• A main tunnel 5.5 miles long and 100 feet deep.
• A project of DC Water's $2.99B Clean Rivers Project, a vast program to improve the water quality in the region.

DC Water has issued notice to proceed to the CBNA-Halmar Clean Rivers Joint Venture comprising CBNA (a US-based subsidiary of Bouygues Construction) and Halmar International for the design-build contract for the Potomac River Tunnel. This is a major environmental project designed to control combined sewer overflows and to improve water quality in the Potomac River in Washington D.C. The contract value is $819 million (€758 million).*


The purpose of this project is to collect and store combined sewer system discharges and stormwater run-off during storm events that exceed the capacity of the combined sewer system along the Potomac River in the District and convey them to DC Water’s Advanced Wastewater Treatment Plant at Blue Plains. The project will increase the capacity of the sewer system using deep storage tunnels and will significantly decrease CSO overflow events impacting the Potomac River, the fourth-largest river along the US East Coast.

The main tunnel, which is 5.5 miles (8.9 km) long and approximately 100 feet (30 m) deep with internal diameter of 18 feet (5.5 meters), will cross variable geological conditions (clay, alluvium, hard rock) and will pass close to Washington D.C's iconic monuments. It will require the use of two tunnel boring machines (TBM) customized specifically for these soil conditions. Ancillary structures comprise of 9 shafts, adits connecting to the main tunnel, and near surface structures which link the new infrastructure to the existing sewage system.

"We are proud of the trust placed in us by our client DC Water to carry out this project. Bouygues Construction is mobilizing all its expertise and confirming its commitment to major projects that contribute to improving water management in the United States", said Bertrand Burtschell, Managing Director of Bouygues Travaux Publics.

"We are honored to be part of such a great team to build this complex tunnel system that is so vital to protect a great natural resource like the Potomac River. We look forward to working with DC Water on this ambitious project and witness its benefits for years to come", said Chris Larsen, CEO of Halmar International, LLC.

Works on the project are expected to start end of 2023 with a construction duration of almost 6 years. It is expected to employ 400 people at peak times, with a strong commitment to local employment and integration of local and disadvantaged businesses.
The CBNA-Halmar Clean Rivers JV will be supported by leading engineering companies COWI and Hatch to carry out the design and is committed to completing this important project through a sustainable delivery approach.

Bouygues Travaux Publics is already building a tunnel in Pawtucket (Rhode Island, USA) to store rainwater and sewer overflows, as part of a program to improve water quality in Narragansett Bay.

* Total amount for the CBNA-Halmar Clean Rivers Joint Venture: $819 million (€758 million), of which $749 million (€693 million) has already been taken in the Joint Venture orderbook and $70 million (€65 million) is allowances. The share of orders for Bouygues Construction is $523 million (€482 million).