Electrokinetic component of the self-potential for complex aquifer system characterization

The study focuses on the analysis of the electrokinetic component of the self-potential (SP), which may be associated to the diagenetic processes that control the hydrogeological behaviour of widespread pyroclastic lithostratigrafic unit in saturated conditions. In silica rocks, such a component is usually associated with the drag of the excess of positive charges resulting in a positive electrical potential in the groundwater flow direction. With regard to the most important and widespread pyroclastic formation of Southern Italy (i.e. Campanian Ignimbrite), this study points out that an inversion of the charge carrier's sign can be observed in presence of zeolitc zones and quaternary ammonium compounds. An example of this occurrence is here presented with reference to an area characterized by high antropic impact and periodic flooding events, where SP, resistivity and hydrogeological surveys were performed. An integration of the SP data with the hydrogeophysical model of the pyroclastic-alluvial aquifer, allowed to individuate diagenetic processes, which likely modify the hydrogeological behavior of the intercalated ignimbrite unit and control the contaminant propagation. Finally, some hints on groundwater contamination emerge from a preliminary study on the correlation between the residual map of the SP anomalies and the measured redox potential.