The Skanska-led joint venture is performing a $157 million contract for D.C. Water for the design and construction of the First Street Tunnel in the Bloomingdale neighborhood of Washington, D.C.’s Ward 5. The tunnel is being constructed along 1st Street, NW from Channing Street, located within the existing McMillan Sand Filtration site, and will terminate near the intersection of Rhode Island Avenue and 1st Street, NW. The tunnel will temporarily store excess stormwater, and will provide much needed flooding relief for the area’s residents. The project is part of D.C. Water’s D.C. Clean Rivers Project.
The First Street Tunnel project will aid in reducing surface flooding and sewer backups that have affected the Bloomingdale and LeDroit Park neighborhoods in the District. The tunnel will add six million gallons of combined sewer storage to relieve undersized sewers that traverse the Bloomingdale neighborhood.
The project includes four diversion chambers that will divert stormwater for storage, drop shafts to convey the diverted flows into the tunnel via adits, and pumping stations to discharge the stored water to the existing collection system. The team will use a tunnel boring machine (TBM) to mine the 21-foot-diameter, 2,700-feet-long tunnel.
Skanska, its joint venture partner and design subconsultant developed a low-cost, low-risk mitigation approach that minimizes the impact to the surrounding community. The major solution that the Skanska team devised was the use of ground freezing as support of excavation and ground improvement. Choosing this method resulted in a solution that allows for earlier completion, reduced noise, better accommodations for fire and emergency services, and improved air quality. The team is also using piped-in natural gas as the primary fuel sources for power generation. This will significantly reduce hydrocarbon emissions and noise, while also eliminating a significant amount of truck traffic associated with the diesel fuel delivery.
The team is working closely with D.C. Water and community groups to ensure the public’s safety and satisfaction during the design and construction of the project.
Ultimately, through a separate contract, the First Street Tunnel will connect to the remainder of the D.C. Clean Rivers Project tunnel system, and will allow captured stormwater flows to be transported directly to D.C. Water’s Blue Plains Advanced Wastewater Treatment Plant.