Indian Journal of Soil Conservation

An intensive study on groundwater quality in west Delhi was carried out to provide an insight into possible mechanisms that control the chemical composition of groundwater and to identify the source and extent of groundwater pollution. Higher level of groundwater pollution at southern part of the study area near Najafgarh drain indicated the leaching of pollutants from heavily contaminated drain water. The presence of high nitrate in the groundwater was not only an indicator of agricultural pollution but its relation with other ions has confirmed its anthropogenic origin also. Chloride distribution in the study area showed that, groundwater with chloride concentration of < 30 me L⁻¹ was originated naturally, but the origin of higher concentration was anthropogenic in nature. Wide variation of δ¹⁸O and δ²H in groundwater indicated that the natural mixing was a slow process. The stable isotope data revealed the presence of two types of recharge zone in the study area through which recharge was occurring by a range of surface mechanisms like direct rain infiltration, various degree of surface evaporation before infiltration and mixture of these two. Deuterium-excess analysis confirmed that the isotopically enriched areas were situated near the depressions and Najafgarh drain. The rela tionship of δ¹⁸O with Cl and NO 3 suggested that the groundwater was originated from two isotopically distinct sources which were mixing very slowly within the study area. Evaporation of irrigation water in the unsaturated zone has been played a major role in significant enrichment of the groundwater with heavier isotopes. Thus, the characterization of groundwater quality, and identification of pollution source can be very effective to start with developmental activities for minimizing pollution threat and increasing recharge to the groundwater.