When large portions of urban areas are heavily paved-over the combined sewer system can become stressed, especially during large storms.  And as we continue to increase carbon dioxide and other greenhouse gases into the atmosphere, storms and most weather systems are becoming more and more extreme.

In California’s Mediterranean climate, precipitation is heaviest in the winter months.  When these winter storms become extreme, this can create a huge flow of water that the City’s combined sewer system cannot effectively clean.  It is then, during heavy storms, that the stressed sewer system releases untreated (contaminated) water into local waterways.

These large winter storms in San Francisco sometimes force the SF wastewater treatment plant staff to discharge untreated water into the SF Bay or the Pacific Ocean.  By removing pavement we capture stormwater in the ground, reducing  pressure on San Francisco’s combined sewer system.

There are two wastewater treatment plants in San Francisco.  80% of all the waste from all of San Francisco’s nearly 1 million residents heads to the SFPUC’s Southeast Treatment Plant located in the Bayview neighborhood.  The other 20% flows to the Oceanside Treatment plant adjacent to the SF Zoo.

As the City’s population grows, important green infrastructure improvements to the sewer system are happening currently (and will continue for many years to come) all the while improving services and environmental quality in San Francisco.