The effects of dispersion and mixing on radionuclide dating of groundwater

Abstract

In general, the decay age of a water sample and the average age or transit time of the sample are the same only in the case of zero mixing or piston flow. A unified discussion of the theoretical distributions of ages and transit times in hydrologic systems is presented, focusing on transit time distributions for piston flow, exponential, dispersive and mixing cell models. Distributions of two component systems and the errors caused by not considering a two component mixture in radionuclide dating are also considered. After outlining the mathematical treatment of multiple tracer data, these concepts are employed along with computer models to examine hydrochemical data from the Bunter aquifer in England. This analysis indicates the importance of model selection to the interpretation of radionuclide data.