Hydrogeologically, the Central Coal Basin (Asturias, Spain) is characterized by predominantly low-permeability materials that make up a multilayer aquifer with very low porosity and permeability values, where the sandstones act as limited aquifers, and wackes, mudstones, shales and coal seams act as confining levels. Preferential groundwater flow paths are open fractures and zones of decompression associated with them, so the hydraulic behaviour of the system is more associated with fracturing than lithology. Thus, abandoned and flooded mines in the area acquire an important role in the management of water resources, setting up an artificial "pseudo-karst" aquifer. This paper evaluates the potential application of the abandoned mines as underground reservoirs, both for water supply and energetic use, mainly through heat pumps and small hydropower plants. In particular, the groundwater reservoir shaped by the connected shafts Barredo and Figaredo has been chosen, and a detailed and multifaceted study has been undertaken in the area. The exposed applications fit with an integrated management of water resources and contribute to improve economic and social conditions of a traditional mining area in gradual decline due to the cessation of such activity.

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In the current energy transition, there is a growing global market for innovative ways to generate clean energy. Storage technologies are potential and flexible solutions to deal with the intermittent nature of renewable resources. Closed mines can be used for the implementation of plants of energy generation with low environmental impact. This paper explores the use of abandoned mines for Underground Pumped Hydroelectric Energy Storage (UPHES), Compressed Air Energy Storage (CAES) plants and geothermal applications. A case study is presented in which the three uses are combined in just one mine. This preliminary study allows estimating an electrical energy generation of 153 and 197 GWH year −1 at the UPHES and CAES systems, respectively, and a thermal energy generation of 0.41 GWh year −1 at the geothermal system, with a total cost of 358 M€. An underground closed mine can be used to store energy for re-use and also for geothermal energy generation, providing competitive renewable energy with a low CO 2 footprint. These initiatives aid to ensure sustainable economic development of communities after mine closure.

Analytical results of soil samples taken in three different mercury mining sites in Northern Spain are studied to assess the potential adverse health effects of the exposure to trace elements associated with the mining process. Doses contacted through ingestion and inhalation and the dose absorbed through the skin were calculated using USEPA's exposure parameters and the US Department of Energy's toxicity values. The results of the risk assessment indicate that the highest risk is associated with ingestion of soil particles and that the trace element of major concern is arsenic, the exposure to which results in a high cancer risk value for all the sites ranging from 3.3 Â 10 À5 to 3.6 Â 10 À3

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behaviour of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22ºC) and increases with depth, so, considering the available flow (>100 L s -1 ), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use.