jeacner's
~]~YaCl<.ing J ollution — A Hazardous
INTRODUCTION:
This activity presents the student with a real world
problem and provides a simple, but not always accurate
tool for investigating the problem.
The problem is that a town's drinking water is
contaminated. In many small towns like Riverville, every
home and most businesses have a private well. Lab
results from several wells showed that the ground water
has been contaminated with a kind of fuel stored by
three companies. Of the three possible suspected
sources of contamination, each suspect has a
reasonable argument as to why they are not responsible
for the problem:
1. The Heating Oil Company is the prime suspect since
they store the most fuel and sell it to the other two
suspected companies.
2. The Heating Oil Co. has just tested their tanks and
knows they are safe. They argue that the Trucking
Company is the source of pollution.
3. The Trucking Co. says the source could just as likely
be the Heating Oil Co. or the Gas Station. They claim
there is no proof that they are responsible.
The only way to find out who is responsible is to produce
some evidence to help decide which of these is the
actual source of contamination. Emphasizing the
expense of cleaning up ground water contamination and
the need for certainty before forcing a business to begin
cleaning up lets the student know that there is often a lot
at stake in this kind of investigation.
£° O5JLCTIVD
Students will make a topographic map, use it to predict
ground water flow and investigate the most likely source
of ground water contamination.
GLNLKAL fKOCLDUKrl5=
1. It will be best for students to work together in groups
of at least two. Each group will need:
A medium sized rubber band about 1/8
inch in width
A ruler, pencil and pen
Student activity sheet
2. Read over with the class the Introduction on the
Student Activity Sheet. Ask them which of the three they
think is the actual source and have them write down their
best guess.
Well
3. You might also explore whether anyone can think of
any simpler ways of finding out the source of
contamination than by doing this activity. Point out the
fact that another way of finding out whodunit is to test
the contaminated wells again to find out which wells
have more contaminant in the water. The wells nearest
the source should have the highest levels; those farthest
from the source will be lower. This can be expensive
though, since lab tests are between $100 to $200
apiece.
4. The contours of a landscape can be estimated even if
the elevation is known for only a few points, provided the
points are well scattered around the area. The procedure
used here assumes a constant slope between these
known points. If one point is at 10 ft. above sea level
and another point is at 50 ft., then when the distance
between the points is divided into four equal segments,
the elevation will increase 10 ft. over the length of one
segment. This process is described in more detail on the
next page.
5. The rubber band is used to divide lines into equal
segments, depending on the difference in elevations of
the endpoints of the line. This process of dividing the
lines can be very tedious if done mathematically, and
diverts from the point of the activity. Using the rubber
band method simplifies the process considerably. Cut
the 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 inches apart beginning from
about the middle of the band. Step 6 on the next page
describes how to use it to divide a line.
-------
©Contaminated well
•Uncontaminated well
6. LIGHTLY, with pencil, draw lines between each well
and its nearest neighbors having at least a 20 foot
difference in elevation. To divide these lines into equal
segments representing 10 ft. increases in elevation,
stretch the marked rubber band so that a mark is over
each well at the line's endpoints, with the necessary
number of marks between to allow you to count up by
tens from one well to the next. For example, a line
between the two wells at 10 and 40 ft. needs two marks
between the wells.
8. Using a PEN, every half inch or so along each
contour line, draw short arrows outward perpendicularly
from one contour line to the contour line having the next
lowest elevation. It is important that these arrows be as
perpendicular as possible to give the best estimate of
the direction of ground water flow. Erase the contour
lines and other penciled-in lines to make the map less
confusing. To get a better sense of overall direction of
flow, you might want to draw a few longer arrows which
average out the shorter ones.
©Contaminated well
•Uncontaminated well
Stretch the band so that a mark falls at each endpoint
on the line and two marks lie between the endpoints.
Make marks on the line at each of the two intervening
marks on the stretched band. Label these marks 20 and
30 ft. Repeat for each line.
7. LIGHTLY draw smooth curved lines connecting all
wells and marks having the same elevations. These
are contour lines.
9. Draw a loop that groups together all of the
contaminated wells. From the flow arrows, note that the
plume has spread in two directions, to the top right
corner and to the lower left. It should be clear that the
Trucking Co. (T) is the source of pollution. Also, the
uncontaminated well found within the cluster of
contaminated wells is a newer, deep well which taps an
aquifer protected by an underground layer of dense
rock (shale) which keeps fuel out. This may serve as a
lead-in to the Resource Management Activity.
Office of Water (4606M) • EPA 816F08023 • 06/2008 • www.epa.gov/safewater
------- |