TBM Mary started her northbound journey from a 30m-deep overflow mining shaft and starter tunnel. She will bore approximately 3.87km from West Potomac Park to Georgetown University, excavating through hard bedrock.
The second TBM, Emily, is scheduled to arrive from Germany later this spring and will excavate south towards Joint Base Anacostia-Bolling, completing the full 8.9km tunnel system.
TBM Mary has a 6.4m diameter, weighs 1,200 tons and is 213m long.
“Launching Mary is a significant step forward for this project and for the future of the Potomac River,” said DC Water CEO and general manager David L Gadis. “This moment reflects years of planning, and the incredible co-ordination, engineering, and dedication required to bring a machine of this scale to life underground. It’s how we turn planning into progress.”
The US$819m (€714m) Potomac River Tunnel is part of DC Water’s Clean Rivers Programme, a long-term initiative to reduce pollution in the Potomac River and Chesapeake Bay. Currently, about 650 million gallons of untreated combined stormwater and sewer overflow enter the river each year. Once completed, the 8.9km tunnel system will reduce overflow volume by 93% and cut the number of overflow events from 74 to just four in a typical year.
