Unconventional Pumping Tests in Carbonate Aquifers, Without Interruption of Drinking Water Exploitation

The Gran Sasso carbonate aquifer is the largest and most productive in the Apennines. Its hydrogeological structure has been deeply studied since the middle of the last century for springs’ characterization for drinking purposes and for drilling of a motorway tunnel. Meanwhile, its hydrodynamic parametrization is less developed and is mainly limited to monitoring the discharge and chemical and isotopic parameters of springs. Starting from the ‘80s of the last century, the aquifer has also been exploited through wells especially in its southern portion where it was possible to reconstruct the geological structure and perform pumping tests because of the lowest groundwater table depth. The aquifer is characterized by secondary porosity, i.e. by fracturing and karst features, and an underlying impermeable marly complex, which represents the basal aquiclude. In such aquifers, it might appear inappropriate to characterize the hydraulic properties via pumping tests, as their reliability is proven in homogeneous and isotropic media. However, the high extent of the aquifer (about 700 km2), the location of the wells, as well as the scarcity of information available and the lack of alternatives forced to estimate some hydrodynamic parameters as in porous aquifers and to test the aquifer experimentally, especially in conditions of maximum pumping even for the evaluation of the influence radius. Furthermore, since the aquifer testing was performed during the normal activities of abstraction and distribution, it was not possible to perform canonical tests, i.e. with only one pumping well and observing the adjacent wells. However, the high transmissivity of the aquifer, the use of a single pumping well would have not sufficed to induce a drawdown that allowed data processing. Therefore, the step-drawdown test was obtained by turning on an increasing number of wells over time and keeping fixed the observation points. This kind of test, in addition to avoid interrupting the water supply, allowed: - estimating hydraulic conductivity and transmissivity; - estimating drawdown in pumping wells and in observation piezometers in operating conditions; - evaluating the extension of the perturbation induced to the aquifer both at the test and stress discharges; - evaluating flow directions in operating conditions.