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Federal Wet Weather Regulations

Clean Water Act
NPDES Permitting Program                        
Combined Sewer Overflow Control Policy    
Sanitary Sewer Overflows and Peak Flows (Proposed) Regulations

Clean Water Act

The U.S. Congress passed the Clean Water Act (CWA) in 1972 to help protect the country’s water resources. The Act was created to regulate all types of discharges to U.S. waterways, and has significantly reduced direct pollutant discharges, funded the construction of municipal wastewater treatment facilities and requires management of polluted stormwater runoff.  “Direct pollutant discharges” include wet weather sewer overflows from combined sewer and sanitary sewer systems, discharges from municipal sewage plants and industrial facilities and stormwater runoff from streets, construction sites, farms, etc.  Under the CWA, all overflows from sanitary sewers (designed to carry wastewater only) are prohibited and overflows from combined sewers (designed to carry wastewater and stormwater in the same pipe) must be reduced to only a few each year.

The EPA’s Office of Wastewater Management (OWM) has created numerous programs and policies to promote compliance with the requirements of the Clean Water Act, including the National Pollutant Discharge Elimination System Permitting Program, the Combined Sewer Overflow Control Policy and the proposed Sanitary Sewer Overflows and Peak Flows regulations.

More information on the Clean Water Act.

National Pollutant Discharge Elimination System (NPDES) Permitting Program 

NPDES is the federal permitting system authorized by the Clean Water Act.  As in most states, NPDES permitting process and authority is delegated to the state’s environmental agency, in this case, the Pennsylvania Department of Environmental Protection.  

The discharge of any pollutants (industrial, municipal or agricultural waste) from a point source into the waters of the United States must be authorized by an NPDES permit. A point source is any discernible, confined and discrete conveyance, such as a pipe, ditch, channel, tunnel, conduit, or container. It also includes vessels or other floating craft from which pollutants are or may be discharged.  Typical municipal point source discharges include discharges from publicly owned treatment works (POTWs) combined sewer overflows and storm sewers. 

Combined sewer systems, which frequently overflow untreated sewage into the waterways during wet weather, are regulated under the NPDES program.  The City of Pittsburgh and many older Allegheny County municipalities operate combined sewage collection systems under an NPDES permit.  In general, the permit serves as a license to discharge a specified amount of a pollutant into receiving waters under certain conditions. 

In order for the NPDES permit to be renewed, the permit holder must meet certain requirements (or commit to a schedule to meet the requirements), such as the “Nine Minimum Controls,” outlined in the Combined Sewer Overflow Control Policy.  

More information on EPA’s NPDES Permitting Program.

Combined Sewer Overflow (CSO) Control Policy

As part of the NPDES permitting system, communities with combined sewer systems, which carry both wastewater and stormwater in the same set of pipes, must comply with the federal Combined Sewer Overflow (CSO) Control Policy.  The CSO Control Policy was created to provide guidance to municipalities on meeting the Clean Water Act’s pollution control goals.  If a community does not comply with the CSO Control Policy, its NPDES permit (required for any entity discharging pollutants into the waterways) may not be renewed.

A critical component of the policy is a section called “The Nine Minimum Controls (NMCs),” which are operation and maintenance measures that combined sewer communities must implement to control CSOs without requiring significant engineering studies or major construction. 

The Nine Minimum Controls include:
1.  Proper operation and regular maintenance programs for the sewer system and the CSOs
2.  Maximum use of the collection system for wet weather storage
3.  Review and modification of pretreatment requirements to assure CSO impacts are minimized
4.  Maximization of flow to the publicly owned treatment works (POTW) 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 

CSO communities are also required to develop long-term control plans (LTCPs) that will ultimately result in full compliance with the Clean Water Act. 

More information on the EPA’s CSO Control Policy

Sanitary Sewer Overflows and Peak Flows (Proposed) Regulations

Communities with separate sanitary sewer systems, which carry wastewater only, have not historically been required to obtain an NPDES permit because the permitting program is designed for entities that discharge pollutants from a “point source.”  Any overflow from a sanitary sewer system is illegal under the Clean Water Act; therefore the system should not have any discharge pipes or point sources from which pollutants can contaminate the waterways.

However, EPA estimates that at least 40,000 overflows occur nationwide from sanitary sewers every year.  These overflows may occur through manhole lids, deteriorated pipes or as basement backups into people’s homes.   Thus, the EPA is developing SSO and Peak Flow rulemaking, which could require separate sanitary sewer communities to obtain an NPDES permit for their collection systems.  The goal of the regulation is to improve the operation of municipal sanitary sewer collection systems, reduce the frequency and occurrence of sanitary sewer overflows and provide more effective public notification if overflows do occur. 

More information on the proposed Sanitary Sewer Overflows and Peak Flows regulations.