Stratigraphic and geophysical integrated methodologies for the interpretation of sulphur water formational environment in Salento (Italy)

The Salento coal deposits (south-eastern Italy) are unutilized because these deposits are thin and nearly uneconomic but they have a high scientific and economic value due to their high organic sulphur content. The studied area is located in the western Salento peninsula where wells used by a fish-farm (“Ittica Ugento”) have shown high concentrations of hydrogen sulphide. Data from surface and boreholes stratigraphic surveys integrated with electrical resistivity tomography (ERT) allow us to define the structure, depths and geometry of the aquifer and its relationship with saltwater intrusion. Induced polarization (IP) with pole-dipole array survey has been carried out near the coastline. The value measured was over 50 msec. A direct relationship is shown to exist between IP values and the aquifer containing sulphur water. The high resolution of the data obtained with the applied methods not only shows the validity of the methodology but is the key to evaluating the groundwater resources of the area. The proposed mechanism is that of entrapment of sulphur water in a graben structure: when sulphate-enriched waters of marine origin come into contact with organic substances and lignite deposits (Galatone Formation, Oligocene), they are deprived not only of free oxygen, but also generate hydrogen sulphide as a result of the reduction of sulphates.