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Preventing slick roads gets more scientific

Scott Sippel is a plow driver for the Minnesota Department of Transportation, and last week's storm was a perfect opportunity to see how he decides what to apply to the pavement.

A loader fills a plow with salt at the Minnesota Department of Transportation's truck station in St. Paul on Tuesday. Elizabeth Dunbar / MPR News 90.3 FM
A loader fills a plow with salt at the Minnesota Department of Transportation's truck station in St. Paul on Tuesday. Elizabeth Dunbar / MPR News 90.3 FM

Scott Sippel is a plow driver for the Minnesota Department of Transportation, and last week's storm was a perfect opportunity to see how he decides what to apply to the pavement.

"Right here I have my gauges," he explained to a passenger Tuesday. "I have my air temperature, says 36 here, and my road temperature is 34. It's good to know if it's going to freeze to the road or what."

If it's warm enough, crews can apply salty brine ahead of a storm. The liquid helps prevent the pavement from icing up and also helps reduce the amount of salt that might be needed after the snow starts falling.

Sippel goes through training every year aimed at optimizing the amount of salt plows put on the road. Doing so helps the state save money and minimize the amount of salt that could reach lakes and streams.

"It's more of a science than what it used to be," said Craig Eldred, public services director for the city of Waconia, Minn., just west of the Twin Cities.

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Local public works officials say Fargo-Moorhead road crews are also more precise than they were in decades past. Fargo aims to use the least amount of salt necessary, Fargo Public Works supervisor Lee Anderson said.

"We calibrate all of our sand trucks and our anti-ice trucks," Anderson said. "We aren't just dumping it willy nilly. When we put liquids on the roads we apply 50 gallons per lane mile. With our salt trucks for normal winter conditions above 15 degrees, we apply 200 pounds of salt per lane mile."

Brine used in the Fargo area also has a local touch when temperatures dip below 15 degrees. When it's that cold, straight salt brine is no longer able to melt snow quickly enough to be effective. So Fargo and Moorhead mix salt brine with a sugar beet byproduct and sand for added traction.

"The salt brine is 77 percent water so we have to be careful in our part of the country," Anderson said.

The carbohydrates from the beets lower the temperature at which the solution freezes. Any carbohydrate can be used, but local road crews get their carbs from sugar beet processing plants.

"They use other carbohydrates in other areas. Here, beet juice is king. It is readily available and cheap for us to use," Moorhead Public Works Director Steve Moore said.

In the event of extra-cold temperatures, Moorhead keeps a special solution in reserve for bridges and underpasses. It freezes at a lower temperature than the normal solution, but is more expensive so they use it as infrequently as possible.

"We also have some treated salt that we use at lower temperatures," Moore said. "We save that for the bridges. We have that in reserve if the temperature gets really low to treat the bridges and underpasses."

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Eldred, who has 20 years of experience in the industry, said MnDOT and cities like his are using real-time weather and road-condition data to help plow drivers make better decisions about how to treat the roads.

Keeping track of salt use year to year means always getting better, he said.

"If you have good data you can really be on the forefront and make some changes," Eldred said.

It's not just about lowering maintenance costs. Cutting back on salt is also good for the environment, because when it makes its way to lakes and rivers, as the pollutant chloride, it can harm fish and plants.

Moore said he doesn't think road treatments have much environmental impact in Moorhead.

"Any pretreatment or salt can go into the storm drains, but it is not an amount that has any lasting impact," Moore said. "By the time it goes through the storm drains it is so diluted that there won't be much impact."

The bigger concern, he says is limiting the use of sand, allowing the least amount possible to enter storm drains. Buildups of solids in the storm drain can cause water to back up and impede road drainage.

"Having solids in the storm drains causes problems," he said. "If you use less sand, you have to do less cleanup."

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But state officials consider about 80 bodies of water in the Twin Cities metro area too salty or at risk of being too salty. They hope better training and technology will help plow drivers keep that number from rising.

Brooke Asleson of the Minnesota Pollution Control Agency pointed out that chloride can't be removed from a lake.

"The only way for us to address this pollutant is through prevention," said Asleson, a project manager in the watershed program at the MPCA.

She'll be speaking Thursday at an annual road salt symposium - the 15th year environmental advocates have met with the road maintenance industry to find the right balance between treated roads and clean water.

This year, attendees will talk about climate change and will hear from University of Minnesota climatologist Mark Seeley about Minnesota's warmer, shorter winters and wetter conditions.

Asleson said the state will need to collect more data to know whether climate change will mean applying more or less road salt. It's not as simple as applying more salt when there's more snow.

"There's not a direct correlation, because salting events are not any one weather condition," Asleson said.

Besides snow, workers must contend with refreezing, black ice and frost. And with warmer winters, Minnesota might see more freeze-thaw events that make roads slick.

Despite the uncertainty, environmental advocates are pleased with the progress so far. The old method of "applying salt by gut feel" is a thing of the past, said Steve Woods, executive director of the Freshwater Society, which is organizing the road salt symposium.

Forum reporter Adam Watts contributed to this report.

Related Topics: WEATHER
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