It is fairly normal to see suds in an urban stream after a storm. The amount of suds may be significant if it has been a long time since it last rained (or there was snow melt). Two common sources of suds are:
- Surfactants washing off roadways that were deposited by vehicle emissions (exhaust); and
- Naturally occurring surfactants from organic matter building up in gutters and along streams edges.
The amount of suds may increase in intensity depending on how long the dry period prior to the rain event (or snow melt) was.
Roadways: Gasoline contains detergent additives intended to keep the engine components clean and running smoothly. The detergents are also called surfactants. As gas is burned, the surfactants are deposited as a waste product on streets and are then washed into nearby waterways during storm events. The result is suds, particularly downstream of drop structures and riffles where the surfactants get worked up. The problem tends to be worse after long dry spells and in areas with lots of impermeable surfaces (such as parking lots and roads).
Natural: There are also natural surfactants in organic matter. As leaves and other organic matter break down, its primary components build up in gutters and along stream edges. The longer the dry period, the more natural surfactant material builds up. During storm events this material is washed into area waterways and makes suds.
Other sources: Other sources of suds include detergents from car washing (residential, commercial, or car sales lots), power washing of streets, lots, buildings, and sidewalks, business operations (i.e., restaurants and others with alleys), and window cleaning. Illicit sanitary wastewater connections from businesses and residences into the storm sewers. Storm sewers discharge directly to streams.
If you see suds when there hasn’t been any rain or if the suds smell like a perfumed detergent, please call 311.