Reduction of Saline Waters Discharge from Coal Mines Through Filling and Sealing of Underground Voids

Drainage and discharge of mine waters belong to main environmental issues that must be appropriately addressed by underground coal mining industry. Large area of mine fields in Upper Silesia Coal Basin (USCB), which belong both to currently active and already closed mine, together with the geological and hydrogeological structure of the rock mass in USCB, create conditions requiring drainage and discharge of about 118 million m3/yr of mine waters of differentiated salinization. Increasing average depth of mining works and necessity of drainage of numerous closed mines results in increasing amounts of chlorides and sulphates being introduced into water environments, even then coal production of Polish mining industry is decreasing. Majority of mines waters are discharging directly to watercourses and the only significant environmental protection measure is control of the concentration of salt in main rivers. Balance of mine waters and Clˉ + SO42- ions demonstrates weight of this issue and give a background, on which technology of filling of underground voids has been discussed as a method, which, under several conditions, may reduce the discharge of brines and highly salinized mine waters (mineralisation above 42 g/dm3) by about 30%. Although technology of filling of voids with mixtures of water and finely grained solids (mostly fly ash) is well known and adopted by most of coal mines, its potential in reduction of saline waters discharge is being wasting due to inconsequence in its use and underestimating its value in terms of saline waters management. Influence of waters salinity on the physical properties of the fill, as well as benefits gained by the coal mines as result of filling of voids, show that this operations should be conducted in the possibly largest extent, limited only by availability of fly ash and volume of voids, being created as result of coal extraction.