CAREER: Predicting Transport, Mixing, and Reaction in Three-dimensional Heterogeneous Fractured Media Across Scales

全球约99%的未冻结淡水储存在地下水系统中，地球上约75%的近地表含水层破裂。最近的实地研究表明，地下水中存在新出现的污染物，如微塑料、病毒和有害细菌，而裂缝往往是污染物以异常快的速度长距离迁移的主要途径。然而，传统的地下水模型忽略了裂隙流，因此往往无法预测污染物在地下的运移。为了确保可持续的水资源，迫切需要一种新的模型来预测裂隙介质中的流动和传输。这个项目提出了一个综合的研究、教育和推广计划，将推进目前对裂隙介质建模和教授裂隙岩石水文地质学的实践。该项目将首先将可视化实验室实验和直接数值模拟相结合，以阐明支配单个裂缝尺度上的流动和传输的基本物理规律。然后，确定的关键单裂缝规模过程将被纳入现场规模模型。最后，开发的模型将通过在裂隙含水层现场的现场实验进行验证。该项目有三项与拟议研究直接协同的主要外联和教学活动：(I)将成立一个专业的水文地质学家工作组，以弥合学术界、产业界和政府机构在裂隙岩石水文地质领域的差距；(Ii)将为K-12和大学教育开发可视化的地下水教学工具；以及(Iii)将为一门新的城市实地课程开发基于受污染的裂隙含水层场地的可访问模块。最近的研究表明，复杂的三维(3D)流动可以改变整个混合和反应动力学，甚至可以达到场尺度，但潜在的过程以及它们如何在裂缝网络中放大仍然不太清楚。该项目将建立对单裂缝尺度上三维流动对传输、混合和反应(TMR)影响的机理理解，并将这些知识跨尺度转化为预测裂缝网络尺度上的过程。该项目首先将可视化实验室实验和直接数值模拟相结合，以阐明裂缝非均质性(例如裂缝粗糙度和孔径变异性)和流动边界条件(雷诺数)之间的相互作用如何在单个裂缝尺度上控制3D流动和TMR。然后，单裂缝尺度过程将被合并到裂缝网络尺度模型中，并将开发预测TMR的扩展模型框架。将生成一个全面的数据集，并使用基于机器学习的方法进行分析，以产生一个强大的地图，将放大的模型参数与关键介质属性和流动条件联系起来。开发的放大模型将通过在裂隙含水层现场进行受控现场示踪实验来验证。总体而言，该项目将改变我们理解和模拟裂隙介质的方式，并将为模拟生物地球化学和流体流动提供新的基础。这项建议由地球科学部的水文科学和教育与人力资源计划共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

About 99% of global unfrozen freshwater is stored in groundwater systems, and about 75% of near-surface groundwater aquifers on earth are fractured. Recent field studies have shown the presence of emerging contaminants such as microplastics, viruses, and harmful bacteria in groundwater, and fractures are often major pathways through which contaminants migrate long distances at anomalously fast rates. However, conventional groundwater models ignore fracture flow, and as a result, often fail to predict contaminant transport in the subsurface. To secure sustainable water resources, there is urgent need for a new model that predicts flow and transport in fractured media. This project presents an integrated research, education, and outreach plan that will advance the current practices of modeling fractured media and teaching fractured rock hydrogeology. This project will first combine visual laboratory experiments and direct numerical simulations to elucidate fundamental physical laws that govern flow and transport at single fracture scales. The identified key single-fracture scale processes will then be incorporated into field-scale models. Finally, the developed models will be validated through field experiments at a fractured aquifer site. The project has three major outreach and teaching activities that are directly synergistic with the proposed research: (i) a professional hydrogeologists’ working group will be formed to bridge the gap between academia, industry, and government agencies in the area of fractured rock hydrogeology, (ii) visual groundwater teaching tools will be developed for K-12 and college-level education, and lastly (iii) accessible modules based on a contaminated fractured aquifer site will be developed for a new urban field course.Conventional groundwater models often treat aquifers as two-dimensional continuous porous media, thereby missing critical complexities that govern flow and transport in fractured aquifers. Recent studies have shown that complex three-dimensional (3D) flows can alter the overall mixing and reaction dynamics up to the field scale, but the underlying processes and how they scale up in fracture networks are still not well understood. This project will establish a mechanistic understanding of 3D flow effects on Transport, Mixing, and Reaction (TMR) at single-fracture scales and translate that knowledge across scales to predict processes at fracture network scales. This project first combines visual laboratory experiments and direct numerical simulations to elucidate how the interplay between fracture heterogeneity (e.g., fracture roughness and aperture variability) and flow boundary conditions (Reynolds number) controls 3D flows and TMR at single fracture scales. The single-fracture scale processes will then be incorporated into fracture network-scale models, and an upscaled modeling framework that predicts TMR will be developed. A comprehensive data set will be generated and analyzed with machine-learning-based methods to yield a powerful map that links upscaled model parameters to key medium properties and flow conditions. The developed upscaled model will be validated through controlled field tracer experiments at a fractured aquifer site. Overall, this project will transform how we understand and model fractured media and will provide a new foundation for modeling coupled biogeochemistry and fluid flow.This proposal is co-funded by the Hydrologic Sciences and Education and Human Resources programs in the Division of Earth Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.