There’s too much salt getting into our rivers and streams.
A new study in the Proceedings of the National Academy of Sciences finds over the past 50 years, freshwater systems across the country have become saltier, and that can cause problems for people, wildlife and our infrastructure.
Gene Likens is an author of the study. He's a research professor at the University of Connecticut and president emeritus of the Cary Institute of Ecosystem Studies.
He says this excess salt is coming from a variety of sources.
"Road salt is one big factor in the wintertime. We just had a big blizzard here on the east coast last week, and massive amounts of road salt were added in order to try to make the roads safe for drivers," he says.
The study found agricultural fertilizers, mine drainage, fracking brine, and sewage also contribute salt to freshwater systems, depending on the region of the country.
The researchers used data from 232 monitoring sites from the U.S. Geological Survey, and they found "37% of the drainage area of the contiguous U.S. experienced a significant increase in salinity." A recent study from the Global Lake Ecological Observatory Network found North American lakes are getting saltier too.
Likens says there are many implications of what he calls "freshwater salinization syndrome."
"The effects on the system can be large if the increases are large. Many organisms are unable to tolerate the higher concentrations, even we as humans. If the salt gets into the groundwater, it may contaminate wells or lakes adjacent to these roadways," he says.
Likens says excess salt can also harm infrastructure.
“At high concentrations of these substances: calcium and magnesium, sodium and potassium, it can become very corrosive. And so the inside of pipes and aquaducts and whatnot might be corroded, the surfaces of concrete roadways may be corroded, dissolved away, literally,” he says.
So what do we do about this?
Likens says we have to keep our roads safe in the winter, but he says there are ways to cut down on salt use.
“There are other forms of de-icers that could be used. Potassium acetate is usually added in liquid form. It’s much more expensive, but it’s much less corrosive, and if you consider all the impacts that road salt, sodium chloride, does and you add up all those costs, it may not be that much more expensive," he says.
The Cary Institute of Ecosystem Studies lists some options for managing road salt pollution:
Some strategies for managing road salt pollution already exist, as outlined in the Cary Institute report Road Salt: Moving Toward the Solution. They include pre-wetting salt to allow it to stick to roads, using brine to prevent ice from forming on road surfaces, reducing the salt content of sand, and using pavement sensors and weather information systems to guide salt application.
In Michigan, of course, we use a lot of road salt in the winter.
Mark Geib is the engineer of operations for the Michigan Department of Transportation.
“Really our top goal is the safety of the motoring public. So with that in mind, of course, is a reality of being prudent in how we do a lot of what we do, including the usage of salt,” he says.
He says pollution from salt is a big concern. He says they do several things to use no more salt than they need.
That includes using special spreaders, driving trucks more slowly so more salt stays on the road, and pre-wetting salt with a brine.
“It makes it so when we dispense it onto the roadway, it doesn’t bounce as much and sticks to the pavement. And also we try to drop it right where it's actually needed on the pavement, so it's getting it right where it needs to be, and so ultimately then you can use a little bit less," he says.
Geib says the brine treatment also helps the salt do its job of de-icing faster, so it's also better for safety reasons.
Here's a list of MDOT's salt management initiatives from spokesman Jeff Cranson:
— Bounce and scatter study. Completed a few years ago and as a result, MDOT engineers determined that driving slower (25 MPH range) when salting keeps almost all the salt on the road (no waste). So an operator drives slower when it can be safely done, and that conserves salt.
— Innovative, more efficient equipment such as zero-velocity spreaders and salt-slurry spreaders that conserve salt and keep more on the road.
— Development of a Maintenance Decision Support System (MDSS), which includes using sensor and weather data to provide real-time information to plow operators as to the best rates and proper amounts of salt to put down depending on pavement and weather conditions. This increases efficiency and service levels while reducing salt usage.
— Pre-wetting salt with brine solutions so more salt stays on the road where needed and activates more quickly.
— When appropriate, anti-icing ahead of storms when conditions are right to then ultimately have less need for anti-icing later and after a storm.
— Interaction with other state DOTs, AASHTO and organizations like Clear Roads to share best practices and innovations and exchange new methods and materials.
— On-going training for our plow truck drivers in both sound practices and the environmental effects of salt so they understand the importance of using salt judiciously.
MDOT's Mark Geib says there are good alternatives to road salt but they’re more expensive. He says in Michigan, we already spend around $25 million a year just on salt.