DC Water's Potomac River Tunnel Project is to begin controlled underground blasting as part of the excavation work for DC Water’s Potomac River Tunnel Project. Weekly controlled underground blasting operations at the West Potomac Park construction site will begin as early as next week and continue through February 2026. The site is located along the Potomac River at Ohio Drive and Independence Avenue Southwest.
The blasting operations are part of constructing two mining shafts needed to begin tunnelling. These shafts, approximately 31 m (103 feet) deep, will be used to lower and launch the two TBMs named for Mary and Emily Edmonson, who made a daring attempt to escape from slavery on the Potomac River in 1848 and became heroes of the abolitionist movement.
Mary and Emily will dig the 8.85 km (5.5-miles) tunnel in opposite directions slowly cutting through bedrock and soil. Mary will work north 3.86 km (2.4 miles) toward the tunnel’s endpoint near the entrance of Georgetown University on Canal Road Northwest. Emily will head south, tunnelling 4.99 km (3.1 miles) to connect to the Anacostia River Tunnel system.
At the end of April Mary, the first of two TBMs for Potomac River tunnel completed the factory acceptance testing. The dual mode TBM 6.4m (41 feet) diameter will head across the pond to DC in the fall 2025 to start work on the Potomac River Tunnel. The second TBM will be delivered in 2026.
The TBMs are being built by Herrenknecht, which also built the TBM’s for DC Water’s other tunnels in the Clean Rivers Project. Manufacturing is already underway on Emily. Factory acceptance testing is expected to occur in October, after which it will be shipped to DC too.
The Potomac River Tunnel is designed to reduce the volume of sewer and stormwater released into the river by 93% in an average year of rainfall. That amounts to more than 2.27 bn liters (600 million gallons) of wastewater and stormwater which will be captured and sent to the Blue Plains Advanced Wastewater Treatment Facility for treatment. It’s expected to be completed in 2030.
