Potomac River Tunnel

DC Water has issued notice to proceed to the CBNA-Halmar Clean Rivers Joint Venture comprising CBNA and Halmar International for the design-build contract for the Potomac River Tunnel.

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.