Snow and sleet continue to fall across huge swathes of the U.S., and the national supply of road salt is running low. New York has declared a state of emergency, while Wisconsin, Illinois, Indiana, Pennsylvania, and other states have also disclosed their difficulties in covering streets and sidewalks amid a long-running cold snap. What exactly is road salt and where does it come from?
The U.S. first began using salt on roads in 1938, and now spreads between 10 million and 20 million tons annually, according to the Cary Institute of Ecosystem Studies. Heavy salt deployment helps save drivers and pedestrians from icy dangers but isn’t without hazards of its own: The salt used on roads is also partly responsible for the potentially harmful increase in the salinity of our water. The U.S. is the second-largest road salt producer worldwide after China, accounting for an estimated 15 percent of world output in 2013, according to Roskill Information Services.
American companies like Morton Salt and Cargill get their rock salt from mines as well as evaporated salt plants and solar salt operations. Cargill’s salt, for example, comes from Kansas, Louisiana, California, Oklahoma, and New York, which has some of the country’s largest underground salt mines in which workers blast enormous walls of salt before processing the crystals down to size.
With salt reserves running low, companies are now struggling to keep up with orders. “We are working overtime in our mines to try and keep up with demand,” said Cargill spokesman Mark Klein in an e-mail. “In addition to widespread demand, the weather is affecting transportation, slowing trucks, trains and barges.” Desperate states and municipalities are already paying a premium for emergency deliveries. Whereas the Ohio Department of Transportation reported paying only $36 per ton this past summer, it recently shelled out $72 per ton for an extra delivery.
Road salt—also called rock salt (PDF)—is made of granular sodium chloride, the same chemical that’s in table salt. It works by lowering the freezing point of water, often by enough to melt existing ice. A solution with 20 percent salt, for example, freezes at 2F. Even when temperatures are too low for the ice to melt, salt still provides some traction, although it’s less effective than sand in this regard.
Some states are getting creative with alternative solutions. New York launched a pilot program to de-ice roads using beet juice, which helps stop the runoff of salt; waste from beer making would apparently do the same thing. Some New York towns have also used briny wastewater from fracking operations, which has environmentalists up in arms.
New Jersey, meanwhile, is experimenting with pickle brine, and Milwaukee in December began pouring cheese brine on its streets. “You want to use provolone or mozzarella,” Jeffrey A. Tews, a fleet operations manager for the public works department, told the New York Times. “Those have the best salt content. You have to do practically nothing to it.”