Utility Envisions Old Quarries as Storage Sites for Water

Loudoun County authorities have proposed turning old stone quarries into drinking-water reservoirs, siphoning 8 billion gallons of Potomac River water to store for times of drought.

The plan, from the utility Loudoun Water, is designed to keep the county's taps flowing for 120 days during a severe dry spell. The utility still needs approval from county, state and federal regulators. Even if the plan is approved, officials say the first reservoir will not be filled until about 2017.

The amount of water involved sounds massive -- 8 billion gallons is about 12,000 Olympic swimming pools' worth -- but environmental officials said yesterday that the Loudoun plan probably would not harm the Potomac ecosystem.

At most, Loudoun Water plans to withdraw 40 million gallons a day from the river. Other water utilities already take out 450 million gallons on an average day, and the river's total flow is about 7 billion gallons a day, according to the Interstate Commission on the Potomac River Basin.

"If they were taking the water at the high-flow points [when the river is swollen after rains], it's not going to have any significant impact on the river," said Joseph Hoffman, the executive director of the commission, which encourages cooperation among states along the Potomac.

Loudoun Water's proposal came after a long search for new sources of tap water for the fast-growing county. Today, the authority can provide up to 57 million gallons a day, buying it from utilities in Fairfax County and Fairfax City. But by 2035, officials estimate the need will grow to 90 million gallons.

In response, utility spokeswoman Samantha Villegas said, the county wants to build an intake pipe into the river in Leesburg. From there, Potomac water would be piped about 7 1/2 miles underground to a proposed treatment plant.

Beginning in 2017, Villegas said, extra water would be pumped into a quarry once used to mine diabase, a granitelike stone. The first reservoir would hold about 1 billion gallons, she said. The others, with 7 billion gallons of capacity between them, would be built during the next 50 years, she said. The project would cost an estimated $280 million.

The quarries, which are owned by the Luck Stone company, are along Belmont Ridge Road southeast of Leesburg. The quarries will be given to the utility when the mining is finished, Villegas said.