Assessing natural and human-induced drivers of groundwater quality and health risks in coastal deltas: advancing SDG 3, SDG 6, SDG 13, and SDG 15

Abstract Aim and objectives This study aims to evaluate the groundwater quality across four coastal delta districts of Tamil Nadu (Nagapattinam, Thiruvarur, Thanjavur, and Pudukottai) where groundwater serves as a vital resource for drinking and agricultural needs. The objectives are framed to assess spatial and seasonal variations, identify geogenic and anthropogenic influences, and evaluate potential human health risks. Materials and methods A total of 343 groundwater samples were collected during pre- and monsoon seasons to assess seasonal variability. Samples were analyzed for major cations (Ca 2 ⁺, Mg 2 ⁺, Na⁺, K⁺), anions (Cl⁻, HCO₃⁻, SO₄ 2 ⁻, NO₃⁻), and key physicochemical parameters using standard protocols. The assessment combined Water Quality Index (WQI), geospatial mapping, hydrochemical facies classification (Piper diagram), and multivariate statistical modeling to identify geogenic and anthropogenic influences. This integrated approach provided a detailed understanding of groundwater quality patterns and associated health risks, supporting sustainable management strategies. Key findings The results indicated that dominant cations followed the order Ca 2 ⁺ > Mg 2 ⁺ > K⁺ > Na⁺, while anions ranked Cl⁻ > HCO₃⁻ > SO₄ 2 ⁻ > NO₃⁻, with prevailing water types being Ca 2 ⁺–Cl⁻ and mixed Ca 2 ⁺–Mg 2 ⁺–Cl⁻. Hydrochemical analysis using Schoeller diagrams revealed reverse ion exchange processes influencing over 85% of samples. WQI classification showed 56% of samples as “excellent” for drinking in the monsoon season, improving to 75% in pre-monsoon. Multivariate analysis identified strong correlations among TDS, EC, hardness, Ca 2 ⁺, Mg 2 ⁺, Cl⁻, and SO₄ 2 ⁻, indicating combined natural salinization and anthropogenic impacts. Nitrate contamination emerged as a major health concern, particularly affecting children. Geospatial analysis highlighted distinct seasonal variations in ion concentrations, underscoring precipitation’s role in coastal groundwater chemistry. These findings stress the necessity for targeted management to mitigate salinization and nitrate pollution, with emphasis on seasonal dynamics and protection of potable water sources. Urgent measures include bioremediation, desalination, policy enforcement, and active community engagement. Aligning these interventions with SDG 6 (Clean Water and Sanitation), SDG 13 (Climate Action), and SDG 14 (Life Below Water) is essential for ensuring sustainable groundwater protection and enhancing climate resilience in vulnerable coastal aquifer systems.