In the stormwater world, if a rain garden is releasing more pollution into the environment than it’s capturing, word gets around.
So when the city of Redmond crunched its first flush of data from a new roadside rain garden and discovered the water coming out of it was tainted with alarming levels of phosphorus, nitrates, and copper, the stormwater community took notice. Washington State regulators went on the record to say that they would be studying the data and possibly revising their rain garden recommendations. Proponents of the technology fear that the results will be overblown and exploited by skeptics of so-called low-impact development solutions.
But even city officials in Redmond caution that they’re far from giving up on rain gardens.
“It definitely has not lost its merit in my mind,” said Andy Rheaume, Redmond’s senior watershed planner.
Indeed, there’s a decade worth of data showing that rain gardens and related “natural” technologies are effective at treating polluted stormwater runoff. They can do a terrific job soaking up the renegade rain water, diverting it from house basements and preventing it from scouring streams or causing overflows of sewage. And numerous studies demonstrate that rain gardens will filter out and capture a toxic mix of heavy metals, petroleum pollutants, particles and nutrients. In fact, the Redmond rain garden did treat some of the pollution gushing into it.
But rain gardens aren’t fool proof. Depending on the design of the system and the soil mix that’s used, a rain garden’s ability to remove pollutants can vary –– and vary dramatically.
So what is a city or county stormwater engineer to do? Don’t panic.
“We’ve been promoting the message ‘Don’t throw away the baby with the bathwater,’ ” Rheaume said. “We’re pretty sure that (low-impact development) is here to stay.” Read more »










