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Twin Cities' storm water tunnels showing their age

The storm water tunnels deep under the Twin Cities are starting to split apart and are in danger of collapsing, the Star Tribune reported.

Minneapolis has more than 15 miles of tunnels, many of which are more than 100 years old. They collect storm water from city streets and rooftops and send it to the Mississippi River.

The tunnels will cost $75 million to repair.

Many of the tunnel walls are cracked. If a wall were to collapse completely, it would back up the tunnel and flood the surrounding area.

The pressure is so high in a certain St. Paul tunnel that a manhole erupts like a geyser every time it rains. In other places, manhole covers are blown to the sky during storms.

Repairing the tunnels is very dangerous. Two workers repairing cracks in a St. Paul tunnel drowned last July when they were unable to leave during a storm.