DC Water announced that the first phase of the Clean Rivers Project to control combined sewer overflows to the Anacostia River is complete. Nannie, the tunnel boring machine (TBM) named after the famous District educator, Nannie Helen Burroughs, finished the construction of the 2.4 mile long Anacostia River Tunnel in November 2016. The Anacostia River Tunnel is now connected to the Blue Plains Tunnel at Poplar Point, adjacent to the Frederick Douglass Bridge.
“This is just a huge milestone,” DC Water’s Moussa Wone, who is in charge of the project told DCist. “This river was really very, very, very impaired.”
Before the project, the city’s antiquated sewers would overflow into the Anacostia River 84 times a year, dumping an average of 2.1 billion gallons of untreated sewage directly into the waterway. With the new tunnel in operation, overflows are expected to happen only twice a year now, resulting in a dramatic improvement in water quality. Already, the first phase of the project has kept 15 billion gallons of untreated sewage and stormwater out of the river, along with 9,800 tons of trash.
The new tunnel will also cut down on flooding in some areas, including along Rhode Island Ave., where a flood on August 14 killed 10 dogs at a doggy daycare business. Wone said the new tunnel is designed to capture stormwater and prevent flooding for up to a 15-year storm. Such a storm has a 7 percent chance of occurring in any given year.
Before the new tunnel opened, the sewer system could only handle a 2-to-5-year storm without flooding, meaning as much as a 50 percent chance of flooding in any given year.
The August 14 flood was a 20-year event, Wone says, so it would have exceeded the capacity of the new tunnel. But, he says, in such an event, the new tunnel will greatly reduce the amount of flooding.
The tunnel system was an engineering feat: a TBM excavated and constructed the 23 ft. diameter tunnels some 100 ft. beneath the city. The entire Anacostia tunnel system runs about 12 miles, from Shaw in Northwest, to the Blue Plains sewage treatment facility in Southeast. Construction on the system began in 2011. The entire project, including the Potomac and Rock Creek portions, is slated to cost $2.7 billion, much of it paid for by DC Water customers through the Clean Rivers impervious area charge on monthly water bills.
The tunnels function by capturing and storing overflow from the city’s old sewers, and transporting it to Blue Plains to be treated. The new tunnels serve the parts of the city that have combined sewers, which carry stormwater and sewage in the same pipes. During a storm, those pipes can quickly fill up with rainwater.