Sanitary Sewer Improvement Program

What are sanitary sewer overflows?

Sanitary sewer systems collect sewage and other wastewater and transport it to a treatment and disposal facility. A sanitary sewer overflow (SSO) is a spill, release, or discharge of wastewater from a sanitary sewer system upstream of a wastewater treatment facility. SSOs generally occur due to root, debris and "fats, oil, and grease" blockages in sewer pipelines. SSOs also occur as a result of pipeline breaks, excessive stormwater inflow or groundwater infiltration, insufficient sewer system capacity, equipment failures, and vandalism.

SSOs contain untreated wastewater that includes high levels of organic wastes, pathogenic organisms, toxic pollutants, nutrients, and oil and grease. Once an SSO occurs, it is difficult to contain and recover much of the spilled wastewater or directly mitigate for the spill. Thus, SSOs can pollute surface water and groundwater, threaten public health, adversely affect aquatic life, and impair the recreational use and aesthetic enjoyment of surface waters. SSOs can also inundate properties and result in the closure of beaches and other recreational areas.

What is required of sewage collection agencies?

In 2006, the State Water Board adopted requirements for all public agencies that own or operate a sewer system greater than one mile in California. The State Water Board Order No. 2006-0003-DWQ, as amended per Order No. WQ 2013-0058-EXEC, or Sanitary Sewer Order, prohibits any SSO that results in a discharge to waters of the United States or creates a nuisance. The Sanitary Sewer Order requires a public agency that owns or operates a sewer system to (1) develop and implement a sewer system management plan (SSMP), (2) report SSOs to the State Water Board’s online SSO database, (3) notify the California Office of Emergency Services within two hours of becoming aware of any SSO greater than or equal to 1,000 gallons discharged to surface water or spilled in a location where it probably will be discharged to surface water, and (4) conduct an SSMP internal audit, at a minimum every two years, and prepare an audit report to be kept on file. In addition, the Sanitary Sewer Order requires sewer system agencies to conduct water quality monitoring and submit a technical report for any SSO in which 50,000 gallons or greater is spilled to surface waters.

What is the goal of the Sanitary Sewer Improvement Program?

The goal of the Sanitary Sewer Improvement Program is to reduce or eliminate SSOs and inflow and infiltration into aged and defective sewer pipes within the San Francisco Bay Region. To achieve this goal, Regional Water Board staff audits sewer system operations to check for compliance with the Sanitary Sewer Order and to ensure that the sanitary sewer infrastructure is adequately operated, maintained, repaired, and upgraded. When necessary, we also enforce against agencies with poor sewer system performance through the assessment of penalties and issuance of cease and desist orders that require improvements. So far, our efforts and sewer system agencies’ efforts have reduced SSOs within the Region. However, much more improvement is still needed when it comes to the reduction of wet weather related SSOs. In the long term, the efforts will lead to less leaky systems that spill over in the wet season and also lower spikes in wet weather flows going to wastewater treatment facilities.

Over the past years, Regional Water Board staff has prepared status reports on the Sanitary Sewer Improvement Program. These reports assess our Region’s trends in SSOs and describes our past, current and future efforts to reduce SSOs. A copy of each of the status reports is available below:

What sanitary sewage overflows have been reported?
The public may access electronic SSO reports submitted on or after May 2, 2007, through the State Water Board's Interactive SSO Report.

How can I get more information?
For more information, contact Michael Chee at or (510)622-2333.