What's that black stuff? NPS tests ways to safely clean biofilm from Jefferson Memorial

NPS tests ways to safely remove black biofilm from Jefferson Memorial. (ABC7)

The National Park Service says crews began noticing black biofilm on the Thomas Jefferson Memorial in 2006.

“It’s primarily on the dome and then on these horizontal surfaces,” said Catherine Dewey, with the National Mall and Memorial Parks, pointing to the memorial.

The National Park Service is working to find a way to remove the biofilm safely.

“Folks say, ‘Could you just power wash it? Could you scrub it with bleach?’ Those treatments may be actually more detrimental to the actual Vermont marble of the memorial,” said Gay Vietzke, Superintendent of the National Mall and Memorial Parks for the National Park Service.

They are testing the effectiveness of certain chemicals. Test spots can be seen on one side of the memorial. The National Park Service says some areas have changed color, but should wash away with the rain.

“We wanted to make sure people could see this so we could start talking about the biofilm and what we might do to test it,” said Dewey, of the test areas.

A sign posted gives visitors background information on the project.

Crews are looking into whether the biofilm could be damaging the memorial.

“There are studies that it is somewhat minor damaging over time. There are other studies that are starting to question those studies,” Dewey said.

The group has seen the biofilm in other areas of D.C. as well. So far, they don’t have a timeline on when they expect to nail down a treatment.

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