Aquifer terminology and common groundwater well types Select the correct set of statements about aquifers, aquicludes, artesian versus non-artesian conditions, and ordinary gravity (water-table) wells.
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AA confined, impervious bed laid over an aquifer is called an aquiclude.
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BThe topmost water-bearing stratum with a free surface is termed a non-artesian aquifer.
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COrdinary gravity wells that draw from the topmost water-bearing stratum are called water-table wells.
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DA permeable stratum that can yield appreciable quantities of groundwater is called an aquifer.
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EAll the above.
Answer
Correct Answer: All the above.
Explanation
Introduction / Context:Groundwater terminology distinguishes between formations that transmit water and those that do not. Correct use of terms like aquifer, aquiclude, and water-table well is essential for hydrogeologic mapping, well design, and yield estimation.
Given Data / Assumptions:
- Standard hydrogeologic definitions are used.
- Statements relate to common near-surface formations and typical well practice.
Concept / Approach:
An aquifer is a geologic formation that is both permeable and saturated enough to yield useful water. An aquiclude (or aquitard/aquifuge depending on degree) has very low permeability and confines an underlying aquifer. A non-artesian (unconfined) aquifer has a free water surface (water table). A water-table well draws from this unconfined zone and responds to seasonal fluctuations of the water table.
Step-by-Step Solution:
(a) Correct: An aquiclude is an impermeable or nearly impermeable layer that can overlie or underlie an aquifer and act as a confining bed.(b) Correct: A non-artesian aquifer has a free surface; it is the uppermost water-bearing layer open to atmospheric pressure.(c) Correct: Water-table (gravity) wells tap the unconfined aquifer directly.(d) Correct: Definition of an aquifer is a permeable formation yielding appreciable groundwater.Verification / Alternative check:
Introductory groundwater texts (hydrogeology) define these terms consistently; field practice labels wells by whether they are confined (artesian) or unconfined (water-table).
Why Other Options Are Wrong:
- Since (a)–(d) are all true, choosing only one is incomplete; therefore “All the above” is the only comprehensive selection.
Common Pitfalls:
- Confusing aquiclude (essentially impermeable) with aquitard (low permeability but not zero).
- Assuming any top layer is non-artesian without confirming the presence of a free water surface.
Final Answer:
All the above.