ABSTRACT

Movement of hazardous substances in soils and groundwaters can be very fast, on the order of meters per day, or very slow, with only small distances covered over time spans approaching the geologic. In the rare absence of chemical degradation mechanisms and/or volatilization potential, public health risks often depend on the physical and chemical factors which control fluid flow rates. Fluid transport at depth is controlled by hydraulic conductivity, and, to a lesser extent, physical dispersion. Chloride and bromide, and detergents are commonly used as tracers. There is a difference between performing a tracer test using a chemical injected at a wellhead to work out the flow field in an aquifer, and using tracer behavior to separate out dilution and dispersion from sorption and biodegradation. Examination of fluids moving through the subsurface at the molecular level would reveal water moving at a spectrum of velocities differing significantly from the mean calculated by Darcy's law.