The stains on the Gateway Arch's steel surface are not due to significant structural distress, deterioration or corrosion, according to the results of a comprehensive study on the monument's structural health released Thursday.
The report found that the appearance of discoloration is actually due to blemishes and markings from the Arch's initial construction, built-up pollution, graffiti, and stains from superficial corrosion.
Overall, the study finds the Arch to be in “serviceable condition,” or "great shape," as Jefferson National Expansion Memorial Deputy Superintendent Frank Mares said in a statement.
"The great news is structurally we don’t have a problem. We still have that visual problem, but it’s not a structural problem," he said.
Last October, engineers, scientists and architects with the firm Wiss, Janney, Elstner Association, Inc. began examining the Arch's exterior, rappelling down the north leg of the Arch. This phase of study focused on the streaking National Park Service staff had noticed on the Arch's panels, which the firm says hasn't gotten worse in the last several years.
"All these rust-colored stains and other marks and discolorations that generally appear way up high, hundreds of feet up, we could never really get at them to know if they could just be wiped off or if they were a more serious sign that structurally there were some problems," Mares said.
Two previous phases in 2006 and 2012 found the Arch was structurally sound.
Have you ever wondered what it would be like to stand on top of the Gateway Arch? Thanks to this video from the industrial ropes access crew from the team who did the Corrosion Investigation for the Arch, you can experience it virtually! (jrc)
Posted by Gateway Arch, Jefferson National Expansion Memorial on Thursday, April 9, 2015
The WJE team used a variety of methods to determine what caused the Arch's stains. Like many a visitor to the tourist attraction, they viewed the documentary "Monument to the Dream" to see footage of the Arch being built. Thanks to the film, they determined some of the damage to the monument's steel finish happened during fabrication and construction and are "not likely to get worse."
"That wasn’t noticeable until enough decades had passed that, again, grime and other accumulation highlighted those imperfections," Mares said.
The researchers also found graffiti and vandalism ranging from small scratches to "deep hammer indents" on the lower panels of the Arch. Flakes from some of the metal instruments used to deface the Arch were left behind to corrode in red-orange stains, the report said.
Additionally, pollution and other particles have created superficial "brownish-orange" stains on the lowest eight panels of the Arch, particularly around welding spots. The report also notes some staining due to chemicals, though it's not known if those were used on purpose or not. More pollution in the future could make stains appear worse, the researchers said.
But some stains could be removed or reduced with gentle annual cleanings and increased security around the base of the Arch to prevent more vandalism, the report suggests.
Under the guidance of professional preservationists, low pressure water cleaning could remove many pollutants stuck to the Arch's surface, but would only be able to reach about 100 of the structure's 630 foot height. Mares said that could create another problem.
"They even admitted in the report that over time, if you can’t do it all, that will cause a more noticeable difference between the area that’s clean and the areas that are not clean, so we’re cautiously considering that recommendation," he said.
Mares said Arch staff will pursue the recommendation of cleaning out the metal particles embedded in graffiti on the lowest panels that are creating some stains. The report also recommends increasing security around the Arch's base, but says trying to refinish the surface to remove graffiti could make the appearance worse.
"I’m sure everyone would like to have a perfectly flawless stainless steel exterior, but it would be very difficult for the foreseeable future to clean that stuff off way up high," Mares said. "I hate to call Eero Saarinen an architect that had a design flaw, but with no ability to reach the exterior, it’s going to be difficult to ever completely clean it."
The report also suggests monitoring and documenting the visual changes to the Arch's surface each year.