Identification of major ion chemistry and associated hydrogeochemical processes in the groundwater environment in Bangladesh

Detailed hydrogeochemical investigations were carried out in four areas selected from south to north of Bangladesh such as, Lakshmipur District in the southern part, Faridpur and Nawabganj Districts in the central part and North Bengal in the northern part of the country with the main objective to detect and delineate the major hydrogeochemical processes that are responsible for groundwater chemistry in Bangladesh. The study approach includes geochemical analysis, graphical plots and analysis of the hydrochemical data to assess the geochemical evaluation of aquifer system based on the ionic constituents, water types, hydrochemical processes etc.
Derived Gibbs diagrams reveal that the overall hydrogeochemical environment of the study areas is controlled by the rock water interaction dominance. Further analyses with Piper diagrams show that the hydrogeochemical facies in Lakshmipur and Faridpur is mostly Ca–Mg–HCO3 type, though other type waters (Na–HCO3, Na–Cl and Mg–Cl) also observed in Lakshmipur and the hydrogeochemical facies in Nawabganj and North Bengal is mostly Ca–HCO3 type though other type waters (Na–HCO3, Na–Cl and Ca–Cl) also observed in North Bengal. In addition, various relationships related to carbonate dissolution and silicate weathering process support that in all four areas silicate weathering is dominating. The cation exchange process controls the concentration of ions and confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer minerals. The concentrations of sulfate in the groundwater are very low throughout the study areas indicating sulfate reduction. All of these results suggest that weathering and dissolution of silicate minerals, cation exchange processes, rock-water interaction, sulfate reduction etc. are responsible for the groundwater chemistry in Bangladesh regardless of different geologic formation. Thus, the present study and analysis techniques can be useful as an effective tool in groundwater aquifer system evaluation.