222Rn as a tracer for the estimation of infiltration of surface waters into aquifers

Abstract The estimation of the infiltration of lake and river waters into aquifers is of vital interest in many fields. The paper focuses on the use of radon as an indicator for the assessment of such infiltration processes. Radon is produced naturally in every aquifer matrix and thus as the naturally occurring compound is present in groundwater. On the contrary, its concentration in lake and river waters is negligible. It was shown that a qualitative monitoring of the infiltration of surface waters into aquifers is possible by measuring the radon concentrations in observation wells situated close to the respective surface water body. Radon concentrations in groundwater, that are significantly lower than the respective natural background indicate such infiltration processes. However, critical consideration of the boundary conditions such as homogeneity of the aquifer, natural radon background of surface water and influence of percolating rain is needed for sound data interpretation.