| Recent environmental policy in the United States requires unprecedented insight into the subsurface environment. Many new laws have been passed to clean up existing contamination and protect water resources that require information about the physical and chemical properties of subsurface materials. The general principle behind each of these laws is that it is not possible to protect the environment from damage if we do not understand the physics, chemistry, and toxicology of the processes we are attempting to regulate. Most federal and state water pollution control legislation is based on our ability to determine impacts by estimating the effects of an environmental release. Increasingly, models are used to identify the range of probable impacts. Consequently, models of subsurface processes have become tools of public policy.; While policy objectives may always be quite clear (e.g., protect groundwater from pollution) it is less obvious how to assure the desired outcome. Groundwater flow and contaminant transport modeling can be used to gain insight into the environmental factors controlling the range of options available. However, there are several problems with using this particular class of models to guide public policy: 1) Areas of interest often overlap. (2) Models are valid at a particular scale. (3) Transport models can be used to inform our understanding of contamination risk.; Each of these problems stimulated a separate line of research. Modeling was used to assess the potential impacts of global climate change in a regional bedrock aquifer and new techniques were developed to build and interpret very large scale, supra-regional models. New model-building tools and practical techniques for calibration are presented. A set of basin-scale, regional models demonstrate how hydrogeologic properties of a basin can affect hydrologic response to drought. New techniques were developed to nest a local groundwater flow model in a regional domain and to evaluate how the conceptual model of flow through a separating clay layer can change our interpretation of aquifer vulnerability. Numerical experiments were conducted using a saturated-unsaturated flow and transport model to create a drinking water contamination index based on the toxicity, mobility, and persistence of releases. |
