State's roads aim for low-salt diet

  • Article by: JIM FOTI , Star Tribune
  • Updated: January 2, 2010 - 10:04 PM

Amid concern over harmful effects of salt, plow drivers get creative -- and get results.

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The city of Prior Lake has been spraying some of its roads with "supermix."

Photo: Richard Tsong Taatarii, Star Tribune

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Can a lake-loving state with snow-cursed highways go on a low-salt diet?

Joe Wiita in Prior Lake thinks so, and he'd like your city to mix up a batch of his anti-icing cocktail and try it on a street near you.

Amid rising concern over the effects that road salt has on Minnesota's lakes, streams and groundwater, Wiita and other public works officials around the state are whipping up new brews to spread on pavement, moistening rock salt so it sticks better, and working to establish a less-is-more culture while striving to keep motorists safe and happy.

The stakes are high in places such as Prior Lake, a city with 14 lakes. But the impacts are statewide -- an unavoidable result of decades of dropping a pound of salt onto every 10 feet of highway without much concern.

Now, in addition to the environment, money has become a key motivator. Public works departments are caught in the same funding squeeze as everyone else, making creativity and technology key players in changing the rules in the fight against winter.

Dialing it down

You probably think of salt in pinches or teaspoons, or perhaps in terms of the amount of rust on your car. Snowplow drivers, however, measure in pounds per mile -- those are the settings in the cab of the truck.

"Pre-wetting" the salt -- spraying it with brine as it's dropped -- helps it stick to the road better, meaning crews can cut back from 500 pounds per mile to 200 with no real loss of "customer service," said Randy Reznicek, a maintenance supervisor for the Minnesota Department of Transportation in the central part of the state.

Cutting salt use saves money in a couple of ways: less salt to buy, and fewer fuel-burning trips back to the truck station to get more. Salt is about $70 a ton, and a truck can hold 10-12 tons, Reznicek said. University of Minnesota researchers have estimated that 350,000 tons of salt are used in the metro area each year.

Pre-wetting has been around for a while, though its use is limited by the number of trucks with water tanks. Other, increasingly sophisticated tools are available to help crews get the amount of salt right.

Vehicle-mounted electronic thermometers let supervisors know how far above or below freezing the pavement is. Some truck cabs have up-to-the-minute weather radar so crews know how long it'll be before the freezing rain or snow hits.

On average, MnDOT drivers stay close to the salting recommendations made by their supervisors, Reznicek said.

Unknowingly, ordinary motorists and truck drivers also help out by redistributing the salt with their tires and the puffs of wind that are created as their vehicles whiz past. But those same factors can send the salt sailing into gullies if truckers pass what they call a "salt shaker" too fast. With the help of radios, Reznicek said, some truckers will pass more slowly.

One low-tech approach to reducing chemicals is called a living snow fence, which can be made of rows of corn or permanent landscaping and which reduce the amount of snow blown onto a road. Reznicek says that if you look at a map of crashes on westbound Interstate 94 in Stearns County, there's a crash-free gap that corresponds with the site of a landscaped snow fence.

Mixing it up

Wiita is the streets and utilities foreman for Prior Lake, which has cut its use of salt by about 60 percent in the past few years through experimentation and willpower. Salt and other chlorides still do the melting, but the key has been applying them in such a way that they stay on the road, requiring less to be distributed.

That means using brine, magnesium chloride and a sugar beet byproduct, which are mixed via a dozen yellow-handled valves marked with letters of the alphabet. The final product, which the crews call "supermix," is stored in a 6,500-gallon tank that looks like a giant Rubbermaid container.

Food-grade molasses also is sometimes used to help the salt stick, though at this time of year, it can be tricky to pump outdoors, said Wiita, confirming those rumors about molasses in January.

Last winter, Prior Lake created a "liquids only" zone -- no rock salt -- in neighborhoods where runoff flows into a small bowl of a lake called Blind Lake. Chloride levels in the lake dropped from 120 milligrams per liter to about 60 to 70, Witta said. This winter, the liquids-only area was expanded to a full 20-mile route.

"It doesn't take any more work," he said, and "we're seeing a little better results out of that area than we are any of the others." He said he gives as many as a half-dozen tours a month to workers from other government agencies.

Bringing about a change in attitude is part of the challenge in a business where it's not unheard of for a maintenance worker to give a clogged salt spinner a kick, leaving salt chunks to sit uselessly in a parking lot before flowing into the nearest wetland.

Wiita said that as his department began to favor liquid applications, "the old-fashioned guys wanted to see water running behind them," but more modest spraying is more effective than gushing.

Now, he said, "we got a great crew here. They're really apt about reducing the salt levels ... not only to save the money but the environment."

Brooke Asleson of the Minnesota Pollution Control Agency said that chlorides can interfere with the reproduction of fish and, if levels are high enough, cause the death of various kinds of wildlife. About two years ago, the agency released a list of five metro-area streams it deemed impaired by salt, and next month, when the revised list is expected, it's likely to be longer.

The MPCA is working on a multi-year study of how much less salt would have to be applied to meet the state standard, which is 230 milligrams per liter of water. "It's really complex because there's so many different water bodies, and everybody uses different amounts, and the timing really has a big impact."

Once the salt reaches water, especially a lake, it tends to stay there. "There aren't any organisms or fish that would break it down or degrade it so that it would go into a less toxic form," Asleson said.

Private impact

Driveways, parking lots and other privately owned parcels also receive tons of salt every year. The MPCA has a voluntary certification program that teaches best practices to private operators who use salt or other chemicals, and more than 1,500 drivers have been certified. (A list is available on the MPCA website.)

New Hampshire may take things a step further -- its Legislature is set to take up a bill requiring all private applicators to take a certification course. State Rep. Margaret Crisler, the sponsor, said there's a tendency to oversalt commercial areas because of concerns about liability for injuries or property damage, which is why her measure includes liability limits for certified private applicators.

Public agencies already have such limits, said Eric Williams of New Hampshire's Department of Environmental Services. He said some groundwater there is so full of chlorides that streams are contaminated even in the summer.

His state will need to cut chlorides in some watersheds by 45 percent to get to acceptable levels, Williams said. The key, he said, is to put down "all that you need, and not more."

Jim Foti • 612-673-4491

  • related content

  • Joe Wiita is a maintenance worker for the Prior Lake Public Works department.

  • SALTY WORDS

    Anti-icing: Putting brine-based solution on a road before ice or snow have a chance to adhere to the pavement. Pre-wetting: Moistening rock salt with brine so it adheres instead of bouncing over to shoulders or grassy areas. Supermix: What Prior Lake officials call their anti-icing solution, which is 80 percent brine, 10 percent Geomelt (a sugar beet byproduct) and 5 percent magnesium chloride solution. Calcium chloride and magnesium chloride: More expensive salts that are more effective at lower temperatures than regular salt.
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