De-icing Salt is Here to Stay, But can be Used More Wisely

By Todd Paddock and Cynthia Lister,
Academy of Natural Sciences
February, 1990

It's a gray winter day and the forecast is for snow. Out you go to pick up a new can of de-icing salt for your steps. At the office or shopping mall, someone is salting the sidewalks. Along the road the municipal vehicles are parked at the ready, waiting for the signal to plow and salt.

It's a familiar scenario, and likely to remain that way. While the use of de-icing salt can result in the contamination of surface waters, groundwater, and soil, it remains the cheapest and most effective method of keeping pavement free of ice. The use of sand or cinders also increases traction, but large amounts will clog sewers and drains. Alternative de-icing chemicals are available, but are much more expensive. Nevertheless, there are ways to reduce the undesirable environmental consequences of de-icing salt.

Across the northern U.S. "snow belt", the use of de-icing salt (sodium chloride or calcium chloride) to melt ice on highways is a common practice. In the winter of 1988-89, over 10 million tons of salt was used on roads in the United States. The amount of de-icing salt used annually peaked in 1979 at 12 million tons, and has since leveled off to between 8 and 11 million tons, depending on the severity of the winter.

After salt is applied, it is washed off paved surfaces into storm drains or onto adjacent ground, and can then be carried into nearby bodies of water. The normal use of de-icing salt can cause the salinity of the soil, or of a stream, lake, or bog to increase. The increased salinity can have a detrimental effect on plants and animals, although the effects may be temporary. Whether an increase in salinity occurs, and the degree of increase, depends on many factors.

The use of de-icing salt can also affect drinking water supplies in reservoirs and aquifers near roadways. Groundwater-- a naturally occurring subsurface water supply-- is vulnerable to salt contamination because the salt dissolves readily, can percolate through the soil, and can then be carried into the aquifer or reservoir. In Massachusetts, the state has spent about $2.5 million dollars addressing excessive sodium levels in drinking water supplies, caused by the use of de- icing salt.

The state of Massachusetts has examined the costs of using road salt and alternatives. In a draft report released last year, the Massachusets Department of Public Works examined the environmental costs of sodium chloride, including the cost of corrosion to vehicles and bridges, the cost of contaminated water supplies, and the cost of damage to vegetation. According to Frank Bracaglia, Deputy Chief Engineer for Project Development with the Department of Public Works, the study concludes that every additional dollar spent on the use of "pre-mix", a 4 to 1 mixture of sodium chloride and calcium chloride, will result in a savings of at least two dollars in environmental costs. Other de-icing chemicals were not as cost-effective. Based on this report, says Mr. Bracaglia, Massachusetts will be moving to the use of pre-mix rather than straight salt (sodium chloride).

Simply banning the use of salt has not worked. Such ordinances have been passed in a number of cities over the years, in part because of salt's ability to cause corrosion in auto bodies. However, all bans were later rescinded after problems with ice buildup. For example, Tulsa, Oklahoma stopped using salt during the winter of 1985-1986. "We did make it through the entire winter without using salt." says Mr. Winston Anderson of Tulsa's Transportation Section. "However, we had to apply sand over and over, and the sand accumulated on the roads until it was a real problem. We also had areas where the ice never melted. The next year, we returned to our normal practice of applying a mixture of sand and salt."

Many of the most severe cases of contamination have been caused by improper storage. When salt is stockpiled outside, uncovered, precipitation can carry high levels of salt to surrounding soil and water. The Salt Institute, a trade association for the salt industry, developed a model salt-storage building, and has encouraged states to use the model. Mr. Bruce Bertram, Technical Director, says that while they haven't done any surveys, "We feel that most states are moving quickly to cover their salt piles. However, if a community is poor, the cost of proper salt storage can be a great burden."

In addition to proper storage, there are methods for reducing the use of salt. Many cities simply don't use salt in flat residential areas, except during ice storms. Like Tulsa, many use a mix of sand and salt, instead of pure salt. Spreading equipment can be made more accurate, so that less salt is needed. The salt can be wetted before being spread, so that it sticks to the road. Snow fences and rows of trees can keep snow from blowing onto the road. In Minnesota, farmers are paid to leave their corn standing through the winter in fields along the highway, because it can hold blowing snow.

Mr. Rodney Pletan, State Maintenance Engineer for the Minnesota Department of Transportation, says that salt's reputation for causing auto bodies to rust actually prevents his crews from using less of it. "If we could spread salt before forecasted snow or ice arrives, we could prevent road icing and use less salt overall. But citizens aren't happy when they see a truck spreading corrosive salt on dry pavement."

Alternative de-icing chemicals do exist, but are too expensive for most situations. Calcium magnesium acetate (CMA) is an alternative that has been tested. It works, and appears to cause fewer environmental problems, but is approximately 20 times more expensive to use than salt. Verglimit is a mixture of de-icing chemicals that are bonded with an asphalt roadway during paving. It is effective even in very cold temperatures, and causes very little runoff, but its installation doubles the cost of surfacing a road.

Stopping the use of de-icing salt will mean using much more expensive alternatives, or living with ice on roadways. However, the use of de-icing salt can be significantly reduced through a number of measures, and covering salt stockpiles will prevent many of the most severe cases of contamination. These solutions are within reach of most transportation departments.

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De-Icing Salt is here to stay, but can be used more wisely

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