Artesian Well – What It Is and How It Works   Recently updated !


Artesian Well

Artesian wells are fascinating due to their unique ability to bring groundwater to the surface without the need for pumping. These wells take their name for Artois region in France, which has numerous examples. Understanding artesian wells involves hydrogeology, the study of groundwater movement through soil and rock, and appreciating the delicate balance of geological forces that allow these natural phenomena to occur.

Artesian Well Definition

An artesian well is a type of well where natural pressure forces water to the surface. Unlike conventional wells, which require a pump to draw water up, artesian wells tap into confined aquifers—layers of water-bearing rock or sediment that are trapped between layers of less permeable substrate. Tapping a confined aquifer offers an avenue for pressure release, which carries water up toward the surface.

Etymology of the Term “Artesian”

The term “artesian” comes from the name of the French province Artois (formerly called Artesium in Latin). This region has numerous flowing wells, which were drilled as early as the 12th century. The name has since become synonymous with wells that utilize the natural pressure of confined aquifers to bring water to the surface.

How an Artesian Well Works

Artesian wells operate based on the principles of hydrostatic pressure and confined aquifers. Here’s a step-by-step explanation of how they work:

  1. Confined Aquifer: A confined aquifer or artesian aquifer is a water-bearing layer of rock or sediment that is sandwiched between two impermeable layers, such as clay or shale.
  2. Recharge Area: Water enters the aquifer at a higher elevation where the aquifer is exposed to the surface. This is known as the recharge area.
  3. Hydrostatic Pressure: The water that enters the aquifer at a higher elevation creates pressure within the confined aquifer. This pressure increases as more water accumulates.
  4. Drilling the Well: When a well is drilled into the confined aquifer, the natural pressure forces the water up through the well. If the pressure is high enough, the water rises above the level of the aquifer and flows out at the surface. This type of well is a flowing artesian well. However, pressure only carries water up so far before hydrostatic equilibrium occurs. If the surface level is above this height, then the well is still an artesian well, but not one that flows.

Contrast With a Normal Well

Both a normal well and an artesian well supply water, but they do this in different ways:

  • Normal Well: In a typical well, water comes from an unconfined aquifer, which is an aquifer where water seeps from the ground surface directly above the aquifer. These wells require a pump for bringing water to the surface. The water table fluctuates with changes in precipitation and usage.
  • Artesian Well: In contrast, an artesian well draws from a confined aquifer with enough pressure to push the water to the surface naturally. If the pressure is high enough, this leads to a free-flowing well, eliminating the need for a pump. However, if the ground surface is higher than the piezometric level of the confined aquifer, water does not reach the surface and you still need a pump to get the water. In many cases, this level is still higher than the water level from the nearest unconfined aquifer, offering an advantage.

Glossary of Terms

  • Aquifer: A body of permeable rock that can contain or transmit groundwater.
  • Confined Aquifer: An aquifer that is bounded above and below by layers of impermeable rock or clay, creating pressure.
  • Hydrostatic Pressure: The pressure exerted by a fluid at equilibrium due to the force of gravity.
  • Impermeable Layer: A layer of material, such as clay or shale, that does not allow water to pass through.
  • Permeability: The ability of a material to allow fluids to pass through it.
  • Piezometric Level: The piezometric level, also known as the potentiometric surface, is the level to which water rises in a well that taps into a confined aquifer. It represents the hydraulic head or pressure level within the aquifer.
  • Recharge Area: The area where water enters an aquifer from the surface.
  • Unconfined Aquifer: An aquifer that is not bounded by impermeable layers and is recharged directly by water seeping from the surface.
  • Water Table: The upper surface of the zone of saturation, where the soil or rocks are permanently saturated with water.

What Is the Difference Between a Deep Well and an Artesian Well?

A deep well refers to any well that is drilled to significant depths to access groundwater. An artesian well specifically taps into a confined aquifer under pressure, which causes the water to rise toward the surface naturally. A deep well may or may not be an artesian well, depending on the geological conditions.

How Deep Is an Artesian Well?

The depth of an artesian well varies widely depending on the location and the depth of the confined aquifer. Some artesian wells can be as shallow as 50 feet, while others extend several hundred feet below the surface.

Is It Safe to Drink Artesian Well Water?

In general, artesian well water is safe to drink as it often comes from deep, confined aquifers, which are less susceptible to contamination. However, it is still essential to test the water regularly for contaminants such as bacteria, nitrates, and heavy metals to ensure its safety. Artesian well water may or may not be safer or have higher purity than ground water.

How Long Do Artesian Wells Last?

The lifespan of an artesian well depends on various factors, including the quality of construction, the geological conditions, and the rate of water extraction. Properly constructed and maintained artesian wells last for decades.

Can Artesian Wells Run Dry?

Yes, artesian wells can run dry if the rate of water extraction exceeds the natural recharge rate of the aquifer. Over-pumping lowers the pressure in the aquifer and eventually the well stops flowing.

What Are the Advantages of Artesian Wells?

  • Natural Pressure: Artesian wells can bring water to the surface without the need for pumping, reducing energy costs.
  • Consistent Supply: They often provide a reliable and steady water supply, even during dry periods.
  • Protected Source: Water from confined aquifers is generally less prone to contamination compared to surface water sources.

What Are the Disadvantages of Artesian Wells?

  • High Initial Cost: Drilling an artesian well is potentially expensive due to the depth and precision required.
  • Geological Dependence: Not all locations have suitable confined aquifers for artesian wells.
  • Maintenance: Regular maintenance and water quality testing are essential to ensure the well continues to function properly and provides safe water. The need for maintenance also applies to other types of wells, too.

References

  • Chaminé, Helder I (2015). “Water resources meet sustainability: New trends in environmental hydrogeology and groundwater engineering”. Environmental Earth Sciences. 73 (6): 2513–20. doi:10.1007/s12665-014-3986-y
  • Gelhar, Lynn W.; Welty, Claire; Rehfeldt, R. Kenneth (1992). “A critical review of data on field-scale dispersion in aquifers”. Water Resources Research. 28 (7): 1955–1974. doi:10.1029/92WR00607
  • Walton, William C. (1990). Principles of Groundwater Engineering. CRC Press. ISBN 978-0-873-71283-5.
  • Wheeler, H. W (1980). Artesian Bores of South Australia : An Annotated Photographic Record, 1939-1948. Pioneer Books. ISBN 978-0-908065-06-6.