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TBM reaches milestone on $580m US project

17 Apr 20 A Salini Impregilo tunnel-boring machine (TBM) has reached a milestone on a major environmental protection project in Washington DC.

The US$580m (£465m) Northeast Boundary Tunnel (NEBT) environmental protection project is designed to increase the capacity of the existing sewer system to manage flooding during heavy rainstorms. It will prevent untreated sewage from flowing into the Anacostia River  

The TBM operated by Salini Impregilo and its US subsidiary Lane Construction has broken through into the W Street shaft, the only in-line shaft that it will cross during its 8.2km journey underneath the US capital. In times of flooding, the 7m-diameter tunnel will receive flows from the sewer and convey them to DC Water’s Blue Plains wastewater treatment plant. Once connected to the Clean Rivers tunnel network, the NEBT will reduce by 98% the volume of untreated water that would otherwise flow into the Anacostia River.

The breakthrough by the TBM – which is called Chris brings to 60% the completion of the excavation work, which has been proceeding on site while respecting safety rules introduced during the coronavirus pandemic.  

“To date, the portion of the Anacostia River Tunnel that is in service has prevented more than seven billion gallons (about 26.5 billion litres) of combined sewage and 3,500 tons of trash from entering the Anacostia, bringing a resurgence to the waterfront,” said David Gadis, CEO and general manager of DC Water. He added that the Northeast Boundary Tunnel in particular will significantly reduce sewer backups and chronic flooding.

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