DC Water’s Tunnel Boring Machine Reaches Key Project Milestone

(UC) — DC Water’s giant tunnel boring machine, named Chris, broke through a wall of concrete to reach the W Street shaft, a key milestone in the mining of the Northeast Boundary Tunnel (NEBT) project.

Chris will rest for a bit in the shaft and get much-needed maintenance before resuming work.

Excavating through clay and sand, Chris the machine is on a five-mile-long underground journey digging the NEBT which is the last tunnel segment of the Anacostia River Tunnel. This is actually a giant 23-foot-diameter sewage tunnel that can store 90-million gallons of combined sewage during heavy rains to keep from overflowing the combined sewer system in the District. The combined sewage will ultimately make its way to the Blue Plains Advanced Wastewater Treatment Plant where it will be treated, cleaned and recycled back to the Potomac River.

When Chris finishes mining and all work is complete in 2023, the Northeast Boundary Tunnel will connect to the existing First Street Tunnel. The first half of the tunnel opened in March 2018 and has already substantially improved the health of the Anacostia River.

"To date, the portion of the Anacostia River Tunnel that is in service has prevented more than 7 billion gallons of combined sewage and 3,500 tons of trash from entering the Anacostia, bringing a resurgence to the waterfront. The Northeast Boundary Tunnel in particular will significantly reduce sewer backups and chronic flooding in the Bloomingdale and LeDroit Park and other neighborhoods adjacent to Rhode Island Ave, NE,” said David L. Gadis, CEO and General Manager of DC Water. When the entire 13.1-mile Anacostia River Tunnel is completed, it will reduce combined sewer overflows to that river by 98 percent.

The boring machine has been mining since September of 2018 and the tools on its cutterhead are worn from all the work. The construction contractor Salini Impregilo Healy (Lane Construction) Joint Venture will use the shaft to park the TBM while replacing rippers, knives, and disc cutters on its face and performing other maintenance. The TBM is scheduled to resume the final 11,000 feet in early May. Already, Chris has tunneled more than 15,600 feet (2.95 miles).

The Anacostia River Tunnel Project is latest phase of a massive water quality improvement project in the Washington D.C. area called the DC Clean Rivers Project. The National Parks Service recently approved the next major tunneling portion of the project, the Potomac River Tunnel project. That tunnel will hold up to 30 million gallons.

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