Cross-hole Electrical Resistivity Tomography Characterization and Monitoring of Seawater Interface in an Alluvial Aquife

The characterization and monitoring of saline water interface is a key issue to understand the evolution of groundwater resources in coastal areas. In order to go beyond the current knowledge in this issue a new experimental site has been constructed in the lower part of an alluvial aquifer north of Barcelona (Spain). The site, between 30 and 90 m from the seashore comprises 16 shallow piezometers with depths ranging between 15 and 25 meters. Piezometers are also equipped with electrodes in order to perform cross-hole electrical resistivity tomography (CHERT). Periodic CHERT measurements are carried out between the piezometer equipped with electrodes, resulting in parallel and perpendicular vertical cross sections of the site resistivity. The position of the fresh-salt water interface can be identified due to the resistivity contrast between the saline and fresh water. Together with the fiber optics and CHERT investigations, Rn and Ra isotopes are analysed in different piezometers. Preliminary results indicate that the combination of both methodologies is a useful technique to investigate and monitor submarine groundwater discharge groundwater resources in coastal areas.