Submarine groundwater discharge detection on the coast of Buenos Aires using 222Rn and geoelectrical methods

Abstract

Submarine groundwater discharge (SGD) is a complex hydrological process which occurs in the continent–ocean interface and plays an important role in coastal dynamics. The detection of groundwater discharge from the sandy freshwater aquifer towards the Atlantic Ocean was proposed on the western coast of Buenos Aires Province (Argentina). There are different methods used to detect SGD. In this study, 222Rn as a tracer, electrical resistivity tomography (ERT) and flow maps were used as the methodology. 222Rn activity was measured in the wells, at the beach (tidal pools and surf zone) and along a transect 200 m from the coastline where geo-electrical method was also used. Groundwater depth was measured in the wells and groundwater contour maps were made .222Rn activity in the wells varies from 16 and 173 dpm/L, at the beach the values are between 28 and 48 dpm/L and along the coastline they oscillate between 1.3 and 20.5 dpm/L. The ERT shows a high resistivity layer close to a depth of 3-4 m from the sea floor, which would indicate the presence of freshwater. Groundwater contour maps show discharge toward the continental plain to the west and toward the sea to the east. There is no precedent related to the application of these methodologies in the study area, therefore this study is of interest to increase our knowledge of the coastal hydrodynamics.