Effects of compound-specific transverse mixing on steady-state reactive plumes: Insights from pore-scale simulations and Darcy-scale experiments

Hochstetler, David L.; Rolle, Massimo; Chiogna, Gabriele; Haberer, Christina M.; Grathwohl, Peter; Kitanidis, Peter K.

doi:10.1016/j.advwatres.2012.12.007

Cited by 62 publications

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“…his parameterization of D T , inspired by an earlier statistical model of Bear and Bachmat (1967), takes into account the inluence of aqueous difusion not only on the pore difusion but also on the mechanical dispersion term: where Pe = vd/D aq is the dimensionless grain Péclet number with d [L] representing the grain diameter, d (dimensionless) is the ratio between the length of a pore channel and its hydraulic radius, and b (dimensionless) is an exponent accounting for incomplete dilution of the solute in the pore channels. Average values of d = 6.2 and b = 0.5 were determined experimentally considering a wide range of low-through conditions in diferent porous media and were found in good agreement with the outcomes of pore-scale simulations Hochstetler et al, 2013).…”

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confidence: 72%

Diffusive–Dispersive and Reactive Fronts in Porous Media: Iron(II) Oxidation at the Unsaturated–Saturated Interface

Haberer

Muniruzzaman

Grathwohl

et al. 2015

Vadose Zone Journal

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Impact StatementUsing a combined experimental and modeling approach we investigate the coupling between diffusive/dispersive processes and kinetic iron(II) oxidation in batch, 1-D column, and 2-D flow-through systems. 2 Abstract 1Diffusive/dispersive mass transfer is important for many groundwater quality problems as it drives the 2 interaction between different reactants, thus influencing a wide variety of biogeochemical processes. In 3 this study we performed laboratory experiments to quantify oxygen transport in porous media, across the 4 unsaturated/saturated interface, under both conservative and reactive transport conditions. As reactive 5 system we considered the abiotic oxidation of ferrous iron in the presence of oxygen. We studied the 6 reaction kinetics in batch experiments and its coupling with diffusive and dispersive transport processes 7 by means of 1-D columns and 2-D flow-through experiments, respectively. A non-invasive optode 8 technique was used to track oxygen transport into the initially anoxic porous media at highly resolved 9 spatial and temporal scales. The results show significant differences in the propagation of the conservative 10 and reactive oxygen fronts. Under reactive conditions oxygen, continuously provided from the 11 atmosphere, was considerably retarded due to the interaction with dissolved iron(II), initially present in 12 the anoxic groundwater. The reaction between dissolved oxygen and ferrous iron led to the formation of 13 an iron(III) precipitation zone in the experiments. Reactive transport modeling based on a kinetic 14 PHREEQC module tested in controlled batch experiments allowed a quantitative interpretation of the 15 experimental results in both 1-D and 2-D setups. 16 Keywords: diffusion; transverse dispersion; unsaturated/saturated interface; iron(II) oxidation; porous media. 18In natural systems, the geochemical and biological activity at the interface between different 19 compartments, such as the unsaturated and the saturated zone in the subsurface, is determined by the 20 fluxes and exchange rates across the interface. Interface regions are highly active in terms of 21 physicochemical and microbiological processes (e.g., Sobolev and Roden, 2001; Bauer et al., 2009; Jost et 22 al., 2014). A number of experimental and modeling studies have identified diffusive and dispersive 23 processes as key mechanisms for mass transfer of volatile compounds to or from groundwater systems 24 (e.g., Barber and Davis, 1987; Barber et al., 1990; McCarthy and Johnson, 1993; Klenk and Grathwohl, 25 2002;Werner and Höhener, 2002;Prommer et al., 2009; Haberer et al., 2011 Haberer et al., , 2012 Freitas et al., 2011). 26 3Of particular importance is the mass transfer of oxygen to anoxic groundwater since dissolved oxygen 27 plays a key role for many biogeochemical processes. The supply of oxygen influences the subsurface 28 redox conditions and the rates of many biological and geochemical reactions (e.g., Stumm and Morgan, 29 1996; Chapelle, 2001; Mächler et al., 2013; Re...

