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  • 1
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    Measurements and models of reactive transport in geological media (2016)
    Wiley
    Details
    Publication Date: 2016-08-24
    Description: Reactive chemical transport plays a key role in geological media, across scales from pores to an aquifer. Systems can be altered by changes in solution chemistry and a wide variety of chemical transformations, including precipitation/dissolution reactions that cause feedbacks that directly affect the flow and transport regime. The combination of these processes with advective-dispersive-diffusive transport in heterogeneous media leads to a rich spectrum of complex dynamics. The principal challenge in modeling reactive transport is to account for the subtle effects of fluctuations in the flow field and species concentrations; spatial or temporal averaging generally suppresses these effects. Moreover, it is critical to ground model conceptualizations and test model outputs against laboratory experiments and field measurements. This review emphasizes the integration of these aspects, considering carefully-designed and controlled experiments at both laboratory and field scales, in the context of development and solution of reactive transport models based on continuum-scale and particle tracking approaches. We first discuss laboratory experiments and field measurements that define the scope of the phenomena and provide data for model comparison. We continue by surveying models involving advection-dispersion-reaction equation and continuous time random walk formulations. The integration of measurements and models is then examined, considering a series of case studies in different frameworks. We delineate the underlying assumptions, and strengths and weaknesses, of these analyses, and the role of probabilistic effects. We also show the key importance of quantifying the spreading and mixing of reactive species, recognizing the role of small-scale physical and chemical fluctuations that control the initiation of reactions.
    Print ISSN: 8755-1209
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Integrodifferential formulations of the continuous-time random walk for solute transport subject to bimolecular A+B→0 reactions: From micro- to mesoscopic (2015)
    American Physical Society (APS)
    Details
    Publication Date: 2015-03-11
    Description: Author(s): Scott K. Hansen and Brian Berkowitz We develop continuous-time random walk (CTRW) equations governing the transport of two species that annihilate when in proximity to one another. In comparison with catalytic or spontaneous transformation reactions that have been previously considered in concert with CTRW, both species have spatially... [Phys. Rev. E 91, 032113] Published Tue Mar 10, 2015
    Keywords: Statistical Physics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 3
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    A new model for coupled multi-component NAPL dissolution and aqueous-phase transport, with application to creosote dissolution in discrete fractures (2013)
    Wiley
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    Publication Date: 2013-11-22
    Description: This paper concerns a new modeling approach to multicomponent NAPL dissolution and transport, based on analytic solutions and Laguerre series. This approach allows virtually any of the numerous existing 1D analytic transport solutions in the literature to be coupled with arbitrary boundary conditions stemming from nonlinear NAPL dissolution, as dictated by Raoult's Law. A computer implementation of this approach to coupled dissolution and transport in parallel fractures—which no other screening tool known to the authors covers—is presented. This is verified against an existing analytic transport solution that assumes a constant boundary condition. Subsequently, the model is demonstrated via a study of separation of PAH and phenolic plumes generated by dissolution of creosote, using the new computer implementation. The PAH and phenolic constituents of creosote strongly differ in both their dissolution and their transport behavior, and this is shown to necessitate the use of a tool that can account for both processes, such as the one developed here. We also find the possibility of PAH and phenolic plumes becoming entirely disjoint.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Push-pull tracer tests: Their information content and use for characterizing non-Fickian, mobile-immobile behavior (2016)
    Wiley
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    Publication Date: 2016-11-18
    Description: Path reversibility and radial symmetry are often assumed in push-pull tracer test analysis. In reality, heterogeneous flow fields mean that both assumptions are idealizations. To understand their impact, we perform a parametric study which quantifies the scattering effects of ambient flow, local-scale dispersion and velocity field heterogeneity on push-pull breakthrough curves and compares them to the effects of mobile-immobile mass transfer (MIMT) processes including sorption and diffusion into secondary porosity. We identify specific circumstances in which MIMT overwhelmingly determines the breakthrough curve, which may then be considered uninformative about drift and local-scale dispersion. Assuming path reversibility, we develop a continuous time random walk-based interpretation framework which is flow-field agnostic and well suited to quantifying MIMT. Adopting this perspective, we show that the radial flow assumption is often harmless: to the extent that solute paths are reversible, the breakthrough curve is uninformative about velocity field heterogeneity. Our interpretation method determines a mapping function (i.e. subordinator) from travel time in the absence of MIMT to travel time in its presence. A mathematical theory allowing this function to be directly “plugged into” an existing Laplace-domain transport model to incorporate MIMT is presented and demonstrated. Algorithms implementing the calibration are presented and applied to interpretation of data from a push-pull test performed in a heterogeneous environment. A successful four-parameter fit is obtained, of comparable fidelity to one obtained using a million-node 3D numerical model. Finally, we demonstrate analytically and numerically how push-pull tests quantifying MIMT are sensitive to remobilization, but not immobilization, kinetics. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Semi-analytic solution for transport of a two-member decay chain in discrete parallel fractures (2013)
