Mysterious pyramids rise up along the Fore River in South Portland. On sunny days, they glitter white and opaque, as inscrutable as alien spaceships brought to Earth. In rain, they’re covered by gigantic tarps, held down by rows of weights that resemble the terraces of Mesoamerican temples. But they’re not ancient monuments or extraterrestrial outposts. They are immense mounds of salt, thousands of tons of it, shipped from vast mines in central Chile and destined for Maine’s icy roads.
Is there a Maine winter experience more universal than finding oneself in a line of cars behind a plow truck releasing a fantail of white? Each year, Maine municipalities and state highway authorities purchase more than half a million tons of rock salt to spread across tens of thousands of miles of roads, according to the Maine Department of Transportation. There’s plenty of salt to go around: the world’s reserves are considered essentially limitless for human purposes. The trick is getting it where we need it. A staggering logistical effort, stretching across thousands of miles, keeps drivers in Maine from slipping off the roads.
For the great majority of the state’s salt reserves, it all begins in the Atacama Desert, a 600-mile–long strip skirting the Pacific Ocean in central Chile and one of the driest places on Earth. Vast salt flats cover more than a thousand square miles of the Atacama, filling a drainage-free basin, where trapped water evaporates to form huge expanses of salty desolation, bright-white deserts that stretch to the horizon. Under the flats is a salt lake containing one of the world’s largest lithium deposits.
One of Maine’s biggest suppliers, Morton Salt (yes, of the umbrella-girl table salt), harvests sodium chloride from open-pit mines on the Atacama flats using blasting and heavy machinery. The salt is then crushed there in Chile, and before it sets sail for the U.S., Morton runs it through giant sieves that sort it to meet buyers’ specifications. Maine’s highway authorities like a coarser blend, according to DOT highway maintenance engineer Brian Burne — better to cut through the thick ice that forms on the state’s roads. “You don’t want it too fine and dusty,” Burne says. “You want some fine grains to go into action immediately, but also some large grains that have some staying power and can go way down into the ice.” Maine’s highway salt passes through a series of sieves with mesh sizes from a half inch all the way down to numbered sizes — No. 1, No. 2, No. 3, etc. — that sort grains by millimeters and microns. The smallest bits in Maine’s salt cocktail make it through No. 30 and measure just 0.6 millimeters across.
All throughout the year, ships carrying tens of thousands of tons of salt run from the coast of Chile up to the Panama Canal, where they cross en route to the Gulf Coast or East Coast of the U.S. As each salt-bearing ship noses up to the Sprague Energy shipping terminal in Portland, it sets off a swarm of activity that lasts for days.
“Once we start, we just keep going until it’s done,” terminal manager Rolf Westphal says. Longshoremen work in 12-hour shifts, all day and all night, to divest a ship of what is typically some 40,000 tons of Chilean rock salt. Cranes pour the salt into a multistory hopper that transfers it into waiting trucks, which then carry it across the Veterans Memorial Bridge to a storage facility at another Sprague terminal in South Portland. At 500 tons per hour, the process takes about three straight days.
In South Portland, a few hundred yards from the bridge, construction vehicles push the salt into giant piles that loom alongside tanks of oil and clay slurry (the latter is used to make paper for glossy magazines like this one). There the monoliths remain in all seasons, with heavy loaders taking bites to feed salt-hungry highway crews. At the bottom of a pile, the pressure of 40,000 tons compresses the salt into boulders the size of paving blocks.
Longshoremen on the Portland waterfront work in 12-hour shifts, all day and all night, to divest a ship of what is typically some 40,000 tons of Chilean rock salt.
Road salt costs more the farther Morton and other companies have to carry it, but for salt shipped to southern Maine, the DOT typically pays around $60 a ton. The department’s closest salt shed is a few miles down the road from Sprague’s storage facility, in Scarborough. In the late fall, trucks shuttle between the Sprague lot and the DOT shed — and many others like it — preparing for the first snow.
Salt is, of course, corrosive. It eats away at the undersides of cars and, over time, even degrades the integrity of roads. When ice and snow melt, the runoff carries salt into ponds, streams, and groundwater, where it can endanger native flora and fauna. The 15 million tons of road salt dumped on roads across the U.S. each year are estimated to cause an annual $16 to $19 billion worth of infrastructure decay. The elevated levels of lead in Flint, Michigan’s headline-making water crisis are believed to be the result of pipes steadily corroded by water laden with road salt.
The environmental impacts notwithstanding, highway supervisors say that weather remains the main factor dictating how much salt they use. “It’s hard to set limits,” Burne says. Underdoing it can be disastrous; occasionally, highway workers underestimate how much salt to put out, allowing ice pack to form on the roads and forcing graders to hold up traffic as they inch along the highway to scrape off the lanes. When that happens, Burne says, “People just go ballistic on us. That’s the kind of situation you want to avoid.”
So highway workers judge as best they can how much salt to use based on temperature, moisture, and thickness of snow. Advanced onboard computers control how much salt the trucks pour out as they trundle down the highway. As a baseline, Burne says, they might dispense about 200 pounds per lane-mile — that is, a mile in one driving lane. Mounted to the front or back of maintenance trucks, spreader machines ferry salt on conveyor belts to a hopper, which pours it into a spinner and out onto the road.
There’s not (yet) any practical substitute for salt as a de-icer. Chemically, salt lowers water’s freezing point, making it harder for ice to form. New Hampshire was the first state to start using it, in 1941, and other states caught on as the highway system was built in the later 20th century. Compared to most other states, Maine has icier roads in both its northern and coastal reaches and thus proportionally more need for salt. But the state has embraced some ways of limiting salt’s environmental impact. Pre-salting roads before a storm can reduce how much is needed. “Smart” snowplows can dole out more precise amounts. Other materials, such as calcium chloride, can increase efficiency, and sugars can help road salt and its variants stick to roadways (some states use beet juice for this purpose; Maine uses molasses).
Forward-thinking researchers envision a day when emerging technologies like solar road panels or salt-infused asphalt make the roads themselves resistant to snow and ice. Until that day comes, the salt pyramids of South Portland will keep standing, their incongruous shapes and textures reflecting an improbable journey from an arid land to Vacationland.