The Potomac crested at 7:30 p.m. Wednesday, with 142,000 cubic feet of water per second coursing downstream. That flow rate means 92 billion gallons per day of brown, turbid rainwater going directly into the river, along with water flowing in from large tributaries, like the Shenandoah, Monacacy and Rappahannock rivers, according to Julie Fritz, chief of the Water Control section of the U.S. Army Corps of Engineers in Baltimore.
Local water and sewage treatment facilities fared well during Sandy because of preparations beforehand and strategies used during the storm, officials in Arlington, Fairfax County and Alexandria said.
Fairfax Water rotated between their onshore and offshore intakes to keep bar screens free of leaves, branches and other storm debris and did not have service interruptions. By rotating the intakes, the water velocity could be used to clear debris from screens, said Jeanne Bailey, spokesperson for Fairfax Water.
Arlington County saw a three-foot increase in flows in Four Mile Run, but it didn’t cause a problem for the county’s new $568 million pollution control plant that saw daily average flow increase from 20 million gallons to 50 million gallons.
In southern Fairfax County, it is estimated 10,000 cubic feet per second of water was running down Bull Run. The flow into the Occoquan Reservoir crested sooner than the Potomac River and created a challenge for Upper Occoquan Sewage Authority.
A rainfall event like Sandy “replaces water in the reservoir two or three times, said Tom Grizzard, director of the Occoquan Laboratory and professor of engineering at Virginia Tech.
UOSA was able to contain and convey all wastewater to the plant by storing 70 million gallons in holding tanks that were built during recent capital improvement projects, then processing the wastewater over two to three days.
Hurricane Sandy won’t be as damaging to the Chesapeake Bay as Tropical Storm Lee in 2011, according to Bruce Michael, Director of the Department of Natural Resources’ Resource Assessment Service.
“There was not as much rainfall and it was after a dry condition and late in the year,” he said. Michael added he believes the resultant algae plume will be smaller.