Rain gardens keep up to 99% of pollutants out of San Francisco Bay

A study funded by the San Francisco Public Utilities Commission found that hundreds of rain gardens installed throughout the city are having a major positive impact on San Francisco Bay, keeping out over 90% of many common pollutants.

As Carl Smith explains in Governing, the PUC has funded nature-based approaches to stormwater management to reduce the chance that stormwater will overwhelm its sewer system, which is one of the few in the nation that combines wastewater and stormwater. "The city has built or initiated 575 green infrastructure projects that put it a third of the way toward a goal of capturing 1 billion gallons of stormwater each year."

A study of contaminants found that water coming out of rain gardens reduced 21 contaminants by significant margins, often of more than 90%. The gardens were found to filter out 99% of tire wear particles, a major source of micropollution. The rain gardens also filtered out 95% of 6PPD-quinone, a preservative found in car tires that kills coho salmon in the Pacific Northwest.