Work in Progress – Potomac River Tunnel
CBNA-Halmar JV Continues to Advance Potomac River Tunnel Project Despite Challenging Conditions
Over the past two weeks, the team has demonstrated tremendous resilience to make progress on the Potomac River Tunnel Project. Near record-breaking snowfall, historic sleet accumulation, and a sustained 10-day period of below-freezing temperatures presented formidable obstacles; nonetheless, the team maintained momentum and achieved several significant milestones. These accomplishments marked a strong close to 2025 and set a positive trajectory for the start of 2026.
Late 2025, in Washington, DC, the team was actively preparing Emily’s sister TBM, Mary, for her upcoming underground mission. A blessing ceremony held in November marked this important milestone, attended by District of Columbia Mayor Muriel Bowser, DC Water CEO and General Manager David L. Gadis, and members of the CHJV team.
Through the Christmas holidays, CHJV crews also worked tirelessly to complete and deliver a 997-cubic-yard concrete slab placement at the West Potomac Park site. This critical step prepared the shaft for the lowering of “Mary” and facilitated her installation in the Overflow Mining Shaft (OMS), which will serve as the launch shaft for the tunnel boring machines (TBMs).
Mary will excavate the north tunnel section, and in January, the focus shifted to her assembly. In a major milestone for the project, the team began lowering, assembling, and installing the TBM shields, main drive, and cutterhead into the OMS. The front shield, weighing approximately 491,000 lbs., was carefully lowered into the shaft, followed by the cutterhead the next day.
Collaboration between the Tunnel and Plant teams was instrumental as the cutterhead was bolted, welded, and advanced into the North Starter Tunnel. Building on this momentum, the team completed the lowering and setting of the TBM middle shield—a 588,000-lb super-lift representing the largest single pick to date on the project. The shield was then attached to the front section of the machine and advanced further into the North Starter Tunnel.
With the cutterhead and shields now positioned and advanced into the starter tunnel, preparations for the TBM launch are well underway. The TBM and gantry assembly continues, and as of late January, CHJV is preparing for the installation of the thrust frame and the first two back-up gantries. Tunnel boring operations are expected to commence in the second half of March, marking the next major phase of this landmark project.
