DC Water's Potomac River Tunnel Project 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. All streets and sidewalks will remain open during blasting events, with no restrictions on boats or watercraft in the river.

The blasting operations are part of constructing two mining shafts needed to begin tunneling. These shafts, approximately 103 feet deep, will be used to lower and launch two tunnel boring machines (TBMs). These machines will construct the 5.5-mile tunnel. One TBM will excavate north, boring through rock to the endpoint at Georgetown University's entrance on Canal Road Northwest. The other will move south to the Joint-Base Anacostia Bolling (JBAB) site, where the Potomac River Tunnel connects with the Anacostia River Tunnel. The TBM excavating north, named Mary, will be delivered to the West Potomac Park site in the fall of 2025. The second TBM, called Emily, will be delivered in 2026.

Noise levels and ground vibrations will be closely monitored during this operation to ensure safety and compliance with the DC Fire and Emergency Medical Services Department, Metropolitan Police Department, and National Park Service. Residents and businesses in the vicinity may hear moderate noise during the blasting operations. Some mild ground vibrations may be felt in immediate work areas.

Project details

The Potomac River Tunnel is the next major phase of DC Water’s Clean Rivers Project. The project consists of a large-diameter, deep sewer tunnel, diversion facilities, drop shafts, and support structures. The tunnel system will capture the combined overflow of wastewater and stormwater during major weather events until it can be released to the Blue Plains Advanced Wastewater Treatment Plant instead of being discharged into the Potomac River. The project is needed to reduce the sewer overflows to help improve the water quality of the Potomac River and, ultimately, Chesapeake Bay. The tunnel also ensures compliance with the 2005 Federal Consent Decree entered by DC Water, the District of Columbia, the U.S. Environmental Protection Agency, and the U.S. Department of Justice, as amended in January 2016.

When rainfall exceeds the sewer system’s capacity, the overflow is released at outlets into the Potomac River impacting water quality. An estimated 654 million gallons of mixed stormwater and sewage overflows enter the Potomac River in a year of average rainfall. The proposed controls are estimated to reduce the volume of untreated wastewater released into the Potomac River by 93% and reduce the frequency from approximately 74 events to only four times in a year of average rainfall.

 

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