Origin of geothermal waters along the east coast of India

Abstract

New sources of alternative energy are continuously being searched for and exploited to meet the increasing demand of energy. Geothermal energy has been given a high importance being one of the cleanest and reliable renewable energy resources. The management and sustenance of geothermal power plants depend largely on the availability of geothermal water, its origin, as well as on the mixing/cooling processes that take place during the ascent of the geothermal water. In this study an attempt is made to determine the origin of geothermal waters occurring in the eastern part of India. For this purpose, the springs located in the Indian states of West Bengal, Jharkhand and Odisha are considered. The isotopic data for thermal springs of West Bengal and Jharkhand are from earlier studies, while for the thermal springs of Odisha, 40 water samples including thermal water, groundwater, river water, cold springs and precipitation events, were collected for this study and analysed for hydrogen and oxygen isotopes. The thermal springs of West Bengal and Jharkhand have high salinity, however, through isotopic signature it is established that the thermal water is of meteoric origin and the high salinity has been attributed mainly to prolonged rock-water interaction.

The isotopic signature of the non-thermal waters at West Bengal and Jharkhand is characterized by negative shifts from the Global Meteoric Water Line (GMWL) that could indicate a fraction of recycled moisture in the local precipitation. The thermal waters from the areas show a similar isotopic signature. Oxygen and hydrogen isotopic ratios demonstrate that the thermal water of Odisha is of local meteoric origin. Some of the groundwater samples show substantial evaporation but the absence of a significant oxygen shift and relatively low TDS values indicate a limited rock-water interaction. Six of eight thermal springs are located along the northern and southern boundaries of the Mahanadi graben. Their position along the graben boundary helps the surface water percolate to greater depths at a faster rate without providing sufficient time for rock-water interaction. Isotopic composition of the two precipitation events measured from the Odisha region fits the Local Meteoric Water Line (LMWL) well, defined from the GNIP station at Sagar, indicating that the line may also be used as LMWL for the Odisha region. However, some of the thermal waters follow the GMWL demonstrating that more precipitation samples from the Odisha region are needed to describe the Odisha local precipitation line in detail.