Corrosion has been a concern when it comes to the Gateway Arch.  Officials had expressed concern about a growing number of stains on the outside of the landmark, many of them appearing to be rust.  But a new report by the National Park Service says the markings are just cosmetic, and no cause for structural concern.  

Engineers determined the stains were caused by a combination of pollution and lack of adequate cleaning.   Federal officials are now working on a plan to clean the structure, and anticipate the effort will be similar to what was done recently to restore the Washington Monument.


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