Indy’s Deep Rock Tunnel Project Progressing

By Jeff Griffin, Senior Editor | August 2012, Vol. 67 No. 8

Construction is proceeding on the largest combined sewer overflow project ever undertaken by the city of Indianapolis.

The Deep Rock Tunnel Connector project will include a 25-mile-long deep tunnel system, 18-feet in diameter with a storage capacity of 250 million gallons and will significantly reduce the frequency and amount of raw sewage overflows during rains.

Raw sewage captured will be stored in the tunnel and then transported to the wastewater treatment plant. The enhanced tunnel will have the capacity to store raw sewage during large storm events. All sewage transported and stored underground in the tunnel system is sewage that otherwise could have gone directly into the area’s waterways.

Currently, when as little as a quarter inch of rain falls, combined sewers reach capacity and raw sewage overflows into local rivers and streams.

The project is being constructed for Citizens Water, a division of Citizens Energy Group (Citizens). Construction of the $179.3 million project is a joint venture of J.F. Shea, Los Angeles, CA, and the Kiewit Corp., Omaha, NE. Shea-Kiewit has considerable experience with deep tunnel projects.

Phase 1
The first phase of the project is an eight-mile-long tunnel, said John Morgan, manager of Citizens Energy special projects group and manager of construction.

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“This project is the backbone of our deep tunnel storage system,” said Morgan. “Its construction creates the mechanism for the transfer of flow from our entire deep tunnel system. Additionally, it allows for collection of three combined sewer overflows, two of them being ‘worst offenders’ in our system.”

The tunnel system is being built in bedrock below the city using a specialized tunnel boring machine. After the machine bores the tunnel, a concrete tunnel lining will be installed to help keep groundwater out and keep sewage in the tunnel.

Information about the project has emphasized that deep tunnel technology reduces disturbances to neighborhoods along the project route during construction. Because the tunnel is being constructed below groundwater levels, impact to area wells, gas and electrical lines, existing sewers and other utilities will be significantly reduced. Traffic disruptions and property easements needed to construct the project also will be minimized.

Preliminary work and site preparation began in late 2011. Excavation of the tunnel is expected to begin in January 2013.