L’acquifero di Settepolesini di Bondeno: una risorsa idrica potenzialmente alternativa per l’attingimento idropotabile della Provincia di Ferrara.

The paper deals of an applied hydrogeology research for the safe yield evaluation of the Settepolesini aquifer (Bondeno, Ferrara) with the main aim to identify new groundwater resources for municipal water supply. The research, based upon a dual approach either of continuous monitoring of Po river lateral recharge processes to the aquifer or of numerical modelling, has been conducted for 3 years (2002-2005) and had the chance to verify the response of the system to peculiar recharge boundary conditions with extreme hydraulic loadings (big flood of the Po river in December 2002, hystorical drought of summer 2003). The paper puts in evidence the complex mechanism of aquifer lateral recharge: pressure transfert is very fast and aquifer susceptibility to recharge signal is affected by season (higher in late winter-spring, lower in autumn); at the same time mass transfert is very low, locally faster in relationship to the occurrence of paleo-channels with higher hydraulic conductivity. Numerical modelling of the system, calibrated against the results of continuous monitoring and with the aim of forecasting groundwater abstraction schemes, has put in evidence that, with an existing lateral recharge of about 600 L/s from the Po river to the I confined aquifer, it is possible to pump, at a sustainable rate, 250 L/s from the same aquifer trough a rather wide-spread well-field; direct water abstraction from Settepolesini lake cannot be higher than a critical threshold between 150 and 200 L/s. Main factors limiting a more severe exploitation are in relation with subsidence risk (to be evaluated with specific investigations) and with the location of hazard centers near to the possible groundwater abstraction points.