Mine water can be a renewable and economical source of geothermal and hydraulic energy. Nine discharges from closed and flooded coal mines in the Laciana Valley (León, NW Spain) have been studied. Various technologies for the energy use of mine water, as well as the influence of factors such as temperature, the need for water treatment, investment, potential customers and expansion capacity, have been evaluated by means of a decision-making tool. It is concluded that the most advantageous option is an open-loop geothermal system using the waters of a mountain mine, the temperature of which exceeds 14 °C and whose distance to customers is less than 2 km. A technical–economic viability study for a district heating network designed to supply heating and hot water to six public buildings in the nearby town of Villablino is presented. The proposed use of mine water might help areas that have been greatly affected socioeconomically by the closure of the mines and has other advantages compared to conventional energy systems, such as the reduction of CO2 emissions. Graphical Abstract It showing the advantages of using mine water as an energy source for district heating and a simplified layout.

Abstract. Laciana Valley District is a coal mining region located in northern Spain. This region counts with several mining facilities, among them: eight underground mines (six mountain mines and two mine shafts) and three open pit mines. Nowadays, all the mining facilities have been closed down and are flooded. The water found inside them could be used as a geothermal resource due to its thermal properties and the proximity to population. The aim of the study is to analyze the water of the facilities located in Laciana Valley and determine its potential to be used as a geothermal resource for a district heating system. In order to achieve this goal an extensive field work has been performed, nine different mine water discharges have been chosen and several water characteristics have been selected for analysis. The parameters measured have been pH, conductivity, hardness, temperature, turbidity and alkalinity. The results have been evaluated in order to determine the fluctuations of the physico-chemical parameters throughout a hydrological year and the mining facilities have been compared between each other regarding their mine water quality. The analysis of all the information gathered in the study shows a noteworthy thermal potential in the water of the abandoned mines of the region.

Mine water can be a renewable and economical source of geothermal and hydraulic energy. Nine discharges from closed and flooded coal mines in the Laciana Valley (León, NW Spain) have been studied. Various technologies for the energy use of mine water, as well as the influence of factors such as temperature, the need for water treatment, investment, potential customers and expansion capacity, have been evaluated by means of a decision-making tool. It was concluded that the most advantageous option is an open-loop geothermal system using the waters of a mountain mine, the temperature of which exceeds 14ºC and whose distance to customers is less than 2 km. A district heating has been designed to supply, with technical-economic viability, heating and hot water to six public buildings in the nearby town of Villablino. The proposed use of mine water might help areas that have been greatly affected socio-economically by the closure of the mines and has other intangible advantages compared to conventional systems, such as the reduction of CO2 emissions.

Laciana Valley District is a coal mining region located in northern Spain. This region counts with several mining facilities, among them: eight underground mines (six mountain mines and two mine shafts) and three open pit mines. Nowadays, all the mining facilities have been closed down and are flooded. The water found inside them could be used as a geothermal resource due to its thermal properties and the proximity to population. The aim of the study is to analyze the water of the facilities located in Laciana Valley and determine its potential to be used as a geothermal resource for a district heating system. In order to achieve this goal an extensive field work has been performed, nine different mine water discharges have been chosen and several water characteristics have been selected for analysis. The parameters measured have been pH, conductivity, hardness, temperature, turbidity and alkalinity. The results have been evaluated in order to determine the fluctuations of the physico-chemical parameters throughout a hydrological year and the mining facilities have been compared between each other regarding their mine water quality. The analysis of all the information gathered in the study shows a noteworthy thermal potential in the water of the abandoned mines of the region.