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Aquifer: Definition, Types & Facts

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  • 0:00 What Is an Aquifer?
  • 2:29 The Importance of Aquifers
  • 3:46 Human Impact of Aquifers
  • 4:55 Lesson Summary
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Lesson Transcript
Instructor: Laura Nappi
Did you know that when you drink water from a well you may be drinking ancient water? In this lesson you will learn the definition of an aquifer and learn why aquifers are important. In addition, you will learn how humans have impacted aquifers. At the end, test your knowledge with a quiz.

What Is an Aquifer?

Did you drink any water today? Did you know that the water you consumed may be thousands of years old? Nearly half of the world's population drinks water that was pumped out of the ground. Where did this ancient water come from? It all started as rainwater. Rainwater hits the ground and slowly soaks into the soil. At this point, any rainwater located below the ground is considered groundwater. Because of gravity, the groundwater moves downward through the soil. The soil is like a sponge and can become saturated with water. The underground area of saturated soil is called the water table. If you were to dig a hole, eventually you would hit the water table and your hole would fill up with water.

Any excess groundwater will move below the water table and continue moving down until it hits a barrier. This barrier is often comprised of rocks. These rocks are not perfectly conformed to each other and empty pockets of space are often created between them. Eventually, these pockets will start to fill up with groundwater from above, creating a structure called an aquifer, a body of underground rocks or sediment that holds water. You can think of an aquifer like a warehouse that stores groundwater.

Aquifers hold 99 percent of all of the freshwater on Earth. The remaining 1% of freshwater is found on the surface in rivers, lakes, and streams. The size of an aquifer can vary from hundreds of square feet to thousands of square miles. For example, the Ogallala aquifer in the Midwest is so large that it spans beneath 7 states and holds approximately 3 trillion gallons of water.

Some aquifers are only 50 feet below the surface, while others are 6,000 feet down. The groundwater held in very deep aquifers can be thousands of years old. Typically, these aquifers are confined because a barrier, like clay, limits the amount of water entering into the aquifer. Groundwater found in shallower aquifers may be much younger, even just a few days old, because these aquifers are often unconfined, and water can easily enter into the aquifer.

Importance of Aquifers

Groundwater and aquifers are extremely important for our everyday lives. In the United States, approximately 37% of our drinking water comes from aquifers. We use groundwater every day to brush our teeth, flush the toilet, and irrigate our crops.

Aquifers are a crucial part of the hydrologic cycle, the perpetual life cycle of all water on Earth. Groundwater stored in an aquifer is not trapped forever. It can very slowly seep out in the form of a spring and flow into a river. This water can then evaporate and condensate, forming clouds. Clouds hold this water and eventually drop it to the surface as precipitation, like rain, hail, or snow. This precipitation can then infiltrate into the ground and arrive at an aquifer once again.

When water seeps out of an aquifer, the lost water is replaced with new rainwater soaking into the ground. This entry of groundwater into rivers is very important for the health of river ecosystems. This continual input of groundwater is partially responsible for the continuous flow of rivers year round, as water leaks from the aquifer and replenishes the river water.

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