COUPLING GPR AND ERT TECHNIQUES FOR DELINEATING SALTWATER-FRESHWATER INTERFACE IN A COASTAL AQUIFER

Characterization of hydrogeological properties is important for sustainable water resource management and studying surface geophysics is important for hydrogeological investigations at depth, as well as for providing critical data on characteristics of a source aquifer. Geophysical survey is a low-cost, non-destructive and highly precise approach to analyzing hydrogeology. In this research project, we are interested to estimate the water table and the interface between fresh groundwater and salty ocean water in the southern coast of Rhode Island. We pooled electrical resistivity tomography (ERT) and ground penetrating radar (GPR) techniques to investigate the pathways for saline water intrusion into freshwater aquifers. The location of the interface is controlled by the density and pressure differences on the two sides of the interface and the subsurface hydrologic properties that govern fluid movement. We surveyed six transacts from the Atlantic Ocean shoreline to inland to investigate the movement of the interface. Transacts were aligned in a linearly NS azimuths perpendicular to the ocean. The results show that the water table in back-barrier areas is at 3 feet below the surface and the saltwater-freshwater interface was found at 13 feet, leaving the thickness of freshwater lens about 10 feet.