Tracking Pollution  -  A Hazardous Whodunnit

Riverville is a fictional town with a real problem. Each
week, more citizens are complaining that their drinking
water tastes bad. hi many small towns like this one, there is
no central water supply. Every home and most businesses
have a private welL The town's mayor tested die water from
several wells and found that the ground water has been
contaminated with some kind of fuel The wells that have
been ffmtamm^f^ arc marked out on the Tnap on
this page.
The mayor minks the Hearing Oil Company is responsible
for this contamination and wants them to start investigating
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 wilfl
be the "detective"  who helps  prove  where the
pollutant is  coming  from.
Cleaning up ground water contamination is a very expensive
job. You should be very sure of the place you choose to
start cleaning up, otherwise die money win be wasted, ft is
up to you to solve die mystery.
You will make a topographic map, use it to predict ground
water flow and investigate die 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 die 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 deration
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 on back shows the elevations for seven wells and
gives directions for drawing in the cuuiouis of die land.
After  you have finished this procedure, answer the
1. If die flow of ground water and die pollutants in it fbflow
the contour of the land, what is die most 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
drifting with die wind. Describe where on your map you
                 move with time.
3. Which of the uncontaminated weHs do you expect to
become contaminated in die near future? Do you think die
school's water well will be
4. How do you explain die fact dial one wen within die
plume was not contaminated? Give at least two possible
reasons how this could happen. (Hint: see die Resource
Management Activity)
5. Is it -possible you are wrong hi 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
contours of the land, is it possible that there arc two sources
of contamination? What would you expect to find if aU three
companies had iMiffag storage tanks and were actual
1. Get a map of your own community and use it to chart oat
ground water direction. Locate the community's water
supply and any potential sources of cr«"ty"""ar'"n What
kind of precautions should be tairm to keep an  eye on
potential sources of contamination?

                     Co.  ^   ^
Heating OH
                       01   1

          10 <
                                                                          © Contaminated well

                                                                         "• UncontamlnatedweH
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
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 1/2
inch  apart beginning from the
middle of the rubber band. Use the
marked rubber' band to help you
divide   each line  into  equal
segments. Your teacher will show
vou how this is done.
3. Label each mark on the line
between the known elevations with
the estimated elevations.  For
example, if the elevations at each
end of a line are 10 and 40 feet
above sea level, yon 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. Rnd all the contaminated wells
                         and  draw  a  single  loop  that
                         contains only these wells and none
                         of the uncontaminated  wells, if
                         possible. The .area inside this loop
                         shows how far the contamination
                         has  already spread through  the
                         ground water, and  is called  the
                         contamination plume.

                         7.  Use  your  map to  answer
                         questions on page 1.