Factors controlling the groundwater conditions of the Carboniferous strata in the Upper Silesian Coal Basin, Poland

Abstract

Czynniki wpływające na stan wód podziemnych w karbońskich osadach Górnośląskiego Zagłębia Węglowego Hydrogeological conditions vary between the various geological structures of the Upper Silesian Coal Basin (USCB). They depend on geological and mining factors. The most important geological factors which control the groundwater conditions within the USCB include: 1) incomplete insulation of Carboniferous strata by Tertiary clays, 2) occurence of gypsum and salt deposits in the Tertiary strata, 3) regional dislocation and fissility of Carboniferous rock complex, 4) distinct tendency of decreasing permeability of Carboniferous water-bearing sandstones with depth. The influence of mining activity on groundwater conditions in the USCB depends on the duration, size, depth and system of coal exploitation. Displacements, cracks and relaxation of rocks, which accompany mining works, increase permeability and provide hydraulic contact between waters in different aquifers by interruption of the insulating layers. Drainage of rocks by mine workings disturbs the natural hydrogeological regime in the USCB. Generally, groundwater salinity in the investigated depth interval, to 1,200 m, decreases with time due to replacement and mixing of atmospheric waters with buried brines.