Assessing long-term impacts of chlorinated hydrocarbons to freshwater aquifers due to diffusive transport and reactions within clayey aquitards

由于其广泛的工业用途，氯代烃是加拿大和世界各地最丰富的地下水污染物之一。它们以稠密非水相液体(DNAPL)的形式在地表释放后，由于其高密度和低粘度，会迅速垂直运移到地下。在饱和带输送过程中，DNAPL在低渗透层顶部形成油气藏。随着时间的推移，累积的DNAPL通过含水层中的平流和扩散进入下面的低渗透单元。在含水层中羽流强度降低后，低渗透性沉积物发生反向扩散，形成邻近淡水含水层的长期污染源。*影响低渗透沉积物中氯代烃的物理和反应过程尚未完全了解。然而，识别和区分影响低渗透带中氯代烃的相关过程对于估计由于反向扩散而在邻近含水层中的羽流持久性具有重要意义。这项研究计划旨在清楚地了解影响饱和低渗透沉积物中氯代烃的所有物理和反应过程，并评估它们对邻近淡水含水层中因反扩散而长期存在的羽流的影响。这项研究将在三个地点进行，使用先进的高分辨率实地方法，结合新的分析方法以及分析和数值模拟。在两个正在进行的研究中，有两个地点正在进行控释实验，这是我在15年前发起的(位于安大略省萨尼亚和阿利斯顿附近)。这些位置是独一无二的，因为可以在受控条件下调查物理和反应过程，因为污染的初始条件(泄漏时间、体积、成分)是众所周知的。此外，获得的数据集可以与以前的研究进行比较，为了解受控条件下低渗透沉积物中物理和反应过程的时间分辨率提供了无与伦比的机会。第三个地点(靠近美国南卡罗来纳州佛罗伦萨市)提供了一个真实世界的场景，其中混合有机污染物存在于较长的一段时间内(50年)。这项研究将改善预测由于反向扩散导致的羽流持续时间尺度的前景，从而为补救相关的场地管理决策提供更好的基础。

Due to their widespread industrial usage, chlorinated hydrocarbons are among the most abundant groundwater contaminants across Canada and worldwide. After their release at the surface as dense non-aqueous phase liquids (DNAPLs), rapid vertical migration into the subsurface occurs due to their high density and low viscosity. During transport in the saturated zone, DNAPLs form pools on top of low permeability layers. With time, accumulated DNAPLs are transported by advection in the aquifer and by diffusion into the underlying low permeable units. After reduction of plume strength in the aquifer, back-diffusion occurs from the low permeability sediments that form a long-term contamination source for adjacent freshwater aquifers. ******Physical and reactive processes affecting chlorinated hydrocarbons in low permeability sediments are not yet fully understood. However, the identification and distinction of relevant processes affecting chlorinated hydrocarbons in low permeability zones is of major importance for estimating plume persistence in adjacent aquifers due to back-diffusion. This research program aims to gain a clear understanding of all physical and reactive processes affecting chlorinated hydrocarbons in saturated low permeability sediments and to assess their impact on long-term plume persistence in adjacent freshwater aquifers due to back-diffusion. The research will be conducted at three sites using advanced high-resolution field methods combined with new analytical methods as well as analytical and numerical modelling. Controlled release experiments are in progress at two sites in ongoing studies, which I initiated more than 15 years ago (near Sarnia and Alliston, ON). These sites are unique because physical and reactive processes can be investigated under controlled conditions, as the initial conditions of the contamination (spill time, volume, composition) are well known. Furthermore, the datasets obtained can be compared with previous investigations, offering the incomparable opportunity to gain understanding of the temporal resolution of physical and reactive processes in low permeability sediments under controlled conditions. The third site (near the city of Florence, SC, USA) offers a real-world scenario with mixed organic contaminants present over a longer time period (50 years). This research will improve prospects for predicting the time scales over which plume persistence due to back-diffusion occurs, and thereby provide an improved basis for remedial related site management decisions.