Development galleries of the Zn-Pb ore deposit Olkusz-Sub-level are worked in the impermeable Permian strata. However, after crossing the Nothern Faul the working will enter the highly water bearing fissured - karstic Triassic (Muschelkalk). The paper presents hydrogeological conditions of mining in this area (water inflows proved and progrosed) and distribution of pressures within the Triassic aquifer. Hydrogeochemistry is shown of waters migrating into the developing workings from the Permian aquifer (both the free waters and pore solutions) as well as water quality of the Triassic aquifer is prognosed basing upon the available analyses.