Dizzying! Crews collecting stain samples from atop the St. Louis Gateway Arch!

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ST. LOUIS (KMOV.com) — For the first time since the Gateway Arch was completed, crews will be collecting stains from the structure in an attempt to figure out what caused them to form.

The National Park service is hoping to sample the stains and figure out what caused them so they can be removed.

An engineering firm will install ropes on the north leg of the structure and a special team will descend from the apex of the Arch down to about 425 feet from the ground to collect the samples.

“This is a dangerous enterprise that we’re getting into here. We’ve worked on monuments like this before. We worked on the Washington Monument. This one is more complicated than Washington Monument,” said Steve Kelly, an architect and structural engineer.

Team members will use suction cups and ropes to secure themselves to the structure.

The Arch will remain open throughout the project. Public access to areas on the Arch grounds will be restricted and all visitors to the Arch will be able to enter at the south leg. The tram ride to the top of the Arch will still be allowed, but the deck will be partially restricted. Arch officials say there is no visibility of the project from the top of Arch.

Visitors can go to Luther Ely Smith Square, across from the Gateway Arch, to be provided with binoculars and interpretative education to learn more about the project as it takes place.