Eliminating Sewer Overflows in Indianapolis

DigIndy project aims to eliminate combined sewer overflows by building a series of tunnels under the city.
Eliminating Sewer Overflows in Indianapolis
The power behind the DigIndy project, a tunnel-boring machine built by The Robbins Company, positioned at the start of the Deep Rock Connector Tunnel.

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Deep under Indianapolis, a massive machine is slowly chewing its way through the bedrock the city stands on. In its wake, a new tunnel system will provide relief from combined sewer overflows that have plagued the city.

“DigIndy is a very large project that is going to include taking offline a number of CSOs that are currently located within the central part of Indianapolis,” says Tim Shutters, construction supervisor for Citizens Energy Group.

Citizens, a utility service company providing natural gas, thermal energy, and water and wastewater services to about 800,000 customers in central Indiana, began the project in 2012 and expects to complete it by 2025.

“In 2011, Citizens acquired all of the water and wastewater infrastructure from Indianapolis,” says Mike Miller, manager of construction. “That included the city’s commitment to build the tunnel system to conform to the consent decree established by the U.S. EPA.”

The need

When Indianapolis was being built up, the most sophisticated way to handle stormwater removal was via the sanitary sewer system.

“Under dry, slow conditions the sanitary flows run to the wastewater treatment plant and everything is fine and works as it should,” says Shutters. “When rain events come along, however, the system becomes overwhelmed. Overflows were created that exit into the local bodies of water.”

Local officials knew something had to be done to stem the flow of pollution. In 2006, the EPA and the U.S. Department of Justice reached a consent agreement with the city to eliminate 97 percent of CSOs by 2025. “We have about 138 CSOs on the whole system, and this project is going to catch about 100 to 110 of those,” Miller says.

The project

The $1.9 billion project includes using boring machines to create 28 miles of 18-foot-diameter tunnels 250 feet below the city. The first leg of the dig — mining of the 7 1/2-mile Deep Rock Connector Tunnel and the offshoot Eagle Creek Deep Tunnel — was completed in October. The joint venture of contractors Shea-Kiewit took the lead on the project.

“We are currently lining that portion right now with a 1-foot-thick liner to keep groundwater out,” Miller says. “It’s basically a set of framework that is 210 feet long and collapses in on itself and can be moved from the finished port to an open section that’s been mined. Then we pump concrete from the surface into the framework and it leaves the 1-foot liner after we remove the framework.”

That portion of the project should be finished around the end of 2017.

“Originally, the Eagle Creek section was going to be open-cut, but it was going to be very cumbersome and it was going to be deep and near a levee system. We were able to come to an agreement with our contractor and went ahead with tunneling that portion.”

Tunneling also added more storage capacity on the Eagle Creek line; the open-cut process would have used a smaller-diameter pipe.

The completion of the Deep Rock and Eagle Creek tunnels leaves just four remaining segments. The next two segments — the White River Tunnel and the Lower Pogues Run Tunnel — are in the procurement process.

“We have asked a few contractors for pricing,” says Shutters. “Shea-Kiewit has done a great job, but we felt it was necessary to allow some other people to come in and competitively provide pricing so we could get the best value.”

The project is designed so that when each segment is completed, it can go online immediately while work continues on the next. “There will be a big bulkhead that we put between the Deep Rock and the next tunnel so everything south can go online,” Miller says.

The next phase

The White River and Lower Pogues segments are set to begin early this year. The Lower Pogues is expected to affect downtown the most; it will go past Lucas Oil Stadium.

“Most people won’t even notice the deep underground work,” Miller says. “However, there are three drop shafts that we have to construct from the ground surface down in that portion of the project. That is going to be pretty impactful on downtown for the better part of a year.”

Overall, there will be 33 drop shaft sites along the project route. While larger contractors will handle the tunneling portion of DigIndy, local contractors will handle the other parts of the project — installing drop shafts and other street work.

“We’re on the backs of ratepayers, and they want to see the money staying local,” Miller says. “The big tunneling contractors are employing local laborers and subcontractors, and the shallow work stuff will be sent out to local contractors.”

Setting records

The project earned national recognition in 2013 when Shea-Kiewit bored 410 feet in 24 hours, setting a world record for tunnel-boring machines of similar size. “We’ve also broken records for the most production in a week and a month,” Miller says. “Because of that, we’re pretty far ahead of schedule.”

The tunnel-boring machine was manufactured by The Robbins Company in the late 1970s and spent most of its life in New York working on water and subway tunnels.

“It most recently came to us via the Second Avenue Subway Project in New York,” Miller says. “Shea-Kiewit rehabilitated the machine themselves with input from Robbins, and then Robbins manufactured a new cutter head specifically for this project.”

Minor hiccups

All projects have their little hiccups, and DigIndy is no exception. There have been little pauses along the way, including finding unanticipated groundwater during the Deep Rock drilling segment.

“The contractor was very good about working with us on a solution to mitigate the impact of the water during construction,” Miller says. “It wasn’t detrimental to the project. It was just a little more than anticipated in a certain area.”

Crews also had to deal with the alignment of Deep Rock, which includes many turns. Contractors used a conveyor belt system to remove debris from the tunnel.

“A conveyor belt only really likes being in a straight line,” Shutters says. “Every time we put a curve into the tunnel alignment, our contractor had to overcome some obstacles to make that rubber band want to turn.”

Having to deal with those alignment issues led Citizens Energy to look at the rest of the project and modify alignments in the next phase to minimize changes in direction.

“For the most part we have been very lucky with the project,” Miller says.


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