The dome of the iconic Jefferson Memorial was covered in black growing splotches. So the National Park Service called in experts to figure out what was damaging the Washington, DC, building. Dark splotches were growing on the iconic white dome. Growing fast. 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. It occurs all over the place. It’s existed for eternity, but it’s more visible on white marble buildings. 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.
No one knows for sure why this biofilm suddenly became a visible problem only over the last 20% 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. 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.
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