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Combined Sewer Overflow

Combined sewers are a method for conveying both stormwater and sewage in one combined system. Historically, these systems were built in hundreds of communities across the United States before indoor plumbing became commonplace.

During periods of normal rainfall, the systems function properly by conveying both stormwater and sewage to wastewater treatment facilities. However, during floods or periods of heavy rainfall, 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.

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 Water is implementing a $1.6 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).

The Problem

The White River and many of our neighborhood streams are polluted by CSOs during rain and snow storms. When it rains as little as a quarter-inch, these sewers overflow into nearby streams, including White River, Fall Creek, Eagle Creek, Pleasant Run, Bean Creek and Pogues Run.

Raw sewage overflowing in our streams is a health hazard, smells and looks disgusting, hurts the environment and harms the quality of life in our neighborhoods.

The Plan

The CSO Consent Decree is an agreement between Citizens Water, the EPA and IDEM, under which Citizens Water is executing a Long Term Control Plan to curb the overflow of raw sewage from combined sewers into local waterways. The current plan allows Citizens Water to meet the required Consent Decree performance criteria and 2025 timeline, but in a more cost-effective manner.

The backbone of Citizens Water's plan is the Indianapolis Tunnel Storage System.

An additional 3.5 billion gallons of raw sewage will be captured and treated through 2025 when compared to the original Consent Decree schedule. Not only will the amended Consent Decree remove billions of gallons of sewage from entering the combined sewer system, but projects will cost less and involve fewer environmental concerns.

Costs and Benefits

When the federally-mandated plan is complete at the end of 2025, residents and businesses will benefit from the following:

  • Improved public health and quality of life in many neighborhoods now suffering from the sight and stench of raw sewage
  • The capture of up to 95-97 percent of sewage during wet weather on White River and Fall Creek.
  • Reduced overflow frequency from 45 to 80 events per year to two to four events per year; actual overflows will depend on the weather each year
  • Cleaner streams for fish and other aquatic life
  • Reduced odors, sanitary waste and other unsightly materials found overflowing from sewers into streams
  • Minimized impacts on neighborhoods and businesses by constructing most overflow storage facilities deep underground.

Because water pollution has many causes, we need an integrated, statewide effort to achieve our water quality goals. State and regional cooperation will be needed to resolve stormwater runoff and other difficult-to-control water pollution sources. Citizens Water wants to ensure that affordable investments in water pollution control will yield the greatest benefit possible for human health, the environment and the citizens who live in and downstream of Marion County.

For more information on this plan, view the CSO FAQs and the Long Term Control Plan.