Shingle Creek's cautionary tale for Minnesota's water

A front-end loader sits in front of piles of road salt.
A front-end loader sits in front of piles of rock salt, left, and salt mixed with magnesium chloride, right, to be spread on roads at the city of Plymouth maintenance facility last month.
Evan Frost | MPR News

Fifty Minnesota lakes and streams are now on the state's impaired waters list because of too much chloride, mainly from road salt. Excess chloride has widespread implications — everything from affecting aquatic life reproduction to corroding our infrastructure to health problems for humans.

As scientists test more Minnesota lakes and streams, they expect to find more with salty problems.

Shingle Creek was the first body of water added to the impaired list for too high a chloride concentration. But even 20 years of efforts to curb salt use around the creek haven't made much of a dent in the amount of chloride in the watershed, illustrating the long-lasting damage salt can leave behind.

If you've ever driven Interstate 94 in the Twin Cities, you've probably driven over Shingle Creek. It starts in Brooklyn Park and winds southeast to Minneapolis, where it joins the Mississippi River. It drains almost 45 square miles of dense urban area crisscrossed with roads. Lots of roads.

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Palmer Lake Park, Brooklyn Center, Minnesota on Jan. 1, 2016.
Shingle Creek seen in Palmer Lake Park, Brooklyn Center, Minn.
Tony Webster via Wikimedia Commons 2016

For the past 50 years or so, we've been using a lot of salt on those roads to melt ice and snow.

"We've kind of brought this on ourselves a little bit because we have the capability to have very drivable roads in winter," said Ed Matthiesen, an engineer for the Shingle Creek watershed. "The downside is because we can get salt very cheaply and it's one of the things that keeps the roads clear, we tend to apply a lot of it."

When chloride from road salt put Shingle Creek on the impaired waters list some 20 years ago, the state required a 71 percent reduction in chloride. Cities in the watershed agreed to do their part.

Road salt mixed with magnesium chloride lines a street.
Road salt mixed with magnesium chloride lines a street in Plymouth.
Evan Frost | MPR News

Snowplow driver Steve Forness has been clearing the streets of Plymouth for 10 years, and his job has changed a lot in that time.

Now, screens inside the plow's cab give him detailed information about the outside conditions, and what to put on roads to make them safer — whether it's straight salt brine, or a solution with magnesium chloride.

But perhaps the biggest change is in Forness himself. Modern traning has made him and other plow drivers more aware of the harmful effects salt can have on the environment.

"There are times you have to cheat a little bit just because of the conditions and the weather," he said. "But for the most part it's reduced it and everybody's aware of what they're doing more so than before."

Since 2009, Plymouth has cut its salt use by more than half. But the amount of salt in the watershed hasn't gone down much at all.

"It's going to take a long time before we're actually going to start to see the level of chloride come down in our water bodies," said Brooke Asleson with the Minnesota Pollution Control Agency.

She said chloride seeps into the ground — and into shallow groundwater. Depending on the soil, that salt can hang around for a long time.

"So there could be chloride from five years ago, 10 years ago that's we're still seeing kind of making its way to our water bodies through kind of subsurface flow," Asleson said.

Two plow trucks take to the streets in Plymouth, Minn.
Two plow trucks take to the streets in Plymouth.
Evan Frost | MPR News

Even if we quit using road salt today, it would take decades for that chloride to be flushed out of the system.

And because it takes so long for water bodies to recover, scientists say the best solution is starting now to change old habits — like getting snowplow operators to use less salt.

But Forness said getting drivers to change their expectations of dry roads is a tougher battle.

"I think there are some that are aware. For the most part no, they just want the roads cleared," he said. "And it is a safety concern because people just don't slow down."

This is the third in an occasional series of articles on road salt's effects on the environment as part of The Water Main, our new initiative that aims to bring people together, move conversations forward and create meaningful connections that help sustain clean, abundant water for all.