Groundwater Terminology – Classification of water-bearing formations A formation that is partly permeable and allows only seepage, yielding an insignificant supply of water, is called:

Difficulty: Easy

Correct Answer: Aquitard

Explanation:


Introduction / Context:
Hydrogeologic units are classified by their ability to store and transmit groundwater. Correct terminology is crucial when interpreting site investigations, designing wells, and assessing dewatering or recharge schemes.


Given Data / Assumptions:

  • Focus on qualitative transmissivity and yield.
  • Terms used in standard groundwater texts.
  • Steady-state conceptual understanding (no transient behavior implied).


Concept / Approach:

An aquifer is permeable enough to yield significant water to wells/springs. An aquiclude is porous but effectively impermeable (stores but does not transmit). An aquifuge is neither porous nor permeable. An aquitard is of lower permeability—partly permeable—allowing limited seepage and providing insignificant yields. Therefore, the described unit matches an aquitard.


Step-by-Step Solution:

Identify key descriptor: partly permeable with insignificant yield.Match to hydrogeologic class → aquitard.Differentiate from aquiclude (impermeable) and aquifer (high yield) and aquifuge (no storage or transmission).


Verification / Alternative check:

Clayey silts often act as aquitards; coarse sands and gravels are typical aquifers; dense unjointed igneous rock can behave as an aquifuge.


Why Other Options Are Wrong:

(a) implies significant yield; (c) precludes seepage due to lack of porosity; (d) stores water but effectively transmits none—contradicts “partly permeable.”


Common Pitfalls:

Confusing aquitards with aquicludes or assuming all clay layers are aquicludes—fracturing or fissuring can make a clay layer behave as an aquitard.


Final Answer:

Aquitard

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