Colloid-Filtration Theory for Vadose-Zone Systems

0409174 Saiers需要掌握胶体颗粒通过包气带的运输过程的知识，以预测土壤中吸附污染物的运动，评估病原微生物进入饮用水含水层的风险，并估计土壤光照和土壤剖面发展的时间尺度。气-水和固-水界面上的胶体沉积对包气带中胶体的输运速率和孔隙水浓度起着重要的控制作用。尽管胶体侵入带过程的重要性，一个理论适用于预测胶体沉积在不饱和多孔介质中不存在。本研究的重点是采取措施，填补这一知识空白，通过定义，以定量的方式，胶体沉积动力学之间的基本关系，在空气-水和固体-水界面和土壤-水-胶体系统的物理性质。这些关系将通过分析一套孔隙尺度模拟水流和对流扩散胶体运输通过部分饱和空隙空间。现代模型的空气-水配置在饱和多孔介质中将被用来指定的孔隙水域的几何形状，胶体传输的孔隙尺度模拟将进行。回归分析的结果的流动和transportsimulations预计将产生幂律方程，表示与空气-水和固体-水界面的流体流速，colloidsize和密度，多孔介质的纹理，和毛细管压力（控制水饱和度）的函数colloidcollision率。除了需要考虑空气相的存在外，所提出的推导胶体界面碰撞速率幂律方程的方法在概念上类似于已发表的水饱和多孔介质胶体过滤方程的方法。用幂律方程预测胶体沉积动力学将与实验室柱实验中胶体沉积的测量结果相一致。在这些实验中，讨论了胶体沉积速率对胶体直径、粒径、粒径分布、孔隙水流速等变化的敏感性，通过对沉积速率的实测值和预测值的比较，揭示了新理论的不足，并有助于指导新理论的完善。输运过程在部分饱和的地质材料和大大提高我们的理解的关键质量转移反应，影响孔隙水浓度的胶体内包气带。这一拟议中的研究代表了第一次尝试推导和测试胶体过滤理论forunsaturated多孔介质，需要作出定量推断colloidmobility在包气带。这样的理论应作出重要贡献towardsolving关键的水质问题的国家关注的是有关的运动ofmicrobial病原体和胶体相关的污染物通过近地表环境。

0409174SaiersKnowledge of processes that govern the transport of colloid-sized particles through thevadose zone is required to predict the movement of sorbing contaminants within soils, to assessthe risks associated with the entry of pathogenic microbes into drinking-water aquifers, and toestimate the time scales for soil illuviation and soil-profile development. Colloid deposition atair-water and solid-water interfaces plays an important role in controlling the transport rates andporewater concentrations of colloids in the vadose zone. Despite the importance of colloids invadose-zone processes, a theory suitable for predicting colloid deposition in unsaturated porousmedia does not exist.The focus of this proposed research is to take steps towards filling this gap in knowledgeby defining, in a quantitative way, the fundamental relationships between colloid-depositionkinetics at air-water and solid-water interfaces and the physical properties of the soil-water-colloidsystem. These relationships will be derived through analysis of a suite of pore-scalesimulations of water flow and advective-diffusive colloid transport through partially saturatedvoid spaces. Modern models for air-water configuration in variably saturated porous media willbe used to specify the geometry of the porewater domains for which the pore-scale simulationsof colloid transport will be conducted. Regression analysis of the results of the flow-and-transportsimulations is expected to yield power-law equations that express the rate of colloidcollisions with air-water and solid-water interfaces as functions of fluid-flow velocity, colloidsize and density, porous-medium texture, and capillary pressure (which controls watersaturation). Except for the need to account for the presence of the air phase, the proposedapproach for deriving the power-law equations for colloid-interface collision rates isconceptually similar to published approaches used to formulate the colloid-filtration equationsfor water-saturated porous media.Predictions of colloid-deposition kinetics made with the power-law equations will becompared with measurements of colloid deposition made in laboratory column experiments. Inthese experiments, the sensitivity of colloid-deposition rates to variations in colloid diameter,grain-size, grain-size distribution, porewater velocity, and capillary pressure will be examined.Comparison of measured and predicted deposition rates will reveal deficiencies in the newtheory and help direct its refinement.Findings from this study will advance current knowledge of mass-transport processes inpartially saturated geologic materials and substantially improve our understanding of key mass-transferreactions that affect porewater concentrations of colloids within the vadose zone. Thisproposed research represents a first attempt at deriving and testing a colloid-filtration theory forunsaturated porous media that is needed to make quantitative inferences regarding colloidmobility in the vadose zone. Such a theory should make an important contribution towardsaddressing critical water-quality issues of national concern that are related to the movement ofmicrobial pathogens and colloid-associated contaminants through near-surface environments.