Mequon Nature Preserve: Bio-Retention Cell
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An EarthCache adventure is treasure hunting for the caches that the Earth has stored. EarthCache sites do not use stored containers; their treasure is the lessons people learn about our planet when they visit the site. Visitors to EarthCache sites can see how our planet has been shaped by geological processes, how we manage the resources and how scientists gather evidence to learn about the Earth.
This EarthCache is located at the PieperPower Education Center on the grounds of the Mequon Nature Preserve. While the long-term goal of the Nature Preserve is to restore the deciduous hardwood forests and wetlands that existed prior to European settlement, the Education Center's goal is to become environmentally friendly and energy efficient. On the grounds, you will see examples of solar power, wind power and, quite literally, a “green” roof. The focus of this EarthCache, however, is a storm water management practice known as a bio-retention cell.
THE PROBLEM: WASTEWATER RUNOFF
Roofs, roads, sidewalks, and parking lots don’t absorb rainwater or snowmelt. The water that lands on them has to go somewhere, so it runs across these man-made surfaces. A little of the runoff may find some soil and sink in; but it is more likely to flood storm sewer systems and basements; or it may flood and erode ditches and other waterways like streams and ponds. Called “surface runoff,” this water washes pollutants like gasoline, motor oil, road salts, heavy metals, and garbage off the pavement and into natural areas. It picks up fertilizers and pesticides from lawns and farms. The rainwater itself often brings pollutants like acids down from the sky. Surface runoff can move across the landscape too fast to sink in and refresh the ground water system.
A SOLUTION: BIO-RETENTION
Bio-retention cells are small landscaped areas whose purpose is to improve water quality. They do so by catching storm water runoff from roof tops, sidewalks, patios, parking lots and other relatively small impervious areas and passing the water through small landscaped areas that filter out pollutants.
The cell area here at the PieperPower Education Center was excavated to a depth of 4 feet. Once excavated, a layer of filter fabric was placed on the bottom. Then a perforated drainage pipe and 6 inches of gravel were positioned on the fabric. Next, a mixture of sand, topsoil and compost were added almost to the top of the cell leaving a slight depression for water to collect. Finally, the cell was seeded with native meadow grasses and forbs. As rainwater enters the cell, it drains through the soil, which filters out pollutants and then enters a pipe that drains the water into the cistern.
Cisterns collect rain water and store it in above-ground or underground storage tanks. A cistern’s water can be used for watering lawns and planting beds, for household gray water (e.g. washing and mopping) or for drinking water after treatment.
ADVANTAGES OF BIO-RETENTION:
• Removes pollutants.
• Recharges groundwater.
• Enhances habitat.
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QUESTIONS: Email your answers for the following questions to the Cache Owner (NOT in your “Found It” log):
• As rainwater drains off hard surfaces and into the cell, what specific pollutants are removed by the soil and plants?
• Given the example of a 200 gallon cistern, calculate how many gallons of water this cistern would capture in one year.
• When this cistern is full, where does the excess water go?
• What colorful containers do you see nearby that act as an above-ground cistern and how are they employed? (Hint: You could do the same at your house, too.)
OPTIONAL: In your “Found It” log, you are encouraged to include photographs, although they are not a requirement.
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My THANKS go out to the following people for their approval and guidance in setting up this EarthCache at the Mequon Nature Preserve:
Kristin Gies (Director), Jason Nickels (Education and Restoration Manager), Christine Nuernberg (Secretary/Treasurer, Board of Directors), Kate Redmond (Teacher-Naturalist author of the Mequon Nature Preserve Field Guide)
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