Taptapani Geothermal Spring (∼Eastern Ghat Terrain, India): Investigating Hydrogeochemistry, Solute Transport Mechanisms, Geothermometry, and Water Quality Index

This study highlights the hydrogeochemical characteristics and geothermometry of the Taptapani geothermal spring, located along the lineament in the Eastern Ghats Granulite terrain of Ganjam district, Odisha (India). Water samples were collected during pre-monsoon, monsoon, and post-monsoon periods in 2021. Various physico-chemical parameters, including temperature, pH, electrical conductivity (EC), total dissolved solids (TDS), major ions (Ca2+, Mg2+, Na+, K+, HCO3−, F−, SO4−), and toxic trace elements (Fe, Cr, Zn, Cd, Cu, Mn, Ni, and Pb), were measured. Spring exhibits a natural sulfurous odour and is slightly basic, with a pH of 7.2 and a temperature of 42 °C, exceeding ambient levels due to deep meteoric fluid circulation influenced by a high geothermal gradient. TDS and EC values were recorded as 243.3 mg/l and 380.1 µS/cm, respectively. Geochemical characteristics of the spring water are governed by the lithology of the region. Sodium (Na⁺) dominates the cation budget, while bicarbonate (HCO₃⁻) dominates the anion budget, classifying the geothermal water as Na-HCO₃ type. Reservoir temperatures estimated using Na–K and Na–K–Ca geothermometers ranged from 122–135.4 °C and 140.5–152.4 °C, respectively. Based on the Water Quality Index (WQI), the spring was categorized as having poor water quality (WQI > 100), establishing a baseline reference for environmental forensic applications. While most ionic compositions were within permissible limits, except for fluoride (F⁻: 3.8–4.7 mg/l, average 4.20 mg/l), cadmium (Cd: 17–22 ppb, average 19.3 ppb), and nickel (Ni: 32–53 ppb, average 43 ppb) levels exceeded WHO (Citation2022) and BIS (Citation2012) standards. Parameters such as sodium percentage (Na%), sodium absorption ratio (SAR), residual sodium carbonate (RSC), magnesium absorption ratio (MAR), and Kelly Index (KI) were analyzed to assess irrigation suitability. Effective treatments like adsorption, membrane filtration, electrocoagulation, photocatalysis, and ion exchange can remove elevated elemental concentrations from thermal water.