Aquifer Testing 101 : Aquifer Tests
by Glenn M. Duffield, President, HydroSOLVE, Inc.
What Is An Aquifer Test?
In hydrogeology, an aquifer test (pumping test, slug test, constant-head test) is a controlled field experiment used to estimate hydraulic properties of an aquifer system such as transmissivity, hydraulic conductivity and storativity (storage coefficient).
In addition to its role in parameter estimation, the traditional constant-rate pumping test is also an important tool for the identification of aquifer boundaries (no flow and constant head). Modern computer-assisted pumping test evaluation employs derivative analysis to obtain a more robust interpretation of drawdown and recovery data.
Step-drawdown pumping tests are performed to evaluate pumping well performance (well efficiency).
Aquifer Testing Methods
The three aquifer testing methods used most frequently for the estimation of aquifer properties are as follows:
Estimating Aquifer Properties (Overview)
Typically, aquifer properties are estimated from an aquifer test by fitting mathematical models (type curves) to water-level displacement (drawdown) data or pumping rate data using a procedure known as curve matching.
Pumping Tests
Among hydrogeologists, the most familiar type-curve matching procedure for pumping tests is due to Theis (1935). The Theis method allows one to estimate the hydraulic properties of nonleaky confined aquifers having infinite extent (Figure 1).
Figure 1. Estimation of aquifer properties by matching Theis (1935) type-curve solution to time-drawdown data collected in an observation well during a constant-rate pumping test in a nonleaky confined aquifer (data from Walton 1962).
Publication of the work by Theis (1935) marked a major stride forward in groundwater science because of the mathematical rigor applied to the evaluation of transient (nonequilibrium) pumping test data. In the decades since Theis' seminal work, a great number of progressively more sophisticated models have appeared in the literature that further facilitate the interpretation of pumping tests for wide range of well configurations and aquifer geometries encountered in the field. For example, Hantush and Jacob (1955) published the first transient solution for the interpretation of pumping tests in leaky confined aquifers (Figure 2).
Figure 2. Estimation of aquifer properties by matching Hantush-Jacob (1955) type-curve solution to drawdown data collected in three fully penetrating observation wells during a constant-rate pumping test in a leaky confined aquifer. Theis (1935) solution for a nonleaky confined aquifer shown by red curve (data from USBR 1995).
Slug Tests
Beginning in the late 1960s, rigorous mathematical models also became available for the analysis of slug tests including the KGS Model by Hyder et al. (1994) (Figure 3).
Figure 3. Estimation of aquifer properties from time-displacement data collected during a slug test in an unconfined aquifer using the KGS Model (Hyder et al. 1994) type-curve solution (data from Butler 1998).
Constant-Head Tests
The first analytical solution in the groundwater literature for the interpretation of a constant-head (constant-drawdown) test in a nonleaky confined aquifer is due to Jacob and Lohman (1952). Using the Jacob and Lohman solution, one matches type curves to transient discharge data measured at the control well (Figure 4).
Figure 4. Estimation of aquifer properties by matching Jacob and Lohman (1952) type-curve solution to discharge data during a constant-drawdown pumping test in a nonleaky confined aquifer (data from Lohman 1972).
References
Looking for literature relating to aquifer tests? Check out the annotated aquifer testing reference list to find publications and articles pertaining to pumping tests, slug tests, constant-head tests and more.
Glossary
Please visit the glossary for a list of aquifer testing terms and their definitions.
See also: pump tests, aquifer performance tests