Hydrogeochemical characterization of groundwater and critical assessment of its quality in a coastal basin

In the twenty-first century, the ramifications of human civilization on natural resources are immense, which has led to water quantity, quality and environmental problems across the globe. Groundwater is a vital resource for ensuring water, food and environmental securities. This study focuses on in-depth hydrogeochemical characterization, and assessment of seawater intrusion and groundwater suitability in a coastal alluvial basin of eastern India. The groundwater-quality data of pre-monsoon season (April) for the 2012–2021 period were used in this study. The results of different analyses revealed that the comparative order of ionic concentrations in groundwater is: Na+ > Ca2+ > Mg2+ > K+ > Fe2+, and HCO3– > Cl– > SO42– > NO3– > F–. The Piper and Chadha’s Diagrams revealed that the major groundwater types are: ‘Ca–Mg–HCO3’, ‘Mixed Ca–Mg–Cl’, ‘Na–K–Cl–SO4’, ‘Ca–Mg–Cl–SO4’ and ‘Mixed Ca–Na–HCO3’. Based on the USSL Diagrams, groundwater from the irrigation viewpoint is characterized as ‘C2–S1’ type, followed by ‘C1–S1’, ‘C3–S1’ and ‘C3–S2’ types, which suggest that groundwater should be utilized carefully for irrigation in the study area. The Gibb’s Diagrams indicated that mainly ‘Rock-Water Interaction Dominance (Weathering)’ is responsible for controlling groundwater chemistry. The HFE Diagrams suggested that groundwater in ~ 22% of the observation wells is influenced by the ‘Reverse Cation-Exchange (Intrusion Phase)’ process. The ‘Seawater Mixing Index’ values of > 1 in the unconfined aquifer (~ 84% of observation wells) and the confined aquifer (~ 69% of observation wells) indicate that the freshwater-seawater mixing phenomenon considerably influences the groundwater. Furthermore, the Entropy Groundwater Quality Index for unconfined and confined aquifers indicated that the groundwater in 4–18% of the study area is of ‘Good’ to ‘Excellent’ quality, followed by ‘Medium’ quality (36–58% of the area), ‘Poor’ quality (17–36% of the area), and ‘Extremely Poor’ quality (6–24% of the area). On the other hand, the Irrigation Groundwater Quality Index of unconfined and confined aquifers suggested that the groundwater is suitable for irrigation (‘Good’ to ‘Excellent’ quality) in 95–97% of the study area.