BACKGROUND:
Many communities get their drinking water from
underground sources called aquifers. Water suppliers
or utility officials drill wells through soil
and rock into aquifers to supply the public
with drinking water. Homeowners who cannot get
drinking water from a public water supply have
private wells that tap the groundwater supply.
Unfortunately, groundwater can become contaminated
by improper use or disposal of harmful chemicals
such as lawn care products and household cleaners.
These chemicals can percolate down through the
soil and rock into an aquifer—and eventually
into the wells. Such contamination can pose
a significant threat to human health. The measures
that must be taken by well owners and operators
to either protect or clean up contaminated aquifers
are quite costly.
NOTE:
This demonstration should follow a discussion
on potential sources of pollution to drinking
water supplies.
OBJECTIVE:
To illustrate how water is stored in an aquifer,
how groundwater can become contaminated, and
how this contamination ends up in the drinking
water well. Ultimately, you should get a clear
understanding that what happens above the
ground can potentially end up in the drinking
water supply below the ground.
MATERIALS NEEDED:
1 6” x 8” clear plastic container
that is at least 6-8” deep (shoebox or
small aquarium)
1 lb. of modeling clay or floral clay
2 lbs. of white play sand
2 lbs. of aquarium gravel (natural color if
possible) or small pebbles
(Hint: As many small rocks may have a powdery
residue on them, you may wish to rinse
and dry them on a clean towel prior to use.
It is best if they do not make the water cloudy.)
1 drinking water straw
1 plastic spray bottle (be sure the stem that
extends into the bottle is clear)
1 small piece (3” x 5”) of green
felt
1/4 cup of powdered cocoa
Red food coloring
1 bucket of clean water and a small cup to dip
water from bucket
Scotch tape
PROCEDURE:
1. To one side of the container,
place the drinking water straw, allowing approximately
1/8” clearance with the bottom of the
container. Fasten the straw directly against
the long side of the container with a piece
of tape. Explain that this will represent
two separate well functions later in the presentation
(if not placed at this time, sand will clog
the opening).
2. Pour a layer of white
sand completely covering the bottom of the
clear plastic container, making it approximately
1½” deep. Pour water into the
sand, wetting it completely, but there should
be no standing water on top of the sand. Let
students see how the water is absorbed in
the sand, but remains around the sand particles
as it is stored in the ground and ultimately
in the aquifer.
3. Flatten the modeling
clay (like a pancake) and cover half of the
sand with the clay (try to press the clay
into the three sides of the container in the
area covered). The clay represents a “confining
layer” that keeps water from passing
through it. Pour a small amount of water onto
the clay. Let the students see how the water
remains on top of the clay, only flowing into
the sand below in areas that the clay does
not cover.
4. Use the aquarium rocks to
form the next layer of earth. Place the rocks
over the sand and clay, covering the entire
container. To one side of the container, slope
the rocks, forming a high hill and valley (see
illustration below). Now pour water into your
aquifer until the water in the valley is even
with your hill. You see the water around the
rocks that is stored in the aquifer. You will
also notice a “surface” supply of
water (a small lake) has formed. This will give
you a view of the ground and surface water supplies,
both of which can be used for drinking water
purposes.
5. Next, place the small
piece of green felt on top of the hill. If
possible, use a little clay to securely fasten
it to the sides of the container it reaches.
6. Sprinkle some of the
cocoa on top of the hill, explaining that
the cocoa represents improper use of things
like lawn chemicals or fertilizers.
7. Put a few drops of the
food coloring into the straw, explaining that
people often use old wells to dispose of farm
chemicals, trash, and used motor oils. You
will see that it colors the sand in the bottom
of the container. This is one way that pollution
can spread through the aquifer over time.
8. Fill the spray bottle
with water. Make it rain on top of the hill
and over the aquifer. Quickly you will see
the cocoa (pesticide/fertilizer) seep down
through the felt and also wash into the surface
water supply.
9. Take another look at
the well you contaminated. The pollution has
probably spread farther. Remove the top of
the spray bottle and insert the stem into
the straw. Depress the trigger to pull up
the water from the well. (Water will be colored
and “polluted.”) Explain that
this is the same water that a drinking water
well would draw for you to drink.
Side View Of
Container
*Information provided by, U.S. Environmental
Protection Agency
