Environmental Tritium (3H) and hydrochemical investigations to evaluate groundwater in Varahi and Markandeya river basins, Karnataka, India

The present study aimed at assessing the activity of natural radionuclides (3H) and hydrochem. parameters (viz., pH, EC, F-​, NO3 -​, Cl-​, Ca2+, Mg2+) in the groundwater used for domestic and irrigation purposes in the Varahi and Markandeya river basins to understand the levels of hydrochem. parameters in terms of the relative age(s) of the groundwater contained within the study area. The recorded environmental 3H content in Varahi and Markandeya river basins varied from 1.95 ± 0.25 T.U. to 11.35 ± 0.44 T.U. and 1.49 ± 0.75 T.U. to 9.17 ± 1.13 T.U. resp. Majority of the samples in Varahi (93.34​%) and Markandeya (93.75​%) river basins being pre-​modern water with modern recharge, significantly influenced by pptn. and river inflowing​/sea water intrusion. The EC-​Tritium and Tritium-​Fluoride plots confirmed the existence of higher total dissolved solids (SEC > 500 μS​/cm) and high fluoride (MAC > 1.5 mg​/L) in groundwater of Markandeya river basin, attributed to relatively longer residence time of groundwater interacting with rock formations and vice versa in case of Varahi river basin. The tritium-​EC and tritium-​chloride plots indicated shallow and deep circulating groundwater types in Markandeya river basin and only shallow circulating groundwater type in Varahi river basin. Increasing Mg relative to Ca with decreasing tritium indicated the influence of incongruent dissoln. of a dolomite phase. The samples with high nitrate (MAC > 45 mg​/L) are waters that are actually mixts. of fresh water (contg. very high nitrate, possibly from agricultural fertilizers) and older unpolluted' waters (contg. low nitrate levels)​, strongly influenced by surface source