Combined Sewer Overflow Control Program

What is a combined sewer?

Combined sewers were built to collect sanitary and industrial wastewater, as well as storm water runoff, and transport this combined wastewater to treatment facilities. Flows conveyed to the treatment plant are then treated and discharged to a nearby river or stream.

Ohio EPA no longer permits the installation of combined sewers. For newly installed sewers, sewage and storm water are collected in separate pipes with sewage being transported to a wastewater treatment facility and storm water being transported to nearby surface waters. This type of system is called a separate sewer system.

View an illustration depicting both a combined and a separate sewer system.

What is a CSO?

During dry weather and small wet weather events (i.e., rainfall and snowmelt), combined sewers are designed to transport all flows to a treatment plant. During larger wet weather events the volume of storm water entering the combined sewer system may exceed the capacity of the combined sewers or the treatment plant. When this happens, combined sewers are designed to allow a portion of the untreated combined wastewater to overflow into the nearest ditch, stream, river or lake. This prevents the rupturing of pipes, backing up of sewage into basements, and/or flooding of streets. The locations where these discharges of untreated combined wastewater occur, as well as the discharge events themselves, are known as Combined Sewer Overflows (CSOs). CSOs are located at various locations along combined sewers, and are unique to each system.

Why are CSOs a concern?

CSOs contain not only storm water but also untreated human and industrial waste, toxic materials and debris. This is a major water pollution concern for cities with combined sewer systems. CSOs are among the major sources responsible for beach closings, shellfishing restrictions, aesthetic impairments and other water body impairments. Additionally, contact with discharges from CSOs can have adverse effects on human health. A December 2001 report to Congress cited the Center for Marine Conservation as stating that, "[s]ome of the common diseases include hepatitis, gastric disorders, dysentery, and swimmer's ear. Other forms of bacteria found in untreated waters can cause typhoid, cholera, and dysentery." (Report to Congress on Implementation and Enforcement of the CSO Control Policy, December 2001, EPA 833-R-01-003)

How many CSOs are in Ohio?

  • Ohio has approximately 1053 permitted CSOs in 71 remaining communities (June 2021), ranging from small, rural villages to large metropolitan areas.
  • View an inventory of Ohio’s CSO communities

Where are CSOs located in Ohio?

CSOs are located throughout Ohio. View maps of individual CSO outfall locations organized by community.

When should CSOs be avoided?

CSO outfalls and their receiving waters should be avoided during and immediately after any wet weather event (i.e., rainfall and snowmelt). Additionally, these locations should be avoided any time a discharge is observed from the outfall pipe regardless of weather conditions.

What is being done to address CSOs?

Ohio EPA continues to implement CSO controls through provisions included in National Pollutant Discharge Elimination System (NPDES) permits and using orders and consent agreements when appropriate. The NPDES permits for our CSO communities require them to implement the nine minimum control measures. Requirements to develop and implement Long-Term Control Plans (LTCPs) are also included where appropriate.

In 2015, U.S. EPA modified their goal for the Water Safe for Swimming Measure, which seeks to address the water quality and human health impacts of CSOs. The goal includes incorporating an implementation schedule of approved projects into an appropriate enforceable mechanism, including a permit or enforcement order, with specific dates and milestones for 92% of the nation's CSO communities by the end of September 2016. As of June 2021, 83 of Ohio’s 88 CSO communities meet this definition, which equates to 94%.

Community-specific Solutions

What can I do to minimize CSO impacts?

There are multiple ways in which the general public can help reduce the impacts of CSOs. An initial step is to contact your local wastewater utility to notify them of your interest and obtain information specific to your city or village's program. Some municipalities even implement cost-sharing programs to lower the financial aspect of some measures. Topics to discuss include: 

  • Water conservation techniques
  • Disconnection of gutter downspouts and other sources of clean water that may be connected to your combined/sanitary sewer system
  • Proper disposal of grease and/or hazardous materials
  • Litter prevention
  • Proper disposal of yard wastes
  • Composting
  • Green Infrastructure (e.g., rain gardens, rain barrels, green roofs, etc.)

Do any Ohio CSO communities maintain web sites with information regarding their program?

The following links will take you to web sites maintained by the given municipality:

Integrated Planning

In January 2019, Congress enacted H.R. 7279, codifying Integrated Planning as an amendment to the Clean Water Act (CWA). Through passage of this bill, U.S. EPA’s 2012 guidance document Integrated Municipal Stormwater and Wastewater Planning Approach Framework was incorporated into law. 

Integrated Planning allows a municipality to propose a comprehensive plan to meet multiple CWA requirements by identifying efficiencies from separate wastewater and storm water programs, then sequencing investments so that the highest priority projects are completed first and utility costs are manageable. 

Ohio’s Combined Sewer Overflow (CSO) communities have the option to incorporate their Long-Term Control Plans (LTCP) for CSO control into an Integrated Plan. CWA requirements that can be incorporated into an Integrated Plan include but are not limited to: 

  • Sanitary Sewer Overflow (SSO) Elimination
  • Storm Water/Municipal Separate Storm Sewer System (MS4) Management 
  • Water Quality Based Effluent Limits (WQBEL)/National Pollutant Discharge Elimination System (NPDES) limits 
  • Total Maximum Daily Load (TMDL) Obligations 
  • Green Infrastructure 
  • Asset Management
  • Water Reuse or Recycling 

Ohio EPA believes that Integrated Planning can generate real benefits and supports communities that wish to explore the Integrated Planning approach. We encourage all municipalities to research and understand Integrated Planning and assess whether this approach is appropriate and beneficial for their community. 

U.S. EPA has also provided the 2014 Financial Capability Assessment Framework for Municipal Clean Water Act Requirements, intended to serve as a financial compliment to the 2012 Integrated Planning Framework. Although not codified as part of H.R. 7279, U.S. EPA and Ohio EPA are using this financial assessment policy. U.S. EPA is also evaluating new financial assessment methods. 

Additional information can be found on U.S. EPA’s Integrated Planning website

Integrated Planning Workshop

To support Ohio communities engaged in or learning about Integrated Planning, Ohio EPA hosted a workshop on Oct. 2, 2019. Speakers from U.S. EPA, Ohio EPA, and private organizations joined with Ohio mayors and utility directors to provide a variety of perspectives on Integrated Planning. To see all the presentations, view the complete playlist on Ohio EPA's YouTube channel or view topic videos and individual presentation slides through the links below. 

Where can I get more information?

Ohio EPA CSO Program Contacts

Ward, Ashley (614) 644-4852
Brumbaugh, David (614) 644-2138

Integrated Planning Workshop, Oct. 2, 2019
Lima Mayor David Berger and Judy Sheahan, U.S. Conference of Mayors, discuss the importance of integrated planning and affordability studies at the integrated planning workshop, coordinated and developed by Ohio EPA, the Ohio Mayors Alliance, the U.S. Conference of Mayors, and U.S. EPA. For more information, see the Integrated Planning section to the left.