Research article Prediction of the flooding of a mining reservoir in NW Spain R.  Alvarez a, * , A. Ord  o ~ nez a , E. De Miguel b , C. Loredo a a Dep. Explotaci on y Prospecci on de Minas, University of Oviedo, Independencia, 13, 33004 Oviedo, Asturias, Spain b Environmental Geochemistry Research and Engineering Laboratory, Universidad Polit ecnica de Madrid, Spain article info Article history: Received 5 August 2016 Received in revised form 19 September 2016 Accepted 21 September 2016 Available online xxx Keywords: Mining reservoir Flooded mine FEFLOW GRAM abstract Abandoned and flooded mines constitute underground reservoirs which must be managed. When pumping is stopped in a closed mine, the process of flooding should be anticipated in order to avoid environmentally undesirable or unexpected mine water discharges at the surface, particularly in populated areas. The Candín-Fond on mining reservoir in Asturias (NW Spain) has an estimated void volume of 8 million m 3 and some urban areas are susceptible to be flooded if the water is freely released from the lowest mine adit/pithead. A conceptual model of this reservoir was undertaken and the flooding process was numerically modelled in order to estimate the time that the flooding would take. Addi- tionally, the maximum safe height for the filling of the reservoir is discussed. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction It is reported that coal is one of the major global economic contributor (Wolde-Rufael, 2009). The impact of coal mining on the environment, particularly on land use and surface and ground- water, is a global concern (Younger et al., 2002; Bell et al., 2006). Contaminative mine drainage waters constitute a major hydro- geological and geochemical problem, particularly when they are acidic, heavy-metal-containing, sulphate waters derived from py- rite oxidation and are discharged at the surface (Banks et al., 1997). Mining activities, along with the population explosion and the extensive exploitation of the natural resources in a region can contribute significantly to the impact on groundwater (Karan and Samadder, 2016). However, mine waters are not merely to be perceived as a problem, they can be regarded as energy, industrial or drinking water sources. For more than two centuries, up to 70% of all Spanish production of coal came from the Asturian Central Coal Basin (CCB). From late 1980s, mining has resulted in the closure of most coal mines (Moreno and L opez, 2008; Jard on et al., 2013). Historically in the CCB, a first phase of mountain mining was undertaken from valley level to the highest outcrops of the coal seams. Exploitation would then continue through vertical shafts to access lower heights, opening galleries on rock and exploiting coal up to depths of 700 m below the valley. Since mining left a fractured rock mass, the infiltration of rainwater was facilitated and an intense pumping drainage had to be maintained when the mine was active (Ord o~ nez et al., 2012). A correlation between precipitation and water percolating to the mine workings to be subsequently pumped out, has been found in several cases in the CCB (Arquer et al., 2006; Ord o~ nez et al., 2012). These studies also proved that there is a to- tal independence between the drainage and the depth of the mine workings, as the latter does not affect significantly the recharge area; this shows that there are no relevant inputs from potential permeable levels intercepted by such works and the average flow pumped from the mine can be assimilated to the recharge provided by rain. However, the period of delay (time spanning from the infiltration of rainwater on the surface until it is pumped out again from the mine workings) varies depending on the mining reservoir. This pumping is usually interrupted when the mine is closed, proceeding to the gradual flooding of the mine voids or the so- called groundwater rebound (Gandy and Younger, 2007). During this flooding, water level raises through each channel, the faster the larger the hydraulic conductivity, moving fast through free mine voids and leading to a progressive saturation, until hydrodynamic equilibrium is reached (Younger et al., 2002; Arquer et al., 2006; Delgado et al., 2008). The rebound depends on infiltration flow (and therefore on the season) and on void volume, so it will slow down when reaching the height of the mine levels, where a higher void volume concentrates (galleries) and rise faster in between them (Ord o~ nez et al., 2012). In the area affected by mining, fissures constitute preferential flow paths for recharge. Thus, the successive * Corresponding author. E-mail address: alvarezrodrigo@uniovi.es (R.  Alvarez). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2016.09.072 0301-4797/© 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Management xxx (2016) 1e10 Please cite this article in press as:  Alvarez, R., et al., Prediction of the flooding of a mining reservoir in NW Spain, Journal of Environmental Management (2016), http://dx.doi.org/10.1016/j.jenvman.2016.09.072