Seepy Sandwich

The following activity demonstrates how water infiltration can carry pollution underground. The exercise requires:

  • 1. Food coloring to represent the pollutant.
  • 2. Slices of bread to represent the soil and rock (stale or fresh bread can be used).
  • 3. A sprayer to produce rainwater.
  • 4. A waterproof work area.


Student No. 1 - holds a slice of bread vertically.

Student No. 2 - adds a drop of food coloring (pollutant) to the top crust edge of the bread

Student No. 3 - sprays water (rain) on the food coloring Allow drainage to seep through the crust into the bread.

As the polluted water seeps down it spreads out, making it difficult to locate where the pollution originated. The water and food coloring will remain together as the water moves. This illustrates visually how pollutants are carried by water; that pollutants are not filtered out by the ground; and that human activities can affect groundwater quality.


  • 1. Did the pollution (food coloring) continue through the bread or was it filtered, leaving only clean water to progress downward?
  • 2. Did the water spread out or go straight down?
  • 3. Do human activities on the surface have any effect on groundwater quality?
  • 4. What kinds of pollutants might come from common household products?
  • 5. What kinds of pollutants might come from septic tank fields?
  • 6. What kinds of pollutants come from landfill seepage?
  • 7. How can groundwater contamination be prevented?

Courtesy Joe Pitts, Missouri Department of Natural Resources Groundwater Protection Curriculum Guide 1994

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Last updated: April 10, 2015

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