Origin of radon in medicinal waters of Lądek Zdrój (Sudety Mountains, SW Poland)

Abstract In this paper the origin of radon in the underground medicinal waters Lądek Zdroj is presented. This health resort is situated in the Polish part of the Sudety Mountains. The concentration of radon in these waters (exploited by five springs and one bore hole) range from 122 to 1284 Bq/dm 3 , whereas the concentration of radium does not exceed 6.8 Bq/dm 3 . In gneisses, through which the exploited waters flow, the amount of radium reaches about 34 Bq/kg and only locally rises to 50 Bq/kg. The increased concentration of 222 Rn in the medicinal waters of Lądek Zdroj is not influenced by the time of contact of these underground waters with the rocks through which they flow. The concentration of 222 Rn also does not depend on the concentration of 226 Ra which is dissolved in these waters. Radon is dissolved as a gas in underground waters in the zone of their outflow to the surface. It is caused by the increase in the emanation coefficient of rocks in the weathering zone and in dislocation zones, through which the waters outflow to the surface. To a smaller extent, the genesis of radon in the thermal waters of Lądek Zdroj could also be related to a small admixture of shallow circulation waters containing enhanced amounts of dissolved radon. Much higher concentrations of radon in one of the intakes (Jerzy) should be attributed to its location in the area of a fork of a big dislocation zone and the increased quantity of 226 Ra in gneisses of the intake region.