Ding Xiang-Hong, Feng Shi-Jin
Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China.
Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China; Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, Shanghai 200092, China.
Water Res. 2023 Jun 30;238:120021. doi: 10.1016/j.watres.2023.120021. Epub 2023 May 1.
Low-permeability aquitards may serve as secondary sources of slow-releasing contaminants into the adjacent aquifer system, creating considerable obstacles to groundwater cleanup. Accurately capturing the exchange of contaminant mass between aquitards and aquifers can facilitate site management and remediation. Previous simulation studies were mainly limited to one-dimensional (1D) back diffusion from aquitards during the remediation of the source zone. In this study, a novel two-dimensional (2D) back-diffusion model is developed to investigate the storage and release of contaminants in aquitards after source isolation. This model coupled the dynamical decay of isolated sources and the diffusion-sorption process of contaminants in the layered aquitards. Exact analytical solutions for the present 2D multilayer model were derived using the finite cosine transform, Duhamel Theorem, separation of variables, and transfer matrix method. Results indicated that the previous 1D model would overestimate the contaminant concentration in the aquitard and the back-diffusion risk when the source zone was isolated. The proposed 2D back-diffusion model enables quantitative prediction of how source zone width, source concentration, and aquitard heterogeneity impact plume trailing time, thus aiding in understanding the mechanisms of aquifer contamination beyond barrier-controlled source zones.
低渗透性隔水层可能成为向相邻含水层系统缓慢释放污染物的二次源，给地下水净化带来巨大障碍。准确掌握隔水层与含水层之间污染物质量的交换情况有助于场地管理与修复。以往的模拟研究主要局限于源区修复过程中隔水层的一维反向扩散。在本研究中，开发了一种新颖的二维反向扩散模型，以研究源区隔离后污染物在隔水层中的储存与释放。该模型耦合了孤立源的动态衰减以及污染物在层状隔水层中的扩散吸附过程。利用有限余弦变换、杜哈梅定理、变量分离和传递矩阵法推导出了当前二维多层模型的精确解析解。结果表明，当源区被隔离时，先前的一维模型会高估隔水层中的污染物浓度和反向扩散风险。所提出的二维反向扩散模型能够定量预测源区宽度、源浓度和隔水层非均质性如何影响羽流拖尾时间，从而有助于理解屏障控制源区以外的含水层污染机制。
