Prediction of Groundwater Quality Using Transfer Functions – an Approach to Link Historical Data to Future Concentrations

This chapter highlights the importance of the travel time distribution of solutes in aquifers, in order to evaluate the evolution of solutes at pumping wells. This evaluation is important when the solute is a contaminant and when measures are introduced in the groundwater catchment area in order to reduce the solute concentration at a pumping well. When flow and solute transport in the aquifer cannot be easily characterized by determinist numerical simulations, the evolution of the solute at the pumping well can be evaluated with a transfer function approach. The principle of the transfer function approach is to solve the convolution integral, which links the solute concentration at the pumping well to history of solute input in the recharge zone of the aquifer via a transfer function. The transfer function describes the travel time distribution of the solute from the input zone to the pumping well. It can be determined by numerical, analytical or experimental methods, or a combination of them. These methods are compared and their advantages and drawbacks are analyzed. Since the analytical description of the transfer function is one of the most common approaches, the main analytical formulations in the published literature are reviewed. Decay and retardation factors affecting the transfer of nonconservative and reactive solutes are included in these analytical formulations. Strength and weakness of the transfer function approach are highlighted in the conclusion and the areas that would benefit from further development are pointed out.