St. Louis (KSDK) -- Stains on the exterior of the Gateway Arch are no reason for concern and the landmark is as structurally sound as it was when it was built.
The National Park Service said a report issued by Wiss, Janney, Elstner Associated Engineering Firm indicates that the corrosion on the exterior of the Arch is a cosmetic problem.
The engineers believe welds that hold the Arch's sections together may cause the staining because other stainless steel structures have not had the same problems.
"Many of the discolorations of concern are caused by atmospheric pollutants or inadequate cleaning and polishing of the Arch after erection. In addition, if a metal other than the exact type of stainless steel the Arch is made of (Type 304) got into the welds when they were made, the rogue metals might be the cause of the staining," engineers concluded.
Also, visitors are carving their names into the exterior base of the Arch legs. The carved graffiti is showing the same staining. It will also be treated to try and eliminate and repair the damage.
Engineers recommend further close-up testing of the welds to determine the best method for cleaning the metal and stopping the streaking. Samples will be taken from the exterior of the structure and studied to determine the exact type of corrosion present.
The last step would be to clean stainless steel surfaces and dressing and polish the original welds to reduce future staining.