Four-way partnership joins forces as Potomac Tunnel project gets underway


Major project for DC Water in the US will see sewer overflows to the Potomac River reduced by 93%.

CBNA, Halmar, COWI and Hatch have teamed up on a partnership aimed at providing unparalleled expertise in tunnel construction and innovative solutions to DC Water on a design-build contract for the construction of the Potomac River Tunnel (PRT).

The $819m PRT contract represents a pivotal moment for DC Water, marking the largest-ever awarded contract by the authority. The 5.5-mile-long tunnel will serve as a crucial mechanism to control combined sewer overflows into the Potomac River, significantly enhancing the water quality of this vital natural resource. This project is an integral component of the broader Clean Rivers Project, a $2.99bn initiative aimed at improving water quality in the Anacostia and Potomac Rivers and Rock Creek while strengthening the sewer system’s capacity.

Steven Kramer, COWI senior project director, said: “COWI will lead the design of the tunnel and adits, and provide geotechnical support for the entire project. We leverage our domestic and global personnel to bring experts in multiple disciplines. Our team began working in late 2023 and has already delivered several key early lead items which has enabled the design and build team to begin construction.

“Working with CBNA-Halmar through the tender process and now the actual project has been very exciting and gratifying for our engineers. In a design and build project, it is always rewarding to see our design being implemented especially on such a critical project as the Potomac River Tunnel.”

The Potomac River in Washington DC.

Bruce MacKay, Hatch’s managing director for water noted: “At Hatch, we believe in partnerships that align with our core values of sustainable progress and community enhancement. This collaboration exemplifies our dedication to pioneering designs that ensure a healthier, more sustainable future for the District of Columbia and its residents. Working with our partners, Hatch will be responsible for overall design management as well as the detailed design of underground works including support of excavation and concrete structures.”

Traversing beneath and along the Georgetown waterfront, West Potomac Park and the National Mall, the 18-foot-diameter tunnel will extend to Hains Point, ultimately connecting to the existing Anacostia River Tunnel. Utilising advanced tunnel boring machines, the construction will navigate various ground conditions, ranging from soft ground to rock. The surface and subsurface challenges will require precise engineering and the use of innovative construction techniques by the project partners.

Commencing in 2024 and slated for completion in early 2030, the project’s impact will be significant. Once operational, the PRT is projected to curtail combined sewer overflows to the Potomac River by an impressive 93% during typical rainfall years, solidifying its pivotal role in enhancing environmental sustainability for the region.