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.
J Hazard Mater. 2022 Sep 5;437:129410. doi: 10.1016/j.jhazmat.2022.129410. Epub 2022 Jun 18.
Aquitards contaminated by chlorinated solvents may act as a secondary source slowly releasing contaminants into adjacent aquifers, thus severely hampering the remediation of groundwater systems. Accurate predicting the long-term exchange of solvents between aquifers and aquitards can more effectively guide site management and remediation. This study presented a general analytical model for the back-diffusion of chlorinated solvents through multilayer aquitards. This model considers the slow advection and local degradation of dissolved constituents in natural aquitards and the dynamic depletion of dense nonaqueous phase liquid (DNAPL) source zone in aquifers. Transient solutions for the proposed multilayer model were derived using Duhamel's Theorem, the separation of variables method, and the transfer matrix method, verified against experimental and numerical concentration data. Results reveal that advection in aquitards can significantly shorten the trailing time of chlorinated solvent plumes, and highly adsorptive soils may reduce this effect in layered aquitards. The previous no-degradation model is no longer applicable to predict the back-diffusion behavior of chlorinated solvents when the extent and rate of solvent degradation are large, giving a "strong-effect zone". Based on numerous example simulations and data fitting, the forecast functions for the back-diffusion onset time and plume trailing time were proposed, greatly facilitating remediation decisions and risk assessment of chlorinated-solvent contaminated sites.
受氯化溶剂污染的弱透水层可能会成为一个二次污染源，将污染物缓慢释放到相邻含水层中，从而严重阻碍地下水系统的修复。准确预测含水层和弱透水层之间溶剂的长期交换情况，能够更有效地指导场地管理和修复工作。本研究提出了一个用于氯化溶剂通过多层弱透水层反向扩散的通用分析模型。该模型考虑了天然弱透水层中溶解成分的缓慢平流和局部降解，以及含水层中致密非水相液体（DNAPL）源区的动态消耗。利用杜哈梅定理、变量分离法和传递矩阵法推导了所提出的多层模型的瞬态解，并根据实验和数值浓度数据进行了验证。结果表明，弱透水层中的平流可显著缩短氯化溶剂羽流的拖尾时间，而高吸附性土壤可能会降低分层弱透水层中的这种影响。当溶剂降解的程度和速率较大时，即出现“强效应区”，之前的无降解模型不再适用于预测氯化溶剂的反向扩散行为。基于大量的示例模拟和数据拟合，提出了反向扩散起始时间和羽流拖尾时间的预测函数，极大地促进了氯化溶剂污染场地的修复决策和风险评估。
