The old Champlain Bridge is coming down after the new one opens next month, but it will take up to three years and cost taxpayers at least $400 million.

So why not just leave it up and use it for something else?

Because the old bridge is in such bad shape, there's nothing to be done with it, according to Nathalie Lessard, a spokesperson with the Jacques Cartier and Champlain Bridges Incorporated (JCCBI) — the Crown corporation that, established in 1978, is overseeing the project.

"It's a structure that is at the end of life," she said.

"There are drainage problems. There are design issues that have caused corrosion that has attacked the essential components of the bridge. This makes the structure fragile."

The JCCBI says those essential, structural components have deteriorated faster than expected.

Even without vehicle traffic, maintaining and inspecting the old structure would cost up to $7 million annually, and that excludes any major repair work.

Demolition is also a matter of safety, Lessard said.

Dismantling without disturbing ecosystem

A call for tenders is currently in effect to select the company that will demolish the 3,440-metre bridge of steel, concrete and asphalt. Demolition is slated to begin in 2020.

The aim has always been to been to carefully dismantle the bridge so as not to disturb the ecosystem beneath. The JCCBI says there should be no major traffic hindrances during the demolition process.

The new Champlain Bridge is scheduled to open next month. (CBC)

The bridge, which opened in 1962, may be coming down, but that doesn't mean a mountain of material is headed to a landfill.

The JCCBi says 80 per cent of it will be recycled and researchers will study that material to learn more about the wear of time and substances such as de-icing salt.

Redeveloping Montreal, Brossard shorelines

Some seven hectares of land along the St. Lawrence's shoreline will be freed up, allowing for a unique site to be developed, the JCCBI says.

There will be "enhanced access" to the river, and components of the old bridge will commemorate its part in Montreal's history.

Join our online brainstorming about the reuse of <a href="https://twitter.com/hashtag/deconstruction?src=hash&ref_src=twsrc%5Etfw">#deconstruction</a> materials and add your ideas about the “Héritage Champlain” project to redevelop the shoreline and Estacade <a href="https://twitter.com/hashtag/ChamplainBridge?src=hash&ref_src=twsrc%5Etfw">#ChamplainBridge</a> . You have until June 30 to participate online. <a href="https://t.co/BFNT4vRyaR">https://t.co/BFNT4vRyaR</a> <a href="https://t.co/xwZhlJBemW">pic.twitter.com/xwZhlJBemW</a> —@PJCCI

While citizens will have an opportunity to weigh in on redevelopment of the site — including the Champlain Bridge Estacade which parallels the old bridge and is used as a bike path — the aim will be to preserve the shoreline, restore natural fish habitats and create observation points of local species.

That means there will be development of the Brossard and Nuns' Island shorelines.

The St. Lawrence Seaway dike which sits in the river between the two shores will also be renovated, the corporation says.

Citizens will have the opportunity to share their ideas online, particularly about measures that could minimize the demolition project's impact the community, the development project and the recycling of collected materials.

Public information sessions have also been held this month.

The brand new, aptly named Samuel De Champlain Bridge carries a price tag of more than $4 billion and has an expected life span of 125 years.