Modeling refers to the process of generating a model as a conceptual representation of a phenomenon. Mathematical and molecular modeling have become indispensable components of site characterization, risk assessment, and remedial-action implementation. Modeling provides the most comprehensive analysis of the impact of system properties and processes on contaminant transport and fate. SBRP researchers extensively utilize models to predict the fate of pollutants in the environment. Specific applications include models of fluid flow and contaminant transport, remediation of contaminated environments, exposure assessment, and statistical and physiologically based pharmacokinetic modeling.