A major milestone was celebrated in the DC Water and Sewer Authority's Potomac River Tunnel project on Nov. 3, 2025, with the ceremonial blessing of "Mary," the tunnel boring machine (TBM) that will dig the northern leg of the underground passageway.
The event at West Potomac Park, adjacent to Washington's National Mall, marked the official start of tunneling for one of the final and most ambitious phases of the District of Columbia water department's Clean Rivers program.
Washington Mayor Muriel Bowser led the ceremonial blessing with a bottle of D.C. tap water, symbolizing the district's commitment to cleaner waterways and marking the beginning of the TBM's historic journey beneath the Potomac River.
She was joined by Manager David L. Gadis, DC Water CEO and general manager, Dr. Unique N. Morris-Hughes, DC water board chair and other district leaders to celebrate the beginning of this transformative infrastructure project.
"The DC Clean Rivers program plays such an important role in ensuring that we are the safe, clean and beautiful city that we are today," Bowser told the event's guests. "Whenever you make this type of investment in world-class infrastructure, that's an investment in our collective future, it's an investment in safe neighborhoods and clean, swimmable waterways and it's an investment in our position as a beautiful waterfront city."
The machine named Mary honors 19th century abolitionist Mary Edmonson, who, along with her sister Emily, attempted a daring escape from slavery via the river in 1848.
Later this year, another TBM, aptly named "Emily," is scheduled to arrive from Germany to dig the southern leg of the tunnel. Together, they will construct the 5.5-mi. Potomac River Tunnel, designed to intercept and divert nearly 1 billion gal. of combined sewage and stormwater overflow from entering the waterway in an average year of rainfall.
"Today we celebrate not just a machine, but a movement," Gadis said. "The Clean Rivers Program has been a game-changer for our city. We've watched the Anacostia River come back to life, and now, with Mary leading the way, we're turning our focus to the Potomac. This tunnel is one of the final pieces of a legacy that will leave our rivers cleaner, our communities healthier and our future brighter."
At $819 million, the largest-ever construction contract awarded by DC Water went to the joint venture of CBNA Halmar based on its best-value proposal to the agency.
In a design-build contract, the construction and design contractors work together as a team to complete the project. The builders — CBNA, a Miami, Fla.-based subsidiary of Bouygues Construction in Australia and Halmar International LLC of Nanuet, N.Y. — will be working with the tunnel's designers to complete the project.
TBM Blessings Honor Important Tunnels, Their Builders
The tradition of blessing TBMs before they begin tunneling is rooted in centuries-old mining customs, DC Water noted in a news release.
Saint Barbara is revered for her protection against the dangers of underground work, and DC Water has embraced this tradition in past projects, including the Anacostia River Tunnel, as a way to honor the workers and the significance of the infrastructure being built.
Following the Nov. 3 ceremony, attendees toured the launch site and viewed the 100-ft.-deep drop shaft where Mary will begin her excavation. This shaft is a critical part of the tunnel system that will carry stormwater and sewage to DC Water's Blue Plains advanced wastewater treatment plant.
The Potomac River Tunnel project is a key component of DC Water's clean rivers program to reduce combined sewer overflows and improve water quality across the city of Washington and the District of Columbia. Once completed in 2030, the tunnel will reduce overflow events from 74 to just four in an average year of rain and cut overflow volume by 93 percent, according to the agency.
The TBM's blessing marks a turning point in the Clean Rivers Program — a moment that blends engineering excellence with environmental stewardship. As Mary begins her journey underground, she carries with her the hopes of a cleaner, healthier Potomac River, and a legacy of progress for the district.
For more information about the clean rivers program and the Potomac River Tunnel project, visit dcwater.com/prt.
