A slug test is used to determine localized values of what property?

• A. Porosity
• B. Permeability
• C. Hydraulic head
• D. Specific yield

Answer: (B)

Slug tests focus on how easily water can move through the surrounding saturated material in a small, localized zone. By quickly changing the water level in a well and observing how the water responds over time, you can infer how readily groundwater can flow, which is a measure of permeability (often expressed as hydraulic conductivity in field practice). This makes the test ideal for obtaining localized values of permeability at the tested depth.

Porosity, while related to how much void space exists, isn’t what a slug test measures directly. Hydraulic head is the energy state you observe changes in, but the test uses those changes to estimate conductivity rather than measure head itself. Specific yield describes how much water drains from an unconfined aquifer during lowering of the head, a storage property, which slug tests don’t directly quantify. Thus, the property determined by a slug test is permeability.