Seepage

Objective

Through the completion of two activities, the student will be able to define seepage, and how this is related to the spread of contaminants from brownfields.

Procedure

These activities will focus students’ attention on the flow of water through the small holes in the soil (seepage) and demonstrate that this is a concern when thinking about contamination in brownfield sites. The water carries chemicals, metals, etc. through the soil to the groundwater where they become a hazard to humans and the environment.

The Raindrop activity can be used to determine the students’ recollection of information that they have learned about the water cycle in the past. It includes a “fill-in-the-blank” story that reviews the travel of a drop of water through the cycle.

The main activity simulates seepage through layers of soil, sand and rocks under the ground.

Prior to the class the teacher should prepare methyl-ethyl-death liquid for the seepage activity. The methyl-ethyl-death is a mixture of liquid dish detergent, black food coloring, and water. Enough water must be added to allow the mixture to be able to flow. It should be thicker than water so that it seems like an unknown substance. Make sure that students understand that this liquid is a simulated hazardous chemical and that it is not dangerous.

The teacher should prepare the geologic samples using clear plastic vials or bottles (students may also be involved in this process). There will be five layers in each sample. The bottom layer (#5) is sand. Layer #4 is clay. This should be flattened and touching all sides of the container to create the impermeable layer. This will stop the methyl-ethyl-death from seeping to the bottom layer. Layer #3 is made of sand. Layer #2 is made of small pebbles. Fish tank gravel works well for this layer. The top layer (Layer #1) is made of pebbles that are larger than the pebbles in layer two (a different fish tank gravel can be used).

Prior to pouring the methyl-ethyl-death into the vial, students should predict what will happen in the vial. The seepage of the methyl-ethyl-death may take several minutes. The students may add the methyl ethyl death to the geologic layers and then complete other activities while it slowly moves through the sample. This will allow the contaminant to seep down through the layers. It should stop at the top of layer four if layer four is thick enough and properly placed to completely cover layer number five. The remaining questions on the student page should be completed.