Parametric assessment of hydrochemical changes associated to underground pumped hydropower storage

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porous medium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandoned mines for constructing UPHS plants. This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.