'Permanent pollutant': Salt to melt ice on streets posing growing risk to Minnesota's lakes
MOORHEAD — Salt applied to streets and roads to melt snow and ice is becoming a growing environmental concern in some areas of the country, including Minnesota, where 50 lakes are listed as impaired because of their salt levels.
Street and highway maintenance supervisors are aware of the problems that can result from the salt their crews deposit on roads, and have adopted new methods in recent years that help to reduce salt runoff as well as their operating costs.
"We're trying to reduce salt usage on a continual basis," said Kohl Skalin, who supervises road maintenance for the Minnesota Department of Transportation's 12-county Detroit Lakes district, which has 3,604 lane-miles to maintain.
Salt is expensive, though it remains the most cost-effective substance for melting snow and ice, giving street and highway superintendents a strong incentive to minimize use.
"Salt's a high dollar value," Skalin said.
Most of Minnesota's waters that are impaired by chloride, a component of salts, are in the seven-county Twin Cities metropolitan area, where the greater density of roads and higher traffic volumes require greater salt use, said Brooke Asleson, salt prevention program coordinator for the Minnesota Pollution Control Agency.
"But we do have some impairments in northern Minnesota," as well as a couple in southern areas, she said. In Greater Minnesota, with lower traffic volumes than the Twin Cities, "I would say it's not as likely to be as significant a problem," Asleson said.
But the state is mounting a public awareness campaign to try to keep chloride levels from becoming a problem. In Madison, Wis., drinking water wells have become contaminated with high levels of chloride, she said.
"It's toxic to marine life," Asleson added. "Once it gets into our water, there's no way to remove it, so chloride is basically a permanent pollutant."
The DOT has not received any notifications of chloride-impaired waters in the Detroit Lakes district that includes Clay County, Skalin said.
North Dakota's water monitoring program has not detected chloride levels above water quality standards, said Mike Ell, who oversees water quality for the North Dakota Department of Health.
"Generally, it's more sulfate issues than it is chloride," he said.
Sulfate, another salt, occurs naturally in the soil in some areas of the state, including the Turtle River, Park River and Forest River in northeast North Dakota, the result of seepage from artesian springs.
Salt in waterways from road salt has not yet been a problem in the state, Ell said.
"The bottom line is we haven't seen concentrations of chloride in our streams that exceed our standards," at least in the past decade or so, he added.
Road maintenance crews in Minnesota as well as the North Dakota Department of Transportation and the city of Fargo, among others, have equipped their sanding trucks with automatically controlled spreaders. The technology helps to reduce the amount of salt required to keep roads safe, officials said.
"We are really a minor player, I would say, in usage of salt," said Ben Dow, director of operations for public works in Fargo. Various methods have allowed city street crews to significantly reduce usage over the years, partly because of environmental concerns, he said.
"We're very aware of the situation," Dow said, adding that curbing salt use has been a goal of public works operators for years.
Fargo's sanding trucks are calibrated to deposit 200 pounds of sand per lane-mile, which Dow estimates is one-fourth or one-fifth of the level commonly used in the Twin Cities. Fargo orders 3,000 tons of salt per year, but doesn't always use that much, he said.
Also, Fargo, the Minnesota DOT and others apply a salt solution on streets and roads before a snowstorm so the snow doesn't stick and is easier to remove, further helping to reduce salt usage, Dow said.
In temperatures colder than 10 degrees, and especially in subzero cold, salt won't melt snow. Additives, including beet juice, can enable salt to work in colder temperatures. Fargo now uses a different solution, which Dow said works better than beet juice. Although natural, beet juice isn't without its own problems. High levels in waterways can deplete oxygen.
Another common technique is to add salt to a slurry mix, a thick liquid that has the consistency of a mud pie that adheres well to roads, said Mike Kisse, who supervises the maintenance division at the North Dakota DOT.
Kisse and Skalin said the motoring public expects to drive on dry, safe pavement, and people complain when they don't think roads and highways are adequately salted.
"We try to provide the service level that the public is demanding to provide safe conditions for the public," Kisse said. "North Dakota historically has been very conservative in its chloride usage. We try not to over apply."
The Minnesota Pollution Control Agency conducts classes for road crews and private contractors with tips to minimize salt usage while effectively maintaining surfaces, Asleson said. The aim, she added, is "to use as little as possible to get the job done."
Minnesota is trying to be proactive to avoid problems like those in Madison. "We don't want to wait until the water tastes salty," she said.