Lesson Pollutants & Ground Permeability:
The Other Water Cycle

Learning Objectives

After this lesson, students should be able to:

• Identify different materials based on their level of permeability.
• Identify which materials (permeable vs. impermeable) would be better for development of agriculture in various (urban vs. rural, coastal vs. inland) settings and why.
• Describe how pollutants concentrate and runoff over non-permeable surfaces.
• Describe some human impacts on the natural environment.
• Learn how to link anthropogenic pollutants and contaminants to local environmental issues such as water quality and estuary health.
• Describe how non-permeable surfaces cause runoff and affect the health of local watersheds.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Introduction/Motivation

Hook the students by showing a photograph of a large commercial parking lot (such as a Wal-Mart store), focusing on the detention ponds. Ask them what they see in the picture, and what they think the purpose of the ponds is. Expect them to come up with esthetic and practical reasons. Encourage all answers and suggest that they think about why the ponds might be there from an engineering perspective. The purpose of the ponds is to collect and treat surface water runoff.

To aid in an explanation of permeability, show pictures of flooding. Ask questions to encourage students to think about why flooding occurs.

Lesson Background and Concepts for Teachers

Permeability is the degree to which water or another liquid is able to flow through a material. Different substances such as soil, gravel, sand and asphalt have varying levels of permeability. Materials that are densely packed are less permeable than those that are loosely packed. The porosity of the material enables permeability: the more gaps, the more permeable the material. Students can further investigate this idea of permeability with the investigative associated activity Permeability Materials Experiment: What Trickles Down?

As the population of the Earth increases and as more development and urbanization occur, more of the Earth's surface is replaced by impervious or non-permeable surfaces such as roads, houses, parking lots, and buildings. The cumulative effect is a reduction in the seepage of water into the ground and an acceleration of runoff inito ditches, streams and detention basins.

Increases in imperviousness, removal of vegetation and soil, gradation of the land surface, and construction of drainage networks all result in higher runoff volumes and shortened runoff time into streams from stormwater (rain, melting snow).

Over time, this new and human-induced movement of pollutants through an area creates the "other" water cycle, sometimes called the urban stormwater cycle. This cycle is a way to describe the journey of rainfall from the atmosphere to the surface of the Earth, over land, and eventually into the terrestrial water system (groundwater, rivers, ocean and estuaries). In this way, pollutants accompany the natural water cycle and are inadvertently spread and able to contaminate other water sources.

Associated Activities

• Permeability Materials Experiment: What Trickles Down? - Students experiment with different materials and discover their relative permeabilities.

Lesson Closure

Ask students the following questions:

• What is permeability? (Permeability is the degree to which water or another liquid is able to flow through a material.)
• Why is runoff a problem? (Runoff leads to the introduction of pollutants and excess nutrients into the water cycle and leads to the contamination of bodies of water.)
• How can runoff be prevented? (Runoff can be reduced by using more permeable materials in engineering designs and taking advantage of the natural ability of wetlands and soils to capture and filter water.)

Vocabulary/Definitions

asphalt : A brownish-black solid or semisolid mixture of bitumens obtained from n.ative deposits or as a petroleum byproduct, used in paving, roofing and waterproofing.

estuary: An arm of the sea that extends inland to meet the mouth of a river.

permeability: The degree to which water or another liquid is able to flow through a material.

porosity: The ratio of the volume of gaps of a material to the volume of its mass.

runoff: The portion of precipitation on land that ultimately reaches streams, often carrying dissolved or suspended material.

sediment: Material deposited by water, wind or glaciers.

Assessment

• Expect students to be actively involved in the discussion and able to explain which materials are more permeable than others.
• List materials and ask the class to identify which are the most permeable.
• Ask students to give examples of runoff.

Additional Multimedia Support

Surface Runoff - The Water Cycle, U.S. Geological Survey http://water.usgs.gov/edu/watercyclerunoff.html

What Are Detention Ponds and Why Are They Important? Greenville County, SC http://www.greenvillecounty.org/land_development/detention_ponds.asp

Copyright

Contributors

Supporting Program

Acknowledgements

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.