What are the regulations that govern sewer overflows?

In the 1970s, the United States Congress passed the Clean Water Act, a federal law that protects the nation’s waters through various pollution control programs. These programs are enforced by the U.S. Environmental Protection Agency (EPA), which has the authority to issue rules on how best to implement the law.

Under the Clean Water Act, the EPA administers the National Pollutant Discharge Elimination System (NPDES) permitting program and the Combined Sewer Overflow Control Policy. The NPDES requires federal permits for point source discharges, such as CSOs; and the CSO Control Policy provides a national framework for reducing combined sewer overflows. The CSO Control Policy outlined nine minimum controls (NMC). As short-term strategies (24-month implementation), the NMCs are designed to reduce combined sewer overflows and their effects on receiving water quality with a minimal amount of technical analysis and construction. NMC implementation is the first step towards reducing the effects of combined sewer overflows. Since 1992, MSD has reduced combined overflows by 33% through its NMC implementation.

Overflows from sanitary sewers systems are also covered under the NPDES program, although the EPA currently has no formal rules for this type of overflow. EPA has delegated its authority for these clean water programs to the State of Missouri, which has enacted similar state laws and regulations that govern MSD’s systems.