While local water officials monitor drought conditions, and weigh the likelihood of needing to tap water reserves to supplement the Potomac River, more local utility companies are utilizing an age-old method of increasing their backup supply.

“Quarries have been used since Roman times to supply water,” said Michael Nardolilli, executive director of the Interstate Commission on the Potomac River Basin. “Filling them up during times of high flow, and then using it during times of drought or contamination events.”

Loudoun County in Virginia is in the process of converting Luck Stone quarry into a billion-gallon reservoir. That project is slated to finish in 2028.

“Now, you have Vulcan Quarry in Fairfax County,” said Nardolilli. “Which will be called the Edgemon Reservoir.”

The name is a reference to a former general manager of the water company, who died in 2022.

Fairfax and Prince William counties have a backup supply in Occoquan Reservoir, and Montgomery and Prince George’s counties draw a large portion of their water from the Patuxent River. These reservoirs can — and do — release their water into the Potomac River during drought conditions.

However, if the Potomac River were to become contaminated, there is no backup water supply for D.C., Arlington County and the City of Falls Church.

WTOP initially reported in 2016 that water officials were finally making public a long-standing water system shortcoming — the Washington Aqueduct, which processes water from the Potomac River, only has 24 to 48 hours of water supply available.

“We are very mindful of that dependency for D.C. and Arlington,” said Nardolilli. “They are the most vulnerable cities in the United States to a cutoff of their drinking water supply.”

The U.S. Army Corps of Engineers is in the midst of a feasibility study of ways to bolster the resilience of the area’s water supply.

“The study began in September of last year, it’s supposed to take three years and cost about $3 million,” said Nardolilli. “At which time (the Army Corps) will come up with a recommended solution to this vulnerability.”

As WTOP first reported in 2016 , local water officials have been studying the possibility of utilizing the Travilah Quarry — which is on Piney Meetinghouse Road in Rockville, Maryland — to provide water storage.

Turning a quarry into a water supply is a multiyear, multi-jurisdictional challenge, said Nardolilli.

“You need to acquire the land, and you need the right of way to connect the pipes,” Nardolilli said.

The Washington Aqueduct serves over 1 million customers.

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