Team 1 Proposal 07-38955 Principal Investigators: James Butler, Geoffrey Bohling, and Gaisheng Liu Institution: Univ. of Kansas Team 2 Proposal 07-38938 Principal Investigators: David Hyndman and Remke Van Dam Institution: Michigan State Univ. Team 3 Proposal 07-38960 Principal Investigator: Chunmiao Zheng Institution: Univ. of Alabama
Project Abstract A large body of theoretical and experimental research has identified the spatial distribution of hydraulic conductivity (K) as the most significant factor controlling subsurface solute transport. Previous work has shown that detailed characterization of heterogeneous aquifers is necessary to develop predictive models and improve our understanding of transport behavior. Although numerous studies have demonstrated that classic advection-dispersion models can reasonably describe field-scale solute transport in mildly heterogeneous aquifers, efforts to develop predictive transport models in highly heterogeneous aquifers have not met with success. Recent modeling studies have indicated that small-scale variations in hydraulic conductivity may be the primary cause of the highly asymmetric tracer plumes that have been observed in such aquifers. However, the current generation of field methods is not capable of characterizing these variations at the level of detail required for predictive transport modeling. In this project, we will develop new methods to characterize and simulate transport through heterogeneous aquifers. By combining a new direct-push profiling method with novel "full-resolution" 3D ground-penetrating radar methods, we will describe the spatial distribution of K at previously unattainable vertical and lateral resolutions. We will apply our approach at the extensively studied MADE site and demonstrate the value of such detailed characterization by predictively simulating saline tracer tests monitored with time-lapse geophysics, and through reassessment of a previously performed large-scale tracer test. The high-resolution 3D K description of the MADE site will be used to evaluate alternative solute-transport modeling approaches, and to develop new insights into transport processes in highly heterogeneous aquifers. We will demonstrate the broad applicability of the developed techniques and principles at additional sites in the United States and Germany. The project will have significant broader impacts in the areas of science, practice, and education. The unprecedented level of characterization of hydraulic conductivity at the MADE site will provide the necessary detail to address a suite of fundamental questions concerning solute transport in highly heterogeneous formations. These data sets will improve our conceptual understanding of, and modeling capabilities for, solute transport through such systems. The insights and methods developed in this research will also be of great value for applied hydrogeology; their incorporation into practical investigations should dramatically improve the quality of predictive models, leading to more reliable risk assessments and more efficient allocation of resources for site characterization and remediation activities. We will develop high-resolution immersive visualizations of our results to provide practitioners, researchers, and students with an ability to explore subsurface transport phenomena in a highly heterogeneous environment.
Sites of groundwater contamination are found throughout the United States and the world. As a result, there is a critical need to develop sound approaches for assessing the threat that such sites pose to neighboring water users and for cleaning up (remediating) the contamination. State-of-the-practice methods have often proven to be of limited effectiveness for site assessments and clean-ups because of the high degree of variability in geologic material over short distances. In particular, the natural variability in hydraulic conductivity, the parameter that characterizes the ease with which water flows in the subsurface, has greatly confounded efforts to predict how a contaminant will move and to design effective clean-up measures. The major technical goals of this project were to develop new approaches for characterization of the shallow subsurface at a resolution that has not previously been possible, integrate these approaches to provide an unprecedented view of spatial variations in the subsurface properties that are often important controls on contaminant movement, and then use this information to develop methods for predicting how a contaminant will move within geologic materials characterized by a high degree of natural variability. The major education goals of this project were to give students (both graduates and undergraduates) experience with these new approaches and to transfer the methods developed in this work to potential users through short courses, workshops, conference presentations, and scientific reports and papers. Although work is still ongoing, this project has achieved its major technical and education goals. A new suite of integrated technologies has been developed that will likely revolutionize how the natural variability in geologic materials is characterized at sites of groundwater contamination; the power of this new approach was demonstrated at one of the most extensively studied research sites in the United States. The information provided by this integrated approach is currently being incorporated into methods for predicting how a contaminant will move in highly variable geologic materials. The details of the major scientific contributions are described in the 11 articles in scientific journals published during the course of the project and the additional manuscripts under preparation. In terms of education, this project has provided significant training opportunities for five Ph.D. students, four M.S. students, and six undergraduates. These students obtained first-hand experience, virtually all in field settings, with the technologies developed in this work. This project has also made significant contributions to the education of practicing professionals through short courses, workshops, and conference presentations. The primary contribution of this project beyond the science and engineering communities is that it helps strengthen the technical foundations upon which decision makers in government and industry can base informed decisions about the risk posed by sites of groundwater contamination and how to effectively remediate those sites.
