Subsurface Contamination of Groundwater
1991 Woodrow Wilson Biology Institute
The major objective of this demonstration is to show students how difficult it is to study subsurface contaminants contained in underground storage tanks.
Ground water is the water that lies beneath the earth's surface. It is currently estimated that 25% of the available ground water in the United States is contaminated. Common pollutants include gasoline, heating oil, wastes from septic tanks and various toxic chemicals stored in underground storage tanks (UST's). The EPA regulates 30% of the known UST's. The remaining 70% are found on private property, usually hold less than 1,100 gallons of material and are a major source of ground water pollution.
Materials needed are inexpensive household items:
- plastic milk containers or paper cartons
- paper clips
- small rubber balloons
- graph paper
The demonstration begins with a balloon filled with water being buried in a milk container that has been cut lengthwise and filled with sand. Tell the students that there is an underground storage tank [UST] filled with a contaminant buried beneath the sand. Instructed to determine where the UST is located by inserting sharp toothpicks beneath the sand, the students will burst the balloon. With the bursting of the balloon, the class is dramatically introduced to one of the major problems people encounter when dealing with subsurface contaminants, leaking storage tanks. Students will select a card from you which will identify the pollutant by name. Example contaminants are: methoxychlor, benzene, gasoline, toxaphene, endrin, lindane, trichloroethylene, 2,4-D and carbon tetrachloride. Students will determine the pollutant's potential threat to both the ground water supply and humans by doing research on their substance. Primary drinking water standards for the pollutant should be included in student answers. Each group would then determine how to identify the contaminant (s) and how to clean up the spill. Each group should report their findings to the class.
In the second half of the demonstration, I will give students a container that simulates a superfund site. The containers have either a banana or an apple buried beneath the sand. Students are to section off the milk container into small quadrants [approximately 2.5 cm X 2.5 cm] using string and masking tape. Using the graph paper provided, students will devise a way to plot their trials and create a surface map of their area. I will give a paper clip to each group and instruct them to find and identify the UST. They are reminded to poke carefully because each puncture point results in a leak of their tank. As seen in the previous demonstration, leaks can cause environmental problems. Each time the student inserts a paper clip they are simulating the sinking of a monitoring well. Monitoring wells are used to locate buried UST's. Students should sink a minimum of 3 wells per grid. Objects should be recovered at the completion of the lab. A discussion on the difficulties encountered in attempts to deal with UST's and superfund sites would end this lesson.
United States Environmental Protection Agency. Environmental Resource Curricula: Approaching Environmental Science Education Using Case Studies. "Activity 3.1-Subsurface Investigations." Washington , D.C.: 1990.