Mary, a tunnel boring machine (TBM), has successfully completed its factory testing in Germany and is now ready to begin work on the Potomac River Tunnel. The machine, capable of cutting through hard rock and creating tunnels 21 feet wide, will be shipped to Washington, D.C., to help with the tunnel construction.
A team from DC Water and its contractor traveled to Schwanau, Germany, for the testing, where Mary passed all the necessary requirements. Mary is one of two TBMs that will be used for the Potomac River Tunnel, a critical part of DC Water’s Clean Rivers Project. The project aims to reduce the amount of sewer and stormwater entering the Potomac River during rainstorms.
David L. Gadis, DC Water’s CEO and General Manager, expressed excitement about the milestone. “These machines are truly a marvel of modern technology, and they are custom-built for the project,” he said. “We look forward to Mary’s arrival. Along with her sister TBM, Emily, they will work to dig the 5.5-mile tunnel.”
Mary is expected to arrive in Washington, D.C., in the fall. Before it can be shipped, the machine will be carefully disassembled and packed for transport to the U.S. Once in D.C., it will be reassembled and begin its work.
The two TBMs are named after Mary and Emily Edmonson, two sisters who attempted to escape slavery on the Potomac River in 1848. Their brave efforts made them heroes in the abolitionist movement.
Mary and Emily will tunnel in opposite directions, cutting through bedrock and soil. Mary will tunnel north for 2.4 miles toward Georgetown University, while Emily will head south, covering 3.1 miles to connect to the Anacostia River Tunnel system.
The TBMs are being built by Herrenknecht, the same company responsible for manufacturing the TBMs for other tunnels in the Clean Rivers Project. Work on Emily is already underway, and its factory testing is scheduled for October. Afterward, Emily will also be shipped to D.C.
The Potomac River Tunnel is expected to reduce sewer and stormwater releases into the river by 93% in an average rainfall year. This will prevent over 600 million gallons of wastewater and stormwater from flowing into the Potomac, redirecting it instead to the Blue Plains Advanced Wastewater Treatment Facility for treatment. The tunnel project is slated for completion in 2030.
