THE EFFECT OF RECHARGE ON A PUMPING WELL IN A SHALLOW AQUIFER
Lawrence C. Murdoch
Department of Geological Sciences
340 Brackett Hall
Clemson University
Clemson, SC 29631
lmurdoch@clemson.edu
864-656-2597
ABSTRACT
Distributed recharge will have a profound effect on the performance of many
shallow pumping wells, but this effect has been largely overlooked. A conceptual model
for a well in a shallow aquifer has been developed that identifies an early period when
recovered water is released from storage, a transition period when water is both released
from storage and obtained from distributed recharge, and a steady period when the well
affects a large enough area so the pumping rate is balanced by the recharge rate. Most
pumping tests are conducted during the early period, but most recovery wells operate in
the late stage at near steady state. An analytical solution has been derived for this
conceptual model by assuming that recharge is a flux uniformly distributed over the
aquifer. The results quantify the conceptual model and provide a method for anticipating
the early, transition, and steady periods. Simple expressions predict the time when steady
state occurs, the drawdown in the aquifer and at the pumping well, and the radius of
influence of the well. The analysis is also used to predict the effect of a recharge pulse
during a pumping test. Preliminary results suggest that it should be feasible to correct
pumping test data for perturbations caused by recharge.