Drawdown and recovery data obtained for stepped- rate pumping tests can be used to calculate the drawdowns that would occur if the test were carried out a constant rate without stopping. The recovery phase of constant-rate pumping tests can be analyzed by the same method because cessation of pumping can be treated as a step change of pumping rate. The calculation assumes only that pumping during each step is at a constant rate, and that the principle of superposition is applicable, i.e., that the ground-water system is linear and time-invariant. It does not depend on the availability of theoretical expressions for the drawdown due to pumping. The calculation can be carried out for as long as water-level measurements are continued; however, possible errors in the values of calculated drawdown increase with increasing time, thus limiting the practical length of time for which the calculated values are reliable.
The constant-rate drawdown curves characterize the response of the linear time-invariant ground-water system to pumping. They can be used for the determination of formation parameters if an appropriate theoretical model is available. They can also be used directly to predict drawdowns, and the scope of this application can be broadened by use of the reciprocity principle. In either case the use of recovery data can significantly extend the effective duration of pumping tests.