What is a Combined Sewer System and Combined Sewer Overflow (CSO)?

According to the United States Environmental Protection Agency (EPA), a “combined sewer system” and “combined sewer overflow” are defined as follows:

Combined sewer systems are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe.  Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body.  During periods of heavy rainfall or snowmelt, however, the wastewater volume in the combined system can exceed the capacity of the sewer system or the treatment plant.  For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other waterbodies.  These overflows, called combined sewer overflows (CSOs), contain not only stormwater but also untreated wastewater.

Does the Owensboro community currently have a combined sewer system and CSOs?


What is the current boundary of the combined sewer system?

The Owensboro combined sewer system contains three large tunnel sewers that discharge to the Ohio River.  These tunnel sewers are located in the western, central and eastern portions of north Owensboro.  Originally, all wastewater generated by the community was transported through these tunnel sewers that were subject to combined sewer overflows.  RWRA and its predecessor, the Owensboro Sewer Commission, have completed numerous projects to minimize the effects of the CSOs through separation projects that have reduced the boundary of the combined sewer system.  See attached Combined Sewer System Map.

Where are the CSO outfalls located?

Originally, there were 16 designed overflow locations in the Owensboro community.  Eight of the outfalls were in southern locations of the system and discharged to ditches/waterways that eventually ended up in Panther Creek.  RWRA has completed projects that eliminated each of these eight outfalls to Panther Creek.  The remaining eight outfalls are located at various points along the Ohio River, with four of the eight associated with the tunnel sewer discharges.  The tunnel sewer system outfalls account for more than 95% of all combined sewage discharged from the Owensboro community.  These tunnel sewer outfalls are located along the Ohio River at Dublin Lane, Locust Street and Center Street.

Should you avoid these CSO locations during rain?

Yes.  During heavy rain events, large amounts of stormwater along with small amounts of untreated sewage, enters the Ohio River.  In addition to the potential for exposure to contaminants such as bacteria, there is a hazard created due to the turbulence from the water entering the river.  Therefore, all water recreation activities at these locations should be avoided.  RWRA posts CSO flags (orange flags that say “CSO”) during and immediately following rain events to warn the public regarding the conditions around CSOs.

Are there other locations in the community where waters should be avoided during rain events?

Yes.  Any areas that have standing water during and after rain events should be avoided for numerous reasons.  Heavy rains could cause manhole lids to blow off and these locations may be hidden under water and, therefore, create a significant hazard.  All stormwater runoff potentially contains bacteria from sources such as wildlife, domestic pets, etc.  and in some areas, may contain combined sewage.  Therefore, bodily contact with any stormwater is potentially hazardous.  The public and especially children should not walk/play in flooded streets, ditches, etc.

What is RWRA doing to address CSOs in our community?

The City of Owensboro, like many communities along large waterways such as the Ohio River, had combined sewer systems in the late 1800s and early 1900s.  These systems transported both stormwater and wastewater to the receiving streams.  Most of these systems discharged raw, untreated sewage to these streams/waterways until the mid-1950s.  In Owensboro, this occurred until 1958 when the first wastewater treatment plant (now known as the Max Rhoads Treatment Plant) was built on the west side of Owensboro on Ewing Road.  The original sewage treatment at this facility was basic, and technology and recent upgrades to each of Owensboro’s two treatment plants have significantly improved the water quality of treated wastewater discharged to the Ohio River.  The East Wastewater Treatment Plant on Pleasant Valley Road is the second of the two treatment plants.

RWRA has been systematically completing projects to reduce the amount and concentration of wastewater conveyed through the combined system.  These projects involve (1) the construction of additional wastewater storage in the system that will allow combined sewage to gradually be released and treated after a rain event; (2) construction of larger conveyance and treatment facilities to transport and treat additional combined sewage during rain events; and (3) a maintenance program to continually clean pipes, inlets, etc. of debris.

RWRA has also partnered with the City of Owensboro on various stormwater improvement projects to construct ditches and detention basins that will reduce the total volume of stormwater that is contributed to the combined system. Some of these projects allow for the separation of stormwater from the combined system and redirects this water to the Panther Creek watershed.  Other projects are designed to store the stormwater until the rain event is over, etc.

What is the Clean Water Act?

The Clean Water Act is federal legislation administered by the U.S. Environmental Protection Agency that governs the introduction of contaminants and pollutants into waters of the United States.  The Act has goals that all streams/waters should be fishable and swimmable at all times.

What is the CSO Policy?

The CSO Policy was developed after the Clean Water Act by EPA to address the specific concerns related to CSOs and their effects to waters of the United States.  This Policy requires each community with CSOs to develop a Long-Term Control Plan designed to reduce/eliminate the effects of the community’s CSOs.  Click here to view the CSO Control Policy.

What is a Consent Judgment?

A Consent Judgment is a legal document filed in a State Court between the state’s regulatory agency for water and a community with CSOs.  This document outlines the requirements that are agreed upon between the community and the state regulatory agency that are designed to achieve the goals of the CSO Policy.  The Kentucky Division of Water (KDOW) filed a Consent Judgment against the Regional Water Resource Agency on September 5, 2007 which set a timeframe for the completion of a detailed plan to bring the Community’s remaining CSO’s into conformance with the requirements of the CSO Policy.  The Framework document, which spelled out the direction of the program and schedule of the completion date of the Long-Term Control Plan, was submitted to KDOW and EPA on August 30, 2008.  The final version of the Community’s Long-Term Control was submitted on May 31, 2016 and approved in July 2016.  This approval gives the Community ten (10) years to complete the implementation of CSO projects totaling $30,200,000.

Where can I learn more about CSOs and their impact on our community?

Click on the links below for more information about CSOs and their impact on the community.

Kentucky Division of Water – CSOs

Environmental Protection Agency – CSOs



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