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IDEM celebrates DigIndy completion amid 71% drop in statewide combined sewer overflows

Friday, October 10, 2025 at 10:00 PM

IDEM leadership joins 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 stands as one of the most ambitious infrastructure projects in Indiana’s environmental history,” said IDEM Commissioner Clint Woods. “Its completion marks a major milestone in our long-term, best-in-the-country efforts to protect Hoosier waterways and safeguard public health."

DigIndy was completed after a 14-year construction process and will bolster Indiana’s already significant progress in reducing sewage overflow events in 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. The following graph shows the consistent statewide decline over the past 17 years.

“I am proud of the work of our permitting and compliance teams, who have taken a wholesale approach to protecting Indiana’s water quality. ‘Measurable’ is an understatement,” said Martha Clark Mettler, Assistant Commissioner of IDEM’s Office of Water Quality. “Their passion and diligence have led to safer, cleaner water for Hoosiers in every corner of our state.”

Indiana’s CSO reductions are the result of sustained investment and oversight of Long-Term Control Plans (LTCPs), which all CSO communities are required to implement. Municipal utilities across the state have implemented various solutions to mitigate overflow events during wet weather. These include underground storage tunnels, expanded treatment capacity, green infrastructure, and sewer separation projects.

According to data compiled by the U.S. Environmental Protection Agency (U.S. EPA), Indiana is a national leader in submitted LTCPs. Indiana has 110 designated CSO communities with combined sewer infrastructure (the most of any state in the country). As of 2025, every CSO community has submitted an LTCP, with 69 in full implementation.

“Indiana’s vast progress in reducing sewage releases represents one of the single greatest improvements in statewide water quality for Hoosiers,” said Commissioner Woods. “Clean water means safer recreation, healthier ecosystems, and more vibrant communities.”

Municipal utilities across the state have implemented various solutions to mitigate overflow events during periods of heavy rainfall. Notable successes in CSO communities controlling discharges include:
  • Fort Wayne – Completed its tunnel system ahead of schedule and has reduced overflow volumes by more than 90 percent in some areas.
  • Jeffersonville - Fully implemented its approved LTCP and proactively added a fine screen to enhance wet weather treatment efficiency.
  • Mishawaka – Made significant upgrades to eliminate raw sewage discharges into the St. Joseph River.
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.

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