As early as 2015, anyone viewing the Jefferson Memorial from a distance — say, from Independence Avenue across the Tidal Basin, or an aircraft window on approach to Reagan National Airport — could see that something was wrong. One of the capital’s signature monuments, a priceless piece of the nation’s heritage, was starting to look downright shabby. Dark splotches were growing on the iconic white dome. Growing fast.
Faced with the speed of change, and the increasing number of visitors and residents asking what was going on with the memorial, National Park Service analysts concluded they couldn’t fight what they didn’t fully understand. They took a patient approach, calling in scientists and their own conservation experts and embarking on a years-long analysis to determine what was attacking the memorial’s 78-year-old marble dome.
“It was maybe 15 years between the time we first realized the problem and when we finally acted on it,” said Audrey Tepper, a Park Service historical architect with the National Mall and Memorial Parks. “There’s a real logic in not acting too quickly.”
The culprit, they eventually determined, was something that probably had been present on the monument, and nearly every other outdoor structure in most cities, for decades: biofilm.
“It’s a microbial community of bacteria, fungi and algae,” Tepper said. “It occurs all over the place. It’s existed for eternity, but it’s more visible on white marble buildings.”
It’s usually barely visible, and in fact no one knows for sure how long it’s been growing on the Jefferson Memorial dome. It only became a pressing problem when — for reasons scientists are still working to understand — it began to darken.
In collaboration with commercial restoration experts, National Park Service analysts determined that, as bad as it all looked, the biofilm infestation was superficial. If it could be cleaned off, it would leave the underlying marble undamaged. But there was a catch. “Most people in the preservation industry use essentially antimicrobial agents, chemical cleaning agents primarily developed for the health industry and the food industry,” said Judy Jacob, National Park Service senior conservator and an in-house expert on biofilm. But the Jefferson Memorial sits in the sensitive biome of the Tidal Basin. Under the constraints of the 1972 Clean Water Act, the risk of toxic runoff made any use of chemicals to clean it look like a very bad idea.
The centerpiece of the restoration project has been the use of high-tech lasers to vaporize the thickening biofilm without risking the surrounding environment.
Some biofilm probably has been present on the memorial’s marble surface from its early years. But when the marble was new and smooth, this would barely have been visible.
Over the years, natural erosion and weathering wore pits and grooves in the relatively soft stone surface; this happens with all marble monuments.
Conservators suspect this process gave the biofilm greater purchase, more nooks and crannies in which to flourish and thicken.
By the spring of 2016, the thickening biofilm began to darken, discoloring the white dome in unsightly — and growing — patches.
Conservators employed a two-stage process. First they used carefully calibrated pulsed laser beams designed primarily to target pigmented biological cells. Think of them as the big brothers of the lasers sometimes used to remove tattoos. This process, never before attempted on this scale, reduced the pigmented biofilm to a fine ash.
Second, conservators went to work with gentle, low-volume steam cleaning jets to blast the biofilm ash — along with pigeon droppings and any other accumulated sediment — out of the marble’s crevices.
The result is a dome that, at least from Independence Avenue or the windows of approaching airliners, appears as good as new.
Why the sudden change?
No one knows for sure why this biofilm suddenly became a visible problem only over the last 20 percent of the Jefferson Memorial’s life. One theory suggests that hydrocarbons from partially combusted jet fuel might feed the infestation; increased traffic into Reagan National Airport over the past couple of decades might explain the change.
Cleaner air may also be to blame: Since the enactment of the federal Clean Air Act in the 1960s, the amount of particulates in the air has lessened. The cleaner air has allowed more ultraviolet light to reach the dome surface, possibly feeding the biofilm colony.
And the specter of climate change may offer an explanation. Summers are generally longer and hotter now than years ago. Could this be having an effect? National Park Service conservators would love to know. “We need more people studying this,” Tepper said.
One thing preservation experts do know, according to Jacob, is that the Jefferson Memorial’s marble surfaces have weathered over the years.
“Rain alone will slowly erode the surface,” Jacob said. “New marble has a sanded or rubbed finish with a satin sheen to it. That will erode first. With time, that beautiful smooth surface becomes eroded and it has a topography. That texture provides a surface that will stay wet for longer periods of time from rain, condensation, mist. This provides just the perfect environment for microorganisms.”
As restoration jobs went, this was never going to be one of D.C.'s biggest — the $14.5 million budget to restore the Jefferson Memorial is dwarfed by, for example, the $60 million restoration of the Capitol dome in 2016. Still, as the nature and extent of the biofilm infestation became clear to analysts, it also became clear that this job would eat every dime they had allocated, and contingency funds as well.
And as anyone who’s stood in the swamp-like murk of a Tidal Basin summer day will hardly be surprised to hear, it’s a job that will need to be done again. “We think this biofilm will come back and we are continuing to study it,” Tepper said. And they’re not alone.
Conservators across the Potomac at Arlington National Cemetery are dealing with very similar biofilm on their Memorial Amphitheater, which is built of the same Vermont marble as the Jefferson Memorial. The Folger Shakespeare Library’s ongoing $72 million renovation includes abating biofilm discoloration from its facade, constructed of slightly softer Georgia marble. The District of Columbia War Memorial on Independence Avenue across the Tidal Basin from the Jefferson Memorial also features a Vermont marble dome, visibly afflicted with an extensive — and growing — biofilm infestation.
Government funding addressing maintenance shortfalls at National Park Service properties, specifically the 2020 Great American Outdoors Act, along with the agency’s usual dexterity in working the government’s patchwork funding channels, leaves NPS officials cautiously confident that when dark splotches reappear on the Jefferson Memorial dome — “when, not if,” as Tepper puts it — they will be able to respond.
And as for how soon that might happen?
“I have no guess,” said Jacob. “We’ll just have to wait and see.”
Aaron Steckelberg contributed to this report.
About this article
Information sourced from National Park Service; Center for Biofilm Engineering at Montana State University; EverGreene Architectural Arts