CBNA and Halmar broke ground on a $819 million stormwater tunnel in Washington, D.C., last week, the District of Columbia Water and Sewer Authority said in a news release. 

The Potomac River Tunnel Project at West Potomac Park is a 5.5-mile-long, 18-foot-diameter tunnel that will run beneath the Georgetown waterfront and connect to the existing Anacostia River Tunnel. The CBNA-Halmar team, based in Miami and Nanuet, New York, respectively, expect to complete the project by early 2030, according to the release.

Work will consist of building a large-diameter deep sewer tunnel, diversion facilities, drop shafts and support structures to capture flows from existing combined sewer overflows along the Potomac River and direct them to a treatment facility. 

Construction will require two tunnel boring machines, according to DC Water. Both will start from West Potomac Park: One machine will mine south through mostly soft ground, while the other will head north to bore through rock.

The tunnel represents the latest segment of the Clean Rivers Project, which stems from a lawsuit that environmental groups filed in 2000 against DC Water for allowing billions of gallons of untreated sewage to flow into area rivers. DC Water is building the 18-mile, $2.99 billion tunnel system under the city to improve the water quality of the Anacostia and Potomac rivers and Rock Creek. Monthly fees charged to DC Water customers fund the bulk of the project.

The 12-mile, $583 million Northeast Boundary Tunnel went into service in September 2023, built by Italian firm Salini Impregilo and Cheshire, Connecticut-headquartered Lane Construction, while the 2.4-mile-long Anacostia River Tunnel was finished in November 2016. The Piney Branch Tunnel is expected to start construction in 2025, per DC Water.

Once operational, the Potomac River Tunnel will reduce combined sewer overflows to the Potomac River by 93% in an average year of rainfall, according to DC Water, and the tunnel represents the authority’s largest contract ever awarded.