The Role of Pumping Tests in Site Characterization: Some Theoretical Considerations

Abstract Pumping tests are the primary means of estimating the large‐scale storage and transmissive properties of an aquifer for site‐characterization investigations. Most analyses of pumping‐induced drawdown are performed using either the Theis log‐log curve‐matching procedure or the approximate Cooper‐Jacob semilog method. These two procedures provide dissimilar estimates in nonuniform aquifers due to their emphasis on properties in different portions of a unit. The log‐log curve‐matching approach heavily weights the properties of local material, while the semilog procedure emphasizes the properties of material within the front of the cone of depression. The different emphasis of the two procedures results in log‐log parameters being more appropriate for estimating pumping‐well drawdown, while semilog parameters are better for estimating well yield. The magnitude of the difference between parameters estimated by the two approaches is a function of the degree of aquifer nonuniformity and the distance between the observation and pumping wells. The further the observation well is from the pumping well, the smaller the difference between the parameters. The difference between parameters estimated by slug tests and those estimated by pumping tests, on the other hand, will increase with this distance. Due to their emphasis on near‐well materials, slug‐test parameters may be of use in estimating pumping‐well drawdown when employed in a patchy aquifer model. In general, predictions of aquifer behavior can be improved by more careful application of the conventional techniques used in pumping‐test analyses.