Combined Sewer Overflow Control Policy
Policy Framework
Combined sewer overflows (CSOs) are subject to the National Pollutant Discharge Elimination System (NPDES) permitting program, which was created in 1972 through the Clean Water Act to address water pollution. Through the NPDES program, EPA established a national framework for controlling CSOs, called the CSO Control Policy. Communities with CSOs must comply with the CSO Control Policy and have a permit to discharge.
EPA's Combined Sewer Overflow (CSO) Control Policy (pdf) provides guidance on how communities with CSOs can achieve Clean Water Act goals in a flexible, cost-effective manner. The CSO Control Policy also defines expectations for regulated communities, state water quality standards authorities, and NPDES permitting authorities. In December 2000, as part of the Consolidated Appropriations Act for Fiscal Year 2001 (P.L. 106–554), Congress amended the Clean Water Act by adding Section 402(q) (33 U.S.C. (§) 1342 [2020]). This amendment is commonly referred to as the “Wet Weather Water Quality Act of 2000.” It requires that each permit, order, or decree issued pursuant to the Clean Water Act after the date of enactment for a discharge from a municipal combined sewer system shall conform to the 1994 CSO Control Policy.
A Phased Approach
The CSO Control Policy has two phases to help communities manage the complexities and costs of reducing and controlling CSOs.
In Phase I, communities with CSOs must:
- Identify and begin implementing nine minimum controls, which are the minimum technology-based controls to reduce water quality impacts. See Combined Sewer Overflows Guidance for Nine Minimum Controls (May 1995) (pdf)
- Develop a long-term control plan to achieve compliance with water quality standards and other CSO Policy and Clean Water Act requirements. See Combined Sewer Overflows Guidance for Long-Term Control Plan (September 1995) (pdf)
- Submit the long-term control plan to the NPDES permitting authority.
In Phase II, communities with CSOs must:
- Continue implementing the nine minimum controls.
- Implement the long-term control plan.
- Conduct monitoring to verify water quality standards are being met.
New Draft Guidance for Future Permits
Draft Guidance for Future National Pollutant Discharge Elimination System (NPDES) Permits for Combined Sewer Systems.
On February 20, 2024, EPA published a notice in the Federal Register requesting comment on a draft guidance titled, Guidance for Future National Pollutant Discharge Elimination System (NPDES) Permits for Combined Sewer Systems. This draft guidance highlights the available paths forward for permitting communities with CSOs at the next stage in their programs. It summarizes options under the Clean Water Act that are articulated in the original 1994 Combined Sewer Overflow Control Policy as well as the option to use EPA’s 2012 Integrated Planning Framework to look holistically at future investments. The comment period for the draft guidance closed on March 21, 2024.
- Draft Guidance for Future National Pollutant Discharge Elimination System (NPDES) Permits for Combined Sewer Systems (pdf)
- Federal Register Notice
- Docket ID No. EPA–HQ–OW–2023–0475 (https://www.regulations.gov/docket/EPA-HQ-OW-2023-0475)