present one method for determining the horizontal and vertical components of hydraulic
conductivity. In fractured media, the principal components of hydraulic conductivity may be
in directions other than horizontal and vertical. Hsieh and Neuman (1985) provide a method
for determining the primary components of hydraulic conductivity in these settings.
Determining Hydraulic Conductivity Using Field Methods
Sufficient aquifer testing (i.e., field methods) should be performed to provide
representative estimates of hydraulic conductivity. Acceptable field methods include
conducting aquifer tests with single wells, conducting aquifer tests with multiple wells, and
using flowmeters. This section provides brief overviews of these methods, including two
methods for obtaining vertically discrete measurements of hydraulic conductivity. Complete
descriptions of the methods summarized in this section are presented in greater detail in the
references provided.
A commonly used test for determining horizontal hydraulic conductivity with a single
well is the slug test. A slug test is performed by suddenly adding, removing, or displacing a
known volume of water from a well and observing the time that it takes for the water level to
recover to its original level (Freeze and Cherry, 1979). Similar results can be achieved by
pressurizing the well casing, depressing the water level, and suddenly releasing the pressure to
simulate removal of water from the well. In most cases, EPA recommends that water not be
introduced into wells during aquifer tests to avoid altering ground water chemistry. Single
well tests are limited in scope to the area directly adjacent to the well screen. The vertical
extent of the well screen generally defines the part of the geologic formation that is being
The following should be accurately recorded when conducting slug tests: the volume
of the slug added (e.g., plugged stainless steel pipe) or the volume of water removed from the
well; the changing static water elevation ( 0.01 inch) prior to, during, and following
completion of the test; and the time elapsed between water level measurements. Tests in
highly permeable materials often require the use of pressure transducers and high speed
recording equipment. The well screen and filter pack adjacent to the interval under
examination should be properly developed either to ensure the removal of fines or to correct
for drilling effects. The interpretation of the single well test data should be consistent with
existing geologic information (e.g., boring log data).
A modified version of the slug test, known as the multilevel slug test, is capable of
providing depth discrete measurements of hydraulic conductivity. The drawback of the
multilevel slug test is that the test relies on the ability of the investigator to isolate a portion
of the aquifer using a packer. Nevertheless, multilevel slug tests, when performed properly,
can produce reliable measurements of hydraulic conductivity. All equipment necessary for
performing multilevel slug tests is available commercially. The procedure for conducting a
multilevel slug test involves inflating two packers separated by a length of perforated pipe
November 1992
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