The uprising of deep saline waters into the Oltrepò Pavese (Northern Italy) aquifer: early results

This paper discusses the early results of a study carried out in the Oltrepò Pavese plain sector (Southern Lombardy, Italy) where the uprising of deep, mineralized waters into the shallow aquifer, occurs. These waters are characterized by a Na-Cl hydrochemical facies. Monitoring of the chemistry of the waters, by periodical sampling, was carried out both on wells and on the lower reaches of the surface water drainage network which are characterized by high chloride concentrations. This permitted the surveying of the area, parallel to an important tectonic discontinuity, where the phenomenon is more diffuse. We carried out a continuous monitoring of chemical-physical groundwater parameters using multi-parameter datalogger instruments, that allowed us to identify variations in waters salinity, caused by a further uprising of mineralized waters into the shallow aquifer. The amplifi cation of this phenomenon could be caused by an increase of deep circuit water head increase, induced by the pressures from the Apennine margin’s underground water circuits, during recharge events. Some electrical conductivity and temperature logs were carried out in wells in different zones of the investigated area in order to determine the depth and the variation in time of the fresh water-saline water interface. Finally, in those areas in which there were no wells to sample groundwater from, we attempted the use of VLF-EM (Very Low Frequency Electromagnetic) geophysical technique. This technique allows the detection of resistivity anomalies caused by conductive bodies. Carrying out some investigations with this method we found some anomalies that could be associated to the uprising of mineralized waters into the shallow aquifer.