Geological Survey of Finland, Vuorimiehentie 5, PO Box 96, 02151 Espoo, Finland; Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 115, 2800 Kgs. Lyngby, Denmark.
Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 115, 2800 Kgs. Lyngby, Denmark.
J Contam Hydrol. 2021 Feb;237:103754. doi: 10.1016/j.jconhyd.2020.103754. Epub 2020 Dec 17.
Low-permeability aquitards can significantly affect the transport, distribution, and persistence of contaminant plumes in subsurface systems. Although such low-permeability materials are often charged, the key role of charge-induced electrostatic processes during contaminant transport has not been extensively studied. This work presents a detailed investigation exploring the coupled effects of heterogeneous distribution of physical, chemical and electrostatic properties on reactive contaminant transport in field-scale groundwater systems including spatially distributed clay zones. We performed an extensive series of numerical experiments in three distinct heterogeneous sandy-clayey domains with different levels of complexity. The flow and reactive transport simulations were performed by explicitly resolving the complex velocity fields, the small-scale electrostatic processes, the compound-specific diffusive/dispersive fluxes and the chemical processes utilizing a multi-continua based reactive transport code (MMIT-Clay). In each particular domain, numerical experiments were performed focusing on both the forward and back diffusion through the sandy-clayey interfaces. The results illuminate the control of microscopic electrostatic mechanisms on macroscopic mass transfer. Coulombic interactions in the clay's diffuse layer can significantly accelerate or retard a particular species depending on its charge. Furthermore, the chemical heterogeneity plays a major role in mass storage and release during reactive transport. Neglecting such processes can lead to substantial over- or underestimation of the overall transport behavior, which underlines the need for integrated physical, chemical and electrostatic approaches to accurately describe mass transfer processes in systems including low-permeability inclusions.
低渗透性含水层在很大程度上影响了污染物羽流在地下系统中的运移、分布和持久性。尽管这些低渗透性物质通常带有电荷，但电荷诱导的静电过程在污染物运移中的关键作用尚未得到广泛研究。本工作详细研究了物理、化学和静电特性的非均质性分布对包括空间分布的粘土层在内的现场尺度地下水系统中反应性污染物运移的耦合影响。我们在三个具有不同复杂程度的不同非均质砂-粘土地域中进行了广泛的数值实验系列。通过显式解析复杂的速度场、小规模的静电过程、特定化合物的扩散/弥散通量以及利用多连续体基反应传输代码（MMIT-Clay）的化学过程，进行了流动和反应传输模拟。在每个特定的区域中，进行了数值实验，重点研究了通过砂-粘土地层界面的前向和反向扩散。结果揭示了微观静电机制对宏观传质的控制。粘土扩散层中的库仑相互作用可以根据其电荷显著加速或延迟特定物质。此外，化学非均质性在反应传输过程中的质量储存和释放中起着重要作用。忽略这些过程可能会导致对整体传输行为的过度或低估，这突显了需要采用综合的物理、化学和静电方法来准确描述包括低渗透性夹杂物在内的系统中的质量传递过程。
