On the interpretation of multi-well aquifer-pumping tests in confined porous aquifers using the Cooper and Jacob (1946) method

Abstract

The Cooper and Jacob (Trans Am Geophys Union 27:526–534. https://doi.org/10.1029/TR027i004p00526 ; Cooper, Jacob, Trans Am Geophys Union 27:526534, 1946) method is widely used to interpret data from both single- and multi-well aquifer-pumping tests in a porous homogenous and isotropic confined aquifer system. The method can be used to interpret both pumping and observation well drawdown. For observation wells (piezometers), the method said to be valid when u < 0.01 when drawdown observations are made in the near vicinity of the pumping well after a sufficiently long time of pumping. Despite the wide use of the method, the effects of using the Cooper and Jacob method to interpret multi-well aquifer-pumping test data are hardly discussed. The study illustrates and discusses the effect of using the Cooper and Jacob method to interpret multi-well aquifer-pumping tests. This is achieved with the help of simulations in 3 homogeneous one-layered confined and isotropic aquifer models using MODFLOW. Simulated drawdown is interpreted using the Cooper–Jacob method. The study shows that the transmissivity estimated from observation well data exponentially increases with the observation distance irrespective of the value of u. Only interpretation of pumping-well data with the Cooper and Jacob method correctly estimated the prescribed model transmissivity. Storativity estimates from observation data appears to decrease with increase in the observation distance as controlled by the Copper and Jacob equation but remained in the same order of magnitude as the prescribed model storativity. The study contributes towards a better practical understanding of the effects of using of using the Cooper and Jacob method to interpret multi-well aquifer-pumping test data for groundwater practitioners.