Question

What is the difference between an aquifuge and an aquitard?

• A. Aquifuge has higher permeability than aquitard
• B. Aquifuge has lower permeability than aquitard
• C. Aquitard cannot store and transmit groundwater and aquifuge can store
• D. Aquitard is less porous than aquifuge

Hint:

• Aquitard: Low permeability, transmits water slowly. Can store water.
• Aquifuge: Impermeable, neither stores nor transmits water effectively.
• Therefore, an aquifuge has significantly lower permeability (essentially zero for practical purposes) than an aquitard.

Answer 1

The Correct Option is B

Hydrogeological formations are classified based on their ability to store and transmit water:

• Aquifer: Stores and transmits significant quantities of water (e.g., sand, gravel).
• Aquitard: A low-permeability formation that can store water and transmit it slowly. It retards but does not completely prevent groundwater flow. It can act as a leaky confining layer. Examples include silty clay, shale with some fractures.
• Aquiclude: A formation that can store water but is essentially impermeable and does not transmit significant quantities of water. Often used interchangeably with a very low permeability aquitard. Example: dense clay.
• Aquifuge: A geological formation that is impermeable and contains no interconnected pores or fractures. It neither stores nor transmits water. It acts as a complete barrier to groundwater flow. Examples include solid, unfractured igneous or metamorphic rock like granite.

Comparing aquifuge and aquitard:

• Permeability: An aquifuge is considered essentially impermeable, meaning it has virtually zero permeability for practical purposes. An aquitard has low permeability but still allows some slow water movement. Therefore, an aquifuge has lower permeability than an aquitard (option b). Option (a) is incorrect.
• Storage and Transmission: An aquitard can store water (due to porosity, even if pores are small) and transmit it slowly. An aquifuge neither stores (no effective interconnected pores) nor transmits water. Thus, option (c) "Aquitard cannot store and transmit groundwater and aquifuge can store" is incorrect; it's the opposite for storage (aquitard can store, aquifuge cannot effectively) and aquitard transmits slowly while aquifuge does not.
• Porosity: An aquitard (like clay or shale) can be quite porous, but its pores are small and poorly connected, leading to low permeability. An aquifuge (like solid granite) would have very low primary porosity (intergranular) and relies on fractures for any significant porosity, which if absent, means very low overall porosity. It's not straightforward to say one is always less porous than the other without more specifics, but permeability is the defining difference. Option (d) is not necessarily true or the primary distinction.

The key difference lies in their ability to transmit water, which is governed by permeability. An aquifuge is essentially impermeable, while an aquitard is poorly permeable but still allows slow transmission. \[ \boxed{\text{Aquifuge has lower permeability than aquitard}} \]