The District of Columbia Water and Sewer Authority, known as DC Water, is reporting “progress” in efforts to manage a major spill from a collapsed section of the Potomac Interceptor, a sanitary sewer line that runs alongside the Potomac River in Washington, DC and its Maryland suburbs.
A rupture of January 19, 72 days. The pipeline, the cause of which has not been publicly disclosed, sent about 300 million gallons of untreated sewage spilling into the river before being brought under control with a temporary diversion system late last week.
DC Water did not respond to ENR’s requests for information on the scope, timing or cost of the cleanup and repair, or the contractors involved in the containment effort, but reports say the effort could cost up to $10 million.
Built in the 1960s, the 54-mile Potomac Interceptor carries up to 60 million gallons of sewage daily from the Maryland and Virginia suburbs of Washington, DC to the city’s Blue Plains Wastewater Plant for treatment (see map below).
DC Water says the break occurred a quarter-mile from where D.C.-based Fort Meyer Construction Corp. had been working since last fall on an eight-month, $9.6 million project to rehabilitate an 800-foot segment of the 16-foot-deep interceptor using slip methods. This project is part of DC Water’s decade-long rehabilitation program, with an estimated cost of $625 million.
72 inch break. A sewer pipe break along the Potomac River north of Washington, DC on January 19th caused a massive sewage spill that has been contained, but cleaning up and repairing the pipes could be a $10 million effort.
Map: DC Water
With the collapse spewing an estimated 40 million gallons of sewage a day into the river, DC Water says on its website that its contractors worked with the National Park Service to redirect most of the Potomac Interceptor’s flow around the leak through a dry, isolated section of the historic Chesapeake and Ohio Canal, located 125 feet away. As many as eight large pumps are being used to channel the wastewater about 2,700 feet downstream, where it is then directed back to the interceptor, the agency says. According to DC Water, some of the existing flow is safely moved through the collapse site within the sewer line.
The Washington Aqueduct, operated by the U.S. Corps of Engineers, which supplies drinking water to the city and parts of northern Virginia, is not affected by the incident, as the main Potomac River entry point for that system is upstream. of the place of rupture. But the Corps shut down a downstream intake facility as a precaution.
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Ten days after the initial discovery of the sewage leak, DC Water reported that overflows from the breach appeared to have stopped, although maintaining 24/7 operation of the pumps has been complicated by the area’s long period of sub-freezing weather.
The agency is now focusing on stabilizing excavations around the collapse site and clearing debris and obstructions from inside the pipeline. Trench boxes were installed around the damaged section for containment and to prevent further erosion. Once truck-mounted industrial vacuums remove the debris and sewage levels around the collapse subside, the agency says crews will be able to further assess the damage and determine a repair strategy.
One repair possibility being studied is to use a 50-foot section of 72-inch pipe from another recently completed project.
They are also waiting to determine the spill’s environmental effects and possible remediation needs, an effort DC Water says it is coordinating with federal, state and local partners. According to the Potomac Riverkeeper Network, water quality tests of the river immediately downstream of the spill site during the first week found levels of E.coli bacteria to be nearly 12,000 times human safety levels. While the contamination is said to be dissipating further downstream, the expected slow melt from the area’s heavy Jan. 25 snowfall likely won’t help the process immediately.
DC Water says its $625 million investment over the next ten years is for projects to rehabilitate sections of the Potomac Interceptor, which varies in size from 30 to 96 dia. reinforced concrete pipe in the main trunk to 13 ft x 7.75 ft rectangular reinforced concrete pipe in the lower section of the sewer system.
The area where the break occurred should have been part of this program, but it is not known when any work was to be done. At the time DC Water announced Fort Myer Construction’s current rehabilitation project, the agency noted that “a major upgrade” of the interceptor was planned for later in 2025.
