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

了解污染物的运移是地下水资源管理和补救策略实施的基础。特别是，饱和多孔介质中的混合过程在决定化学物质在地下释放的命运和运输方面起着关键作用。事实上，在受污染的含水层中，许多非生物和生物反应受到反应伙伴可用性的限制。在稳态流动和输运条件下，溶解的反应物只通过横向混合接触。在均匀多孔介质中，横向混合是由扩散和孔尺度分散决定的，而在非均匀地层中，这些局部混合过程得到加强。最近的研究研究了二维系统中由于非均质性的存在而增强的横向混合。在这里，混合增强只能归因于高渗透率包裹体内部的流动聚焦。在提出的工作中，我们将使用高分辨率实验室实验和先进的建模技术来研究三维的混合过程。本研究的目的是定量评估水力导电性的三维非均质性和各向异性如何通过(i)流动聚焦和去聚焦，（ii）羽流表面的增加，（iii）流线的扭曲和缠结，以及（iv）溶质在运输过程中的化合物特异性扩散/色散特性来影响混合过程。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，这些参数有助于在现场尺度上正确描述保守和反应性混合，从而解释现场观测、实验尺度实验和当前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.