SAN FRANCISCO (KGO) -- Engineers are taking a look at a section of the Golden Gate Bridge that tourists never see.
The bridge district is preparing to inspect the Golden Gate's massive concrete foundations, hidden beneath the water line in San Francisco Bay.
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A specialized engineering firm is being hired to take sonar images of the sections.
The foundations support the bridge's two main towers.
The process involves high tech equipment lowered into the water as deep as 90 feet.
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"We use something called a side scanning sonar. It's equipment that'll drop over the side of a boat. And it will send down sound waves and it'll bounced back and get a reflection, and you'll actually be able to see what it looks like down there," engineer John Eberle said.
After that, a team of divers will wear special equipment to go under water for hours at a time.
"And they go down and touch the surface and scrape off any barnacles or any moss or any vegetation that may be on there. And they get up real close and personal and touch it and feel it and see if there's any cracks see if they find anything like that. If not we're done, if they do, we'll do some further investigation," Eberle said.
The bridge is inspected every five years.
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Engineers say the foundation and the bridge itself has held up remarkably well since the original construction in the 1930's.
The inspection is expected to start as early as March.
Take a look at more stories and videos about the Golden Gate Bridge.
Golden Gate Bridge's concrete foundations to be inspected
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