INDIANAPOLIS — IDEM leadership recently joined Citizens Energy Group in celebrating the completion of DigIndy, an underground tunnel system in Marion County. The project aims to divert billions of gallons of wastewater annually from Hoosier rivers and streams, and fulfills plans to address nearly all combined sewer overflows in Central Indiana.
DigIndy was completed after a 14-year construction process and will bolster Indiana’s progress in reducing sewage overflow events into Indiana’s waterways. A combined sewage overflow (CSO) is a utility wastewater discharge that occurs when rainfall or snowmelt exceeds the system’s capacity, causing it to be overwhelmed and discharge untreated sewage into rivers and streams, potentially posing a threat to human health and the environment.
In 2008, more than 35 billion gallons of untreated sewage were released from CSO events across Indiana. By 2024, that figure dropped to 10.2 billion gallons, a 71.3% reduction. IDEM tracks CSO volumes through required monthly discharge monitoring reports from utilities, field inspections, and data analysis, one of the most robust assessment programs in the U.S. These tools allow IDEM to assess compliance, measure progress, and ensure that communities are meeting commitments to protect water quality.
The $2 billion DigIndy Tunnel system covers 28 miles, with tunnels around 20 stories below the city. The system’s job is to collect sewage and stormwater overflows during heavy rains, treat it and then release it. The massive project is one of the largest public works projects in Indianapolis history, with 8 tunnels running through all parts of the city, including Irvington, Fountain Square, and Garfield Park.
Citizens Energy Group said it will divert at least 95% of sewage and stormwater so it can protect rivers and prevent flooding. Planning for the project began in 2006, after the city entered into the consent decree with the EPA that work must be completed by 2025.
