The hydrogeological setting of the Cassino plain (central Italy).

The Cassino plain is an intramontane tectonic-basin of central Apennines, filled by Quaternary alluvium and lacustrine sequences. Mesozoic and Cenozoic shallow-water carbonates form the backbone of the main reliefs surrounding the studied area, as Cairo Mt. (NW), Venafro Mts. (E) and Rocca D'Evandro Mts. (SE). However, small carbonatic structures interrupt the flat morphology of the plain (i.e. Trocchio and Porchio Mts). The Cassino plain shows two important springs located on the north-western and south-eastern bounds; Gari springs (mean discharge of 18 m3/s and elevation of 41-30 m a.s.l.) and Peccia springs (mean discharge of 5 m3/s and elevation of 29-25 m a.s.l.). The hydrogeological setting of the plain is debated since the '70 of the last century. In literature, there are two different conceptual models, based on different geological settings. A first conceptual model describes an underground communication between Gari and Peccia springs by a normal fault system along Trocchio and Porchio Mts. The second one supposes the tectonic superimposition of less permeable media between the springs, breaking up the karst hydrostructure, considering Trocchio and Porchio Mts. as klippen. New geological and hydrogeological surveys have been carried out to add more data in this complex reference frame and build a new conceptual model. Then, a geophysical survey (TDEM-Time Dependent Electromagnetic Method) has been performed for fine-tuning the geological setting, while 2D numerical simulations have been used to test the updated proposed model.