Application of environmental isotopes (³H and ¹⁴C) in age dating of thermal water

Geothermal energy can act as an affordable and sustainable solution to reduce dependency on fossil fuels. Environmental radioactive isotopes such as tritium (³H) and carbon-14 are very useful in estimating the age of the thermal water. In this submission, we have discussed the use of these isotopes in estimating the residence time of the thermal waters encountered in the Manuguru geothermal area situated in the Telangana state, India. In geothermal systems tritium is generally used to qualitatively estimate the approximate residence time of the thermal fluids and their mixing with shallow ground water if any. The tritium value of the thermal water ranges from 0.62 to 1.5 TU, and in non-thermal water samples the tritium concentration ranges from 2.2 to 5.7 TU. Most of the thermal water samples have tritium value <1 TU, which points out that these samples have long subsurface residence times (>50 years) and got recharged prior to 1951. Thermal water samples showing tritium concentration >1 TU are probably due to the mixing with cold water in the upflow zone