RUI: Predicting Transport Through Heterogeneous Facies Assemblages: Geostatistical Anatomy of Buried-Valley Aquifers

无法充分描述水力传导度(K)的空间分布是建立可靠的地下水流量和污染物运移预测模型、修复地下水污染以及有效管理和保护地下水资源的障碍。在冰川成因的含水层中，低K相(如冰川或湖相粘土)与高K相(如砂岩和砾石冲积物)并列的情况很常见。在北美西部和中部平原的潜谷含水层中，可渗透的喷流相组合形成了大型的、多产的区域含水层系统。尽管高K和低K相的确切几何形状只能由令人望而却步的地下信息量确定，但条件指示器模拟提供了一种方法来计算具有相同空间协方差结构和符合现有数据的相分布的许多实现。使用大量这样的实现运行传输模拟，并检查模拟的污染物传播时间或模拟的污染物路径的中心趋势和变化，可以洞察污染物将如何在真实系统中移动。然而，条件指示器模拟要求可以根据现场数据定义适当的相组合空间协方差的指示器变异函数模型，而实际上现场数据往往不足以达到这一目的。在本科生机构研究方案下拟议的研究的目标是根据潜谷含水层系统中许多地点的现场数据确定变差函数模型。两名本科生将参与为他们的高级研究项目奠定基础的实地工作。一名理科硕士学生将参与数据的地质统计分析。将特定相组合的概念模型与变差函数模型相结合，建立定量的水相模型。当我们开始对定量相模型进行分类时，我们将比较它们的相似性，并开始检验这样一个假设，即潜谷含水层系统中的一般相组合类型可以形成一个或多个原型定量水相。

The inability to sufficiently characterize the spatial distribution of hydraulic conductivity (K) is an obstacle to constructing reliable predictive models of ground-water flow and pollutant transport, to remediating ground-water contamination, and to effectively managing and protecting ground-water resources. In glacially derived aquifers, it is common to have low-K facies (e.g. till or lacustrine clay) juxtaposed with high-K facies (e.g. sand and gravel outwash). In the buried-valley aquifers of the western and central plains of North America, assemblages of permeable outwash facies form large and productive regional aquifer systems. Although the exact geometry of the high-K and low-K facies can only be determined by a prohibitive amount of subsurface information, conditional indicator simulation provides a way to compute a number of realizations of facies distributions that have identical spatial covariance structure and that honor available data. Running transport simulations using a large number of these realizations, and examining the central tendency and variance of simulated contaminant travel times, or the simulated contaminant pathways, can give insight into how contaminants will move through the real system. However, conditional indicator simulations require that an adequate indicator variogram model of the spatial covariance of the facies assemblage can be defined from field data, when in fact the field data are often insufficient for this purpose. The objective of the proposed research under the Research at Undergraduate Institutions Program is to determine variogram models from field data at a number of locations in a buried-valley aquifer system. Two undergraduate students will be involved in field work that will create the basis for their senior research projects. One M.S. student will be involved in the geostatistical analysis of the data. The conceptual model of a specific facies assemblage will be combined with the variogram model to crate a quantitative hydrofacies model. As we begin to catalogue quantitative facies models, we will compare them for similarities and begin to test the hypothesis that one or more archetypal quantitative hydrofacies can be developed for general types of facies assemblages in buried-valley aquifer systems.