EP 1110-1-27
27 Jan 00
2-2. Well Tests: Purpose and Description
a. General. Reliable, valid tests are critical to well assessment and management. Such assessment
and management is enhanced by a history of valid well data over time, back to installation if possible
(Chapter 3). Valid results depend on their reliable, valid, and reproducible test design, performance,
reporting, and interpretation. In practice, performance and proper reporting of results lag behind
performance standards. This pamphlet briefly reviews pumping test types and how they are used to assess
pump, well, and pumped-formation (aquifer) parameters. It describes minimum valid baseline data to be
reported, including
Minimum data standards for tests.
Minimum data for individual water level measurements (not just final levels), pumping rates,
sand (particulate) or colloidal content, and information on conditions that would affect
results.
How to determine adequate testing intervals.
b. Data collection.
(1) Accurate discharge flow data are needed for any pumping test. All devices should be
calibrated prior to installation, and at regular intervals to ensure proper operation. Flow measurement
devices suitable for pumping tests include:
Orifice weirs: Driscoll (1986) provides a detailed description of the necessary elements of the
construction and use of an orifice weir.
Mechanical flow meters which may also be used.
Sonic-based flow meters available that are accurate and well adapted to this application.
(2) Equally important are time and water level measurements throughout the test. The times of
measurements must be accurately reported and the water levels themselves reported accurately in decimal
units (for analysis input). If there is the potential for water cascading in the well during the test, fit the
well with a drawdown (stilling) tube to shield the water level probe from the cascading water and ensure
accurate water level measurements. Finally, the data must be recorded on a sheet specifically structured to
record and organize pumping test data (an example is supplied in Appendix D). Directly measuring
system gauge pressure is essential in evaluating pump performance and useful in making field decisions
on tests of relatively unknown wells or pumps.
c. Step-drawdown tests. Step-drawdown tests are probably the most valuable hydraulic testing
tool available for assessing well performance in the context of maintenance and rehabilitation. When
properly conducted and analyzed, they provide data on specific capacity and well and aquifer losses.
Additionally, from the analysis, well efficiency and drawdown and specific capacity at a given discharge
rate can be estimated.
(1) Conducting and analyzing step-drawdown tests are treated in detail in Kruseman and de
Ridder (1994). For porous medium aquifers, the Hantush-Bierschenk method of analysis is employed,
which is relatively straightforward. For fractured rock aquifers, Rorabaugh's method may be required,
which is less straight forward. A computer application to solve Rorabaugh's method, such as FASTEP
(Labadie and Helweg 1975), may be useful. Plate D-2 is an example step drawdown plot. Plates D-3 and
D-4 provide an analysis of the step-drawdown test charted in Plate D-2 to determine well and aquifer loss.
Plates are provided in Appendix D.
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