Classification and chemical characterization of groundwater of the 335-m-thick multilayered aquifer system in the Bengal Basin, Bangladesh

ABSTRACT In the Bengal Basin of Bangladesh, the excessive extraction of groundwater is leading to a continuous decline in water levels in various regions, as well as contributing to water quality issues. Consequently, evaluating the available freshwater resources is crucial, taking into account both quantitative and qualitative factors. A total of 1,802 groundwater samples were collected during both dry and wet seasons, which were analyzed to assess the type and chemical quality of water. These samples were sourced from 901 groundwater monitoring wells, reaching depths of up to 335 m. The sediments are characterized by cyclic deposits primarily consisting of medium to fine sand, silt, and clay. The groundwater is predominantly of the Ca-Mg-HCO3 and Ca-Mg-Cl types, while Na-Cl and Na- HCO3-Cl types are also observed. The evaporation-sedimentation process significantly influences the chemical composition of all samples taken from depths of 50 to 335 m, as well as the interaction between water and rock, which is anticipated for deeper groundwater. The results will assist users, policymakers and stakeholders in identifying potential zones for groundwater across different applications.