Now the National Park Service has embarked on an $8.2 million project to reclaim the Washington landmark from the creeping grasp of nature.

Last week, workers were putting up scaffolding to begin the complex process of repairing and replacing roof surfaces, cleaning giant marble roof tiles, and using lasers to attack the biofilm that has spread dramatically in recent years.

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Masonry damaged by water will be fixed. Cracks will be repaired. And the insect colonies will be eradicated.

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The 32,000-ton memorial, which honors the nation’s third president and main author of the Declaration of Independence, houses a 19-foot bronze statue of Jefferson. The site remains open, and the work should be finished by next spring.

The task is varied, “but probably the most visible thing that we’re doing is to clean the memorial of the biofilm,” said Audrey Tepper, a Park Service historical architect with the National Mall and Memorial Parks.

“We’ve been watching it grow ever since” it was first noticed in 2006, she said.

The film — “a microbial community of fungi, algae and bacterial growth,” Tepper said — has left a dingy, gray shadow over one of the country’s most beautiful structures.

During the annual Cherry Blossom Festival, the Jefferson statue has been an exquisite backdrop for countless photographs.

The memorial’s white Vermont marble once was smooth and pristine but has been badly eroded by weather. Now the sugary surface has become ideal for the growth, which “likes all the nooks and crannies,” Tepper said.

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Add the flies, spiders and wasps, and “there’s a bit of a food chain going on here,” she said.

The memorial sits on fill dredged in the late 1800s from the Potomac River, and on 634 pilings and caissons sunk down to bedrock on the south side of the Tidal Basin. One support goes down through 138 feet of soft earth.

Over its seven decades of life, the structure has been affected by the vagaries of Washington weather and by the capricious piece of ground on which it sits.

As early as 1941, two years before its dedication, some of the supports under the memorial’s main steps began shifting. They had to be lashed together with steel cable and turnbuckles, according to an engineering report done for the Park Service in 1965.

Settlement also caused other supports under the steps to bend slightly, the report says. The steps moved so often that park rangers once kept a special tool at the site to realign them, the report says.

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Lesser settlement continued during the 1940s and ‘50s.

By the 1960s, the front plaza, which was not supported by pilings, began to sink — by as much as three feet — and a $1.1 million engineering project was undertaken to bolster it with more pilings and supports.

In 2010, a $12.4 million repair project shored up the memorial’s poorly supported sea wall, which also had been sinking into the tidal ooze.

Above ground, “the idea … was that white marble was really almost temple like, neoclassical in design,” Tepper said. “White marble was kind of the ideal in terms of producing a memorial.”

“They didn’t envision [Reagan National] Airport being over there, and the trains and the planes and the growing city around it, and the wasps and bugs and the spiders,” she said. “They really wanted a white memorial. … It’s not white anymore.”

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Vibration has been a problem, too. “We had some issues with the columns years ago,” Tepper said.

At the tops of some of the memorial’s ionic columns, curlicues called volutes have been anchored with wire, because stone has fallen in years past, Tepper said. And netting is in place on the ceiling near the entrance where stone has come loose.

One humid morning last week, as workers hammered and jets and helicopters zoomed by, Tepper climbed to the top of the memorial to point out some of the problems.

Up close, the spread of the biofilm was extensive, especially on the dome. In some areas, the dome was almost completely covered with dark splotches.

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“This stuff has just grown exponentially,” she said. “Is it [too] moist? Is it humid? Is it hotter? Is there a change in the atmosphere? We simply don’t know. … It’s very aggressive, and it has spread. … Each year, it’s gotten worse and worse.

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“So that’s another thing,” she said. “How long would it take before everything was covered?”

Nearby, a team clad in green day-glow shirts worked inside a small hooded enclosure to test a laser to “ablate,” or erase, the film.

“Ablation occurs when a directed beam of pure light pulses at a targeted area of soiling,” Tepper said. “When the black biofilm heats up, it expands, is ejected from the surface, and vaporizes.”

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They are not sure how long the lasered stone will stay clean, or if the biofilm will come back, but the work continues.

As a giant wasp cruised near the top of the memorial, and the Potomac River stretched in the distance below, Tonia A. Rivers, a senior project manager for Grunley Construction, which is doing the work, paused.

“It’s a lifetime dream to say that you’ve touched one of the world’s most important structures,” she said. “Who gets to do this? Who gets to stand here?”