Colloid Mobilization and Transport in the Vadose Zone: New Observations and Modeling Approaches

胶体（微观的水性颗粒）通过非饱和土壤的预测方法是不可用的。因此，不可能评估胶体大小的污染物通过渗透带进入饮用水含水层的风险，也不可能为旨在将这些风险降至最低的管理决策提供信息。我们的工作旨在解决这些缺陷。具体而言，我们（PI，博士后和博士生）将：(1)测量瞬态流动过程中入渗速率和土壤质地对渗流带土壤胶体运移的影响；(2)阐明了渗流带土壤中胶体流动性对胶体大小、组成和孔隙水化学变化的响应；(3)建立适合于定量地质介质中瞬态非饱和流体中胶体动员和运移的数学模型。我们的工作将从矿物胶体在真实渗流带土壤中的运动的实验室实验开始。本实验部分将包括柱实验，旨在阐明在土壤吸胀和排水过程中，胶体的动员、运输和沉积对土壤质地、孔隙水离子强度和胶体本身的物理化学性质变化的敏感性。柱实验将辅以孔隙尺度的可视化实验，揭示柱实验中检测的物理化学条件下胶体动员和保留的主要机制。这些实验还将阐明在瞬态流动中发生的空气-水结构的变化，这可能会导致胶体的释放。可视化实验将与柱实验一起用于指导瞬态孔隙水流动、胶体输运和胶体传质耦合模型的开发。该模型将基于非饱和多孔介质中空气-水结构的现代概念，并将近似于多种机制对胶体动员的影响，而不是将动员视为没有物理基础的集中过程。到项目结束时，将建立一个综合评估模型，适用于非饱和土壤中胶体迁移率的推断。这项研究的总体结果应该引起水文学家、土壤科学家、水生化学家和对两相流现象、工程纳米颗粒在地质环境中的命运和运输、土壤形成过程、病原体和胶体结合污染物通过非饱和土壤向地下水位的传播感兴趣的工程师的注意。

Predictive approaches for the transport of colloids (microscopic, waterborne particles) through unsaturated soils are unavailable. Consequently, it is impossible to evaluate the risks associated with the transmission of colloid-sized contaminants through the vadose zone and into drinking-water aquifers or to inform management decisions intended to minimize these risks. Our work is aimed at addressing these deficiencies. In particular, we (the PI, a postdoctoral associate, and a Ph.D. student) will: (1) measure the effects of infiltration rate and soil texture on colloid transport through vadose-zone soils during transient flow;(2) elucidate the responses of colloid mobility within vadose-zone soils to changes in colloid size and composition and pore-water chemistry; and(3) develop a mathematical model that is suitable for quantifying colloid mobilization and transport during transient, unsaturated flow through geologic media.Our work will begin with laboratory experiments on the movement of mineral colloids through real vadose-zone soils. This laboratory component will involve column experiments designed to illuminate the sensitivity of colloid mobilization, transport, and deposition during soil imbibition and drainage to changes in soil texture, pore-water ionic strength, and the physicochemical properties of the colloids themselves. The column experiments will be supplemented by pore-scale visualization experiments that will reveal the principal mechanisms of colloid mobilization and retention under the physicochemical conditions examined in the column experiments. These experiments will also elucidate the changes in air-water configuration that occur during transient flow and that presumably drive colloid release. The visualization experiments, together with the column experiments, will be used to guide the development of a model for coupled transient porewater flow, colloid transport, and colloid mass transfer. This model will be based on modern conceptualizations of air-water configuration within unsaturated porous media and will approximate the effects of multiple mechanisms on colloid mobilization, rather than treating mobilization as a lumped process without a physical basis. By the end of the project period, a comprehensively evaluated model will be created that is suitable for making inferences on colloid mobility within unsaturated soils. The overall findings from this research should gain the attention of hydrologists, soil scientists, aquatic chemists, and engineers interested in two-phase flow phenomena, the fate and transport of engineered nanoparticles in geologic environments, soil formation processes, and the transmission of pathogens and colloid bound pollutants through unsaturated soils and towards the water table.