Why does an artesian well flow without pumping?
A. The water table is at the surface in an artesian aquifer.
B. The hydraulic head is very low in the aquifer.
C. The water in an unconfined aquifer is pressurized.
D. The water in a confined aquifer is pressurized.
The Correct Answer and Explanation is:
Correct Answer: D. The water in a confined aquifer is pressurized.
An artesian well flows without pumping due to the natural pressure within a confined aquifer. A confined aquifer is a layer of groundwater that is trapped between two impermeable layers of rock or clay. These layers prevent the free flow of water in or out of the aquifer. When water enters this confined space, typically from a recharge area where the permeable rock is exposed at the surface, it becomes pressurized due to the weight of the overlying water and the confinement of the aquifer.
This pressure is known as artesian pressure, and it can be strong enough to force the water to rise above the level of the aquifer when a well is drilled into it. If the pressure is high enough, the water will flow all the way to the surface without the need for mechanical pumping—this is called a flowing artesian well.
Let’s evaluate the other options:
- A. The water table is at the surface in an artesian aquifer: Incorrect. The water table refers to the top of an unconfined aquifer, and artesian aquifers are confined, not open to the surface.
- B. The hydraulic head is very low in the aquifer: Incorrect. A low hydraulic head would result in little or no pressure, so the water would not flow on its own. Artesian wells require a high hydraulic head.
- C. The water in an unconfined aquifer is pressurized: Incorrect. Unconfined aquifers are not pressurized because they are open to the atmosphere at the top.
- D. The water in a confined aquifer is pressurized: Correct. This pressure is what causes artesian wells to flow naturally.
In conclusion, an artesian well flows without pumping due to the natural pressure in a confined aquifer, which forces the water upward once the aquifer is tapped.