Geochemistry and Utilization of Water from Thermal Springs of Tawang and West Kameng Districts, Arunachal Pradesh

The hydrogeochemical studies provide insights about reservoir conditions of geothermal springs along with utilization of thermal waters for domestic, livestock and irrigation purposes. Most of the hot springs of Tawang and West Kameng districts of Arunachal Pradesh emanated through garnet bearing high grade gneiss-migmatite-schist-quartzite sequence of the Se La Group, except for Dirang hot springs which emanate from river terrace deposits lying on the footwall of deformed quartzite-phyllite. The thermal waters are of mixed Na-Ca-HCO3-SO4-Cl type, meteoric in origin and at the same time immature in nature, moving sluggishly towards mineral-fluid equilibration zone with slow rock-water interactions. Chemical geothermometry showed wide variation in estimation of sub-surface reservoir temperature and quartz geothermometry model fits prominently to provide the most reliable reservoir temperature varying within 90 +/- 40 degrees C. The studies recorded highest reservoir temperature of Thinghu hot spring with 133 degrees C with very high fluoride concentration in all the hot springs except Bishum and Phudung as per BIS (2012) IS: 10500 specifications. High fluoride and sulfate concentration in thermal spring waters make it unsuitable for drinking purpose. The applicability of thermal waters for irrigation is predicted through sodium adsorption ratio (SAR) calculations which showed that waters of Dirang-2, Sorbe and Kitpi-1&2 are not suitable for irrigation purpose due to high salinity and SAR values.