In situ characterization using natural radio-tracers in a submarine freshwater spring, Kiveri, Greece

A medium resolution underwater gamma ray spectrometer was deployed in the submarine groundwater spring of Anavalos and was combined with conductivity and temperature sensors for continuous measurements of natural radioactivity, salinity and water temperature, respectively. The activity concentrations of radon progenies varied from (5-40) kBq m^-3, exhibited reverse dependence with salinity and were found above the guideline proposed by Environmental Protection Agency (11 kBq m^-3). Their ratio was above unity indicating radon gas escape to the atmosphere. Time-series of the activity concentration together with their ratios were provided enabling the system configuration for long term monitoring applications. The in-situ method proved to be an effective tool to study the radioactivity levels of the spring and the groundwater - seawater interaction process. Furthermore, the proposed tool provides cost-effective measurements in terms of real-time and long-term requirements and, it is characterized by flexibility in terms of sensor integration in different platforms to perform submarine groundwater studies in a temporal and spatial manner.