Hydraulic conductivities of low permeability sediments inferred from a triple pumping test and observed vertical gradients

Knowing vertical conductivities of thick aquitards is important for simulat ing regional or local ground mater flow. These hydraulic parameters are bes t determined by calibration of these models. Collection of reliable data fr om heavily pumped ground water reservoirs can be problematic. Another way t o infer these hydraulic parameters is the simultaneous interpretation of di fferent parts of a multiple pumping test using an inverse numerical model. Here, the drawdowns observed in the indirectly pumped aquifers allow us to deduce the vertical conductivities of the aquitards with an equivalent accu racy as the horizontal conductivities of the aquifers, When the hydraulic r esistances of the aquitards are too large, it becomes impossible to induce observable drawdowns in the indirectly pumped aquifers, and the inverse mod el loses valuable input data. Observing vertical gradients in and over the aquitards in case of important vertical now can make up for this loss. Thes e data allow us to estimate the specific discharges through the successive parts of the aquitard and hence their hydraulic resistances, This useful in formation allows us to consider all these hydraulic resistances in one grou p of hydraulic parameters during the simultaneous interpretation of the mul tiple pumping test using an inverse numerical model. As this procedure redu ces the number of identified parameter groups, it enhances their reliabilit y, In this paper it is demonstrated how this reliability can be deduced fro m a number of statistical parameters that can also be used in the collinear diagnosis, The proposed interpretation procedure is demonstrated on a trip le pumping test performed in and around the most important aquitard in Flan ders, Belgium. The obtained results should first be integrated in a local g round water flow model. By the performance of a number of such integrated h ydrogeological studies, the lateral change in the hydraulic properties of t his aquitard can be evaluated.