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Science and Innovations

Snow Season in Flagstaff Pits Ice-Free Roads against Ponderosa Pines

Melissa Sevigny

Chemical deicer is commonly used to keep roads clear of snow and ice, and it makes travel safer. But it also kills ponderosa pines. The City of Flagstaff found that out when they experimented with deicer a few years ago. From the Arizona Science Desk, Melissa Sevigny reports on the tradeoff between public safety and environmental health . . . a tradeoff few cities in the nation have to make.

Credit Melissa Sevigny
Snowplows at ADOT's Flagstaff Maintenance Yard

A row of yellow snowplows fills the long warehouse at the Flagstaff Maintenance Yard. Nearby are giant heaps of what looks like pink sand. It’s actually a salt compound called Ice Slicer. Snowplows sprinkle it on the road and it lowers the melting point of water, turning the ice slushy. That makes roads easier to plow—and safer to drive on.

Credit Melissa Sevigny
This snowplow was decorated by Cub Scouts last year

“The deicing products have really proven to be the most effective solution to clear that snow and ice off the roadway,” says Dustin Krugel, spokesperson for the Arizona Department of Transportation.

In 2007 Flagstaff officials switched from using volcanic cinders on roads to the chemical deicer. At first, the results were promising. Traffic accidents dropped between 10 and 30 percent over the next few years. Then the city’s wildland fire manager, Paul Summerfelt, noticed green needles turning brown on ponderosa pines along the streets.  

Credit Melissa Sevigny
ADOT's Salt Barn is filled with chemical deicer

“It was fairly evident that we were seeing a correlation between the use of that chemical and the resulting damage to the trees,” Summerfelt says. “There was a very valid public safety reason for using it, but there was then also a cost.”

Credit Mary Lou Fairweather
Severe deicing salt damage on ponderosa pines south of Flagstaff

And that cost was dying ponderosas—“hazard trees, in our view,” Summerfelt says. “They were going to fall on the road eventually, and we needed to address that issue and remove those.

Summerfelt wanted proof the deicer was harming ponderosas, so he turned to Mary Lou Fairweather, a tree disease expert with the U.S. Forest Service. “It’s basically a no-brainer that the deicing salts are contributing to these impacts on the trees,” she says.  

Credit Mary Lou Fairweather
Brown-tipped pine needles are classic symptoms of salt damage

Fairweather conducted a study on the effects of deicer on roadside ponderosas. She tested the needles of brown trees and found levels of sodium and chloride – the ingredients of salt – that were as much as six times higher compared to green trees. “Our study contributed to ADOT, the County and the City being able to see that the salts were indeed contributing to tree mortality,” she says.

Fairweather says Arizona doesn’t get enough rain to wash the deicing salts away, so they build up in the soil . . . a phenomenon that happens in few other places in the country.

Credit Melissa Sevigny
The City of Flagstaff's cinder pile on Cedar Hill
Credit Melissa Sevigny
A snowplow on Route 66

To strike a balance between environmental health and public safety, local officials stopped using deicer and switched back to cinders in 2013, though ADOT still uses deicer on state highways.

“We’ve historically used cinders in Coconino County,” says Andy Bertelsen, director of Public Works for the county. “It’s a resource that we’ve utilized to allow for that traction on the roadway after the snow is plowed.”

Cinders are friendlier to the environment than salt or sand, and they’re a local resource, Bertelsen says. But it takes a lot of labor to put them down and sweep them up again—and that drives up the cost. And cinders don’t work as well as deicer on high speed roads.

Bertelsen says there’s no easy answer. “Any decision you made there’s a positive and a negative. There’s nothing that going to save us from winter driving conditions other than ourselves.”

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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