Slug Test Method    

The Slug Test Method is one of a number of different methods that are used to evaluate the permeability (or hydraulic conductivity) of an aquifer.   The procedure involves either adding or removing a measured quantity of water from a well rapidly, followed by making a rapid series of water-level measurements to assess the rate of water-level recovery (either rising-head or falling-head).   These evaluations have advantages and disadvantages when compared with other methods.

Advantages of the slug test method include:

• Relatively low cost.
• Requires little time to conduct slug test(s).
• Involves removal of little or no water from the aquifer.

Disadvantages of the slug test method include:

• Only evaluates a small portion of the aquifer adjacent to the well bore.
• Does not provide an evaluation of portions of the aquifer not screened by the well being tested.
• May be profoundly influenced by gravel or sand pack material in the bore hole adjacent to the well screen.

The type of procedure that is used to evaluate a well is often determined by aquifer conditions.   A bail-down evaluation may be conducted in aquifers that are poorly transmissive and require many minutes to recover after they have been bailed.   However, it is difficult or impossible to test a highly transmissive aquifer by bail-down methods because water level recovery is so rapid.   Assessments using transducer measurements and a data-logger may be used to evaluate hydraulic conductivity in situations where water-level recovery is either slow or rapid.   In either situation, more accurate results are generally obtained when using an in-well transducer to collect periodic water-level versus time measurements.

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