Assessment of geochemical processes in the unconfined and confined aquifers in the Eastern Ganges Basin: a geochemical approach

Groundwater quality is gaining more importance in groundwater management due to rapid growth in population, agriculture and industrial sectors worldwide. The goal of the present study is to evaluate the groundwater chemistry and to identify the geochemical processes governing the water chemistry in the shallow unconfined and deeper confined aquifers in the Eastern Ganges Basin using geochemical methods. Groundwater samples were analysed for major ions and metals (Fe, Mn, Zn, Cu, Pb and As). Shallow wells are found to have high pH, EC, TDS, Ca, Mg, Cl and SO₄, and low HCO₃/Cl ratio compared to the deep wells. However, the average concentration of Na, HCO₃, NO₃, PO₄, F and Mn is not significantly varied with depth which indicates that the variation in the water chemistry between unconfined and confined aquifers is not only due to the natural processes but also indicates that surface contamination sources could have affected the water chemistry in the unconfined aquifer. In the unconfined aquifer, processes like wastewater infiltration, denitrification, reverse ion exchange and mineral weathering govern the water chemistry. The water chemistry in the confined aquifer is regulated by weathering of silicate and carbonate minerals and regional flow.