Assessing aquifer salinization with multiple techniques along the Southern Caspian Sea shore (Iran)

This study focuses on the salinization of the coastal aquifer in the Mazandaran Province (Iran) within four different sites. Many factors can lead to declining groundwater quality, but this study focuses on the seawater intrusion area. Therefore, locating the interface between saltwater and freshwater is very important. For this purpose, three characterization methods with different accuracies have been employed: the Verruijt equation, vertical resistivity sounding, and an electromagnetic survey. Vertical resistivity sounding and the electromagnetic survey were performed near existing exploration boreholes and were used to determine the saltwater interface. The results showed that the Verruijt equation provides a reliable localization in two of the sites, but in the other two sites, the determined interface is lower than the observed data. The geoelectrical method showed acceptable results, but often this method cannot distinguish between the saltwater and saline aquitard boundary. The electromagnetic method showed a high accuracy in all the study sites and proved to be the most reliable method compared with the other techniques employed in this study. The results from this study are useful in helping to identify the most suitable technique for locating the freshwater/saltwater interface, especially in those sites where a detailed characterization via multilevel sampling is not feasible for technical or economic reasons.