Variable-Rate Pumping Tests for Radially Symmetric Nonuniform Aquifers

Conventional pumping test methodology is of limited effectiveness for defining the spatial distribution of aquifer properties because of the nonuniqueness of the parameter estimates. Sensitivity analysis can be used to develop a pumping test procedure that significantly decreases the uncertainty associated with the estimated parameters. This approach employs systematic variations in pumpage rates to achieve reductions in parameter uncertainty. These reductions are obtained by increasing the sensitivity of drawdown to flow properties while simultaneously constraining the growth in the correlation between the effects of different flow properties on observation well drawdown. Numerical experiments demonstrate the importance of the magnitude and frequency of the rate variations, the spatial and temporal pattern of data collection, as well as the dependence of the technique on the total duration of the pumping test. Significant decreases in parameter uncertainty can be expected in any flow system in which the primary component of flow is in the radial direction. This study demonstrates that sensitivity analysis can be an important tool in the development of methodology for the characterization of subsurface properties.