Potomac River Tunnel project
Reducing combined sewer overflows to protect the Potomac River
DC Water Authority
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Washington, D.C., USA
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2024–2030
The largest-ever awarded contract by the DC Water Authority, at $819 million.
Expected to curtail combined sewer overflows to the Potomac River by 93% during average rainfall years.
Part of the $3.29-billion DC Clean Rivers initiative to improve water quality in the region.
Challenges
- In a year of average rainfall, over 70 combined sewer overflow (CSO) events discharge approximately 654 million gallons of CSO in the Potomac River.
- As part of the DC Clean Rivers project, the Potomac River Tunnel (PRT) project aims to construct a 5.5-mile-long tunnel to control these CSO events and improve the river’s overall water quality.
- The PRT project is a critical piece of the broader Clean Rivers project—a $3.29 billion initiative to improve water quality in the Anacostia and Potomac Rivers, and Rock Creek, while strengthening the sewer system’s capacity.
Solutions
- Secured a design-build contract for the construction of the Potomac River Tunnel alongside CBNA, Halmar, and COWI.
- Responsible for overall design management and the detailed design of underground works, including support of exaction and concrete structures.
- The project requires precise engineering and the use of innovative construction techniques to manage unique surface and subsurface challenges.
- Construction will navigate various ground conditions, ranging from soft ground to rock, using advanced tunnel boring machines.
Highlights
- The PRT project represents the largest-ever awarded contract by the DC Water Authority, at $819 million.
- The 18-foot-diameter tunnel will serve as a crucial mechanism to control CSOs and will extend to Hain’s Point, ultimately connecting to the Anacostia River Tunnel.
- By 2030, the tunnel is expected to curtail CSOs to the Potomac River by 93% during average rainfall years.
Described in the Boston Globe as “a far cry from the traditional treatment prescribed by engineers,” the stormwater wetland incorporates both conventional and bioengineered structures designed with a natural “look and feel” that won praise from stakeholder groups.
Project numbers
$819 million budget
5.5-mile tunnel length
18-foot diameter
93% reduction in CSOs
2030, expected completion