The Root of Sewage Spills in the Bay Area

The primary cause of the Bay Area’s sewage spill problem is our massive and crumbling sewer infrastructure. Sewage from Bay Area communities is treated by more than 100 collection systems, more than 40 treatment plants and more than 17,000 miles of publicly owned sewer pipe – and these systems are in very poor condition. Most were built in the 1950s and 60s and are now in dire need of upgrades and repairs.

During the rainy season, large amounts of rainwater seep into the sewer systems through crumbling pipes or through connections between the sewer and storm drain systems. This swells the volume of water flowing into treatment plants, which can overwhelm treatment plant capacity and cause hundreds of millions of gallons of treated and untreated sewage to be discharged into local watersheds. Read about the latest winter sewage spills.

Sewage spills can be traced to one of two sources: wastewater treatment plants and the sewage collection pipes that feed into them.

Spills From Treatment Plants

Spills from treatment plants are typically much larger in volume than spills from collection pipes, though they happen less frequently. In the Bay Area, most treatment plant spills are the indirect result of inflow and infiltration. In all Bay Area cities except for San Francisco, the pipes that carry sewage from your house to the treatment plant are separate from those that drain stormwater from city streets. Inflow and infiltration is the term used to describe when the stormwater (and groundwater) gets into the sewer system.

Find Out How Your Local Treatment Plant Measures Up

View Baykeeper’s map which shows the location of the publicly-owned wastewater treatment plants in the Bay Area and gives information about how old the plant is, which cities each plant serves, and the population of each. Notice the different icons—if your treatment plant has a brown circle, it means they’ve had a major sewage spill (more than 10,000 gallons) in the past year.

Thanks to KQED Quest for developing the treatment plant map and producing the Wastewater Woes news video - click here to watch the video.

Sanitary Sewer Overflows (SSOs)

Sanitary sewer overflows (SSOs) from collection pipes are more frequent but much smaller than treatment plant spills. They indicate that the pipes need to be cleaned, repaired, or replaced with larger pipes. Roots, seeking water, can grow into pipes and block them. Fats, oils and grease from homes and restaurants can stick to the sides of the pipes, slowly building up until the pipe is clogged. Often, however, these pipes are just too small to handle the volume of sewage generated in an area. In 2008, there were 2,100 reported SSOs totaling 12.5 million gallons reaching surface waters in the Bay Area.

Click here to view the State Water Quality Control Board’s Map documenting Sanitary Sewer Overflows.