Radon and radium content of some cold and thermal aquifers from Bihor County (northwestern Romania)

Abstract

AbstractIn the present study, two of the major naturally occurring radionuclides (226Ra and 222Rn) were analyzed in water samples from shallow, medium‐depth, and deep geothermal aquifers, all of which are located in Bihor County, northwestern Romania. Here, the results of radon and radium measurements, performed from 2008 to 2009 in 50 locations, are reported. Radon proved to have a wide range of activity, with values from 4.5 to 110.8 Bq l−1 for shallow aquifers, from 9.3 to 106.0 Bq l−1 for medium‐depth aquifers, and from 10.1 to 34.8 Bq l−1 for deep geothermal aquifers. The shallow aquifers have lower radium concentrations (0.06 to 0.48 Bq l−1), compared to medium‐depth aquifers (0.1 to 0.52 Bq l−1) and deep geothermal aquifers (0.27 to 1.8 Bq l−1). The principal aim was a thorough investigation into the possible correlations between the occurrence of radon and radium in different aquifers and the hydrogeological, hydrogeochemical, and geothermal features of the area. Besides the direct link between the occurrence of uranium and thorium and the 226Ra and 222Rn contents in groundwater, the measurements we performed have allowed us to identify a secondary control on radionuclide distributions caused by the adsorption of dissolved radium onto clay minerals in exchange for sodium (for the sandy clay aquifer of Săcuieni), the high competition for adsorption sites in aquifers with high concentrations of dissolved calcium and magnesium (for the limestone dolomite aquifer of Oradea), and the role of thermal processes.