TBM assembled and ready to launch

Excavation has started on the Northeast Boundary Tunnel as the last contract in the Anacostia River CSO interception project for DC Water, the District of Columbia Water and Sewer agency. The 8m diameter EPBTBM was lowered 100ft into the working shaft in early June to excavate the 8km long segmentally lined tunnel to link the completed First Street Tunnel in Bloomingdale, to the Anacostia River Tunnel, which is already in operation and conveying combined wastewater to the Blue Plains Tunnel and to the Blue Plains treatment plant (Fig 1).

The Northeast Boundary Tunnel is the second contract in the DC Water Clean Rivers program for the JV of SA Healy, now part of Lane Construction, and their parent company Salini Impregilo of Italy, following award of the Anacostia River Tunnel contract to the JV, with design engineer partner Parsons, in mid 2015. Following successful excavation of the 3.8km x 7m i.d. Anacostia River Tunnel in November 2016, the team refurbished the 8m diameter Herrenknecht EPBM for reuse to excavate the full length of the 8km long x 7m i.d. Northeast Boundary Tunnel.

Fig 1. Scope of the DC Water CSO Clean Rivers project

The Northeast Boundary Tunnel is the largest segment of the extensive $2.7 billion Clean Rivers programme by DC Water to reduce combined sewer overflows into the Anacostia River during rain storm events by 98%. It is part of the program to improve the water quality of the Anacostia and Potomac Rivers and Rock Creek and reduce the incidences of flooding in the northeast area of Washington DC.

“Our ratepayers have made a huge investment in the future of the Anacostia and life along the waterway,” said David Gadis, DC Water CEO and General Manager. “The local communities will benefit from healthier waterways and significantly reduced flooding in northeast DC.”

The southern portion of the Anacostia River part of the Clean Rivers project tunnel opened in March 2018 and was immediately put to the test to manage heavy rainstorms. In the first two and half months of operation, the tunnel captured and treated more than 1.4 billion gallons of sewage and more than 100 tonne of trash that would have normally gone into the Anacostia River during these rainy events.

Having started in 2013, the entire 13.1 miles long x 23ft i.d. (21km x 7m i.d.) Anacostia CSO tunnel system is programmed to be complete and in operation in 2023, when the Northern Boundary Tunnel is complete and in operation.

The last and largest contract in the current DC Water Clean Rivers programme for the 27,000ft (8km) long Northeast Boundary Tunnel project is awarded to Salini Impregilo/ SA Healy JV for a contract value of US$580 million. The JV comprises the tunneling division SA Healy of The Lane Construction Corporation with 70% and the Italian parent company Salini Impregilo with 30%.

Fig 1. Alignment of the NEBT connecting the First Street Tunnel to the Anacostia River Tunnel

The NEBT, Project J Northeast Boundary Tunnel, is the second contract in the DC Water Clean Rivers program for the Salini Impregilo/ SA Healy JV following award of the Anacostia River Tunnel contract to the JV and design engineer partner Parsons in mid 2015. That contract is currently more than 90% complete following successful excavation of the 3.8km x 7m i.d. tunnel in November 2016.

Members of the Salini Impregilo/ SA Healy team confirmed to TunnelTalk that it is in talks with Herrenknecht to rebuild the Herrenknecht 8m diameter EPBM it used on the Anacostia River project to complete the full 8km long, 7m i.d. length of the NEBT. Shane Yanagisawa is appointed Project Manager for the JV and work on the new contract is expected to begin in September 2017. Tunneling is programmed to begin in January 2019 and the project completed in 2023.

Three shortlisted rival bids were submitted for the NEBT contract with the JV winning the contract with the best technical score and based on its experience on the Anacostia River Tunnel contract and the lowest bid price at $580 million. Rival bids, to a highest bid price of $688 million, were submitted by Kenny/Obayashi JV, the Kiewit-Shea Constructors JV, and the Traylor/Skanska/Jay Dee JV which completed the program’s Project A Blue Plains Tunnel in 2015.

The 27,000ft (8km) NEBT Project J will run north from the northern end of the Project H Anacostia River Tunnel at the Robert F Kennedy Stadium to the Rhode Island Avenue NW and 6th Street NW intersection, connecting on the way to the south end of the completed First Street Tunnel Project P. Running at 50ft to 160ft (15m-50m) below ground, the NEBT is aligned to relieve chronic flood conditions along Rhode Island Avenue and includes five diversion chambers from existing sewers, six dropshafts, five stormwater inlet connections and a ventilation control facility (Fig 1).

Anacostia River EPBM will see rebuilt duty on the NEBT

When complete, this second design-build contract for the JV will connect all elements of the current Clean Water program to create a continuous 21km long CSO tunnel network from the completed First Street Tunnel (Project P) through to the completed Project H Anacostia River Tunnel and the completed 7.2km Blue Plains Tunnel (Project A) to convey combined sewer/stormwater flows to the Blue Plains water treatment plant in the south (Fig 2).

A targeted NEBT completion date in 2023 will complete project two years ahead of the 2025 Consent Decree deadline imposed on the District of Columbia Water and Sewer Authority by the national EPA (Environmental Protection Agency), to reduce combined sewer overflows into the Anacostia and Potomac Rivers on the banks of which the US national capital has developed. CSO overflows are to be reduced by 98% and to mitigate the frequency, magnitude and duration of sewer flooding in the urban areas to the north.

Once the current $2.6 billion program is completed, another phase of the Clean Rivers project is being studied to comply with an EPA Consent Decree mandates to reduce CSO overflow into the upper Potomac reaches. The program includes study of new CSO tunnels to intercept overflow structures and link with the Project A Blue Plains Tunnel of the existing program to convey all flow to the Blue Plains treatment plant.