Parameter identification for axi-symmetric density-dependent groundwater flow based on drawdown and concentration data

A new tool for the simultaneous interpretation of a pumping and upconing test of saltwater is developed. The forward model is verified and a synthetic example checks the functioning of the inverse model. The new model interprets the movement of the transition zone between saltwater and freshwater towards the pumping well and the evolution of the drawdowns at different depths and different distances from the pumping well simultaneously. The drawdown and concentration observations are considered in their logarithmic space during the definition of their residuals. These two different types of data are interpreted by minimising a composite object function through a Gauss–Newton algorithm with sensitivities calculated by the perturbation method. The method is fast and relatively free of numerical dispersion because it uses an axi-symmetric grid and particle tracking for the solute transport.