ANALYSIS OF PUMPING TESTS IN A BURREN LIMESTONE AQUIFER IN THE WEST OF IRELAND

The properties of the limestoneaquifer which used asa source of water supply forAthenry,Co.Galway. Ireland, were investigated by pumping tests. Three tests were conduced, on 18th July 1994, 8th March 1995. Data from these pumping tests were analysed to determine the flow conditions during the tests. The time-drawdown curves showed that the flow regime during pumping was unsteady. The aquifer's behaviour during the tests was complex. According to the driller's report the aquifer was confined but when data from all the tests were plotted in the form of time-drawdown curves, they showed the trend qualitatively similar to the Neuman's theoretical curves for unconfined aquifers with delayed yield. The geological data from the well logs showed that the aquifer consists of weathered and dolomite below 10 m. The data was processed with four different methods starting from simplest, i.e. the Theis's curve matching. The Neuman's curves for unconfined aquifers with delayed yield were then matched with the measured data. The parameters of the Neuman's curves were also optimized by the non-linear method of least squares based on a modified version of the Rosenbrock algorithm. Inallthree cases,substantial deviationsof field data fromthe theory used were found. Finally, the Bourdet-Gringarten method for double-porosity fractured aquifers was used. In this method, the early and late time data from selected wells were matched with the classical Theis type curve. The estimated parameter values had wide range of variation in all cases except for the Bourdet-Gringarten curve matching which gave consistent values of transmissivity, but the values of storativity are very uncertain even with this method, their average variation is between 0.0005 and 0.005. The average estimate of the aquifer transmissivity is 0.075 m2/min.The results of pumping tests show that no single classical theory of confined, unconfined, semi-confined or even fractured aquifers can fully succeed in interpreting the field data. More complex theories and their combinations should be applied in future if the aquifer behaviour is to be explained satisfactorily. In particular it appears that the flow in the fractured aquifer near the well may be non-darcian.