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Sierra Club Water Sentinels

Sewer Overflows

Overflowing sewer systems are a major contributor to microbiological contamination of our waters.

There are two types of sewer systems. Sanitary sewer systems are designed to transport just sewage from houses or industry to treatment or disposal facilities. Combined sewer systems collect and carry both sewage and storm water runoff.

Any overflows from a sanitary sewer system-called sanitary sewer overflows (SSOs)-are illegal under the Clean Water Act. Overflowing manholes and basement backups are examples of SSOs.

An overflow from a combined sewer system is called a combined sewer overflow (CSO). While CSOs are not illegal, the Clean Water Act mandates that they must be reduced to a minimum. The EPA has defined nine minimum controls that must be must be adopted by communities with combined sewer systems to help reduce overflows. These controls were to have been adopted by January 1, 1997, but most communities have yet to implement them.

The Water Sentinels are committed to eliminating all sanitary and combined sewer overflows.

Combined Sewer Overflows

Nine Minimum Controls

1. Proper operation and regular maintenance programs for the sewer system and the CSOs
2. Maximum use of the collection system for storage
3. Review and modification of pretreatment requirements to assure CSO impacts are minimized
4. Maximization of flow to the publicly owned treatment works for treatment
5. Prohibition of CSOs during dry weather
6. Control of solid and floatable materials in CSOs
7. Pollution prevention
8. Public notification to ensure that the public receives adequate notification of CSO occurrences and CSO impacts
9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls

We hope you will join us.

Find out more:

• Microbiological Contamination

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