Thermal waters in Bulgaria

The geological structure of Bulgaria is a complex mosaic of plates and orogenic structures, characterized by deep faulting and lithofacial and magmatic contrasts. Three types of reservoirs are found in the country: stratified (northern Bulgaria), fractured, and mixed, where mineral water from a fractured reservoir is secondarily accumulated in a younger sediment reservoir (southern Bulgaria). The water temperature of all discovered geothermal reservoirs ranges between 25 and 100 °C, while those with temperatures up to 50 °C prevail. The flow rate varies from 1 to 20 L/s in about 75 % of the reservoirs. The established chemical content (TDS) is in the range from 0.1 to 1.0 g/L in southern Bulgaria and 0.1 g/L (100-150) g/L in northern Bulgaria. About 70 % of the discovered thermal waters are slightly mineralized (less than 1 g/L) and suitable for drinking. Direct thermal water application has an ancient tradition in Bulgaria. Current uses include balneotherapy, space heating and air-conditioning, greenhouses, thermal water supply, ground source heat pumps (GSHP), bottling of potable water and soft drinks. The present installed thermal capacity amounts to about 83.1 MWt, excluding GSHP. An extensive review of the geological background, thermal water characteristics and existing applications is presented. Thermal waters are an integral part of Bulgaria’s total water resources but due to their particular qualities, they are treated separately by legislation. Water management and legislation are briefly presented. © Springer International Publishing Switzerland 2016.