Road salt puts motorist safety and environmental damage in the balance
As public works directors rush crews to spread salt and keep winter roads safe for drivers, they're balancing another concern: the environment.
A teaspoon of salt can contaminate five gallons of water, and salt trucks spread about 300 pounds of salt per mile.
“Personally, in Rock County, we are concerned because runoff goes to some of our lakes and rivers,” said Ben Coopman, Rock County highway commissioner.
“I think that is a statewide concern. But the biggest reason it doesn't seem to cause anything to change is the economics of it. There isn't a cheaper, more environmentally-friendly product out there," Coopman said.
Counties and municipalities have a responsibility to maintain clear roads for drivers, said Kevin Brunner, Walworth County public works director.
“We are trying to minimize salt,” Brunner said. “It's a tough balancing act because the expectation is bare pavement … (People) expect right after a storm to be able to get to wherever they have to get to.”
Residents bear some of the responsibility because they demand snow-free roads, said Connie Fortin, owner of Fortin Consulting, a Minnesota based environmental consulting firm.
“When you call and whine because your cul-de-sac is slippery or you can't get to work in 10 minutes, those guys just dump on more and more salt,” Fortin said. “Most homeowners have no idea what is happening to the lakes, rivers and ground water, and they don't know there is a negative side to complaining.”
Road salt affects water density and nutrient levels, causing changes in aquatic animal and plant life expectancy.
A study published in 2008 by the Ecological Society of America indicates road salt could travel up to 172 miles from a highway into wetlands, decreasing the survival rate of frogs and salamanders.
“It doesn't biodegrade, it doesn't break down, it doesn't go away,” Fortin said. “Every winter we add this to our water and our lakes and our rivers and it has been accumulating for however many years we have been deicing.”
A 2010 study by the U.S. Geological Survey found that all streams studied in eastern and south central Wisconsin had elevated chloride levels that at some point in winter exceeded the U.S. Environmental Protection Agency chronic water quality criteria.
During the winter months, researchers found chloride levels greater than 10,000 milligrams per liter, higher than the water quality criteria of 230 milligrams per liter and acute water-quality criteria of 860 milligrams per liter. Aquatic animals begin to die when chloride levels are greater than 230 milligrams per liter.
“There isn't anything really out there yet that is environmentally friendly,” said Michael Sproul, Wisconsin Department of Transportation winter maintenance engineer.
“They are all chlorides of some sort, they all get into the ecosystem and pollute. The object is to use as little as possible, that is where we are trying to be more environmentally friendly. If we only use the amount of salt necessary to get the snow or ice in plowable form … then we're saving our environment," Sproul said.
THOUSANDS OF TONS
The amount of salt used each year is dependent on Mother Nature and pavement temperature. A salt truck typically drops 300 pounds of salt per lane mile. With the use of an additive, it goes down to about 200 pounds.
In the 2008-09 winter, Rock County and the municipalities it supplies used 1,612 tons of salt. The winter before, 8,685 tons were used. Last winter, 11,471 tons of salt were used, and this winter is shaping up to be about the same.
Rock County is responsible for maintaining 2,900 lane miles, the equivalent of a one-way trip to San Diego, Coopman said.
Until the mid-2000s, the county used a sand-salt mix. Now, it uses straight road salt, Coopman said.
Why not sand? Though the abrasive helps tires find a grip, when sand is mixed with salt, each reduces the effectiveness of the other. Sand can be harmful, too. An Oregon Department of Transportation study in the early 1990s found 50 to 90 percent of sand applied to pavement remained in the environment after clean-up.
The rock salt sprinkled onto roads is effective until the temperature drops below 16 degrees. That's when additives, such as calcium chloride or magnesium chloride come in handy. They decrease the temperature that salt can melt ice to as low as minus 25 degrees.
The goal of deicing is not to melt the ice entirely but to break the adhesion between the pavement and the ice so plows can remove it later.
“In winter maintenance, the first priority is to plow,” Sproul said. “The goal is to only use the smallest amount of salt needed to melt and then be able to plow.”
So far this winter, Walworth County has used about 17,000 tons of its 30,000-ton salt supply, Brunner said. The county has an additional 2,750 tons on order.
County crews are responsible for maintaining Interstates, state highways and county roads. Town, village and city roads are the responsibility of the municipalities.
Walworth County is responsible for about 700 lane miles. That's compared to Whitewater, the county's largest city, which is responsible for about 50 lane miles, Brunner said.
The salt that county trucks sprinkle is pre-wet and has calcium chloride added. Pre-wetting helps the salt stick to the road.
“We pre-wet everything so it stays on the highway more,” Brunner said. “(We) found that by pre-wetting, about 30 percent more (salt) stays on highway.”
Public works directors, winter maintenance supervisors and environmentalists agree that 30 percent of dry salt broadcast onto roads bounces off and lands on road shoulders or nearby vegetation.
Salt that bounces onto road shoulders can kill trees and plants because they have a difficult time absorbing water with an increased salt content.
Pre-wetting cuts the amount of salt used about 25 percent because it has more melting power. It also reduces the bounce rate to 3 percent.
Only four counties in the state don't do pre-wetting, a method Sproul and Fortin recommend all counties use to protect their pocketbooks and the environment.
Area municipalities are coming up with creative ways to decrease the melting temperature and cut the costs of winter maintenance.
Beloit began adding beet juice to its salt several years ago. The juice is leftover after sugar is removed from sugar beets. Beet juice is used for deicing and anti-icing municipal roads.
Milwaukee is in the midst of a pilot program to use cheese brine, a product leftover from making cheese, to help pre-wet the roads and rock salt. Brine can be added to salt and then be applied before a snowstorm. It doesn't allow snow or ice to form a bond with the road, making it easier for plows to come through and clear the roads. Milwaukee sends trucks to Wisconsin's 140 cheese plants to pick up the brine.
In Walworth County, county officials are taking a look at using Kikkoman soy sauce and mixing it with salt to make brine, Brunner said. Soy sauce has a high salt content that can expedite melting.
Fortin, who provides training for Minnesota and Wisconsin winter maintenance crews, understands that science has not come up with a complete alternative for salt, but she is adamant that there are practices that are better for the environment.
It starts with choosing plowing over salt and homeowners being proactive.
To minimize residential salt use, homeowners should shovel snow as it falls or before it's compacted by walking or driving, she said.
She also suggests homeowners use salt sparingly--no more than a half pound per 150 square feet. An average coffee mug can hold one pound of salt, and an average parking space is 150 square feet.