RUI: Measurement and Microtomographic Imaging of the Air-Water Interface in Unsaturated Porous Media

清楚地了解渗透带的特征和影响流体和溶质通过渗透带运移的过程对地下水资源的保护、风险评估和补救至关重要。影响污染物在气包带中迁移的许多基本特征和过程已经得到了很好的研究；然而，空气-水界面（AWI）在气包带中的重要作用直到最近才被认识到。AWI被认为(a)影响流体的输送和分配；(b)控制溶质的平衡保留，包括化学品、病原体和非生物胶体；(c)介导动力学传质过程，如水溶液溶解和挥发。具体来说，空气-水界面面积（AI）的大小对于这些过程的任何定量描述都是至关重要的。尽管这一点至关重要，但人们对AWI最基本的特性却知之甚少。关于多孔介质物理性质的影响以及促进界面形成的个别过程（例如吸附和毛细作用），人们知之甚少。这个提议的多面项目将填补我们目前对渗透层系统中AWI的理解中的几个基本空白。具体来说，这个项目的目标是：1。使用三种互补的AI测量方法评估界面微观形貌对AI的影响。使用创新的同步加速器x射线微断层扫描（uCT）三维成像，量化AI、表面积、含水饱和度（Sw）和颗粒形状之间的关系。使用uCT量化单个毛细管和吸附对AI的贡献，作为表面积、Sw和颗粒形状的函数。用于实现这些目标的方法包括使用uCT和气相和水相界面示踪剂测量AI。uCT是一种尖端的极高分辨率三维成像技术，直到最近才被应用于多孔介质中人工智能的测量，并显示出非凡的前景。界面示踪测试依赖于已建立的实验室土柱混相位移技术，并已被证明可以提供合理的人工智能估计。更广泛的影响拟议的项目将为本科生提供跨学科科学训练的绝佳机会。具体来说，它将为学生提供使用最先进的同步加速器x射线设备的机会，定制设计，建造和使用实验室实验系统，并使用复杂的软件来分析视觉和数值数据。在PI在明德学院的第一年，两名学生与PI一起前往阿贡国家实验室的先进光子源（APS）进行uCT实验，并处理了图像并提取了人工智能值。重要的是，他们在APS的经历提高了他们对项目的热情，增加了他们应对新的科学挑战和与其他专业科学家互动的信心。这两名学生作为共同作者被包括在AGU的海报上（2006年12月），并在随后的两篇手稿中发表。每年将继续招收3名本科生。NSF-RUI奖将使米德尔伯里学院的学生和PI继续在协作跨学科环境科学研究方面取得卓越成就。

Intellectual MeritA clear understanding of vadose-zone characteristics and processes that influence fluid and solute transport through the vadose zone is critically important to the protection of groundwater resources, risk assessment, and remediation. Many of the fundamental characteristics and processes that influence contaminant transport in the vadose zone have been well studied; however, the important role the air-water interface (AWI) plays in the vadose zone has only recently been appreciated. The AWI is recognized to (a) influence fluid transport and distribution; (b) govern equilibrium retention of solutes, including chemicals, pathogens, and abiotic colloids; and (c) mediate kinetic mass-transfer processes, such as aqueous dissolution and volatilization. Specifically, the magnitude of the air-water interfacial area (AI) is critical to any quantitative description of these processes. Despite this critical importance, even the most basic features of the AWI are poorly understood. Little is known regarding the influence of physical properties of porous media and about the individual processes that promote interface formation (e.g., adsorption and capillarity). This proposed multi-faceted project will fill several fundamental gaps in our current understanding of the AWI in vadose zone systems. Specifically, the objectives of this project are to 1. Evaluate the influence of interfacial micromorphology on AI using three complimentary AI-measurement methods.2. Quantify relationships among AI, surface area, water saturation (Sw), and grain shape using innovative synchrotron X-ray microtomography (uCT) three-dimensional imaging.3. Quantify individual capillary and adsorption contributions to AI as a function of surface area, Sw, and grain shape using uCT.The methods used to achieve these objectives include measurement of AI using uCT and both gas- and aqueous-phase interfacial tracers. uCT, a cutting-edge extremely high-resolution 3-dimensional imaging technique, has only recently been applied to measurement of AI in porous media and shows exceptional promise. Interfacial tracer tests rely on established laboratory soil column miscible displacement techniques and have been shown to provide reasonable AI estimates.Broader ImpactThe proposed project will offer undergraduate students superb opportunities for interdisciplinary scientific training. Specifically, it will provide opportunities for students to use state-of-the-art synchrotron X-ray facilities, to custom-design, build, and use laboratory experimental systems, and to use sophisticated software to analyze visual and numerical data. In the PI's first year at Middlebury College, two students traveled with the PI to Argonne National Laboratory's Advanced Photon Source (APS) to conduct uCT experiments and have processed the images and extracted AI values. Importantly, their experience at APS has heightened their enthusiasm for the project and increased their confidence in addressing new scientific challenges and interacting with other professional scientists. These two students are included as coauthors on a poster to be presented at AGU (December 2006) and on two manuscripts anticipated to follow. Inclusion of 3 undergraduates per year will continue in the proposed work. An NSF-RUI award will enable Middlebury College students and the PI to continue on a path of excellence in collaborative interdisciplinary environmental science research.