Integrated geophysical survey for 3D modelling of a coastal aquifer polluted by seawater

Geophysical surveys are carried out in the coastal area of Petrosino (south-western Sicily) to study the time evolution of seawater contamination of the coastal aquifer, probably increased due to human impact. The overexploitation of the aquifer, due to an intensive agricultural use has affected significantly the natural hydro-geochemical state of the basin. The study is based on a processing and integrated analysis of hydrogeological, geochemical and geophysical data. In particular in the last two years seasonal time-lapse electrical resistivity tomographies (ERT), new TDEM soundings and Multi-Analysis Surface Wave soundings (MASW) have been carried out. The interpretation of the total set of previously existing and new geophysical data made it possible to reconstruct a three-dimensional model of the electrical resistivity of the aquifer, aimed at defining the extent and geometry of the seawater intrusion. Furthermore, the execution of a series of high-resolution time-lapse electrical tomographies and a correlation analysis between geophysical measures and geochemical, geological and hydrogeological data allowed to discriminate the effects of the salt concentration in the groundwater and the porosity and saturation degree of the rock on the time variations of the measured electrical resistivity. Finally, the average porosity of the rocks forming the reservoir was determined.