On January 8, 2026 Citizens Energy Group announced that the DigIndy tunnel is fully operational and meets all federal and state regulations. Our speaker will talk about the engineering that was involved in this 14 year project that created a 28 mile tunnel beneath the city.
Our Speaker will be Mike Miller who has led the DigIndy project for Citizens Energy Group since it's inception.
Sponsor: Bill Halsema
Program: The Engineering of DigIndy and Its Impact on Water Quality
Speaker: Mike Miller, MSCE, PE, who has led the DigIndy project for Citizens Energy Group since its inception
Introduced By: Bill Halsema
Attendance: NESC: 109, Zoom: 37
Guest(s): Jerrod Carter, Diane Evans, Bernie Heile, Terry Langdon, David and Mag Zauner
Scribe: Alan Schmidt
Editor: Carl Warner
Talk’s Zoom recording found at: https://www.scientechclubvideos.org/zoom/03232026.mp4
Speaker: Mike Miller is the Manager of Technical Services & Construction at Citizens Energy Group and has led the DigIndy project from its inception. He holds a BSCE in Civil Engineering and MSCE in Biotechnical Engineering from Michigan State University.
On January 8, 2026, Citizens Energy Group announced that the DigIndy tunnel system is fully operational and in compliance with all federal and state regulations. This presentation explored the engineering and planning behind the 14-year effort to construct a 28-mile tunnel beneath Indianapolis, designed to significantly reduce combined sewer overflows and help protect the White River and surrounding waterways.
The city of Indianapolis sewer system began in the 1870s with the sewer water flow combined with rainwater flow with excess above treatment capacity going to the White River. The Clean Water Act of 1971 had stricter requirements to achieve cleaner surface water. In 2011 the city of Indianapolis sold the sewer system to Citizens Energy Group. Before DigIndy, 40 to 60 times a year the sewers would overflow into the White River by a total of 5 to 6 billion gallons - equivalent to filling the Lucas Oil Stadium 17 times. There were 130 points around Indianapolis dumping into rivers. The DigIndy project started in January 2012 to meet the Clean Water Act requirements with a massive storage tunnel deep underground so excess sewage could be stored and then pumped back up and treated over time. DigIndy started January 2012 and was completed January 8, 2026, on time and within the $2 billion budget. They met eight major milestones from 2017 to 2025. Each milestone reduced raw sewage flow into the White River, improving water quality. The DigIndy project is 28 miles of 250-foot deep, concrete-lined, rock tunnel 18 feet in diameter for a 290-million-gallon storage tank. It was that deep because there was good stable rock at that depth. Helping along the way were sustainable green infrastructure such as porous pavers, rain gardens, green roofs, and planting 10,000 trees. Tree leaves hold rainwater on the leaves rather than contributing to water runoff. There were closure problems such as a portion of Meridian Street downtown being closed for 10 months.
We are not alone with the sewage situation. 100 cities or towns in Indiana and 800 US cities, mainly in the northeast and Midwest, have similar problems they are dealing with. DigIndy was the biggest tunnel project in the world, and we received good press along the way. The four-kilovolt tunnel borer machine, with a 95-ton cutter head, needed to be lowered in pieces by a huge crane from South America and reassembled in the tunnel. It needed to be refurbished twice. There is a one-foot thick concrete liner in the tunnel to keep additional groundwater out. 165,000 cubic feet of fresh air/min needed supplied to the tunnel during construction. It used 650 cubic feet of concrete/day, for 350,000 cubic feet of concrete total. The eight billion pounds of spoils rock was given to an aggregate processing group as a means of disposal.
Learn more:
https://info.citizensenergygroup.com/digindy
https://en.wikipedia.org/wiki/DigIndy
https://events.in.gov/event/dig-indy
https://indyencyclopedia.org/digindy/
https://www.malcolmdrilling.com/wp-content/uploads/2023/10/2019-NATJ-VRM-Indy.pdf
https://www.youtube.com/playlist?list=PLCXasbpKbFazM46QR5fCANHFbZGFa-sdI
Mike Miller
