ABSTRACT
A major emphasis of environmental science today also concerns an assessment of risk and performance of disposal or remediation systems. Computer programs, called predictive models, attempt to predict the behavior and migration of subsurface fluids and contaminants. Predictive models are keys to this type of work, and many licensing and government regulations depend upon the results of these predictive models. The physical processes acting in the subsurface determine how a chemical partitions in the subsurface media, which can have a significant effect on the environmental fate of a substance. Molecular diffusion also tends to disperse fluids and dissolved solutes through the random walk of individual molecules resulting from the thermal kinetic energy of each molecule and the driving force of entropy. Diffusion is important when volatile compounds are present and in situations where flow velocities are extremely low.
