Characterizing seawater intrusion and groundwater vulnerability to salinization along the east coast of India

The groundwater resource in the coastal aquifers is highly vulnerable to seawater intrusion and salinization, triggered by multiple physical and anthropogenic factors. Therefore, the present study aims to address this pressing issue in the eastern coastal region of India based on 10 hydrochemical parameters of 1228 groundwater samples coupled with 15 lithologs, and annual groundwater draft for irrigation, industry, and domestic data for 37 coastal districts of the study area. The results reveal that 39.09 % of the samples are recorded as saline by the hydrochemical facies evolution diagram, while 55.09 % of the samples exhibit SMI >1, indicating the widespread presence of seawater intrusion into coastal aquifers. The region-specific study of SMI reveals that 91 out of 134 samples (67.91 %) are identified as SMI > 1 in West Bengal while the corresponding proportions are 63.61 % for Tamil Nadu, 56.10 % for Andhra Pradesh, and 32.49 % for Odisha. The study has also revealed hotspots for SMI, and the coastal regions of Odisha, Andhra Pradesh, and Tamil Nadu are found with significant hotspots for groundwater salinization. The fine sand and silt layers of the aquifers play a conducive role for the presence of saline water through direct seepage from the sea. Moreover, the excessive groundwater draft (0-7.94 × 10⁸ m³) for irrigation, (0-1.878 × 10⁷ m³) for industrial, and (0-2.029 × 10⁸ m³) for domestic uses shifts the hydraulic gradient landward, leading to the movement of saline water to the coastal aquifers.