A non-rigorous mathematical model is developed to estimate the effect of backward spreading. The model assumes that advection and longitudinal dispersion are the transport mechanisms in a radially converging flow field. To demonstrate the applicability of the model, a field tracer test is carried out. The experimental data are fitted with the type curves of this study, and those of Moench's study, to determine dispersivity and aquifer porosity. Results show that dispersivity values estimated by matching the two type curves are different. Because it neglects backward dispersion, Moench's solution overestimates the dispersivity and effective acquifer porosity.