Protecting the Nation's Groundwater

Each year, the Department of Energy alone invests on the order of $6 billion to address the environmental consequences of its past national security activities. Among the most recalcitrant problems that DOE faces are soils and groundwaters contaminated by plumes of chlorinated hydrocarbons, organic solvents, heavy metals (mercury, chromium, etc.), and radionuclides. Reliable prediction of the movement and chemical alteration of these underground plumes is critical for decisions on virtually every waste disposal option, from remediation technologies such as in-situ bioremediation to evaluations of the safety of nuclear waste repositories. Such predictive capabilities will also impact the responsible utilization of our Nation's energy resources, particularly with respect to oil and gas.

The ability to predict the transport of underground contaminants is one of the most challenging problems facing the nation. The overarching scientific issue is how we take scientific knowledge about the behavior of chemicals and fluids obtained in the laboratory and use that knowledge to accurately predict contaminant movement through miles of soils and groundwater over many years.

There are two key challenges to simulating the movement and alteration of underground contaminants. First, theoretical models of how contaminants interact chemically with minerals and other constituents of the soil must be improved. Second, the capabilities of the computer systems and modeling software must be extended to handle the huge number of minerals, inorganic and organic chemicals, microbes, etc. and chemical contaminants that exist underground. The generation of computational capabilities predicted to become available early in this century will provide a significantly improved basis for predicting the fate of underground contaminants. This new capability will stimulate advances in the numerical simulation of the flow and reactions fluids with the solid phases as found in geologic systems—phases, which are inherently complex, physically heterogeneous, three-dimensionally anisotropic, and chemically reactive. Recent progress has demonstrated the capability for calculating the paths for fluid flow in well-characterized, yet realistic models of the subsurface environment. Obtaining these flow-paths required the solution of mathematical equations containing many millions of unknowns, and points the way to future advances for this field.

As is the case in many other fields, computational simulation is the key to translating breakthroughs in scientific knowledge about the behavior of chemicals and fluids in the subsurface into practical applications. Only through computational modeling will it be possible to understand and predict the intricate web of interactions between contaminants, the constituents of the soil, and the flow of the plume through the layers of the soil.