Three weeks after the lifting of a boil water advisory for all of D.C. and most of Arlington, Virginia, the Washington Aqueduct can now add a new chemical to its water treatment process to prevent future problems when algae in the Potomac River threatens the main water source for much of the region.
Earlier this month, increased algae in the Potomac River clogged filters at the aqueduct, leading to cloudy drinking water and a low water supply.
WTOP has learned the aqueduct, which is owned and operated by the U.S. Army Corps of Engineers, has been granted permanent authority from the Environmental Protection Agency to add a chemical that will head off future problems with algae gumming up the drinking water treatment facility.
“On July 3, when we were in the middle of the algae issues, we got emergency temporary authorization from the EPA to use copper sulfate as an oxidizing agent,” said Rudy Chow, general manager of the Washington Aqueduct.
Since then, Chow said, the aqueduct has been granted permanent authorization from the agency to add the chemical to its treatment process to combat algae attacks.
The improvement is evident, even to the naked eye, Chow said while standing next to the aqueduct’s sedimentation basin, where water from the Potomac River sits before it enters the treatment plant to be filtered and sent out as drinking water.
“This is where solids, or turbidity, settles out, so we get clear water overflowing into our filters, so it can be filtered. And that’s where the finished water comes from,” Chow said. “During the July 3 event, the water coming over was pretty much all green, with a very strong, green color to it.”
At the time, Chow saw “floating algae mats on top of the sedimentation basin, which got washed into the filter building, thus clogging up the filters.”
Chow said chemicals being added to the raw water as it flows into the Potomac River intakes is helping reduce the amount of algae floating in the sedimentation basin.
“We’re adding triple the amount of aluminum sulfate, which is a coagulant agent to help solids settle out,” Chow said. “On top of that, we’re adding copper sulfate as an oxidizer coming through at the headworks, so by the time it gets here to the sedimentation basin, it can settle out properly.”
Other water providers using the Potomac River as their main water source, including WSSC Water and Fairfax Water, have been able to weather this year’s algae bloom without affecting their drinking water output.
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