Enhancing Mixing During Groundwater Remediation via Engineered Injection‐Extraction: The Issue of Connectivity

Abstract

Most in situ groundwater remediation schemes are based on the injection of a treatment solution into the subsurface in order to promote reactions that remove or transform the contaminants into harmless products. For instance, the success of both bioremediation and in situ chemical oxidation is based on the mixing between contaminated groundwater and nutrients or oxidant agents, which can promote the occurrence of target reactions and facilitate pollution removal. These systems can be enhanced by favoring increased mixing, that is, by promoting mass transfer between the different solutions. The physical processes that boost mass transfer in porous media are mechanical dispersion and molecular diffusion (Tartakovsky, 2010). The former spreads a solute throughout the porous medium, increasing contact surface and concentration gradients, and the latter homogenizes it leading the solute to occupy a larger volume in the porous medium. However, these processes are typically slow in natural conditions, and thus are often unable to provide sufficient mixing-and hence degradation.Mixing in porous media has received much attention in the last few decades, largely because chemical reactions in the subsurface are often limited by mixing (

Dispersion Versus Diffusion in Mixing Fronts

“…The constant compression rate obtained locally in the considered non-uniform flow is analogous to chaotic flows, where a constant compression rate is sustained globally by repeated stretching and folding. This phenomenon is known to occur naturally at pores scale (Heyman et al, 2020;Lester et al, 2013Lester et al, , 2016Souzy et al, 2020) and can be created by engineered pumping and injection (Fernàndez-Garcia & Rodríguez-Escales, 2023;Mays & Neupauer, 2012;Neupauer et al, 2014;Trefry et al, 2012). The obtained scaling laws (Table 1) and impact of diffusion/dispersion are thus expected to be relevant for such chaotic flows.…”