Aging storm water tunnels under the Twin Cities are slowly crumbling, risking a collapse that could flood streets and buildings, according to a Star Tribune report published February 17. More than a century old in some cases, 15 miles of tunnels in Minneapolis and another 28 miles owned by Saint Paul and the Minnesota Department of Transportation once carried sewage before storm and sanitary sewers were separated.

The tunnels are 30 to 150 feet deep and lie beneath the most developed parts of the urban area. All reach the Mississippi River. It will take $75 million in repairs in Minneapolis alone to prevent failures. If a tunnel collapses in an urban area, it could cause massive flooding and the accompanying property damage.

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