GIS–entropy based appraisal of groundwater quality, health hazards, and irrigation potential in the Samalpatti–Sevathur carbonatite terrains, South India

Groundwater pollution is an emerging universal issue. This study evaluates groundwater suitability for drinking and irrigation in Samalpatti-Sevathur carbonatite complexes, focusing on Fluoride (F⁻), and Nitrate (NO₃⁻) contamination and associated health risks. Seventy-five groundwater samples were collected in February 2025 and analyzed. F⁻ concentration in groundwater ranged 0.18-4.6 mg/L, and NO₃⁻ ranged 4.99-182.55 mg/L. Only 33.3% of F⁻ and 57.7% of NO₃⁻ samples met standards, with 37.3% samples deemed potable by Entropy Water Quality Index (EWQI). Ca²⁺ reflects a negative correlation with F⁻ and positive with NO₃⁻, indicating geogenic F⁻ from mineral dissolution and anthropogenic NO₃⁻ input, supported by Ca-HCO₃ facies and Gibbs rock dominance evidence. Irrigation indices, including SAR, EC, Na%, KR, RSC, and PI, along with interpretative plots like Wilcox, Doneen, and USSL diagrams, indicated that most of the samples were appropriate for irrigation. However, MHR revealed 78.7% of samples unsuitable due to high Mg²⁺ over Ca²⁺, reflecting geology and potentially impacting long-term soil quality and crop productivity. Health risk analysis shows children are more vulnerable to NO₃⁻ and F⁻ than adults. The study underscores health risks from NO₃⁻ and F⁻, advocating community awareness and sustainable groundwater management to protect health, support livelihoods, and achieve Sustainable Development Goal 6.