Closing of hard coal mines leads to quantitative and qualitative changes of a number of environmental factors. Water and ground are one of the most endangered environments under the negative impacts of mines' closing operations. Among the most important hazards are methane and carbon dioxide emissions from the coal beds. Intensification of gas flow to the surface area is most frequently caused partial or entire stopping of mine's waters pumping. This results in reconstruction of the Carboniferous aquifer, and consequently, the so-called 'piston effect'. In the closed mined this effect may be considerably intensified after stopping ventilation of the abandoned workings. The results of geochemical analyses within a closed Coal Mine KWK Morcinek are presented in the paper. The investigations were aimed at evaluation of the scale of occurrence of mine's gases in the surface zone and principles of its detailed geochemical monitoring.