Utility officials say it is unclear whether the death of a construction worker at the Deep Rock Tunnel-Connector (DRTC) site in Indianapolis was the result of an accident or a medical condition.

Twenty-five-year-old William Isacc Simpson died more than 250 feet below grade early Friday morning while working on an overnight shift for the project, an eight-mile tube intended to help prevent raw sewage overflows when completed in 2017.  Simpson, one of eight to 10 workers excavating the tunnel when the incident occurred, was employed by a joint venture of Walnut, Calif.-based J.F. Shea Construction Co. Inc. and Omaha, Neb.-based Kiewit Corp., which hold $179.3-million contract with Citizens Energy Group (CEG), Indianapolis.

Both the Occupational Safety and Health Administration and local police are investigating the fatality.
CEG declined to provide details on what occurred on site.

“I can't describe anything that went on underground because that is part of the investigation,” a  CEG spokesperson told reporters Saturday. She indicated previous reports of a tunnel collapse were untrue and that no other incidents have occurred on the two-year-old project. “We've had a great safety record on this site, so we are certainly shaken by this loss,” she said.

Simpson worked on the 19-ft-diameter tunnel for more than a year. Excavation involves use of a 450-ft-long boring machine to cut through bedrock. Workers are transported from tunnel entrance to site via small trains.

Work was halted on the project following the incident and was not expected to resume until at least Monday.

When completed, DRTC will connect a 25-mile-long system of rock tunnels and drop shafts.