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Water and geology
What is groundwater?

When rain falls to the ground, the water does not stop moving. Some of it flows along the surface in streams or lakes, some of it is used by plants, some evaporates and returns to the atmosphere, and some sinks into the ground.

Groundwater is water that is found underground in cracks and spaces in soil, sand and rocks. The area where water fills these spaces is called the saturated zone. The top of this zone is called the water table and it may be only a foot below the ground’s surface or it may be hundreds of feet down.

Groundwater can be found almost everywhere. The water table may be deep or shallow; and may rise or fall depending on many factors.

Groundwater is stored in – and moves slowly through – layers of soil, sand and rocks called aquifers. The speed at which groundwater flows depends on the size of the spaces in the soil or rock and how well the spaces are connected.

Aquifers typically consist of gravel, sand, sandstone, or fractured rock, like limestone or basalt. These materials are permeable because they have large connected spaces that allow water to flow through. Water in aquifers is brought to the surface naturally through a spring or can be discharged into lakes and streams. This water can also be extracted through a well drilled into the aquifer.

Some wells, called artesian wells, do not need a pump because of natural pressures that force the water up and out of the well. Groundwater supplies are replenished, or recharged, by rain and snow melt.

Groundwater is used for drinking water by more than 50% of the people in the United States, including almost everyone who lives in rural areas, and the largest use for groundwater is to irrigate crops.

Water related resources:

    A close look at the rocks exposed in road cuts can show the types of openings in which groundwater can occur. The gaps between layers can contain water that percolates into these spaces.

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