Multi-scenario groundwater numerical modeling of the Popoli Gorges complex aquifer (Central Italy)

Groundwater modeling has become extremely important in the last decades, as it allows to understand groundwater systems, to estimate the parameters of aquifers, to analyze pollution fenomena and to predict the results of certain actions. In this research, a numerical model has been implemented to test the validity of the hydrogeological conceptual model of the Popoli Gorges complex aquifer, that has been defined in previous studies (Conese et al.,1999; Di Curzio et al., 2014), in order to refine it. For this reason, the groundwater flow, the relationships between groundwater and Pescara river and the transport of polluting particles for three different scenarios have been analyzed. The Popoli Gorges are the result of the incision of the Morrone limestone aquifer, which has subsequently been filled by heterogenous continental deposits. The porous aquifer is fed by groundwater draining from the limestone aquifer. Moreover, somewhere in the riverbed, the aquifer discharges into Pescara river, highlighting clear groundwater/surface-water relationships. The numerical model, performed in steady state conditions, has been implemented by means of the computer code MODFLOW-2005 (Harbaugh, 2005). The procedure for defining the numerical model consists of 3 main steps: (1) horizontal and vertical discretization of the numerical domain, (2) assignment of the hydraulic properties to the active cells, and (3) selection of the most appropriate boundary conditions. The model has been calibrated using the “trial and error” method, by means of hydraulic head measurements (summer 2007), and adapting the hydrodynamic parameters. Using the post-processing code ZONEBUDGET, the inflow from the limestone aquifer and the discharges into surface-water have been calculated. In addition, MODPATH (Pollock, 2012) has allowed to obtain the paths of the polluting particles, coming from an important polluted site located in the study area. Under normal pumping conditions of the wells-field, or when it is turned off, Pescara river drains the aquifer; instead, in case of over-pumping, aquifer is fed by the river. Furthermore, due to the different behaviour in the three scenarios, there is a noticeable difference in the number of particles that are intercepted by the wells.