ABSTRACT
Coupling the numerous potential reactions and interactions with the non-uniformity of the real world flow regime and the variability associated with all measurements, the assessment of subsurface transport and fate would seem to be an exercise in futility. The complexity of the problem can be attributed mainly to the nature of the environment in which the materials are moving, i.e., the porous medium. Porous media flow always involves two phases: a solid phase and a liquid phase. In unsaturated conditions, the gases present in the porous matrix represent a third phase. The gaseous phase can be significant when considering volatile contaminants. Tracer studies are engineered investigations designed to determine transport characteristics of the subsurface including: hydraulic conductivity, porosity, dispersivity, chemical distribution coefficients, and other properties. Owing to the inherent three-dimensional nature of the flow regime, recent investigations have focused on assessing the temporal, spatial, and vertical distribution of tracers.
