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Potomac Interceptor
Sewer Line
The Potomac Interceptor, a 6-foot diameter sewer pipe, collapsed near Lock 10 of the C&O Canal in January 2026, unleashing millions of gallons of raw sewage into the Potomac River. The collapse and overflow of the sewer affected the river all the way from near the American Legion Bridge downriver to Georgetown. Bacteria levels in the river soared along the river, raising health concerns. Repairs on the pipe consisted of a rerouting of the sewage into the C&O Canal and then back into the sewer below the collapse, but that plan was disrupted by the discovery of blockages in the pipe below the spill. Estimates of complete repair have been put at several months, leading into Spring 2026.
The Potomac Interceptor began as a major mid-20th-century infrastructure project designed to link the rapidly developing suburbs of Northern Virginia and Maryland to Washington, DC's wastewater system. Authorized by Congress in 1960 under Public Law 86-515, it was conceived as a high-capacity sanitary sewer capable of carrying flows from communities near Dulles Airport, including Fairfax and Loudoun Counties, the Town of Vienna, Herndon, Dulles Airport itself, and parts of Montgomery County, to the Potomac Pumping Station in the District, and ultimately to the Blue Plains Advanced Wastewater Treatment Plant. Its construction reflected the region's explosive postwar growth and the need for a modernized, consolidated wastewater network that could protect the Potomac River from untreated discharges.
Over the decades, the Potomac Interceptor became one of the most critical--and least visible--pieces of wastewater infrastructure in the region, carrying roughly 60 million gallons per day beneath the Potomac River corridor. But by the 2020s, the system's age began to show. A section of the line, more than 60 years old, collapsed on January 19, 2026 near the Clara Barton Parkway, triggering one of the largest sewage spills in U.S. history. The failure released hundreds of millions of gallons of wastewater into the Potomac, with DC Water estimating approximately 243 million gallons discharged before emergency bypass pumping reduced the flow. The incident exposed the vulnerability of aging regional infrastructure and prompted public outcry, environmental concern, and a renewed focus on long-term rehabilitation.
The aftermath highlighted both the complexity of the system and the challenges of repairing a massive 72-inch sewer line buried in difficult terrain. Crews faced setbacks including rock obstructions, groundwater intrusion, and pump failures during high-use periods, all of which extended the repair timeline. Environmental groups documented elevated E.coli and other contaminants downstream, underscoring the ecological consequences of the collapse. In response, DC Water emphasized its commitment to restoring the line, improving monitoring, and accelerating long-term rehabilitation efforts already underway for the Potomac Interceptor system.
The Potomac Interceptor has been the site of several repair projects in the area affected by January's collapse. In 2025, DC Water did an emergency repair to a section of the sewer line along the Union Arch Trail after a torrential rain event exposed the pipe in July. Other studies have focused on repairs to the sewer line where it crosses the Potomac at Great Falls. And in September, DC Water began an 800-foot long slip-lining project on the sewer line directly above the area that collapsed.
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DC Water
1385 Canal St. SE
DC 20003
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