Radon Concentrations in Mineral Waters of the Sikhote-Alin, Primorsky Krai

The geological and hydrogeological conditions of 19 occurrences of thermal waters in the southern Russian Far East are considered in this paper. Radon concentrations were measured in waters, and uranium and thorium concentrations were determined in host rocks and secondary minerals. The results were compared with the chemical composition of waters and gases in the mineral springs. It is established that water-bearing rocks are classified into rocks of low and normal radioactivity. The contents of uranium (<0.56 mu g/L) and thorium (<0.1 mu g/L) in the waters are low. Measurements of radon concentrations in mineral water springs in Primorye indicate that most of them are weakly radioactive (0.2-1.5 kBq/L), whereas two are moderately radioactive (1.5-7.5 kBq/L). From a medical-balneological point of view, waters in 7 of 19 springs were defined as radon waters, with 4 of them classified as nitrogen thermal water and 3 as CO2-rich mineral waters. The CO2-rich mineral waters of the Shetukha Group exhibit the highest level of radioactivity. Such natural objects reflect the state of the geological environment and can be utilized both for medical purposes and for monitoring a wide range of hydrogeochemical parameters. Based on the analysis of geological conditions and geochemical features of thermal water occurrences, the factors that determine the radioactivity level were identified and general schemes for the radon transport to the surface in different geological and hydrogeological conditions were proposed.