A mathematical solution and analysis of contaminant transport in a radial two-zone confined aquifer

An aquifer with a wellbore surrounded by a finite-thickness skin, such as a gravel pack, can be regarded as a radial two-zone system. In this study, a mathematical model is developed to describe contaminant transport in a radial two-zone confined aquifer system. The solution of the model equations can be used to delineate contaminant transport in such a two-zone aquifer system and to investigate the skin effect on the temporal and spatial concentration distribution. The present solution is shown to reduce to an existing solution for transport in a homogeneous aquifer in the case when there is no wellbore skin. The results predicted from the solution indicate that the skin effect has a significant impact on the concentration distribution at early time. But an abrupt change in the spatial concentration distribution may occur at the interface of the skin zone and aquifer formation zone. The results from a sensitivity analysis reveal that dispersivity in the formation zone has a more significant effect on the concentration distribution than do the effects of skin thickness and dispersivity in the skin zone.