More than 100 years ago, Indianapolis built its first sewer system to carry stormwater away from streets, homes and businesses. When indoor plumbing came along, sewage lines from homes and businesses were hooked to these same sewers, combining stormwater and sewage in one pipe and sending it directly to our rivers and streams. These “combined sewers” were state of the art at the time. Most communities did not even have sewers back then.

As sanitation engineering techniques improved and the city grew, the city built wastewater treatment plants to treat the sewage. During periods of normal rainfall, the systems function properly by conveying both stormwater and sewage to wastewater treatment facilities. However, during rain events with ¼-inch of rainfall or more, the combined system can cause raw sewage to overflow, called Combined Sewer Overflows (CSOs), into our streams and rivers causing a threat to public health. In the central part of Indianapolis within the combined sewer system, even a light rain storm can cause raw sewage to overflow and pollute Indianapolis waterways. Without the ability for the sewers to overflow, raw sewage would back up into people’s basements and onto streets.

In new neighborhoods today, we build separate sewers for stormwater and sewage. However, combined sewers remain in many of the city’s older neighborhoods. Raw sewage overflows are a major cause of wet-weather pollution in portions of White River, Fall Creek, Eagle Creek, Pleasant Run, Bean Creek, Pogues Run, Lick Creek and State Ditch.

Understanding Combined Sewer Overflows

Combined sewers convey both storm water and wastewater (sewage) in one piping system. Historically, more than 800 communities across the United States built combined sewers once indoor plumbing became commonplace in the late 1800s.

During normal rain events with ¼-inch of rainfall or less, the combined system capacity can become overwhelmed, resulting in a mixture of storm water and wastewater overflowing into area waterways. This is referred to as a combined sewer overflow (CSO) event, which causes a threat to public health and the environment.

Under the U.S. Environmental Protection Agency (EPA) Clean Water Act, Indianapolis and other combined sewer communities must develop plans to reduce these overflows to protect human health and the environment. Ignoring these problems makes it more difficult to attract new businesses, jobs and residents to our world-class city. To address CSOs, Citizens is implementing a $2 billion Long Term Control Plan that is required to be completed by 2025 under a consent decree with the EPA and the Indiana Department of Environmental Management (IDEM).

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