SENSITIVITY ANALYSIS OF PUMPING TESTS IN NONUNIFORM AQUIFERS

An approach for better understanding of the physical implication of es timated aquifer parameters is demonstrated by analysing the pumping te st data at Cottam in the Nottingham aquifer, UK. A sensitivity analysi s showed that the area represented by the estimated parameters was muc h smaller than the area covered by the depression cone. After paramete rs are estimated, further research should be carried out to understand what portions of the aquifer the parameters represent. The parameters estimated at Cottam represented mainly aquifer features between rough ly 100 and 2000 m. The sensitivity analysis also showed that the obser ved drawdown being satisfactorily matched by a model with uniform para meters does not prove that the aquifer is homogeneous. Slightly anomal ous data may imply the existence of large anomalous zones. Although th e drawdowns at Cottam could be 'satisfactorily' fitted by a model with uniform parameters, the fit could be improved by a model using a more permeable aquifer but with a zone about 700 m wide and with 42% less transmissivity.