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De-icing: What does city and county use?

... And what effect does it have on environment?
A Colorado Department of Transportation snowplow works along U.S. Highway 550 north of Durango. (Durango Herald file photo)

When snow and ice strike the streets and roads of Durango and La Plata County, about the only thing that stands between a safe commute and a wintry demolition derby are the road maintenance crews who plow roads, and spread sand and de-icing agents.

It is the de-icing agents that raise environmental-minded eyebrows and beg the questions – what agents are being used and what effects do they have on the environment?

The first part of the question is simply answered. The state, county and city of Durango all use sand derived from crushed rock. Durango and the state also use magnesium chloride and Ice Slicer. La Plata County skips the magnesium chloride and relies on Ice Slicer.

The second part of the question is trickier in that it goes down the proverbial rabbit hole of degrees – as in how much is too much, resulting in harm to water, plants and animals – and how little is enough to make roads safe without harming the environment?

Again, the simple answer is that too much de-icer will damage the environment and those who live in it – while smaller and diluted amounts that city, county and state officials say they use – are monitored to assure they are not harming the environment.

“Through our stormwater management program we are very conservative in our use of magnesium chloride,” said Allison Baker, Durango’s public works director. “We have a stormwater master plan and an MS4 permit through the state that requires pretty much continuous monitoring throughout the year. And we monitor at multiple points throughout the city.”

Municipal separate storm sewer system (MS4) permits are issued for discharges of urban stormwater into streams, rivers and lakes. The process is designed to keep Colorado waters clean enough to support recreational use and aquatic life.

Magnesium chloride can be extracted from brine or seawater. It is an inorganic compound in the salt family. It is used for low-temperature de-icing and helps to prevent ice from bonding with pavement, allowing snowplows to more easily clear roads.

A research paper published by the Colorado Department of Transportation in 2001 said magnesium chloride may contribute to the mobilization of trace metals from the soil to surface and groundwater, but noted that field evidence of this impact is limited. There is also the potential of increasing the salinity of rivers, streams, lakes and groundwater. Chloride de-icers also have the potential to cause oxygen depletion of streams near roads where they are applied and can result in mortality of fish and other aquatic organisms. However, the dilution estimated to occur from the roads to the streams reduces the likelihood of these effects.

The paper says chloride-based de-icers can damage “terrestrial vegetation” to a distance of 650 feet, but magnesium chloride does not attract wildlife because the main chemical attractant is sodium.

“A few years back, CDOT completed a study into the effects of magnesium chloride on the roadside environment and found that the product does not significantly harm aquatic or plant life,” CDOT representative Lisa Schwantes said in an email to The Durango Herald. “CDOT requires all vendors and suppliers of liquid road treatment products to meet the specifications designated by its research.”

La Plata County does not use any liquid de-icing agents such as magnesium chloride, said county Road Maintenance Supervisor Mike Canterbury.

“La Plata County uses an environmentally safe product called Ice Slicer,” he said. “We mix 10% Ice Slicer into our sanding material. We do use Ice Slicer at 100% on isolated areas such as dangerous hills, curves and intersections.”

Ice Slicer is touted by one supplier, Envirotech Services Inc. as a more environmentally friendly alternative to road salt because less is needed, resulting in fewer chlorides in the environment. They describe it as a “complex red salt that contains sodium chloride, calcium chloride, magnesium chloride, potassium chloride and inert ingredients like clay.”

Durango uses both magnesium chloride and Ice Slicer because they actually serve different purposes, Baker said.

“Ice Slicer we use as related specifically to traction, whereas magnesium chloride is used to prevent ice from accumulating and to help us be able to remove it when plowing,” Baker said. “So they’re not equivalent products.”

Both Baker and Joey Medina, who is in charge of streets in Durango, are new to their positions, so pinning down how long magnesium chloride has been used in Durango will take more research, Baker said. But it has been used for at least the past three years that she is aware and used commonly across the U.S. for the past 10 years.

“Magnesium chloride is an alternative to salt,” Baker said. “It does much less damage to vehicles over the course of time than say sodium chloride, which used to be used. This is not a new technology, this is very much in place throughout the country. It’s very effective.”

La Plata County’s current contract cost for Ice Slicer is $126.40 per ton when mixed with sand. The county used 200 tons last winter. Baker and Medina didn’t have those numbers broken down to indicate the application or mixing process but said they will next year. They did provide purchasing data showing magnesium chloride costing a $1 a pound and Ice Slicer at $104.50 per gallon.