Water hazard has been accompanying underground mining since the first mines were built. The hazard is particularly often in the areas of mines situated in hydrogeologically outcropped part of USCB and in water rich formations of Cracow Sandstone Series. To plan properly mining actions and technical measures at each stage of life of a mine it is necessary to evaluate hydrogeological and geomechanical conditions and their changes. The conditions determine formation, occurrence and volume of the most serious sources of water hazard. Symptoms obtained in geomechanical tests and observations of forming and dewatering reservoirs of underground water, show that it is necessary to update constantly evaluation and classification of sources of water hazard or the state of water hazard in the coal mines of USCB. Development of underground mining in 1945-1990, which resulted in a quick increase in production, determined development and the range of influence of mining operations on the rock mass and the influence on the state of drainage and saturation of the rock mass. The result of the changes was an apparent influence on the changes in the state and shaping water hazards in the course of time. Since 1989 economic conditions of functioning of mines have been tightly associated with the conditions and rules of market economy. As a result of each of the so-called restructuring of mining activity a certain number of mining companies was closed, merged or split. The consequence is that in the vicinity of active mines and prospective mining areas, more and more often there are partially or completely flooded abandoned coal mines. Flooded coal mines have changed and still do hydrogeological conditions of their surrounding and force active mining companies to introduce changes in mining activities they are planning and conducting. The current state of flooding mine workings, is a result of realizing previous plans of restructuring mining industry, and all the changes of the state require hydrogeological documentation and evaluation of water hazard. In the today's conditions of functioning of mining industry, sources of water hazards like water reservoirs in goafs, are one of six main types of sources of hazard, and at the same time the biggest problem and the most serious threat for active mine workings. As the hydrodynamic conditions in the closed areas stabilise and the water piles up close to the surface, an increase in the influence of reservoirs on the state of environmental and public hazard (subsidence, overflowing, flooding, pollution of water in the aquifers located in the overburden and surface water). As there is a qualitative change in the directions, causes and sources of water hazard, it shall be expected that the changes will tend to increase the threat level from the closed mines. Hence since 2000 the Central Mining Institute has been focused mainly on methodology research, both laboratory ones of various scale of observation referring to the properties of rocks and rock debris, and in situ ones and forecasting ones accompanied by proposed multidirectional applications of the developed methods in mining and environmental practice. The effect of the works was developing and patenting a few new methods. The effects of works which have been conducted in the last several years were proposed changes in defining water hazard, classifying the hazard and its sources. Classifications of underground water reservoirs, deposits located in the vicinity of reservoirs in closed coal mines and water safety of shafts were proposed. The devised test and evaluation methods have wide practical applications in evaluating water hazard and limiting the hazard, as well as estimating volume of water in reservoirs of closed mines and estimating energy of the water and free methane deposit in the abandoned goafs and mine workings. Their application in hydrogeology plays an important role in estimating volume of water in aquifers built of porous hard rocks. It is also important and applicable in environmental engineering to evaluate volume of water, estimating conditions of its accumulation and flow, and migration of pollution mainly within surface water reservoirs reclaimed with waste rock.
