TBM finished boring Northeast Boundary Tunnel
DC Water’s Clean Rivers Project passed another milestone with the breakthrough on the Northeast Boundary Tunnel by the Herrenknecht tunnel boring machine (TBM) called Chris.
The TBM completed it 8 km (5 mile) boring of a 7-m (23-ft) wide tunnel combined sewage overflow (CSO) tunnel in April. The tunnel is part of DC Water’s Clean Rivers Project that consists of 28 km (18 miles) of tunnel.
“It’s amazing accomplishment,” Carlton Ray, vice president of DC Water’s Clean Rivers Project told DCist.com.
This sewage overflow is a result of D.C.’s antiquated sewer system, and one of the major reasons the city’s water bodies are too polluted to swim or fish in.
“The federal government left D.C. this undersized sewer system that basically when it rains, we have raw sewage or combined sewage overflows into the river,” Ray said. “We’re capturing that that sewage and ultimately are going to make the Anacostia River fishable and swimmable.”
When the new tunnel is in operation — anticipated in the summer of 2023 — it will divert sewage and stormwater to the sewage treatment plant at Blue Plains, at the southern tip of the District. There, the overflow can be treated and discharged into the Potomac River. The $2.7 billion project is expected to prevent 98 percent of sewage overflows into the Anacostia.
Prior to starting work on the project, D.C’s century-old combined sewer system overflowed into the city’s rivers 75 times a year on average, dumping more than 3 billion gallons of sewage mixed with rainwater. The first tunnels to prevent overflow in the Anacostia went online in March, 2018, and have so far prevented 89 percent of overflows.
The new tunnel will also reduce flooding in the neighborhoods it serves by between 7 and 50 percent in any given year, according to DC Water.
The 650-ton tunnel boring machine was christened at a ceremony in June, 2018, before being lowered into a shaft near RFK Stadium to begin digging. The machine was named after Christopher Allen, a DC Water official who oversaw the Clean Rivers Project prior to his death in 2017.
From RFK, Chris proceeded roughly 15 m/d (50 ftpd) before finally arriving at the intersection of 6th and R St. NW.
The new tunnel, known as the Northeast Boundary Tunnel, is the biggest piece of the Clean Rivers Project, and there is still a fair amount of work to be done before it can be put in operation. For one thing, DC Water has to remove Chris, which will now be unceremoniously dismantled and hauled out by crane. The tunnel also needs to be connected to the existing sewer system, via a series of shafts and smaller tunnels.
The Clean Rivers Project, which DC Water plans to complete by 2030, was a long time coming: D.C.’s rivers have been used to dump sewage since the city was founded. Sewer pipes were installed starting in the late 1800s, but they served only to conduct sewage out of homes and directly into the rivers. There was no sewage treatment whatsoever until 1938, when the Blue Plains facility was built.
Construction on the next major phase of the Clean Rivers Project, the Potomac River Tunnel, is expected to begin in 2023.