Crews in Washington, D.C., recently christened the second tunnel boring machine for the $819 million Potomac River Tunnel project, naming her “Emily.”
DC Water, the independent government body that oversees the District’s drinking water and wastewater management, broke a bottle of DC tap water over Emily’s front face to celebrate the occasion and will deploy her as the second TBM to dig out the 5.5-mile Potomac River Tunnel. Emily was delivered unassembled to DC Water earlier this year and was manufactured by Herrenknecht.
Mary, the first TBM to work on the Potomac River Tunnel project, was christened in November 2025.
Emily will travel 3.1 miles south toward Joint Base Anacostia-Bolling, where the final tunnel will connect with the existing Anacostia River Tunnel. Mary is currently digging 2.4 miles north from West Potomac Park to Georgetown University.
The final Potomac River Tunnel will capture a mixture of rainwater and wastewater that would otherwise end up in the Potomac River and is expected to reduce the overall amount those overflows produce — 654 million gallons — by 93%. The number of annual overflow events is also forecast to drop from 74 to four.
Beyond the 18-foot-diameter sewer tunnel being excavated, other infrastructure being built includes diversion facilities, drop shafts and support structures that will divert flows from existing combined sewer overflows and direct them to the Blue Plains Advanced Wastewater Treatment Plant.
Powered byDC Water expects the final tunnel to be operating by 2030. The project’s design-build contract was awarded to the CBNA-Halmar Clean Rivers Joint Venture.
The Potomac River Tunnel project falls under DC Water’s Clean Rivers Program, a long-term program to deliver cleaner waterways and improve the health of both the Potomac River and the Chesapeake Bay.
