3D-imaging of shallow fractured aquifers along the Scansano-Amiata ridge (Tuscany, Italy).

A series of high-resolution geophysical surveys including 3D seismic refraction and resistivity tomography, 2D resistivity tomography and Ground Probing Radar, were recently conducted in three sites of the Scansano-Amiata ridge in southern Tuscany (Italy). The goal of the survey was to clearly image the geometry and the properties of some small scale aquifers hosted in high-angle faulted and fractured zones. In the recent years fresh water availability has become a major issue in the Italian peninsula as various agricultural and industrial activities as well as urban settlements depend on a constant and predictable supply. In the Appennine area, aquifers very often consist of fractured reservoirs within low-permeability formations, where established alluvial aquifer modeling techniques appear inadequate to protect the resource from pollutants or plan new extracting plants. The existing well distribution was compared with the fault network revealed by satellite image interpretation. The most productive aquifers resulted invariably located along major faults, thus pointing out the importance of secondary (tectonic) permeability. A prominent sub-vertical fault system ("Patrignone" fault), oriented north-south was investigated with high-resolution geophysical methods and direct excavation at three different sites: "Aione", "Ripacci" and "Poderino". We report here some of the results obtained at the "Poderino" site where 3D-geophysical data have been also collected (Figure 1). The different geophysical images clearly outlined the structural framework of the subsurface down to a depth greater than 100 m and the final synthesis provided a comprehensive insight into the architecture of faulted and fractured zones and in the overall permeability structure.