Steady-State Dilution and Mixing-Controlled Reactions in Three-Dimensional Heterogeneous Porous

了解污染物的迁移是地下水资源管理和实施补救战略的基础。特别是，饱和多孔介质中的混合过程在确定地下释放的化学品的命运和运输方面发挥着关键作用。事实上，受污染含水层中的许多非生物和生物反应受到反应伙伴的限制。在稳态流动和输送条件下，溶解的反应物仅通过横向混合接触。在均质多孔介质中，横向混合由扩散和孔隙尺度弥散决定，而在非均质地层中，这些局部混合过程得到增强。最近的研究调查的横向混合的增强，由于在二维系统中的非均匀性的存在。在这里，混合增强可以完全归因于高渗透性夹杂物内的流动集中。在拟议的工作中，我们将使用高分辨率实验室实验室规模实验和先进的建模技术来研究三维混合过程。拟议的研究的目的是定量评估3-D的异质性和各向异性的水力传导性如何影响混合过程，通过（一）流聚焦和散焦，（二）增加羽流表面，（三）扭曲和缠绕的流线和（四）化合物特定的扩散/分散性能的溶质物种进行运输。实验和建模研究的结果将使我们能够确定有效的大尺度参数，用于正确描述保守和反应混合在现场尺度允许解释现场观测，实验室规模的实验和当前的随机理论之间的差异。

Understanding transport of contaminants is fundamental for the management of groundwater re-sources and the implementation of remedial strategies. In particular, mixing processes in saturated porous media play a pivotal role in determining the fate and transport of chemicals released in the subsurface. In fact, many abiotic and biological reactions in contaminated aquifers are limited by the availability of reaction partners. Under steady-state flow and transport conditions, dissolved reactants come into contact only through transverse mixing. In homogeneous porous media, transverse mixing is determined by diffusion and pore-scale dispersion, while in heterogeneous formations these local mixing processes are enhanced. Recent studies investigated the enhancement of transverse mixing due to the presence of heterogeneities in two-dimensional systems. Here, mixing enhancement can solely be attributed to flow focusing within high-permeability inclusions. In the proposed work, we will investigate mixing processes in three dimensions using high-resolution laboratory bench-scale exper-iments and advanced modeling techniques. The objective of the proposed research is to quantitatively assess how 3-D heterogeneity and anisotropy of hydraulic conductivity affect mixing processes via (i) flow focusing and de-focusing, (ii) increase of the plume surface, (iii) twisting and intertwining of streamlines and (iv) compound-specific diffusive/dispersive properties of the solute species undergoing transport. The results of the experimental and modeling investigation will allow us to identify effective large-scale parameters useful for a correct description of conservative and reactive mixing at field scales allowing to explain discrepancies between field observations, bench-scale experiments and current stochastic theory.