Groundwater Reaeration and Hydrocarbon Plume Length: A Modeling Analysis

Neale, C. Nelson; Holder, Anthony W.; Ward, C. H.; Hughes, Joseph B.

doi:10.1061/(asce)0733-9372(2002)128:1(40)

Cited by 6 publications

(4 citation statements)

References 14 publications

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“…Including this term is an advantage of the UZF-RT3D model. On the basis of the results from Neale et al (2000Neale et al ( , 2002, the groundwater reaeration equation used in the reaction package accounts for soil type (in the form of porosityφ), water content θ , the thickness of the unsaturated zone z, and the difference between the saturation concentration of O 2 in groundwater,C O 2 (aq),sat , and the present O 2 concentration, C O 2 (aq) , and is given by (Neale et al 2002):…”

Section: Description Of Testing and Numerical Experimentsmentioning

confidence: 99%

“…Including this term is an advantage of the UZF‐RT3D model. On the basis of the results from Neale et al (2000, 2002), the groundwater reaeration equation used in the reaction package accounts for soil type (in the form of porosity φ ), water content θ , the thickness of the unsaturated zone z , and the difference between the saturation concentration of O 2 in groundwater,, and the present O 2 concentration, , and is given by (Neale et al 2002): where the diffusion coefficient of O 2 in porous media D s is a function of φ and θ (Millington and Quirk 1961): where D o is the diffusion coefficient of O 2 in air (L 2 /T), with values ranging from 1.52 to 1.99 m 2 /d, and θ a = φ − θ is the volumetric air content of the porous media in the unsaturated zone. Thickness z and θ a are updated at each time step, with θ a calculated using the average θ for the cells in the unsaturated zone.…”

Section: Description Of Testing and Numerical Experimentsmentioning

confidence: 99%

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Modeling Variably Saturated Multispecies Reactive Groundwater Solute Transport with MODFLOW‐UZF and RT3D

et al. 2012

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A numerical model was developed that is capable of simulating multispecies reactive solute transport in variably saturated porous media. This model consists of a modified version of the reactive transport model RT3D (Reactive Transport in 3 Dimensions) that is linked to the Unsaturated-Zone Flow (UZF1) package and MODFLOW. Referred to as UZF-RT3D, the model is tested against published analytical benchmarks as well as other published contaminant transport models, including HYDRUS-1D, VS2DT, and SUTRA, and the coupled flow and transport modeling system of CATHY and TRAN3D. Comparisons in one-dimensional, two-dimensional, and three-dimensional variably saturated systems are explored. While several test cases are included to verify the correct implementation of variably saturated transport in UZF-RT3D, other cases are included to demonstrate the usefulness of the code in terms of model run-time and handling the reaction kinetics of multiple interacting species in variably saturated subsurface systems. As UZF1 relies on a kinematic-wave approximation for unsaturated flow that neglects the diffusive terms in Richards equation, UZF-RT3D can be used for large-scale aquifer systems for which the UZF1 formulation is reasonable, that is, capillary-pressure gradients can be neglected and soil parameters can be treated as homogeneous. Decreased model run-time and the ability to include site-specific chemical species and chemical reactions make UZF-RT3D an attractive model for efficient simulation of multispecies reactive transport in variably saturated large-scale subsurface systems.

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Section: Description Of Testing and Numerical Experimentsmentioning

confidence: 99%

Section: Description Of Testing and Numerical Experimentsmentioning

confidence: 99%

Modeling Variably Saturated Multispecies Reactive Groundwater Solute Transport with MODFLOW‐UZF and RT3D

et al. 2012

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“…Once an anaerobic plume discharges from beneath a landfill, oxygen may begin to enter the groundwater due to diffusive mass transfer with the oxygen present in the unsaturated zone and recharge of oxygenated water. Recent modeling work has shown that diffusive mass transfer of oxygen can be very important and may limit the downgradient migration of aerobically degradable contaminants (41).…”

Section: Groundwater Quality Impacts Of Landfill Leachatementioning

confidence: 99%

Critical Evaluation of Factors Required To Terminate the Postclosure Monitoring Period at Solid Waste Landfills

Barlaz

Rooker

Kjeldsen

et al. 2002

Environ. Sci. Technol.

107

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Regulations governing the disposal of solid waste in landfills specify that they must be monitored for 30 years after closure unless this period is extended by the governing regulatory authority. Given the wide range of conditions under which refuse is buried, technical criteria, rather than a specific time period, are preferable for evaluation of when it is acceptable to terminate postclosure monitoring. The objectives of this paper are to identify and evaluate parameters that can be used to define the end of the postclosure monitoring period and to present a conceptual framework for an investigation of whether postclosure monitoring can be terminated at a landfill. Parameters evaluated include leachate composition and leachate and gas production. Estimates of leachate production from closed landfills are used to assess the potential environmental impacts of a hypothetical release to surface water or groundwater. The acceptability of gaseous releases should be evaluated against criteria for odors, the potential for subsurface migration, and greenhouse gas and ozone precursor emissions. The approach presented here must be tested on a site-specific basis to identify additional data requirements and regulatory activity that might be required to prepare regulators for the large number of requests to terminate postclosure monitoring expected over the next 20 years. An approach in which the frequency and extent of postclosure monitoring is reduced as warranted by site-specific data and impact analysis should provide an effective strategy to manage closed landfills.

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“…Gas transport in the unsaturated zone is an important environmental process. Geochemistry of groundwater is affected by fluxes across the water table of O 2 [ Neale et al ., ; Young et al ., ] and CO 2 [ Jurgens et al ., ], with consequences for regional water quality. Gas transport to the water table affects interpretations of residence times of groundwater based on tracers with known historical concentrations in the atmosphere [ Johnston et al ., ; Engesgaard et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Multimodel analysis of anisotropic diffusive tracer‐gas transport in a deep arid unsaturated zone

Green

Walvoord

Andraski

et al. 2015

Water Resources Research

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Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multimodel approach to analyze results of a gas-tracer (SF 6 ) test to clarify characteristics of gas transport in deep unsaturated alluvium. Thirty-five separate models with distinct diffusivity structures were calibrated to the tracertest data and were compared on the basis of Akaike Information Criteria estimates of posterior model probability. Models included analytical and numerical solutions. Analytical models provided estimates of bulkscale apparent diffusivities at the scale of tens of meters. Numerical models provided information on localscale diffusivities and feasible lithological features producing the observed tracer breakthrough curves. The combined approaches indicate significant anisotropy of bulk-scale diffusivity, likely associated with highdiffusivity layers. Both approaches indicated that diffusivities in some intervals were greater than expected from standard models relating porosity to diffusivity. High apparent diffusivities and anisotropic diffusivity structures were consistent with previous observations at the study site of rapid lateral transport and limited vertical spreading of gas-phase contaminants. Additional processes such as advective oscillations may be involved. These results indicate that gases in deep, layered unsaturated zone sediments can spread laterally more quickly, and produce higher peak concentrations, than predicted by homogeneous, isotropic diffusion models.

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Groundwater Reaeration and Hydrocarbon Plume Length: A Modeling Analysis

Cited by 6 publications

References 14 publications

Modeling Variably Saturated Multispecies Reactive Groundwater Solute Transport with MODFLOW‐UZF and RT3D

Modeling Variably Saturated Multispecies Reactive Groundwater Solute Transport with MODFLOW‐UZF and RT3D

Critical Evaluation of Factors Required To Terminate the Postclosure Monitoring Period at Solid Waste Landfills

Multimodel analysis of anisotropic diffusive tracer‐gas transport in a deep arid unsaturated zone

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