In early March, Seattle Mayor Mike McGinn announced a new goal for managing the city's polluted stormwater runoff. By using natural drainage systems rather than traditional pipe and tank systems, the mayor wants to push through a citywide goal of 700 million gallons
of stormwater managed annually through green stormwater infrastructure (GSI) by 2025.
"Whenever possible, we should be looking for ways to better manage our stormwater with natural processes and leveraging our drainage investments," the mayor said
. "Seattle residents and businesses care about the environment and that's why we are inviting the whole community to join us in this effort."
Stormwater runoff accounts for one-third of all polluted water in Washington State, and is acknowledged as the largest source of pollution in the Puget Sound. The Department of Ecology notes that a one-acre parking lot can create 27,000 gallons of stormwater runoff after just one inch of rainfall.
Hundreds of millions of gallons of polluted stormwater runoff flow into area creeks, lakes and Puget Sound
each year, oftentimes containing bacteria from sewage overflows and pet waste, oil, grease and heavy metals like copper from cars, household chemicals, including pesticides and nutrients like nitrogen from fertilizers.
GSI techniques help prevent pollution by slowing runoff and using natural systems to filter and clean the water. The various GSI practices make use of soils and vegetation, in combination with approaches like rain barrels and permeable pavement, to infiltrate, evaporate, capture and reuse stormwater.
Seattle has pioneered the use of GSI with things like rain gardens
and green roofs
, approaches that filter the rainwater much like a natural forest ecosystem would. Taking it from small scale to mainstream, the city's new goal — the first of its kind in the nation — would mean treating 1,000 gallons of stormwater per resident with green infrastructure by 2025.