Agnieszka Operacz1, Barbara Tomaszewska2,3. 1. Department of Sanitary Engineering and Water Management, Faculty of Environmental Engineering and Land Surveying, University of Agriculture in Krakow, Mickiewicza 21 Av., 31-120, Krakow, Poland. a.operacz@ur.krakow.pl. 2. Faculty of Geology, Geophysics and Environmental Protection, Department of Fossil Fuels, AGH University of Science and Technology, Mickiewicza 30 Av., 30-059, Krakow, Poland. 3. Mineral and Energy Economy Research Institute, Polish Academy of Sciences, Wybickiego 7, 31-261, Krakow, Poland.