Understanding stable isotope systematics of salinity affected groundwater in Mewat, Haryana, India

Mewat district in Haryana located in the semi-arid region of India has been reported continual increase of groundwater salinity. Stable isotopes, δ18O and δD, of groundwater and rain water were successfully used for characterization and source identification of salinity affected groundwater in the area. Eleven representative groundwater samples were of the pre-monsoon (May), monsoon (August) and post-monsoon (November) seasons were analyzed for determining EC, δ18O, δD and other parameters. The mean EC of the samples was determined 6712 μS/cm for the pre-monsoon, 4743 μS/cm for the monsoon and 6602 μS/cm for the post-monsoon. The slope of LMWL (8.13) obtained from the bivariate plot showed a very close to the GMWL (8) and the slope of rain water (7.47) and groundwater samples found lied on the right of the LMWL for all the seasons. Slopes observed for the pre-monsoon (6.76), monsoon (5.63) and post-monsoon (6.11) seasons indicated some evaporative enrichment of water before the groundwater recharge. The increase of d-excess values from 0.74 in pre-monsoon to 3.75 in monsoon and 4.46 in post-monsoon seasons suggested modern recharge with low evaporation. The recharge by meteoric water was noted from the decrease in the mean value of EC in the monsoon season and its increase in the post-monsoon season, which suggested possible ‘mechanism of mixing’. All these processes qualitatively predicted the recharge and discharge locations in the study area.