Tracking Pollution
..A Hazardous.Wnoaunit
INTRODUCTION:
Riverville is a fictional town with a real problem. Each
week, more citizens are complaining that their drinking
water tastes bad. In many small towns like this one, there
is no central water supply. Every home and most business-
es have a private well. The town's mayor tested the water
from several wells and found that the ground water has
been contaminated with some kind of fuel. The wells that
have been contaminated are marked out on the map on the
next page.
The mayor thinks the Heating Oil Company is responsible
for this contamination and wants them to start investigat-
ing their fuel storage tanks which are buried underground
and to check the tanks for leaks. The Heating Oil Co. says
they just tested their tanks and knows they are safe. They
think the Trucking Company is the source of pollution. The
Trucking Co. says the source could just as likely be the
Heating Oil Co. or the Gas Station, since all three places
have underground tanks for storing the same kind of fuel.
So Riverville has a problem and no one is sure who is
responsible. The mayor needs some way of proving who is
causing the pollution and who should clean it up. You will
be the "detective" who helps prove where the pollutant is
coming from.
Cleaning up ground water contamination is a very expen-
sive job. You should be very sure of the place you choose
to start cleaning up, otherwise the money will be wasted.
It is up to you to solve the mystery.
A O5JECT1VE:
You will make a topographic map, use it to predict ground
water flow and investigate the most likely source of
ground water contamination.
GENERAL PROCEDURES:
To decide which of the suspected businesses is the most
likely source of contamination, the easiest thing you can
do is find out the direction that ground water flows. Since
ground water generally flows downhill, following the slope
of the surface of the land, you can be fairly certain that the
suspected source which is farthest "upstream" is the real
source of contamination.
This activity shows you how to estimate ground water flow
by making a contour map. As in many very small towns,
only a few people in Riverville know the exact elevation
above sea level for their property. To make a contour map,
it usually helps to know the elevations of as many places
as possible. But this simple procedure can be used even
though you only know a few elevations.
The map shows the elevations for seven wells and gives
directions for drawing in the contours of the land. After
you have finished this procedure, answer the questions
below.
QUESTIONS:
1. If the flow of ground water and the pollutants in it fol-
low the contour of the land, what is the mostly likely
source of the contamination, the Heating Oil Co., the
Trucking Co. or the Gas Station?
2. The contamination plume will continue to spread slowly
through the ground, much like smoke from a chimney drift-
ing into the wind. Describe where on your map you think
the plume will move with time.
3. Which of the uncontaminated wells do you expect to
become contaminated in the near future? Do you think the
school's water well will be contaminated?
4. How do you explain the fact that one well within the
plume was not contaminated?
5. Is it possible you are wrong in assuming that ground
water flow follows the contour of the land? What else
could you investigate to be sure?
6. Assuming that ground water flow does follow the con-
tours of the land, is it possible that there are two sources
of contamination? What would you expect to find if all
three companies had leaking storage tanks and were actu-
al sources of contamination?
EXTENSIONS:
1. Get a map of your own community and use it to chart out
ground water direction. Locate the community's water
supply and any potential sources of contamination. What
kind of precautions should be taken to keep an eye on
potential sources of contamination?
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•) Contaminated Well
Uncontammated Well
1. Start with a well with a known elevation. Using ruler and
pencil, LIGHTLY draw a line from this well to the nearest
wells having at least a 20-foot difference in elevation.
2. Cut a rubber band open and lay it out flat, without
stretching it, along the edge of a ruler. With a pen, make at
least five marks c inch apart beginning from the middle of
the rubber band. Use the marked rubber band to help you
divide each line into equal segments.
3. Label each mark on the line between the known eleva-
tions with the estimated elevations. For example, if the
elevations at each end of the line are 10 and 40 feet above
sea level, you should make two marks on the line, dividing
the line into three equal lengths. The first mark should be
labeled 20 and the next one labeled 30.
4. Connect all marks having the same elevation with a
smooth line. These are contour lines.
5. Every half inch or so along each contour line, draw a
short arrow perpendicular from one line out towards the
line having the next lowest elevation. Ground water flows
in the direction of the arrows.
6. Find all the contaminated wells and draw a single loop
that contains only these wells, if possible. The area inside
this loop shows how far the contamination has already
spread through the ground water, and is called the con-
tamination plume.
7. Use your map to answer questions on page 1.
Office of Water (4606M) • EPA 816-F-04-022 • 06/2004 • www.epa.gov/safewater
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