Isotope hydrogeological factors control transport of radon-222 in hard rock fractured aquifer of Bangalore, Karnataka

Abstract

Radon-222 is a daughter element of radium-226 and are member of the uranium decay series.Radon-222 concentrations in groundwater of Bangalore city in different geological units were measured in 42 tube wells. The study area is underlain by Granite, Migmatite, Granodiorite and Gneiss rock and many dolerite dykes. The radon-222 concentration in groundwater is widely varying and ranging from 14 to 1000 Bq/L with an average value of 172.4 Bq/L. Significant differences in the radon-222 concentrations in groundwater among geological units were observed. The radon-222 distribution in groundwater is related to the presence of uranium in aquifer materials of the various rock types. Uranium concentration in groundwater is ranging from 0.2 to 523 μg/L. Transport of radon-222 through bedrock by water depends mainly on the percolation of water through the pore and along fractured planes of the rocks.Rn-222 cannot travel farther than several hundred meters away from their origin because of its short half-life of 3.8 days. It may travel the farthest within fractured or fissured geological formation where groundwater movement is fastest. The study shows that radon concentration in groundwater is controlled by geohydrological and hydrochemical characteristics of the study area.