Upon completion of surface sulphur mining activities in 1971, the Piaseczno mine was exploited for quartz sand in the years 1971-1980 and since then the post-exploitation workings were left in an unliquidated state. In the mine excavation a reservoir of water has formed, in which the water level is kept constant by the use of surface pumps. A 1997 mine liquidation program proposed the construction of a horizontal isolating layer and the synchronization of dewatering activities with the nearby Machów Sulphur mine at which the exploitation of sulphur has also been completed. As a result of financial and organizational decisions this program was not implemented. A realise method for liquidating the Piaseczno works will depend upon the filling of the reservoir to a height of 146.0 m a.s.l. and improving the surrounds. Simulation studies performed on a hydrogeological model of the Tarnobrzeg Sulphur Depression enabled the hydrodynamic effects of liquidation of the sulphur mines Machow and Piaseczno to be evaluated as they would occur during each phase of liquidation. This will to a large degree depend on the attained increase of the water level in the reservoir and the progress of liquidation works at Machów. The presented prognosis of changes to the water relations allows the description of the inflows from the Quaternary and Tertiary formations and also characterizes the expected distribution of the hydrodynamic fields. Consideration of all the possible situation development scenarios in both liquidated post-exploitation excavations showed that the immediate filling of the reservoir in Piaseczno would be beneficial. Achievement of the target water level height should be preceeded by the implementation of a melioration system. A lack of primary and specialized drainage trenches can lead to the degradation of agricultural grounds. and for some regions can constitue a direct threat due to flooding.