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confidence: 72%

Diffusive–Dispersive and Reactive Fronts in Porous Media: Iron(II) Oxidation at the Unsaturated–Saturated Interface

Haberer

Muniruzzaman

Grathwohl

et al. 2015

Vadose Zone Journal

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“…Due to the small spatial scale at which mixing occurs, resolving steep concentration gradients at the field scale remains challenging despite the rapid development of improved monitoring techniques [e.g., Annable et al ., ; Anneser et al ., ; Devlin et al ., ]. Therefore, laboratory experiments [e.g., Castro‐Alcala et al ., ; de Anna et al ., ; Haberer et al ., ; Rolle et al ., ] and numerical simulations at multiple scales [e.g., de Dreuzy et al ., ; Herrera and Valocchi , ; Hochstetler et al ., ; Porta et al ., ; Rolle et al ., ; Tartakovsky et al ., ] are fundamental for the understanding of dilution in porous media. Most of these studies, however, focused on (quasi) two‐dimensional systems, while detailed experimental and modeling investigations in three‐dimensional domains are less common [e.g., Herrera et al ., ; Rashidi et al ., ; Silliman , ; Yoon and McKenna , ; Cirpka et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Enhancement of plume dilution in two‐dimensional and three‐dimensional porous media by flow focusing in high‐permeability inclusions

Chiogna

Cirpka

et al. 2015

Water Resources Research

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In porous media, lateral mass exchange exerts a significant influence on the dilution of solute plumes in quasi steady state. This process is one of the main mechanisms controlling transport of continuously emitted conservative tracers in groundwater and is fundamental for the understanding of many degradation processes. We investigate the effects of high-permeability inclusions on transverse mixing in threedimensional versus two-dimensional systems by experimental, theoretical, and numerical analyses. Our results show that mixing enhancement strongly depends on the system dimensionality and on the parameterization used to model transverse dispersion. In particular, no enhancement of transverse mixing would occur in three-dimensional media if the local transverse dispersion coefficient was uniform and flow focusing in both transverse directions was identical, which is fundamentally different from the two-dimensional case. However, the velocity and grain size dependence of the transverse dispersion coefficient and the correlation between hydraulic conductivity and grain size lead to prevailing mixing enhancement within the inclusions, regardless of dimensionality. We perform steady state bench-scale experiments with multiple tracers in three-dimensional and quasi two-dimensional flow-through systems at two different velocities (1 and 5 m/d). We quantify transverse mixing by the flux-related dilution index and compare the experimental results with model simulations. The experiments confirm that, although dilution is larger in threedimensional systems, the enhancement of transverse mixing due to flow focusing is less effective than in two-dimensional systems. The spatial arrangement of the high-permeability inclusions significantly affects the degree of mixing enhancement. We also observe more pronounced compound-specific effects in the dilution of solute plumes in three-dimensional porous media than in two-dimensional ones.

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“…2, insert). A similar constant shape behavior has been noted for viscous fingering in heterogeneous velocity fields (Jha et al, 2011a, b).…”

Section: Mixingmentioning

confidence: 53%

On the validity of effective formulations for transport through heterogeneous porous media

Dreuzy

Carrera

2016

Hydrol. Earth Syst. Sci.

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Abstract. Geological heterogeneity enhances spreading of solutes and causes transport to be anomalous (i.e., nonFickian), with much less mixing than suggested by dispersion. This implies that modeling transport requires adopting either stochastic approaches that model heterogeneity explicitly or effective transport formulations that acknowledge the effects of heterogeneity. A number of such formulations have been developed and tested as upscaled representations of enhanced spreading. However, their ability to represent mixing has not been formally tested, which is required for proper reproduction of chemical reactions and which motivates our work. We propose that, for an effective transport formulation to be considered a valid representation of transport through heterogeneous porous media (HPM), it should honor mean advection, mixing and spreading. It should also be flexible enough to be applicable to real problems. We test the capacity of the multi-rate mass transfer (MRMT) model to reproduce mixing observed in HPM, as represented by the classical multi-Gaussian log-permeability field with a Gaussian correlation pattern. Non-dispersive mixing comes from heterogeneity structures in the concentration fields that are not captured by macrodispersion. These fine structures limit mixing initially, but eventually enhance it. Numerical results show that, relative to HPM, MRMT models display a much stronger memory of initial conditions on mixing than on dispersion because of the sensitivity of the mixing state to the actual values of concentration. Because MRMT does not restitute the local concentration structures, it induces smaller non-dispersive mixing than HPM. However long-lived trapping in the immobile zones may sustain the deviation from dispersive mixing over much longer times. While spreading can be well captured by MRMT models, in general nondispersive mixing cannot.

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Effects of compound-specific transverse mixing on steady-state reactive plumes: Insights from pore-scale simulations and Darcy-scale experiments

Cited by 62 publications

References 32 publications

Diffusive–Dispersive and Reactive Fronts in Porous Media: Iron(II) Oxidation at the Unsaturated–Saturated Interface

Diffusive–Dispersive and Reactive Fronts in Porous Media: Iron(II) Oxidation at the Unsaturated–Saturated Interface

Enhancement of plume dilution in two‐dimensional and three‐dimensional porous media by flow focusing in high‐permeability inclusions

On the validity of effective formulations for transport through heterogeneous porous media

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