Halmar to build Potomac River Tunnel

A major environmental project for Washington D.C.

• Main tunnel 5.5 miles long and 100 feet deep
• Project part 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 of CBNA (a US-based subsidiary of Bouygues Construction) and Halmar International for the designbuild 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 DC. The contract value is $819 million US dollars.

The main tunnel, which is 5.5 miles long and approximately 100 feet deep with an internal diameter of 18 feet, will cross variable geological conditions (clay, alluvium, hard rock) and will pass close to Washington DC’s iconic monuments. It will require the use of two tunnel boring machines (TBMs) 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.

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.

“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“ – Chris Larsen, CEO of Halmar International, LLC.

Works on the project are expected to start near the end of 2023 with a construction duration of almost 6 years. It is projected 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.