DC Water Investigating Sanitary Sewer Overflow from Potomac Interceptor in Maryland

January 19, 2026
Map of the impacted area.

WASHINGTON, DC — DC Water is investigating a Sanitary Sewer Overflow (SSO) from the Potomac Interceptor (PI) sewer line in C & O Canal National Historical Park in Montgomery County, Maryland. Flow was observed coming out of the PI this evening, and DC Water has mobilized its crews and contractors to mitigate the overflow and keep it contained as much as possible so they can assess the damage and begin repairs.

The damaged pipe is close to the Clara Barton Parkway, just east of the 495 interchange, and workers have closed the right inbound lane as a precaution. Drivers should anticipate delays during the morning rush hour and consider alternate routes. Trails and parking areas along the Parkway may also be impacted. 

The overflow is expected to reach the Potomac River. It is important to note that DC Water's drinking water system is separate from the wastewater system and is NOT affected by the overflow. The overflow is downstream from the Washington Aqueduct’s intakes at Great Falls.

The PI carries about 60 million gallons of wastewater daily from areas near Dulles Airport to the Potomac Pumping Station in the District. Flows from the pump station are then sent to the Blue Plains Advanced Wastewater Treatment Plant for treatment.

Untreated sewage can contain many pathogens causing a variety of illnesses ranging from E. coli to hepatitis. If people come in contact with the untreated overflow, they risk getting sick and bringing these pathogens into their homes; and should take the steps below:

  • Leave the area immediately.
  • Wash exposed skin thoroughly with soap and clean water.
  • Disinfect any affected areas or items.
  • Do not consume food or water that may have been exposed.
  • Seek medical attention if symptoms occur.
  • Report exposure to DC Water at (202) 612-3400.

Residents who live near the impacted area may notice an odor from the overflow. Emergency measures will be taken to prevent further spillage. The extent of the repairs and duration are still being determined. 

If you have additional questions or need information you may contact DC Water’s Customer Care team at (202) 354-3600 (Monday-Friday, 8 a.m. to 5 p.m.) or the 24-Hour Command Center at 202-612-3400.

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Photo of the vegetation growing back in the culvert area
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April 24, 2023

Monday 9:00 AM

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View of Mary at bottom of shaft inside tunnel shown from above
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First turn of cutterhead signals the start of excavation for the Potomac River Tunnel Project

In a defining moment for one of the District’s largest infrastructure investments, DC Water has marked its next major milestone in the Potomac River Tunnel Project. The first tunnel boring machine, Mary, has launched her northbound journey breaking through the soil to signal the start of excavation.

With the first turn of Mary’s drill-like cutterhead underground, the machine pushed forward to begin tunneling, representing the transition from years of planning and preparation to active tunnel construction on the $819 million project.

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April 15, 2026
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