Isotopic and geochemical studies of groundwater from the Ramganga basin and the middle Ganga Plains: implication for pollution and metal contamination

Abstract

Hydrochemical and isotopic studies in groundwater were carried out along the entire Ramganga Basin and parts of middle Ganga Plain to examine the quality of shallow groundwater accessed by hand pumps. The aim of the study was to determine the spatial distribution of arsenic (As) in groundwater of the Middle Ganga (Haridwar–Banaras–Saidpur region) and of the Ramganga (Ramnagar–Kannauj) basins. Groundwater samples were collected from a shallow depth because most of the population in the study area use locally drilled hand pumps for obtaining drinking water. A large area encompassing the Rampur, Bareilly, Bilsi, Faridpur, Badaun, Farrukhabad and Varanasi districts were found to have levels of arsenic above the drinking water criterion of 10 ppb. Sampling has indicated that arsenic (As) and nitrate (NO3) present in groundwater in elevated levels are the chemical constituents of most health concern in the shallow alluvial aquifers of Ramnagar, Bareilly, Badaun and Jaunpur districts of Uttar Pradesh in the middle Ganga Plain. These chemical constituents in groundwater are likely to have been derived from both geogenic and anthropogenic sources. The geochemical characteristics of groundwater may be influenced by factors like changes in climatic conditions, mineral weathering (silicate, carbonate), mixing of polluted surface water at shallow depths, ion exchange and anthropogenic activities. Stable isotopes of oxygen (δ18O), hydrogen (δD) and carbon (δ13CDIC) suggest that the process of carbonate weathering during the post-monsoon season has increased the input of chemical constituents into shallow groundwater. A shift in δ18O suggests soil–water interaction at shallow depths, which is reflected in elevated metal concentrations. The results indicate that arsenic concentrations in groundwater increase in the dry season and are decreased by recharge during the monsoon season.