Nannie, the newest member of the DC Water’s $2.6 billion Clean Rivers Project team didn’t have much to say at her formal introduction on the banks of the Anacostia River on December 12. But then, tunnel boring machines (TBMs) tend to do most of their “talking” underground.
Christened to honor Nannie Helen Burroughs, a prominent 20th century African-American educator and civil rights activist, the 350-ft long, 1,248-ton Herrenknecht-built TBM and her 26-ft diameter cutterhead will be the key player in mining the $254 million 14,000-lf, 23-ft diameter Anacostia River Tunnel for the Impregilo-Healy-Parsons design-build joint venture.
The tunnel is second major segment in a combined sewage overflow (CSO) containment network designed to capturing and treating at least 96 percent of the three billion gallons of raw and combined sewage that currently overflows from older sections of the District’s sewer system each year.
Once complete, the Anacostia River Tunnel will tie into the 24,300-lf Blue Plains Tunnel, which the TBM Lady Bird has been working on since July 2013 for the design-build joint venture of Traylor/Skanska/JayDee, supported by CH2M Hill/Halcrow. As of December 12, Lady Bird had completed 61% of the new reinforced concrete tunnel, leaving just over 9,300 lf to go before reaching her destination at a southeast DC pumping station.
A third tunnel, the 27,000-lf Northeast Boundary Tunnel, is currently in design with construction scheduled to begin by the end of 2016. As each tunnel is completed, CSOs in DC Water’s service area will be channeled to the Blue Plains Advanced Wastewater Treatment Plant, where a new a $400 million state-of-the-art anaerobic digester system.
Nannie’s reticence didn’t last long. Within hours of her official naming ceremony, she was on Twitter, trading good-natured sisterly barbs with Lady Bird and ready to continue the tradition of TBMs serving as an online project ambassadors to the public.