Continuous-resistivity profiling for coastal ground-water investigations: Three case studies

Continuous-resistivity profiling (CRP) was used at three sites to investigate submarine groundwater discharge (SGD) and to delineate the subsurface saltwater/freshwater interface. At the first site, in Georgetown, South Carolina, CRP was used to locate possible areas of SGD in the Winyah Bay estuary. The data show evidence of SGD in the Pee Dee River, feeding into Winyah Bay, at approximately the location of the forest/marsh boundary. In Waquoit Bay, Massachusetts, CRP was used to further map the extent of SGD already measured by sea floor seepage meters and to delineate the subsurface saltwater/freshwater boundary. The data show evidence for a focused groundwater plume beneath the bay that may extend 350 meters (m) out from the shore. Finally, CRP was used in Orleans, Massachusetts, to verify a groundwater model prediction of freshwater-saturated sediments underlying an area of Cape Cod Bay, just west of Rock Harbor. The data support the prediction of freshwater-saturated sediments beneath the bay. Results from all three sites show the value of CRP in coastal groundwater investigations.