Geochemical evolution of groundwater in the Western Delta region of River Godavari, Andhra Pradesh, India

Abstract

The present study on geochemical evolution of groundwater is taken up to assess the controlling processes of water chemistry in the Western Delta region of the River Godavari (Andhra Pradesh), which is one of the major rice-producing centers in India. The study region is underlain by coarse sand with black clay (buried channels), black silty clay of recent origin (floodplain) and gray/white fine sand of modern beach sediment of marine source (coastal zone), including brown silty clay with fine sand (paleo-beach ridges). Groundwater is mostly brackish and very hard. It is characterized by Na+ > Mg2+ > Ca2+:HCO3− > Cl− > SO42− > NO3−, Na+ > Mg2+ > Ca2+:Cl− > HCO3− > SO42−, and Mg2+ > Na+ > Ca2+ > or < K+:HCO3− > Cl− > or > SO42− facies. The ionic relations (Ca2+ + Mg2+:HCO3−, Ca2+ + Mg2+:SO42− + HCO3−, Na+ + K+:TC, Na+ + K+:Cl− + SO42−, HCO3−:TC, HCO3−:Ca2+ + Mg2+, Na+:Cl− and Na+:Ca2+) indicate that the rock weathering, mineral dissolution, evaporation and ion exchange are the processes to control the aquifer chemistry. Anthropogenic and marine sources are also the supplementary factors for brackish water quality. These observations are further supported by Gibbs mechanisms that control the water chemistry. Thus, the study suggests that the initial quality of groundwater of geogenic origin has been subsequently modified by the influences of anthropogenic and marine sources.