    Wiley
    Details
    Publication Date: 2013-08-10
    Description: A wide variety of analytic solutions have been developed for 1D contaminant transport, but to date the author is aware of none modeling a decay chain in parallel discrete fractures in porous media. In this note, the derivation is presented for a two-species first-order decay chain in such an environment, with an arbitrary concentration history specified up-gradient, fracture advection, and diffusion into the porous matrix. The solution is presented in brief, followed by corroboration of its numerical implementation against two different existing numerical codes. An appendix contains a detailed derivation of the solution, and a Mathematica notebook that implements it and may be used by practitioners is enclosed as supplementary material.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Water, Vol. 11, Pages 1525: Exploring Compatibility of Sherwood-Gilland NAPL Dissolution Models with Micro-Scale Physics Using an Alternative Volume Averaging Approach (2019)
    MDPI
    In: Water
    Details
    Publication Date: 2019
    Description: The dynamics of NAPL dissolution into saturated porous media are typically modeled by the inclusion of a reaction term in the advection-dispersion-reaction equation (ADRE) with the reaction rate defined by a Sherwood-Gilland empirical model. This stipulates, among other things, that the dissolution rate is proportional to a power of the NAPL volume fraction, and also to the difference between the local average aqueous concentration of the NAPL species and its thermodynamic saturation concentration. Solute source models of these sorts are ad hoc and empirically calibrated but have come to see widespread use in contaminant hydrogeology. In parallel, a number of authors have employed the method of volume averaging to derive upscaled transport equations describing the same dissolution and transport phenomena. However, these solutions typically yield forms of equations that are seemingly incompatible with Sherwood-Gilland source models. In this paper, we revisit the compatibility of the two approaches using a radically simplified alternative volume averaging analysis. We begin from a classic micro-scale formulation of the NAPL dissolution problem but develop some new simplification approaches (including a physics-preserving transformation of the domain and a new geometric lemma) which allow us to avoid solving traditional closure boundary value problems. We arrive at a general, volume-averaged governing equation that does not reduce to the ADRE with a Sherwood-Gilland source but find that the two approaches do align under straightforward advection-dominated conditions.
    Electronic ISSN: 2073-4441
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by MDPI
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  • 7
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    Direct Breakthrough Curve Prediction from Statistics of Heterogeneous Conductivity Fields (2018)
    Wiley
    Details
    Publication Date: 2018-01-05
    Description: This paper presents a methodology to predict the shape of solute breakthrough curves in heterogeneous aquifers at early times and/or under high degrees of heterogeneity, both cases in which the classical macrodispersion theory may not be applicable. The methodology relies on the observation that breakthrough curves in heterogeneous media are generally well described by log-normal distributions, and mean breakthrough times can be predicted analytically. The log-variance of solute arrival is thus sufficient to completely specify the breakthrough curves, and this is calibrated as a function of aquifer heterogeneity and dimensionless distance from a source plane by means of Monte Carlo analysis and statistical regression. Using the ensemble of simulated groundwater flow and solute transport realizations employed to calibrate the predictive regression, reliability estimates for the prediction are also developed. Additional theoretical contributions include heuristics for the time until an effective macrodispersion coefficient becomes applicable, and also an expression for its magnitude that applies in highly heterogeneous systems. It is seen that the results here represent a way to derive continuous-time random walk transition distributions from physical considerations rather than from empirical field calibration.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Inferring subsurface heterogeneity from push-drift tracer tests (2017)
    Wiley
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    Publication Date: 2017-06-20
    Description: We consider the late-time tailing in a tracer test performed with a push-drift methodology (i.e., quasi-radial injection followed by drift under natural gradient). Numerical simulations of such tests are performed on 1000 multi-Gaussian 2D log-hydraulic conductivity field realizations of varying heterogeneity, each under eight distinct mean flow directions. The ensemble pdfs of solute return times are found to exhibit power law tails for each considered variance of the log-hydraulic conductivity field, . The tail exponent is found to relate straightforwardly to EQ and, within the parameter space we explored, to be independent of push-phase pumping rate, pumping duration, and local-scale dispersivity. We conjecture that individual push-drift tracer tests in wells with screened intervals much greater than the vertical correlation length of the aquifer will exhibit quasi-ergodicity and that their tail exponent may be used to infer EQ . We calibrate a predictive relationship of this sort from our Monte Carlo study, and apply it to data from a push-drift test performed at a site of approximately known heterogeneity—closely matching the existing best estimate of heterogeneity.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Direct Breakthrough Curve Prediction From Statistics of Heterogeneous Conductivity Fields (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-01-01
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by American Geophysical Union
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  • 10
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    Local Equilibrium and Retardation Revisited (2017)
    Wiley
    Details
    Publication Date: 2017-07-19
    Print ISSN: 0017-467X
    Electronic ISSN: 1745-6584
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Published by Wiley
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