DC Water begins $580M leg of Anacostia River tunnel

Dive Brief:

DC Water, the agency that provides drinking water and wastewater treatment services for more than 670,000 Washington D.C., residents, is scheduled to begin this month the five-mile, $580 million last leg of its 13-mile Anacostia River Tunnel System, part of the $2.7 billion Clean Rivers Project.
Once the design-build joint venture of Salini Impregilo and S.A Healy is complete with this last portion — the Northeast Boundary Tunnel — in 2023, the system will be able to divert 98% of sewage overflows into the Anacostia River to the Blue Plains Treatment Plant and ease the sewer flooding that plagues multiple areas of Northeast D.C. Work includes using a 680-ton tunnel boring machine for the next two-and-a-half years to dig a 23-foot-diameter reinforced concrete tunnel 160 feet below the ground.
The first portion of the Anacostia tunnel project opened in March after a five-year construction process and has succeeded in keeping 92% of area sewer overflows out of the river.

Dive Insight:

Tunnel for water or transportation systems can be tricky since the boring activity takes place so far underground.

New York City crews, led by Kiewit-Shea, are currently using a boring machine dubbed Nora to dig a $1 billion bypass tunnel 55 stories under the Hudson River in order to create a stable water delivery pathway around the 85-mile Delaware Aqueduct, which is leaking 18 million gallons a day. Gravity forces bring half the city's daily water supply from the Catskill Mountains through the aqueduct.

When the machine has completed its tunneling through solid rock and has completed the bypass, water will be diverted out of the Delaware. Vincent Sapienza, the commissioner of the city Department of Environmental Protection, called it "the largest and most complex water tunnel repair that the city of New York has ever done."

When boring machines break down, however, serious project delays can occur. A malfunction with Bertha, the boring machine crews used to dig a tunnel for the $2.2 billion Alaskan Way (SR 99) project in Seattle, delayed the project two years after it stopped operating in 2015. Once crews got it operational again in early 2017, Bertha finished tunneling in April of that year.