Road salt spreading into our water

Paul Sancya, Associated Press

Loading road salt.

Professor says U study is a "wake-up call" to adjust deicing before it creates a significant problem.

By TOM MEERSMAN, Star Tribune

Last update: February 10, 2009 - 10:59 PM

Rain and melting snow in the Twin Cities have flushed away road salt residue from hundreds of streets and tens of thousands of cars. But that might not be a good thing.

Now a University of Minnesota study estimates that 70 percent of the deicing salt used on metro-area roadways does not travel far when it drains off the pavement. It gushes into area wetlands and lakes and seeps into groundwater, and it is making them saltier with each successive year. About 30 percent goes to the Mississippi River.

"This is a wake-up call," said Heinz Stefan, a civil engineering professor at the university's St. Anthony Falls Laboratory. "Fortunately we don't have an acute problem right now, but we may have a significant problem in 50 years with groundwater if we keep on doing this."

The use of road salt is no small matter. Snowplow drivers apply nearly 350,000 tons of it in the greater metro area each winter, said Eric Novotny, one of the researchers who tracked movement of the salt using state data.

He found that salinity in 39 metro-area lakes has increased steadily over the past 22 years, following a similar increase in road salt purchases by the state of Minnesota. The researchers also analyzed salinity in three major rivers, 10 tributaries and numerous wells near roadsides.

The salt solution that enters lakes is denser than water and forms a layer just above the bottom, said Novotny. That can potentially change the water chemistry enough to kill aquatic insects and change plant growth.

Five creeks are too salty

Glenn Skuta, manager of the watershed section for the Minnesota Pollution Control Agency, said that chloride is an emerging issue in the metro area. "Yeah, this is a problem," he said. The agency worked with city, county and state officials years ago to cover salt piles and prevent erosion, and more recently on ways to use less salt.

Skuta said that five metro-area creeks are listed as impaired because their salt levels are too high: Minnehaha Creek, Nine Mile Creek, Bevens Creek, Shingle Creek and Battle Creek. The creeks have chronic levels above the state standard of 230 parts per million -- equivalent to 1 teaspoon of salt in 5 gallons of water.

That may not be enough to taste, Skuta said, but it's enough to affect the bugs and plants needed by fish and waterfowl.

The MPCA is studying the creeks to determine how much the salt levels need to come down and how that can be accomplished.

Reining in road salt

Beverly Farraher, maintenance engineer for the Minnesota Department of Transportation metro district, said the agency has made steady improvements in reducing the amount of road salt needed to keep roads clear. Crews apply anti-icing chemicals in many areas before a snow and ice storm, she said, and they spread de-icing salt after plowing to melt the residue.

Usually, 200 to 300 pounds of salt per mile for two lanes is used, Farraher said, although it can be more, depending on pavement temperature, storm severity, time of day and other factors.

"We try not to simply put down salt indiscriminately," said Farraher. "We try to do the mechanical removal of plowing and use salt to take care of the last bit." She said that the agency has been educating snowplow drivers about the latest equipment, chemicals and techniques for minimizing salt use while treating treacherous roads.

The study shows that the Twin Cities seems to have a much higher salt-retention rate than do Chicago and Toronto, where smaller salinity studies have been done, Stefan said.

The reason may be that Minnesota has so many more wetlands and lakes, he said. Stefan said the metro-area system routes storm-water runoff to those areas. That system may need to be changed during winter and spring melt to capture some of the salt.

Glenn Strand, board member of Citizens for Minnehaha Creek Corridor, said he's concerned about the amount of salt that city workers spread on parkways and trails near creeks and how much homeowners use on sidewalks. The university is rightfully concerned about water quality, he said, but salt also has corroded bridges and rusted the bases of traffic lights and street lamps along parkways.

Tom Meersman • 612-673-7388

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