Road salts keep drivers safe in snowy and icy conditions. Chemicals like Sodium Chloride (Rock Salt) or Magnesium Chloride work by lowering the temperature at which water can freeze. But come Spring as snow melts, chlorides are making their way into streams and groundwater around the country where they stay. Removing them is difficult and costly. Are we trading mobility for environmental degradation?
Jamie: When the snow starts to fly in Colorado, skiers get giddy with excitement. And others hunker down waiting for Spring.
Frani: But for Chris Brewer, it’s showtime. He’s a plow driver for the Colorado Department of Transportation or CDOT, and he’s letting us ride along in his vehicle and as luck would have it, we’re in the middle of a sizable snowstorm.
Chris: We’re westbound at the 259 getting on I-70 and it’s snowin’ moderately. We’ve had crews out for the last forty-eight hours and our road conditions are pretty good.
Jamie: As the lead of his patrol, Chris is communicating with six other trucks who are working in tandem to maintain this segment of highway in the foothills above Denver.
Frani: And we’re not putting anything down...We’re specifically just clearing the road surface?
Chris: Correct. Right now. All we use material for is traction and to get the pack off the road. That's what we don’t want on the road.
Frani: We’re traveling in the right lane and cars are passing us on the left. At this point the road is now clear down to pavement, so Chris will have the truck apply a liquid product to prevent the next round of snow from sticking.
Chris: Right now I’m shooting out my left sprayer and my center sprayer. I’m shooting the left land and the center lane at the same time. Now watch these people will drive right through the middle of it. They don’t care if it hits their car...
Jamie: “It” is magnesium chloride. The state of Colorado, along with most states in cold climates, do a balancing act of what chemicals to put down on roads to keep drivers safe, but reduce the impact on the environment.
Dave Wieder: Magnesium chloride in our opinion, was the lesser of the three evils that we had to choose from.
Jamie: That’s Dave Wieder, maintenance and operations branch manager. Before we went out with the plows we met him at CDOT headquarters in Denver and he’s showed us a Powerpoint presentation that lays out the pros and cons of three chlorides commonly used for snow removal.
[ Dave describing salts ]
Jamie: Mag chloride has the benefit of being able to melt ice at lower temperatures, has potentially lower impacts on the environment and is less corrosive than rock salt, so it gives CDOT more bang for the buck.
Dave: And you can see that magnesium chloride clearly outperforms everything so being good stewards of the taxpayer dollars we went with the magnesium chloride.
Frani: But in the eyes of many industry watchers, chlorides are economical only if you’re looking at purchase price. There are indirect costs such as corrosion to bridges and cars, and the longer term costs to remove or remediate salts that accumulate in surface and groundwater. According to a scientist who’s studying these issues, as human beings our attention is too focused on the short term.
Xianming Shi: But if we look at a longer time window our grandchildren will be drinking much saltier water.
Jamie: That’s Xianming Shi. He’s the Assistant Director of the Center for Environmentally Sustainable Transportation in Cold Climates (CESTiCC). His group is trying to find more sustainable products to put on our roads.
Xianming Shi: These chlorides, they are not degrading. They stay in the environment and eventually at least half of them goes down to your groundwater and aquifer and stays there. And there’s no turning back because we’ll keep adding more. They’re very difficult to remove.
Frani: And this problem isn’t confined to Colorado. Road salts are used in thirty states across the country and for good reason. They reduce traffic accidents by a whopping 87%. And according the American Highway Users Alliance in some snow belt states, the daily economic costs of road closures can reach as high as $300-$700 million. Even slowed traffic causes economic damage, so salts, with their negative consequences do keep people safe, communities mobile and businesses humming.
Jamie: But what is clearly a good winter solution is creating a year-round problem. Several studies including one from the USGS just a few months ago suggest that chlorides infiltrate groundwater during the winter and are slowly being released into streams throughout the year. That means that long after the snow has melted, the impacts of treating roads is getting into high gear.
Frani: What’s more, Steve Corsi, who led the USGS study said that at many of the streams, concentrations have now exceeded those that are harmful to aquatic life.
Jamie: And maybe impacting human health, too. In many cities across the Midwest and on the east coast, drinking water wells are steadily becoming more salty. While chloride isn’t toxic to humans, if you’re on a low-sodium diet you might be consuming more salt than you realize.
Frani: So what to do about this snowball effect? Dr. Shi says there are two ways forward: The first is to incorporate agricultural products as additives. Things like beet juice or leftover cheese brine that can make salts more powerful, yet less corrosive. There are even tests under way to use winery byproducts. And then there’s the potent idea of using barley residue from vodka distilleries...
Jamie: If less is more when it comes to salts, Dr. Shi says the second thing to do is add technology to make de-icing more precise. Cities are using systems that integrate weather data and road sensors to help drivers know what to put down and when. New Smart snowplows, not only read temperature but also measure residual salt from previous applications, helping operators apply less in later runs.
Frani: Back in the truck with Chris, he’s showing us his dashboard full of knobs, buttons and computer screens.
Chris: I’ve got a sensor on my truck that reads ambient temperature and then road temp.
Frani: We’re driving in a diagonal formation across all three lanes of the highway,
and an SUV comes along side of the truck and it nearly strikes us trying to pass between two plows.
Chris: Slow down, Henry...Slow down, Henry...
Frani: Oh my god. I’m amazed he made it through there! Wow.
Chris: Oh yeah...he was close. He probably came within two feet of both of our plows. I’m glad you got to see that. Because down the road I’ve seen it many times, the car that’s gone around me is in a ditch, or upside down.
Jamie: So although highway departments are committed to making our roads safer, and protecting the environment, there will always be an impatient few making that mission more challenging. 💧