New Type Curves for Estimation of Aquifer Properties from Water-Level Recovery Under Theis ConditionsSuggested Citation:
Goode, Daniel J., 1996, New type curves for estimation of aquifer properties from water-level recovery under Theis conditions: (abs.), p. S95 in 1996 Spring Meeting, supplement to Eos, 23 April 1996, American Geophysical Union, Washington DC.
* Type Curve Plot: Postscript (142K) or PDF (250K)
* Data, dimensionless drawdown vs normalized time: tab-delimited or comma-delimited text
* FORTRAN source code for program to compute type curve for any dimensionless pumping duration
New type curves are proposed for estimation of aquifer hydraulic properties, transmissivity (T) and storage coefficient (S), from water-level recovery data after cessation of a constant-rate discharge test. When Theis first presented his solution for water-level decline during constant-rate pumping in an infinite, homogeneous, confined aquifer, he also presented the solution for recovery. His proposed method for analysis of the recovery data, based on the large-time (Cooper-Jacob) approximation, remains the standard method used today. However, S cannot be determined, and early-time data cannot be analyzed. New log-log type curves are developed from Theis' solution that allow the simultaneous estimation of T and S from recovery data, without making the large-time approximation. The drawdown is plotted versus the ratio of time since pumping stopped to duration of pumping. Type curve matching, in contrast to the Theis procedure for pumping data, is performed by shifting only the drawdown axis; the time axis is fixed because it is a relative or normalized time. The match-point for the drawdown axis gives T. S is determined from matching the curve shape, which depends on early-time data. Recovery data from the pumped well is usually not sensitive enough to accurately determine S, unless the pumping duration is relatively short. However, observation-well data are often suitable for S estimation. Multiple well data can be plotted and matched simultaneously (a composite plot), with wells at different radii falling on different curves, but having consistent parameters. In addition to providing confirmation of results for the pumping period, this method can be superior to analysis of the pumping period data when discharge is erratic or drawdown is affected by well loss. Several examples from the literature and tests in fractured rock in Pennsylvania confirm the accuracy and utility of the new type curves.
See also: Goode, Daniel J., 1997, Composite Recovery Type Curves in Normalized Time from Theis' Exact Solution: Ground Water, v. 35, no. 4, p. 672-678.