Water Discharges Management in Abandoned Underground Connected Coal Mines in Northern Spain
Ordoñez, Almudena; Alvarez, Rodrigo; Loredo, Jorge
University of Oviedo, Spain
The Carboniferous basin of El Bierzo (Northern Spain) has been intensively exploited by underground mining since the 19th century, mine shafts, spoil heaps, coal washeries and other mining installations remain as a legate of the historical mining activities in the district. From this coal mine district, the presented study is focused into the Torre del Bierzo Sector, where an important task to know is if the underground works of the nine abandoned coal mines are interconnected.
The water resources of these nine inactive coal mines have been calculated independently, considering the infiltration of effective rainfall –according to the permeability of outcrops in their drainage basin-, the infiltration from agricultural irrigation and the losses from watercourses into the mining works. This calculation has allowed estimating which mines are currently drained at the point of discharge, the average drainage flow of the system and the effective volume of the underground mining reservoir, which could be employed for mine water storage and water or geothermal use. This drainage is currently discharged into a small creek and high concentrations of Fe, Mn and sulphate are sometimes reached.
In order to know if the underground works from the nine mines of the sector act as an whole hydraulic system drained to the surface waters by one of the shafts, and to have an estimation of the mine water flow, origin and continuity of the water flow over the time and chemical quality, an approach based in geological, hydrological, hydrochemical and hydrogeological studies has been accomplished. To know if potential interconnections which could to define one or more hydraulic systems that could be considered as underground mine reservoirs, the potential water interconnections through low permeability massifs has been studied.
The fact to maintain a centralized pumping on the mine operations in one of the mines and the water discharge at the lowest mine portal of the whole system in the sector, point out that the whole of the underground mine works are interconnected and that the receiving water is drained towards this mine portal as corresponding to an unique hydrologic system. The water contribution received by each one of the mining subsystems (resources) anyway the whole volume of water stored on the mine voids (reserves) have been estimated, and in order to reduce iron, manganese and sulphates concentrations of water discharge, passive treatments could be applied, especially if the mine water flow could be reduced.