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Editorial comment

Tunnel trouble

The megasewer system that sits underneath the US city of Chicago is tasked with the job of removing millions of gallons of wastewater from downtown sewers and streets, funnelling water into three huge suburban reservoirs. Conceived in the 1970s, the Deep Tunnel, formerly the Tunnel and Reservoir Plan, was completed in 2006 and is described as potentially “the world’s most ambitious and expensive effort to manage urban flooding and water pollution” in a recent article by Henry Grabar in Slate.1

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The Metropolitan Water Reclamation District of Greater Chicago built and operated the 50 year multi-billion dollar tunnel and reservoir project to prevent flooding that, since urban sprawl in Chicago became widespread, regularly spewed sewage-infused water into basements and onto sidewalks and into the Chicago River, causing hundreds of millions of dollars’ worth of flood damage to property all over the city. Rainstorms are getting stronger and metropolitan development has effectively sealed up natural land that once would have flooded and provided a collection point for extra water. I was fascinated to learn from Grabar’s excellent article that before major settlement in the Chicago area, the Des Plains River would (some years) flood the mud flats west of Lake Michigan, creating a temporary inland water passage across the continent.

Just like other metropolitan, flood-vulnerable cities such as Houston, or Miami, rainwater – mixed with sewage and sea or river water – increasingly threatens to damage and pollute homes and businesses. The Deep Tunnel is what experts call a ‘grey infrastructure’ solution: meaning that tunnels, pipes, tanks and so on are pitted against mother nature’s awesome force.

Many have questioned the success of the Deep Tunnel project: a handful of big storms have proved too much for the tunnel system in the last ten years, and flooding in Chicago is still commonplace. It seems it won’t be quite enough to employ the tunnel’s ‘grey infrastructure’. ‘Green infrastructure’ in various forms is probably needed too, perhaps by the way of porous pavements and other natural or man-made water-collecting or bypassing methods.

Another tunnel project facing mixed reviews is the plan to build a pipeline tunnel beneath the Great Lakes, to house the replacement dual pipelines for Enbridge’s Line 5, which since 1953 has transported oil and NGLs from Superior, Wisconsin (USA) to Sarnia, Ontario (Canada). In late December, the Mackinac Straits Corridor Authority (a newly formed state panel) approved an agreement with Enbridge Energy LLC to build a tunnel beneath the Straits of Mackinac that will house the new pipelines and other utilities. Then Michigan Governor Rick Snyder, in his last days in office, approved a transfer of property rights so that Enbridge could construct the tunnel as deep as 30.4 m in the bedrock. The tunnel, once completed, will be handed over to the Mackinac Straits Corridor Authority, which will then lease space in the conduit. Snyder is confident that the US$350 - 500 million tunnel venture will provide a safe home for the replacement pipelines, rendering the pipelines impervious to the risk of anchor strike and adding another layer of protection in the (rare) event of a pipe failure during operation.

However, on 1 January, incoming Governor Gretchen Whitmer took her post and immediately made moves to block the project. As she had promised to voters, she put in a formal request to the new Attorney General Dana Nessel for a legal opinion on several key parts of the project. Gov. Whitmer argues that the construction of the tunnel will leave Michigan at risk of a major spill while works are being carried out (the time frame for the tunnel project is seven to 10 years). Whitmer (a Democrat) makes the case that Snyder (a Republican) rushed through the agreement with Enbridge and relied on recent legislation that was passed in a Republican-controlled Legislature during the recent ‘lame-duck’ session.

The tunnel is expected to be complete in 2024. Enbridge will be held to certain operational terms, including requirements to: keep staff on site at the Straits; be ready to shut down the line within 15 mins in adverse conditions (if waves go above a certain height, for example); employ radar technology to track waves; and to set aside US$1.9 billion for clean-up in the event of a disaster. Enbridge will also increase leak detection at other water crossings in Michigan.


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