Delineating the fresh-saline interface in heterogeneous coastal aquifers is an important but challenging problem, particularly in the presence of discontinuous conductive clay layers. Electrical Resistivity Tomography (ERT) is one of the most efficient geophysical methods to characterize salinity at various scales. To avoid salinity overestimation through direct ERT interpretation, we use a petrophysical relationship to discriminate clay lenses from saline aquifers.