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

胶体(微观的、含水的颗粒)在非饱和土壤中传输的预测方法是不可用的。因此，不可能评估胶体污染物通过包气带进入饮用水含水层的风险，也不可能为旨在最大限度减少这些风险的管理决定提供信息。我们的工作旨在解决这些不足之处。特别是，我们(PI，博士后助理和博士生)将：(1)测量渗入率和土壤质地对瞬变渗流过程中包气带土壤中胶体运移的影响；(2)阐明包气带土壤中胶体运移对胶体大小和组成以及孔隙水化学变化的响应；以及(3)建立一个数学模型，适合于量化在瞬变、非饱和渗流过程中胶体在地质介质中的迁移和运移。我们的工作将从实验室实验开始，研究矿物胶体在实际包气带土壤中的运动。这一实验室部分将包括柱状实验，旨在阐明土壤吸胀和排水过程中胶体动员、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。柱实验将由孔尺度可视化实验补充，该实验将揭示在柱实验中检查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变流动过程中发生的空气-水结构的变化，以及可能驱动胶体释放的变化。可视化实验和柱状实验将被用于指导建立耦合瞬变孔隙水流动、胶体传输和胶体传质的模型。该模型将基于非饱和多孔介质中空气-水构型的现代概念化，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。到项目期结束时，将建立一个全面评估的模型，适用于对非饱和土壤中胶体运移的推断。这项研究的总体结果应该引起水文学家、土壤学家、水生化学家和工程师的注意，他们对两相流现象、工程纳米颗粒在地质环境中的去向和传输、土壤形成过程以及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输感兴趣。

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.