On the practical application of the Cooper and Jacob distance-drawdown method to analyse aquifer-pumping test data

Abstract

Studies have illustrated how Infinite Acting Radial Flow (IARF) can be used as an objective criterion than the u condition to evaluate the valid of applying the Cooper and Jacob time-drawdown (1946) method. The Cooper and Jacob (1946) time-drawdown and distance-drawdown methods work on the same principle which incorporates the u condition. A similar study to assess the use of IARF as a criterion to determine the applicability of the Cooper and Jacob distance-drawdown (1946) method to analyse aquifer-pumping tests would be beneficial to groundwater practitioners. This study uses numerical groundwater flow modelling to assess and evaluate the application of the Cooper and Jacob (1946) distance-drawdown method to analyse multi-well aquifer pumping tests in ideal homogenous porous and isotropic confined aquifers under unsteady-state flow. Three multi-well aquifer-pumping tests are simulated in ideal one-layer homogeneous and isotropic confined aquifer models using Processing MODFLOW and the data is analysed by the Cooper and Jacob (1946) distance-drawdown method. The results shows that the Cooper and Jacob (1946) distance-drawdown method can only estimate correct transmissivity and storativity parameters when it is applied to observation data after IRAF. The u values calculated for the analysis vary over a wider range and do not satisfy all the literature prescribed u values. The study demonstrates and recommends how IRAF should be used as an objective criterion to determine the validity of applying the Cooper and Jacob (1946) distance-drawdown method.