Pumping tests in semiconfined aquifer systems near Dorsten (F.R.G.) caused anomalous reverse water level fluctuations in observation wells tapping the overlying confining bed (aquitard) at different depths (multilevel piezometer). Whenever water is pumped from a well that is screened in the aquifer of the “Halterner Sande”, the piezometric surface in the aquitard (“Bottroper Mergel”) rises. After that increase, the water level falls according to the drawdown of head within the pumped aquifer (Noordbergum effect according to Verruijt, 1969). Conversely, the piezometric surface in the aquitard falls whenever the pump is shut off (Rhade effect). The anomalous water level reactions propagate with decreasing amplitude from the aquifer-aquitard boundary to the top of the semipermeable layer. Such water level fluctuations (“swelling effects”) may be explained by the capability of a water-saturated, compacted material to change volume when subjected to sudden pressure changes. On a practical basis, the Noordbergum and Rhade effects must be taken into consideration for evaluating long-term changes in chemical and hydraulic properties in pumped, semiconfined aquifer systems.