3M and PFC groundwater contamination in Minnesota

Winter road salt ending up in lakes and streams

Snow plow
A new report from the University of Minnesota says we're slowly turning our fresh water lakes into salt water.
MPR Photo/Bob Kelleher

Heinz Stefan and his research team measured the salt content of 39 metro-area lakes. They found that over the last 24 years the salinity has been increasing. You might think the salt would just run off and travel down the Mississippi River to the ocean. But what they found was that 70 percent of the salt that's applied to roads in the metro area stays in the area.

It's not a strong concentration, just one-and-a-half milligrams per liter. The state standard is 200-times that much.

But Heinz Stefan is looking ahead.

"If we keep on doing this for another 50 years, we may have a significant problem," Stefan said. "Ccertainly if groundwater becomes saline, when we use that water we may have to treat it, at significant cost, by reverse osmosis, to remove that salt."

Reverse osmosis is what desert countries do to get drinking water from the ocean.

Already several streams are saltier than the state standard of about one teaspoon per five gallons of water. They include Minnehaha Creek, Battle Creek and Nine Mile Creek.

The salinity could make life difficult for the small critters that live at the bottom of lakes and streams, and that could hurt the fish. There's also a chemical reaction with heavy metals like lead and cadmium that come from our cars, Heinz Stefan said.

"They're now in soils near roadways, and when chloride is added, these heavy metals are released from the soils, which means they go back in solution in the water and are then transported where we don't want them to be," Stefan said.

The Minnesota Pollution Control Agency is studying several creeks and lakes in the metro area to try to find out how serious the problem is. Layers of saltier water can prevent the natural seasonal mixing that keeps lakes healthy, according to Brooke Asleson, who works in the MPCA's watershed program.

"Sometimes if you get lots of chloride, that changes the density of the water in the lake, which can cause it to not mix anymore, which causes a problem for the natural cycle of that lake as well as all of the organisms living in the lake," Asleson said.

The MPCA has mounted a training program to get road crews to use less salt. After training at the University of Minnesota, workers cut the amount of salt they used by 40 percent, saving $50,000 in one year.

Highway crews are using various techniques to cut down on the salt, according to MnDOT spokesman Kevin Gutknecht. They often lay down a thin layer of salt before a storm, so ice doesn't get a chance to form in the first place. They also mix salt and sand with water so it will stick better. Updated equipment applies the salt more efficiently, he said.

"It's an issue of better equipment, better training, better awareness," Gutknecht said.

The MPCA urges homeowners to use salt judiciously. When it's colder than 20 degrees, salt won't melt ice. That's when you work out some of your frustrations with the chipper.

We may need to adjust our expectations. Instead of thinking we should be able to drive anywhere two hours after it snows, Heinz Stefan said, we should be willing to close businesses occasionally as well as schools.

"We sit at home and drink tea, and wait till things get better naturally, in a few hours or a day, and ultimately I don't know what the economics of it are, but I would like to study them," Stefan said.

Instead, he's trying to learn in more detail how the salt might affect the natural systems in area lakes.