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.

4.3.4.1

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

tested.

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

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