Radon concentration in groundwater of Varahi and Markandeya river basins, Karnataka State, India

The present study presents an overview of the distribution of radon (Rn-222) activity concentration in the groundwater samples and their annual effective dose exposure in the Varahi and Markandeya command areas. Radon measurement was made using Durridge RAD-7 radon-in-air monitor, using RAD H2O technique with closed loop aeration concept. The measured Rn-222 activities in 16 groundwater samples of Varahi command area ranged between 0.2 +/- A 0.4 and 10.1 +/- A 1.7 Bq L-1 with an average value of 2.07 +/- A 0.84 Bq L-1, well within the EPA's maximum contaminant level (MCL) of 11.1 Bq L-1. In contrast, the recorded Rn-222 activities in 14 groundwater samples of Markandeya command area found to vary from 2.21 +/- A 1.66 to 27.3 +/- A 0.787 Bq L-1 with an average value of 9.30 +/- A 1.45 Bq L-1. 21.4% of the samples (sample no. RMR5, RMR11 and RMR12) in the Markandeya command area exceeded the EPA's MCL of 11.1 Bq L-1 and it was found that some samples in both the command areas were found to have radon values close to MCL value. The spatial variation in the radon concentration in the Varahi and Markandeya command area were delineated by constructing the contour map. The total annual effective dose resulting from radon in groundwater of both Varahi and Markandeya command areas were significantly lower than the UNSCEAR and WHO recommended limit for members of the public of 1 mSv year(-1).