Collaborative Research: Unraveling Transport in Porous Media through the Integration of Isotopic Tracers, Geophysical Data, and Numerical Modeling

各种估计表明，与美国受污染的地下水相关的经济负担高达数千亿美元。这些地点中的每一个都对环境和人类健康构成了潜在威胁；近90%的传统法院规定的战略未能充分补救受污染的地点。在许多情况下，这些失败可归因于依赖于污染物运移的经典概念模型的补救策略，这些模型既不能充分反映地下的非均质性，也不能捕获优先流动和低渗透率的溶质圈闭。因此，将模型应用于实际问题仍然存在很大的不确定性。虽然存在许多不同的迁移模型，但对于给定的问题，了解哪一个是“最正确的”对于预测污染物迁移和反应以及场地清理是基本的。该项目将利用污染物运输、地球物理、元素和同位素地球化学以及混合驱动反应等领域的方法来满足这一需求。这项研究最终将大大改进修复设计战略，并改进对受污染的地下水场地造成的人类健康风险的评估。作为这项研究的一部分，将在科罗拉多州高中课程的基础上，与丹佛一所公立高中合作，开发新的高中化学实验室，重点关注酸碱化学、pH缓冲剂和金属地球化学。这些实验室将通过国家地球科学教师协会的“地球科学家”期刊传播到当地发展之外的地方。污染物运移预测的可靠性取决于数值/概念模型对现场地质学的适当性。主要问题是：(1)哪些物理可测量参数控制溶质传质和地球化学反应，(2)哪些参数可以先验预测，以及(3)哪些数学公式准确地描述了不同流速和非均质条件下的现场特定运移。现有的许多运移模型的主要局限性是模型中控制溶质运移的拟合参数与物理系统之间的联系较差。这项工作的目的是探索对现有物理传输模型预测能力较差的控制，特别是那些包括化学反应的模型。扩散诱导的元素分馏、扩散诱导的锂同位素分馏和地球物理特征将综合起来，以探索对溶质运移和反应的控制。虽然保守的示踪剂浓度过去一直被用来限制平流-弥散输送参数，但同位素示踪剂在扩散过程中发生分馏，因此可以在扩散主导离子输送的情况下提供关于固定孔隙空间的信息。这个项目的力量将是在溶质运移模型中对已知参数的控制增加显著的约束，确定它们对传输过程的控制，并量化在多孔介质中活跃的传输长度尺度的分布以及随后对反应动力学的影响。所产生的实验数据将用于验证水文界常用的现有理论(即“本地”输送与“非本地”输送)，并在必要时探索新数据推动的新理论，以发展对输送和反应行为的新认识。

Various estimates suggest that economic liabilities associated with contaminated groundwater sites in the U.S. run into the hundreds of billions of dollars. Each of these sites poses a potential threat to the environment and human health; nearly 90% of the conventional court-mandated strategies fail to remediate polluted sites adequately. In many cases, these failures can be attributed to remediation strategies that rely on classical conceptual models of contaminant transport, which neither represent subsurface heterogeneity sufficiently nor capture preferential flow and low permeability solute traps. As a result, the application of models to practical problems retains significant uncertainty. While many different models for transport exist, understanding which is "most correct" for a given problem is fundamental to the prediction of contaminant transport and reaction and site clean-up. This project will utilize methods from the fields of contaminant transport, geophysics, elemental and isotope geochemistry, and mixing-driven reactions to address this need. The research will ultimately enable significantly improved remediation design strategies and improved assessment of human health risk from contaminated groundwater sites. As part of this research, new high school chemistry labs will be developed following the Colorado high school curriculum focusing on acid-base chemistry, pH buffers, and metal geochemistry in collaboration with a Denver public high school. These labs will be disseminated beyond local development via the National Earth Science Teachers Association's "The Earth Scientist" Journal.The reliability of contaminant transport predictions depends on the appropriateness of the numerical/conceptual model to site geology. The primary questions are: (1) which physically measureable parameters control solute mass transfer and geochemical reactions, (2) which parameters can be predicted a priori, and (3) which mathematical formulations accurately describe site specific transport under varying flow rates and heterogeneity. The main limitation of many existing transport models is the poor connection between fitting parameters governing solute transport in models and the physical system. The objective of the work is to explore controls on the poor predictive ability of existing physical transport models, especially those that include chemical reaction. Diffusion-induced elemental fractionation, diffusion-induced lithium isotopic fractionation, and geophysical characterization will be integrated to explore the controls on solute transport and reaction. While conservative tracer concentrations have been used to constrain advective-dispersive transport parameters in the past, isotopic tracers fractionate during diffusion and can therefore provide information on immobile pore space in cases where diffusion dominates ion transport. The power of this project will be to add significant constraints to the controls of known parameters in solute transport modeling, determine their controls on transport processes, and quantify the distribution of transport length scales active in a porous medium and the subsequent impact on reaction kinetics. The experimental data produced will be used to validate existing theories commonly used by the hydrology community (i.e., "local" versus "non-local" transport), and explore new theories as motivated by emerging data, if needed, to develop new insight into transport and reaction behavior.