Understanding the hydrogeochemical processes and physical parameters controlling the groundwater chemistry of a tropical river basin, South India

Detailed investigation on hydrogeochemistry of hard rock terrains is important to identify the major geochemical processes and the source of ionic constituents in groundwater. The present study is carried out to understand the hydrogeochemistry of groundwater resources and the major hydrogeochemical processes, controlling the concentration of major ions in groundwater in the Kallada River Basin (KRB), South India. About 166 groundwater samples were collected from KRB during pre- and post-monsoon of 2016 for hydrogeochemical analysis. Most of the groundwater samples in KRB were within permissible limits of drinking water quality. The dominant groundwater types during pre-monsoon were Ca²⁺-Mg²⁺-Cl^- which was changed to Na⁺-Cl^- during post-monsoon. This is supported by the inverse relationship of depth of wells and change in EC during pre- and post-monsoon periods. Rock-water interaction processes such as reverse ion exchange and silicate weathering are major geochemical processes responsible for the hydrogeochemical signatures of KRB. The shallower wells (< 10 m) show strongest relation with the water types Na⁺-HCO₃^- and Ca²⁺-Mg²⁺-Cl^- which have been changed to Na⁺-Cl^- and Ca²⁺-Mg²⁺-HCO₃^- during post-monsoon. However, in deeper wells, Na⁺-Cl^- is the dominant type of water during both seasons. The hierarchical cluster analysis displays different hydrogeochemical associations representing diverse physicochemical parameters both spatially and temporally. This study could shed light on diverse hydrogeochemical processes which are responsible for the hydrogeochemistry in KRB. Major hydrogeochemical processes in the Kallada River Basi.