Aquifers & Groundwater


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What is groundwater?

Groundwater comes from rain and snowmelt that seeps into the ground.  Gravity pulls the water down through the spaces between particles of soil or through cracks in rocks.  Eventually the water reaches a depth where all openings in soil or rock are filled with water. This is called the saturated zone. The water in the saturate zone is called groundwater.

The top of the saturated zone is called the water table. The water table rises and falls according to the season and the amount of rain and snowmelt that has occurred during a particular year.

Bedrock below the saturated zone can prevent the water from penetrating more deeply.

Diagram of how ground water occurs underground



Water moves through spaces in soil and rock

Different kinds of soil and rock vary in the size of the spaces for water to move through.  Gravel has very large spaces so water moves through it very fast. On the other hand, the spaces in clay are so small that almost no water moves through.

Some layers of rock are so solid that they don't let water move through.  Others are very crumbly or have lots of big cracks.  If the cracks are connected to each other, then water can move thorough the rock.

Types of Aquifers

Groundwater below a layer of solid rock or clay is said to be in a confined aquifer.  The rock or clay is called a confining layer.  Aquifers that are not below a confining layer are called unconfined aquifers.  Because the top of these aquifers is the water table, they also are called water table aquifers.  In a water table aquifer, the water level in a well is the same as the water table level outside the well.

unconfined aquifer illustration 



How does this affect my well?

Under persistent dry weather conditions, the water level in your well may drop below the submersible pump causing a loss of water. 

If the water level permanently drops below the submersible pump, it may be possible to lower the submersible pump within the existing well.  However, in most cases this will only provide a short-term solution to the problem.  More permanent solutions require either deepening of the existing well or drilling of a new well.  Be aware that deepening an existing well may not increase the well yield and could produce water of different water quality characteristics. 

Pumping too much water too fast draws down the water in the aquifer and eventually causes a well to yield less and less water and even run dry. In fact, pumping your well too fast can even cause your neighbor's well to run dry if you both are pumping from the same aquifer.

Proper management of private wells during droughts will become more important as competition for water in rural areas increases.  It is critical to implement water conservation strategies that may prevent your well from going dry.



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This site was last updated 03/19/06