LAUSR

The Indian state of Odisha has a number of thermal springs. These thermal springs are located at eight places (Attri, Tarabalo, Deulajhari, Magarmuhan, Bankhol, Badaberena, Taptapani and Boden) and belong to Mahanadi Geothermal Province, which is an Archean/Pre-Cambrian Geothermal Province. The thermal water discharging from these springs shows moderately acidic to moderately alkaline character (pH: 5.05–8.93) and the temperature ranges from 28 (Boden) to 58 °C (Tarabalo). Total dissolved solids (TDS) also shows a wide variation between 16.9 (Bankhol) and 595 mg/L (Deulajhari). A wide variation in the chemical characteristics of the thermal waters has been observed as they are located in different geological settings. Based on water chemistry, all the thermal springs can broadly be grouped into three water types: Na–Cl, Ca–HCO3 and Na–HCO3. The thermal spring water from Attri, Tarabalo and Deulajhari belongs to Na–Cl water type which is due to the circulation through granitic rocks. Higher concentrations of Cl and F in these thermal waters further suggest limited mixing and longer residence time as compared to the other areas where Ca–HCO3 and Na–HCO3 water types were found. Anion variation diagram clearly indicates that the thermal waters from Attri, Tarabalo and Deulajhari are fast ascending and fall in the mature water field; thus, their chemical signatures can be used to determine the reservoir temperature. However, in other areas, water chemistry is shaped by near-surface groundwater mixing processes and thus the chemical geothermometers may not be applicable to determine the reservoir temperature. No appreciable temporal variations have been observed in the water chemistry of the thermal waters.