Use of radioactive and neutron-activatable tracers to determine effective hydrogeologic parameters

The migration of nuclides in a geologic medium is controlled by the hydrogeologic parameters of the medium such as the dispersion coefficient, pore water velocity, retardation factor, degradation rate, mass transfer coefficient, water content, and fraction of dead-end pores. The breakthrough curve (BTC), which is the graphical relationship between the tracer concentration and the elapsed time since introduction, is an integrated picture of the hydrogeologic parameters that produced the BTC. Both radioactive and neutron-activatable tracers have been used to generate BTCs. The BTC of a 92Br radioactive tracer generated under saturated conditions in a nonhomogeneous (fractured) soil column is shown. From BTCs, the effective hydrogeologic parameters can be identified if appropriate techniques are applied