Analysis of continuous and pulsed pumping of a phreatic aquifer

In a phreatic aquifer, fresh water is withdrawn by pumping from a recovery well. As is the case here, the interfacial surface (air/water) is typically assumed to be a sharp boundary between the regions occupied by each fluid. The pumping efficiency depends on the method by which the fluid is withdra wn. We consider the efficiency of both continuous and pulsed pumping. The m aximum steady pumping rate, above which the undesired fluid will break thro ugh into the well, is defined as critical pumping rate. This critical rate can be determined analytically using an existing solution based on the hodo graph method, while a Boundary Element Method is applied to examine a high flow rate, pulsed pumping strategy in an attempt to achieve more rapid with drawal. A modified kinematic interface condition, which incorporates the ef fect of capillarity, is used to simulate the fluid response of pumping. It is found that capillarity influences significantly the relationship between the pumping frequency and the fluid response. A Hele-Shaw model is set up for experimental verification of the analytical and numerical solutions in steady and unsteady cases for pumping of a phreatic aquifer. When capillari ty is included in the numerical model, close agreement is found in the comp uted and observed phreatic surfaces. The same model without capillarity pre dicts the magnitude of the free surface fluctuation induced by the pulsed p umping, although the phase of the fluctuation is incorrect. (C) 1999 Elsevi er Science Limited. All rights reserved.