Army Corps: Reservoir expansion ‘doesn’t fix, but improves’ DC’s drinking water supply for future Potomac River emergency
Developing a regional solution to enable all local water companies to share drinking water in the event of a future Potomac River emergency remains a long-term challenge facing the U.S. Army Corps of Engineers. But the Corps is leaning-in to near term solutions, for now, because current issues “are quite, quite dire.”
In an interview with WTOP, Trevor Cyran, Chief of the Civil Works project management office of the Baltimore District Corps of Engineers, elaborated on the Corps’ ongoing three-year feasibility study funded by Congress and the Metropolitan Washington Council of Governments.
Last week, during a House Transportation and Infrastructure Committee hearing, lawmakers pressed the U.S. Army Corps of Engineers to explain what’s being done to secure solid backup options for the D.C. region’s drinking water.
D.C. Del. Eleanor Holmes Norton challenged the Corps after learning that the study that Congress authorized to identify a secondary water source for the region was being narrowed to only expanding the current Dalecarlia Reservoir, adjacent to the Washington Aqueduct, which remains the only source of drinking water for D.C., Arlington, and parts of Fairfax County, Virginia.
“Expansion of the reservoir is not a secondary water source,” Norton said. “With only a one day of backup water supply, human-made or natural events that make the river unusable would put residents, the District government and the regional economy at risk.”
Cyran said the U.S. Army Corps of Engineers doesn’t disagree.
“We’re trying to find a quick win that addresses some of the near-term issues, because they are quite, quite dire,” Cyran said. “The Dalecarlia expansion would add approximately 12 hours of water storage into the system,” he said. “So, while we know that doesn’t fix the problem, it improves the situation.”
Recently, drinking water in D.C., Northern Virginia and Maryland has remained safe because the January collapse of a portion of the aging Potomac Interceptor regional sewer line happened downstream of the main Potomac River water intake serving the Washington Aqueduct.
“We’ve moved forward with the Dalecarlia expansion, as our most probable recommendation,” said Cyran. “The Corps is laser focused on delivering something right here, right now that can actually help with the issue, while still exploring some of those long term solutions.”
Cyran said the dangers to public health and the economy are substantial, with the Potomac as the sole drinking water source. “It’s not a great situation — we’ve seen a very real risk come to fruition recently, with the spill.”
How would increased storage at Dalecarlia Reservoir look?
According to the Army Corps, expanding the Reservoir over 54 available acres would provide approximately 70 million gallons per day, doubling the capacity at Dalecarlia. Since the land is already owned by the Washington Aqueduct, it would not require acquiring any land.
Cyran said it’s not yet certain whether the expansion would provide an extra 12 hours of storage of raw water from the Potomac, or finished water, after it had gone through the Washington Aqueduct’s water purification process.
Regardless, either option would result in the Aqueduct having more water on hand, if drawing water from the Potomac was suddenly unsafe.
Another near-term option that wouldn’t require land acquisition would be advanced treatment, Cyran said.
“We could implement something that allows us to treat for a wider array of contaminants, if you had a spill,” said Cyran, although noting the recent spill from the Potomac Interceptor, which poured approximately 240 millions of raw sewage into the Potomac, “might not be a good example” of how the technology would work.
The Army Corps list of possible solutions includes reusing water. In November 2025, DC Water outlined its own plans to recycle water from the utility’s Blue Plains Advanced Wastewater Treatment Plant, the largest of its kind in the world.
Quarry storage cannot happen quickly
During its ongoing study, the Army Corps has identified possible long term regional solutions, including the potential use of the Travilah Quarry in Montgomery County, Maryland, and two quarries in Loudoun County, Virginia, owned by Luck Stone.
10 years ago, in December 2016, WTOP first reported that the Travilah Quarry, located on Piney Meetinghouse Road in Rockville, was quietly being considered by DC Water, WSSC Water, and Fairfax Water, as an alternative source of water, if the Potomac River were unavailable.
“The three utilities, and the Interstate Commission on the Potomac River Basin, along with the Metropolitan Washington Council of Governments have been working over the last several years to look at alternatives to get better interdependencies, to have more resilience in our system,” said Tom Jacobus in 2016, while he was general manager of the Aqueduct.
Now, a decade later, the logistical, real estate, and financial challenges of obtaining a quarry which could be interconnected between DC Water, WSSC Water, and Fairfax Water remain.
“We’re not saying they can never happen, we’re just saying they cannot, in any way, shape, or form, happen quickly,” said Cyran. “Travilah is still an active quarry, so that can’t even be considered for storage until they’re done mining, which might be 30 years from now.”
The Dalecarlia Reservoir expansion would not be regional solution, Cyran said.
“That would only benefit folks who are tied directly to the Aqueduct at this time,” he said. “However, while we’re going to be looking at other alternatives that we could potentially spin off and continue to look at, that would address some of those more regional issues.”
‘We can’t hand half-baked ideas to Congress’
While an interconnected, resilient system, that could provide additional water sources and storage to DC Water, WSSC Water, and Fairfax Water would be optimal, Cyran said the Corps is limited by a Congressional paradigm that limits its feasibility study to four years and five million dollars.
“We can’t hand half-baked ideas to Congress,” Cyran said.
With the Corps’ current focus of implementing near-term improvements, quickly, the agency will continue to use its expertise to envision a more resilient, long term solution.
“We are committed to looking at this issue and try to explore some regional solutions, within the paradigms of the legislation that we have to operate within,” said Cyran. “If Congress wants to consider something else to expand our authority, we could maybe look at a bigger solution, with more time and money.”