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Although nearly half of all Americans get their drinking
water from wells, many people have never heard of
ground water. Use of ground water supplies is increasing
at twice the rate of surface supplies, and the trend is
expected to continue. Until the late 1970's, it was widely
believed that ground water was protected from
contamination by the natural filtering effect of the many
layers of soil, sand, gravel and rocks. We now know that
pollutants can travel through all these layers. Incidents of
serious contamination have been reported in every state
in the nation
A O5JLCTIVD
The student will use a model of an aquifer to describe
how ground water flows through an aquifer, how ground
water can become contaminated, and why it is so
difficult to clean contaminated ground water.
TrLACHLRSUGGrLSTIONS
This model can be a very flexible tool which will allow
students to simply study groundwater flow, look at how
well placement affects yield, or examine how ground
water is vulnerable to contamination.
Depending on the resources, the teacher may lead
groups of four or five students in building their own
models as described below, or the teacher may build a
single, larger (the longer the better) version for
demonstration. If students are able to make their own
models, then it would create less traffic and crowding if
all materials for students 1-4 are placed at different
stations around the room. Then it will be easier for each
group to pick up what they need and take it back to their
own work area.
Begin by orienting the students to how the earth looks
below the surface, demonstrating a working model and
relating its parts to a diagram of the hydrogeologic cycle.
Using unassembled materials, go over the basic assembly
plan illustrated in Steps 1 - 9 on page two, briefly showing
students how to put the model together. Then divide
students into groups to build their own model.
STUDLNT ACTMTIrLS - MODLL
ASSLM5LY:
For a group having four or five students, responsibilities
may be divided among students as below.
Station/student 1 - Get two plexiglass panels (one with
hole in it, as shown), duct tape, and a ruler and begin
assembling model as show in steps 1 to 4 on page two.
Station/student 2 - Collect plastic soap bottles, tubing
(1/2" I.D. and 1/2" O.D.), foam strips, and syringe or other
aspirator. Force foam up about one inch into each of the
large (1/2" I.D.) pieces of tubing for use in step 5.
Station/student 3 - Collect sand, gravel, felt sheet and
straws. Soak felt sheet in water, wring out, then roll the
sheet into a tight coil about 3/4" thick and 20" long. Use in
step 6.
Station/student 4 - First help student 1 with assembly
steps 1 to 4, then get food coloring, water supply, cups.
Student 5 - Help with model assembly in steps 1 to 9.
Once the model is assembled, and water is flowing
through the sand, into the river valley and out of the
collector tube, do the activities on page two.
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INVESTIGATIONS
1. Which wells have the most water in them? Raise the
water supply bottles as high as possible without pulling out
the tubing - what happens to the water level in each of the
wells and to the amount of water coming out of the
collector tube? Next, lower bottles and observe what
happens. How does the height of the water supply affect
the water flow rate?
2. Pour out half of the water from the supply bottles, mark
the water level, then pour a 4 ounce cupful of water into
each bottle. Every few minutes, as the water reaches the
mark, pour in another cupful of water. Also measure the
total amount of water added during the time periods before
the dye appears in water from the collector tub and after
the dye is no longer visible in water from this tube.
3. At the same time, place 10-15 drops of food coloring on
the sand at Point A shown in the assembly diagram for
steps 7-9. On the plexiglass, mark the point with a water
soluble marker. Every two minutes, make a mark on the
plexiglass at the front edge of the dye as it moves through
the sand. Measure the distance between the marks and
record the distance moved per unit time.
4. Ask your teacher to show you how to do a 10-tube
series of 1:2 dilutions of food color in water. Number each
tube 1 to 10. Use this dilution series as a guide for
estimating the concentration of dye in the water coming
out of the collector tub. After the dye you added in Step 3
above begins to appear in the water from the collection
tube, collect a sample in a test tube every two minutes.
Compare the color of this sample with each tube in the
dilution series and record the number of the tube which is
nearest in color to your sample. This will be a rough
estimate of the amount of "pollution" in your sample.
5. Graph your data, plotting time
distance on the y-axis (Step 3).
on the x-axis and
Also, plot time vs.
concentration after dye appears in water coming out of the
collector tube (Step 4). How long does it take for ground
water to become clean again after being contaminated?
First, empty any water in the water supply bottles into the
model and remove bottles and tubing. Then, place screen
over a bucket and flush sand and gravel onto screen - use
a screen with a mesh large enough to allow sand to sift
through but small enough to catch the gravel. Rinse out
foam strips and felt roll.
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Office of Water (4606M) • EPA 816F08022 • 06 / 2008 • www.epa.gov/safewater
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