SAN FRANCISCO (CBS) – While the new eastern span of the Bay Bridge will open to traffic in September, the work needed to take down the old roadway is expected to take years.

“These bridges define us…in some ways as much as the bay itself,” said Brad McCrea, regulatory director of the Bay Conservation and Development Commission, the state agency that oversees protection of the bay.

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McCrea said that building the new bridge will only be half the challenge. “Taking the old Bay Bridge down is as practically as big a project as putting the new one up,” he said.

Environmental restrictions mean the structure will have to be carefully taken apart in sections, in the reverse order that it was originally built.

“They have great documentation about how this old structure was built in the 1930s,” McCrea said. “So they will use the architectural drawings from the 30s, they’ll use all of the photographs they have from the 30s, and they’ll use that as a road map to un-doing what was done 75 years ago.”

First to be removed will be the cantilever section, that’s the part that looks like a giant erector set. It sits dangerously close to the new bridge and Caltrans wants that removed as soon as the new roadway is opened.

They are hoping drivers on the new span won’t be too distracted by the sight of workers suspended from the old steel as they dismantle it.

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“After the cantilever is demolished we have the main portion of the bridge, the superstructure that we’re looking at right here. And then the final demolition is of the marine foundations,” said Caltrans engineer Deanna Vilcheck.

And those won’t be easy. Some of the caissons are buried 175 feet into the mud. Because they’re not solid, but honeycombed inside, the engineers have an idea.

“If you use micro charges all throughout them, you could effectively have them fold into themselves, in theory, and have it work down and all the debris would actually just collapse down into the bay mud itself. And they would just leave it there,” McCrea said.

The rules on working over the bridge are pretty strict. How strict? Workers who drop something into the water technically have to fish it out. That may not be easy to do in 75 feet of murky seawater.

Once the bridge has been dismantled, any concrete or steel will be recycled or sold for scrap, but other reuses may be limited because of the toxic lead paint that has coated the span for decades.

Some estimate the demolition could take seven years to complete and cost more than $240 million. When the project is finished, Caltrans plans to create a regional park in the area where the old span now makes landfall. It will be a place where people can come to view the new bridge and remember the old.

“There’s definitely part of me that will be sad to see it go,” McCrea said.

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Finally, there is one piece of steel that will undoubtedly be saved. It is a little figure called the Bay Bridge Troll. Secretly put here in 1990 by steelworkers repairing the quake damaged structure, the troll has guided millions of cars safely across the Bay. It could end up in a museum, but some say it should be attached to the new bridge as it continues the mission of connecting all the people in the Bay Area.