Role of hydrogeochemical process in increasing groundwater salinity in the central Godavari delta

Groundwater salinization is an ever increasing problem in coastal aquifers due to seawater intrusion resulting from excessive groundwater withdrawals, lithological conditions of the aquifer and industrial and agriculture pollutant loads. Identification of salinity sources is challenging and a prerequisite for the protection of coastal fresh water aquifers. The present aim of the study is to identify the salinity sources and to understand its dynamics in the central Godavari delta, Andhra Pradesh where groundwater is highly saline with total dissolved solids (TDS) of ∼5000 mg/L at shallow depths of <3 m bgl. Groundwater samples were collected from 42 representative observation wells in the area and analyzed for major ions and stable isotopes (δ¹⁸O). Different hydro-chemical mixing models and multivariate statistical techniques, including factor and cluster analysis, are applied to these data sets. The results revealed that very high salinity (∼25,000 mg/L) in pumping wells is due to up-coning of salt water and the salinity is palaeo in origin. The salinity in the wells along the drains and near the coast (∼10,000 mg/L) is due to the infiltration of marine waters resulting from backwaters and intrusion of seawater along the drains. The salinity (∼5000 mg/L) in the wells away from the coast is attributed to dissolution of evaporites in the groundwater and ion exchange process.