How Do Aquifers Work?

The Edwards Aquifer is the main source of water for south

central Texas. It is a huge aquifer that stretches over 180 miles. People use the water to

drink, water crops and for recreation.

The Edwards Aquifer began forming about 100 million years ago when San Antonio was under the sea. During that time, marine

organisms fell to the bottom of the sea and formed a layer of

sediment.

Over time, the sea level went

down and pressure

turned the layer of marine organisms into

limestone.

(This process is a part of the rock cycle which forms

sedimentary rock!) The limestone, called Edwards Limestone, is porous like a

sponge.

It contains holes, some as small as a dot and others as large as a

classroom! The holes are perfect for holding water.

There are three main parts to the Edwards Aquifer—the drainage area, the recharge zone and the artesian zone. Each part has a

separate job that keeps the aquifer working.

Drainage Area

The drainage area is the largest part of the Edwards Aquifer. It

captures the water for the aquifer.

Rain that falls over the drainage area runs off into streams. The

streams flow into the next part of the aquifer, the recharge zone.

Recharge Zone

The recharge zone provides a way for water to get inside the aquifer. The limestone of the

aquifer is on the surface in the recharge zone.

Remember that the Edwards limestone has many holes in it.

The water from the streams in the drainage area

reaches the limestone and sinks into the ground.

Rain that falls over the recharge zone can also seep into the

ground through the openings in the limestone.

The more Edwards limestone at the surface,

the more water can be let into the aquifer!

Think of it like this. If you had one bucket of large rocks and one bucket of sand, and you

poured water into each bucket, which bucket would the water reach the bottom

first?

The bucket with large rocks has more spaces for the water to

move through, the water would reach the bottom of the rock

bucket first. This is similar to the recharge zone of the aquifer.

Artesian ZoneThe third part of the aquifer is the

artesian zone.

Water cannot flow directly into this zone because it is

covered by a layer of impermeable rock.

The artesian zone is the water storage area for the aquifer. It is not a large lake underground like many people think. It is made up

of limestone with connecting spaces.

The spaces vary in size from microscopic to large open

caverns. These spaces fill up with water that seeps in from the

recharge zone.

Since the water in the artesian zone is trapped between two

impermeable layers of rock, the water is under pressure.

In some places, people can drill wells and the pressure from

the water forces the

water up to the surface.

So the three parts of the aquifer work together as a system. As

people use water from the aquifer, the level of water inside

the aquifer goes down.

If rain does not fall over the drainage and recharge areas, the

artesian area does not receive the water to keep it filled.

So, it is important to conserve water in order maintain a certain

level of water in the aquifer.

The unique nature of the Edwards Aquifer makes it susceptible to pollution.

In the recharge zone, remember that the Edwards limestone is at

the surface.

There is no layer of soil to act as a filter to keep pollutants from

seeping into the aquifer.

Once pollutants enter the aquifer,

it is extremely difficult to

remove them.

Runoff from the drainage

area may pick up pollutants

and carry them into the aquifer.

Businesses and homes that are built on the recharge zone can

contribute to pollution of the aquifer by using pesticides,

fertilizers or other hazardous materials.

Because of the risk of pollutants entering the aquifer, restrictions have been put in place to protect

the Edwards Aquifer.