Stochastic Analysis of Reactive Transport Processes in Heterogeneous Porous Media

Author(s):  
Thomas Harter
2021 ◽  
Author(s):  
Xavier Sanchez-Vila

<p>The more we study flow and transport processes in porous media, the larger the number of questions that arise. Heterogeneity, uncertainty, multidisciplinarity, and interdisciplinarity are key words that make our live as researchers miserable… and interesting. There are many ways of facing complexity; this is equivalent as deciding what colors and textures to consider when being placed in front of a fresh canvas, or what are the sounds to include and combine in a music production. You can try to get as much as you can from one discipline, using very sophisticated state-of-the-art models. On the other hand, you can choose to bring to any given problem a number of disciplines, maybe having to sacrifice deepness in exchange of the better good of yet still sophisticated multifaceted solutions. There are quite a number of examples of the latter approach. In this talk, I will present a few of those, eventually concentrating in managed aquifer recharge (MAR) practices. This technology involves water resources from a myriad of perspectives, covering from climate change to legislation, from social awareness to reactive transport, from toxicological issues to biofilm formation, from circular economy to emerging compounds, from research to pure technological developments, and more. All of these elements deserve our attention as researchers, and we cannot pretend to master all of them. Integration, development of large research groups, open science are words that will appear in this talk. So does mathematics, and physics, and geochemistry, and organic chemistry, and biology. In any given hydrogeological problem you might need to combine equations, statistics, experiments, field work, and modeling; expect all of them in this talk. As groundwater complexity keeps amazing and mesmerizing me, do not expect solutions being provided, just anticipate more and more challenging research questions being asked.</p>


Author(s):  
Yoram Rubin

Many of the principles guiding stochastic analysis of flow and transport processes in the vadose zone are those which we also employ in the saturated zone, and which we have explored in earlier chapters. However, there are important considerations and simplifications to be made, given the nature of the flow and of the governing equations, which we explore here and in chapter 12. The governing equation for water flow in variably saturated porous media at the smallest scale where Darcy’s law is applicable (i.e., no need for upscaling of parameters) is Richards’ equation (cf. Yeh, 1998)


2020 ◽  
Author(s):  
Maria Prieto Espinoza ◽  
Sylvain Weill ◽  
Raphaël Di chiara ◽  
Benjamin Belfort ◽  
François Lehmann ◽  
...  

<p>Reactive transport in porous media involves a complex interplay of multiple processes relative to flow of water and gases, transport of elements, chemical reactions and microbial activities. In surface-groundwater interfaces, the role of the capillary fringe is of particular interest as water table variations can strongly impact the transfer of gases (e.g. oxygen), the evolution of redox conditions and the evolution/adaptation of bacterial/microbial populations that control biodegradation pathways of contaminants. Although the understanding of individual processes is advanced, their interactions are not yet fully understood challenging the development of efficient reactive transport models (RTM) for predictive applications. In this context, the combination of microbial approaches with isotope measurements and modelling may be useful to understand reactive transport of halogenated pollutants in hydrogeological dynamic systems, to improve processes representation in RTMs, and to reduce model equifinality. Dichloromethane (DCM) is a toxic and volatile halogenated compound frequently detected in multi-contaminated aquifers. Although mechanisms of DCM microbial degradation under both aerobic and anaerobic conditions have been described, little is known about the relationships between the hydrogeochemical variations caused by water table fluctuations, as well as their effects on the diversity and distribution of bacterial communities and degradation pathways.<br>            In this study, two laboratory aquifers fed by contaminated groundwater from the industrial site Thermeroil (France) were designed to collect water samples at high-resolution to investigate the reactive transport of DCM in porous media under steady and dynamic hydrogeological conditions. The effect of water table variations on hydrochemical, microbial and isotopic composition (δ<sup>13</sup>C and δ<sup>37</sup>Cl) was examined to derive DCM mass removal and potential changes in degradation pathways. For the latter, Compound-Stable Isotope Analysis (CSIA) has been used as a tool to evaluate natural degradation of halogenated hydrocarbons. A RTM model (CubicM) is currently being developed to include dual-element CSIA and biological processes - such as growth, decay, attachment, detachment or dormancy – and relate changes in redox conditions with the evolution of DCM degrading populations. A two-phase flow model (i.e. water and gas) has been developed to account for the volatilization and the associated transport processes of halogenated volatile compounds in porous media. Currently, the model is tested on the experimental results to assist in the interpretation of DCM dissipation and the observed biogeochemical and microbial processes to determine the best-suited formalism to address the effect of water table fluctuations on DCM reactive transport in porous media. Such model will enable to assess natural attenuation of DCM at contaminated sites accounting for dynamic hydrogeological conditions.</p>


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