CONFIRMED90% CONFIDENCEDC Water's[1] own release of April 10, 2026 announces the launch as having happened that day.
- Start
- Apr 10, 202690% CONFIDENCEfrom the source
DC Water Launches the Boring Machine Mary Under the Potomac
DC Water lowered the tunnel boring machine Mary into a 100-foot-deep shaft in West Potomac Park and started her north towards Georgetown University, the first 2.4 miles of a 5.5-mile combined sewer overflow tunnel. The $819 million tunnel is part of the Clean Rivers Project and will cut Potomac overflow events from 74 a year to four; a second Herrenknecht machine, Emily, bores south towards Joint Base Anacostia-Bolling.
- DC Water launched tunnel boring machine Mary on her northbound journey, "breaking through the soil to signal the start of excavation" on the $819 million Potomac River Tunnel Project[1]
- Mary bores approximately 2.4 miles north from West Potomac Park to Georgetown University, through the District's hard bedrock[1]
- Preparation included a 100-foot-deep overflow mining shaft and an excavated starter tunnel; the front portion of Mary was lowered and assembled inside them earlier this year[1]
- Fully assembled, with gantries attached one by one to carry power, ventilation, material transport and worker access, she is "a 21-foot diameter, 1,200-ton, 700-foot-long mammoth tunneling machine"[1]
- At launch the first concrete tunnel ring is installed and connected to a thrust frame so the TBM's hydraulic jacks can push it forward, with crews building the lining from precast concrete segments behind the rotating cutterhead[1]
- Sister machine Emily is "scheduled to arrive from Germany later this spring" and will excavate south toward Joint Base Anacostia-Bolling, completing the 5.5-mile tunnel system; the release does not name Herrenknecht as the pin does[1]
- The tunnel is part of DC Water's Clean Rivers Program to cut pollution in the Potomac River and Chesapeake Bay; about 650 million gallons of untreated combined stormwater and sewer overflow enter the river each year at present[1]
- Once complete, the system will reduce overflow volume by 93% and cut overflow events "from 74 to just four in a typical year"[1]
- CEO and General Manager David L. Gadis: "Launching Mary is a significant step forward for this project and for the future of the Potomac River... It's how we turn planning into progress"[1]
References 190% CONFIDENCE
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- [1]90%dcwater.com/about-dc-water/media/news/dc-water-launches-tunnel-boring-machine-mary-marking-important-stepdcwater.com· Posted Sep 20, 2026· Starts Apr 10, 2026 ✓· 100% of score
DC Water's own release of April 10, 2026 announces the launch as having happened that day.
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United States Bureau of Reclamation
