It’s well known that rain gardens are great for infiltrating stormwater but people may not realize that they also help destroy common stormwater pollutants. Several studies have found that rather than accumulating pollutants in their soils, rain gardens tend to biodegrade them instead. One study (LeFevre et al., 2011) investigated petroleum hydrocarbon levels in 58 rain gardens in Minneapolis, MN representing a wide range of sizes, vegetation types, and contributing area land uses. The researchers found that petroleum hydrocarbon levels were well below regulatory limits in all the rain gardens sampled. And a tip for future rain garden installers, rain gardens planted with more robust vegetation with deeper roots did a better job at breaking down pollutants than those planted with only turf grass.
A rain garden’s ability to biodegrade pollutants is in contrast to what happens in more conventional stormwater management structures like retention ponds. Retention ponds are often installed with larger developments to receive a large volume of stormwater from impervious areas (ex. houses and roads in a subdivision, roof and parking lot of a Home Depot). Other studies (Van Metre et al., 2009; Van Metre et al., 2000; Kamalakkannan et al., 2004), found that pollutants like PAH’s (polycyclic aromatic hydrocarbons), a type of petroleum hydrocarbon, accumulate in the sediments of stormwater retention ponds. This creates a very expensive maintenance issue for retention pond owners when the time comes to remove and dispose of built up contaminated sediments.
Side note – stormwater can pick up PAHs from dust on pavements treated with coal tar sealants which are commonly used on parking lots, driveways, and playgrounds (but they have recently been banned from use on State and local highways in CT).
Jen McGuinness who blogs at Frau Zinnie wrote an excellent blog post about the rain garden presentation Dr. Mike Dietz of UConn Extension presented at the Master Gardener Symposium in March. In Jen’s words:
MANCHESTER, Conn. – With April showers imminent, you’ll soon be reminded of how much stormwater leaves your property. Water rushing through gutters and down driveways will find its way to the street’s sewer if you don’t have a way to trap it.
Instead of letting stormwater wash away, create a rain garden to keep it on site.
At the 2013 Connecticut Master Garden Association’s Symposium, Michael Dietz, Ph.D, NEMOprogram director and water resources educator, explained how a rain garden can be installed. The benefits can be clearly seen in densely populated (and paved) cities.
“Older cities have a runoff problem,” said Dietz. “The sewage and runoff from the house combine and overload the sewer treatment plants. If it’s overloaded, it goes into the rivers.”
Well don’t fret – you can turn that frown upside down. Install a rain garden! Rain gardens are depressions in your landscape that are designed to soak up stormwater rather than send it into the storm drain. In addition to adding beauty to your yard, rain gardens remove pollutants from stormwater runoff and help keep our water bodies safe for swimming, drinking, and fishing.
Rain gardens are fairly easy to install for the average DIYer, but you need to know how to design and install them properly. Lucky for you, UConn has just released the Android version of its award-winning Rain Garden smartphone app (previously available only for iPhones). Through a variety of videos, tools, and information, the app walks you through how to properly site, size, design, and install a rain garden.
So stop bumming about your cancelled beach day and start planning your garden (a great thing to do on a rainy day). And the next time it rains, won’t it feel good to look at your yard and smile knowing you’ve done your part to protect your local water body?