Diffusive solute transport and reaction processes in natural and contaminated porous media

该研究项目的重点是多孔介质中的扩散和反应过程，主要是浅层地下水系统，有或没有人为污染。***长期目标是提高对耦合扩散-反应过程及其对地下水和地表水系统中溶质迁移的控制的理解。拟议的研究计划将解决两个目标：***1。在受污染的裂隙岩石含水层中，可以证明CrVI的自然衰减或氯化溶剂污染，我们将通过识别特定反应的反应物、产物、机制和相对贡献来建立概念模型。概念模型将进一步发展成一个具有反应传递代码MIN3P的数值框架（Mayer et al. 2001）。* * * 2。我们将提高对发生在湖泊水-沉积物界面的铁锰结核生长带的生长机制和化学和同位素组成的时间序列变化的理解。关于含水层中的人为污染物可通过化学和生物过程进行自然衰减的认识，很好地结合了对受污染地下水系统管理办法的基于风险的评估。如果可以证明自然衰减机制是活跃的，而且对人类和生态系统健康的风险很低，监管机构可能会决定，没有必要采取激进的、破坏性的和昂贵的补救办法。我们正与波音公司和美国环保局合作，研究裂缝性基岩含水层基质孔隙空间中Cr（VI）和氯化溶剂自然衰减的扩散和反应过程。我们的贡献包括扩散传输速率的测量，以及地球化学和矿物学方法的发展，以确定矿物反应物和反应产物，使我们能够定义衰减反应过程。***在水-沉积物界面的湖泊中已观察到淡水铁锰结核。铁和锰被认为来自下伏的沉积物孔隙水。在冰川地区，结核可能和湖泊一样古老。我们将通过对孔隙水化学和稳定同位素组成的详细研究来研究它们的起源。来自岩心的孔隙水数据将允许对铁、锰和微量元素的向上迁移速率进行定量研究。这些根瘤的生长与树木年轮呈放射状相似，将被分析以确定它们沿生长方向的年龄分布（210Pb, 226Ra, 14C）。这将使我们能够确定增长率和总年龄。这些研究将有助于了解主要和微量元素的预算和通量随时间的变化。我们的目标是在区域尺度上构建痕量元素通量的时间序列，这将对理解工业化后污染物的扩散有价值。

The research program is focused on diffusion and reaction processes in porous media, primarily shallow groundwater systems, with or without anthropogenic contamination. ***The long-term objective is to improve understanding of coupled diffusion-reaction processes and their controls on solute mobility in groundwater and surface water systems. The proposed research program will address two objectives:***1. In contaminated fractured rock aquifers where natural attenuation of CrVI or chlorinated solvent contamination can be demonstrated, we will build conceptual models by identifying the reactants, products, mechanisms and relative contributions of specific reactions. The conceptual models will be further developed into a numerical framework with the reactive transport code, MIN3P (Mayer et al. 2001). ***2. We will improve the understanding of growth mechanisms and time-series variability of chemical and isotopic compositions in growth bands of Fe-Mn nodules that occur at the water-sediment interface in lakes. ***Knowledge that anthropogenic contaminants in aquifers may undergo natural attenuation by chemical and biological processes integrates well within a risk-based assessment of options for management of contaminated groundwater systems. In cases where it can be shown that natural attenuation mechanisms are active, and risk to human and ecosystem health are low, regulators may decide that aggressive, disruptive and costly remediation approaches are not necessary. We are working with partners in Boeing Corp. and the US EPA to study diffusion and reaction processes that contribute to natural attenuation of Cr(VI) and chlorinated solvents in the matrix pore space of fractured bedrock aquifers. Our contributions include measurement of diffusion transport rates, and the development of geochemical and mineralogical methods to identify mineral reactants and reaction products that allow us to define attenuation reaction processes. ***Freshwater Fe-Mn nodules have been observed in lakes at the water-sediment interface. The Fe and Mn is thought to be derived from the underlying sediment porewater. In glaciated terrains the nodules are likely as old as the lakes. We will study their origin by conducting detailed studies of the porewater chemistry and stable isotopic composition. Porewater data from the cores will allow for a quantitative study of the upward transport rates for Fe, Mn and trace elements. The nodules, which grow radially similar to tree rings, will be analyzed to determine their age profiles (210Pb, 226Ra, 14C) along the growth direction. This will allow us to define growth rates and total age. These studies will contribute to the understanding of major and trace-element budgets and fluxes to lakes through time. We aim to construct time series for trace-element fluxes at the regional scale that will be valuable in understanding post-industrialization contaminant dispersion.