist of one base case simulation and 33 sensitivity analysis simulations. These simulations examined the infilt...

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Section: Results Of Soil Vapor Extraction Simulationssupporting

confidence: 86%

“…The simulations results reported herein generally support the conclusions reported by Oostrom et al (2004;2006).…”

Section: Conceptual Model Implicationssupporting

confidence: 90%

mentioning

confidence: 72%

Section: VIIImentioning

confidence: 99%

mentioning

confidence: 99%

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Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-18 Crib and 216-Z-1A Tile Field at the Hanford Site: Multifluid Flow Simulations and Conceptual Model Update

Oostrom¹,

Rockhold²,

Thorne³

et al. 2006

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Saturation‐Dependent Hydraulic Conductivity Anisotropy for Multifluid Systems in Porous Media

Zhang

Oostrom

Ward

2007

Vadose Zone Journal

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The hydraulic conductivity of unsaturated anisotropic soils has recently been described with a tensorial connectivity–tortuosity (TCT) concept. We extend this concept to unsaturated porous media with two or three immiscible fluids. Mathematical expressions to describe the conductivity of each fluid in anisotropic porous media under unsaturated condition are derived in the form of symmetric second order tensors. The theory is applicable to the generalized hydraulic conductivity model and compatible types of saturation–pressure formulation. The extended model shows that the anisotropic coefficient of any one of the fluids is independent of the saturation of other fluids. Synthetic Miller‐similar soils generated to be anisotropic were defined by allowing the saturated hydraulic conductivity to have different correlation ranges for different directions of flow. The extended TCT concept was tested using synthetic soils with four levels of heterogeneity and four levels of anisotropy. Numerical experiments of infiltration of two liquid phases, water and the nonaqueous phase liquid (NAPL) carbon tetrachloride, were performed to test the extended model. The results show that, similar to water in a two‐fluid (air–water) system, NAPL retention curves in a three‐fluid (air–NAPL–water) system were independent of flow direction but dependent on soil heterogeneity, whereas the connectivity–tortuosity coefficients are functions of both soil heterogeneity and anisotropy. The extended TCT model accurately describes unsaturated hydraulic functions of anisotropic soils and can be combined into commonly used relative permeability functions for use in multifluid flow and transport numerical simulations.

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Carbon Tetrachloride Flow and Transport in the Subsurface of the 216‐Z‐9 Trench at the Hanford Site

Oostrom

Rockhold

Thorne

et al. 2007

Vadose Zone Journal

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As a result of past practices, up to 580 m3 carbon tetrachloride (CT) was discharged to waste sites at the 200 West Area of the USDOE's Hanford Site near Richland, WA. Three‐dimensional modeling was conducted to enhance the current conceptual model of CT distribution beneath the major disposal site (216‐Z‐9). The simulations, using the STOMP code, focused on migration of dense nonaqueous phase liquid (DNAPL) consisting of CT and codisposed organics under scenarios with differing sediment properties, sediment distribution, waste properties, and waste disposal history. Simulation results support a conceptual model for CT distribution where CT in the DNAPL phase migrated primarily in a vertical direction below the disposal site and where some CT DNAPL likely migrated across the water table into the regional aquifer. Results also show that the lower permeability Cold Creek unit retained more CT DNAPL within the vadose zone than other hydrologic units during the infiltration and redistribution process. Due to the relatively high vapor pressure of the CT, the resulting vapor plumes are extensive and influenced by density‐driven advection. Any continued migration of CT from the vadose zone to the groundwater is likely through interaction of vapor phase CT with the groundwater and not through continued DNAPL migration. Additional simulations assessed the impacts of soil vapor extraction (SVE) as a remediation method. These simulations showed rapid CT removal associated with the assumed local equilibrium of CT between the phases. Additional efforts are needed to enhance the understanding of rate‐limited volatilization to improve simulation of the SVE process and to provide a basis for refining the design and operation of SVE systems.

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Three-Dimensional Modeling of DNAPL in the Subsurface of the 216-Z-9 Trench at the Hanford Site

Cited by 11 publications

References 33 publications

Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-18 Crib and 216-Z-1A Tile Field at the Hanford Site: Multifluid Flow Simulations and Conceptual Model Update

Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-18 Crib and 216-Z-1A Tile Field at the Hanford Site: Multifluid Flow Simulations and Conceptual Model Update

Saturation‐Dependent Hydraulic Conductivity Anisotropy for Multifluid Systems in Porous Media

Carbon Tetrachloride Flow and Transport in the Subsurface of the 216‐Z‐9 Trench at the Hanford Site

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