More than eight months after one of the largest sewage spills in American history, the Potomac River is testing normal again, according to the utility that caused it. On Oct. 7, DC Water said expanded sampling found no current signs of harm from January’s collapse of the Potomac Interceptor.
DC Water said that since August it has added tests for oxygen levels, nutrients and metals, which can affect water quality and aquatic life. The work covered five sampling rounds at six sites in Maryland, upstream and downstream of the overflow. All results fell within the river’s normal range, the utility said. It did not publish numerical thresholds in its statement.
DC Water’s Interim General Manager, Matthew T. Brown, said community concerns, especially from people who use the river, prompted the added testing, and called the results reassuring. The utility also said E. coli sampling, done daily for more than six months at up to 10 locations, had already returned to the range normally found in the river and that health advisories were lifted. Full results are posted on DC Water’s Potomac Interceptor water quality monitoring page.
What happened
On Jan. 19, a section of the 72-inch Potomac Interceptor collapsed along the Clara Barton Parkway in Montgomery County, sending an estimated 243 million gallons of untreated wastewater into the river, according to MDE. A bypass began rerouting flow Jan. 24, and emergency repairs were completed March 14. DC Water says long-term rehabilitation of about 2,700 feet of pipe is expected to take nine to ten months as part of a 10-year, $625 million program.
What it meant for Charles County
The Charles County Health Department issued a recreational advisory, and Maryland closed one downstream shellfish harvesting area in Charles County on Jan. 25 as a precaution. MDE lifted the shellfish closure March 10 and says there were no active leases in the closed area. MDE also says the Charles and Prince George’s advisories are no longer active, and that all Maryland drinking water intakes sit upstream of the spill and were unaffected. MDE’s page does not mention St. Mary’s County.
Open questions
MDE’s sampling has found sewage-related markers in sediment near Minnie’s Island, and there are no established health thresholds for sediment testing. The Potomac Riverkeeper Network expanded its own monitoring from 28 to 37 sites this season and has urged continued monitoring that includes sediment. Maryland and the U.S. Justice Department filed separate lawsuits April 20 against DC Water; Maryland seeks civil penalties and compensation for testing, cleanup and lost natural resource value. A class action was filed March 6. The District’s environment agency plans a survey of fish and wildlife in spring 2027.
What to watch
The detailed data on DC Water’s monitoring page, MDE’s next sediment results, the status of the lawsuits, and DC Water’s board meeting Oct. 8.
