Factory testing completed for DC Water’s Potomac River tunnel boring machine

(UI) — DC Water announced that factory testing is now complete on its first tunnel boring machine (TBM) for the upcoming Potomac River Tunnel project, marking a major milestone in the utility’s effort to reduce combined sewer overflows into the river.

The TBM, named Mary, recently passed acceptance testing in Schwanau, Germany, and will now be disassembled, crated, and shipped to Washington, D.C., where it will be reassembled for use later this year. Mary is one of two custom-built TBMs that will dig the 5.5-mile-long tunnel beneath the District as part of DC Water’s Clean Rivers Project.

“We are excited to mark this major milestone. These machines are truly a marvel of modern technology and must be custom built for the project,” said DC Water CEO and General Manager David L. Gadis. “We look forward to Mary’s arrival. She and her sister TBM, Emily, will have their work cut out for them to dig the 5.5-mile tunnel.”

The tunnel is designed to capture and treat more than 600 million gallons of sewer and stormwater runoff in a typical year, reducing overflows into the Potomac River by 93%. Once completed, all collected flows will be routed to the Blue Plains Advanced Wastewater Treatment Facility.

The tunnel boring machines are named in honor of Mary and Emily Edmonson, two sisters who attempted a daring escape from slavery via the Potomac River in 1848 and later became abolitionist icons.

Mary will bore 2.4 miles north toward the tunnel endpoint near Georgetown University, while Emily, which is still being manufactured, will dig 3.1 miles south to connect to the Anacostia River Tunnel system. Factory testing on Emily is scheduled for October.

Both machines were built by Herrenknecht, the same manufacturer that supplied TBMs for DC Water’s previous Clean Rivers Project tunnels. The Potomac River Tunnel is expected to be completed by 2030.

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