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ST. LOUIS (KSDK) - It's been nine years since the National Park Service began studying the stains that can be seen on the Gateway Arch. Nearly 10 years later, the NPS continues its studies.

In a 2012 investigation, NewsChannel 5 showed $731,000 has been spent on three reports that looked at what's causing the corrosion and how to fix it.

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In November 2012, a NPS spokesperson said experts needed a closer look at the Arch, so a fourth study was needed. That fourth study has yet to happen.

Ann Honious with the Jefferson National Expansion Memorial said the fourth study is slated to begin this fall. It's estimated it will cost around $300,000. Add that to the previous costs, and that means more than a million dollars will have been spent on studies. The previous studies were paid for by tax dollars. The National Park Service is hoping to use private funding for the fourth study.

In an email, Honious said, "In its current condition, the safety and structural integrity of the Arch are not at risk, nor will it be for the foreseeable future. Formulating a long-term maintenance plan for the Arch is important to the NPS. We are making progress toward that goal through the various studies. The Arch is a unique structure; there is no existing maintenance plan nor is there access to the exterior.​"

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