Contractor CBNA-Halmar JV with its design partners Cowi and Hatch will operate TBM Emily to excavate the southern leg of the Potomac River Tunnel in Washington DC.
Led by CEO and general manager David Gadis, DC Water’s team travelled to Herrenknecht’s factory in Germany to ceremonially activate the cutterhead.
“Seeing Emily in action was a powerful moment for our team and underscores the scale and impact of what we’re building,” said Gadis. “It’s one thing to plan and design a tunnel boring machine, but watching it take shape reminds us why we do this work — to build a cleaner, healthier future for the district.”
Emily will join sister TBM Mary, which is scheduled to begin digging the northern leg of the tunnel in early 2026. The two machines are named after Emily and Mary Edmonson – two sisters who escaped slavery in 1848 by sailing down the Potomac River and then became prominent US civil rights figures. Emily is engineered for softer soils, while Mary is designed to cut through hard rock.
TBM Emily will now be disassembled for transport and reassembled at the West Potomac Park site in spring 2026.
The 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 sewer overflow enter the river each year. Once completed, the 8.8km tunnel system will reduce overflow volume by 93% and cut the number of overflow events from 74 to just four in a typical year.
