Recovery Tests

by Glenn M. Duffield, President, HydroSOLVE, Inc.

Confined Aquifers

Theis (1935) devised a method of analyzing data from a recovery test in a confined aquifer in which residual drawdown, s', is plotted as a function of t/t', where t is the time since pumping began and t' is the time since pumping stopped. In a confined aquifer, the data from a recovery test are expected to fall on a straight line on a plot of s' vs t/t'.

Theis Residual Drawdown Curve.gif (8519 bytes)
Figure 1. Theis (1935) residual drawdown solution for a fully penetrating line source following a constant-rate pumping test in a confined aquifer.

Double-Porosity Aquifers

Fractured Finite-Diameter Pumping Test Schematic.gif (10942 bytes)
Figure 2. Pumping test in a double-porosity fractured aquifer with well bore storage.

Fractured media are sometimes represented by double-porosity models in which the fractures and matrix are treated as overlapping media. Dougherty and Babu (1984) and Moench (1984) proposed models for the analysis of pumping tests in double-porosity systems (Figure 2). Figure 3 compares the response for recovery tests in single- and double-porosity media.

Moench Slab Residual Drawdown Curve Wd=50.gif (10886 bytes)
Figure 2. Recovery test in a double-porosity aquifer using Moench (1984) solution for a double-porosity aquifer with slab-shaped blocks.

See also: recovery tests