The Deicing Debate: Will It Ever Be Put On Ice?
by Kristine Bradof
This article originally appeared in the January 1994 issue of the Wellspring newsletter, published by the MTU Regional Groundwater Education in Michigan (GEM) Center, now the Center for Science and Environmental Outreach at Michigan Technological University.
"Road Salt is Hell on Earth!" proclaims a bumper sticker. "When salt is stored and applied properly, there should be no criticism of its use," counters the Salt Institute (SI). Whenever winter has the Snow Belt in its icy grasp, the debate about the use of road salt and alternative chemical deicers heats up. Sadly, finding the facts in this emotional debate, involving often-conflicting concerns about health, safety, environmental degradation, and economic costs, can be as slippery a business as traveling snow-and-ice-covered roads.
Some basic points of agreement do exist. Road salt (sodium chloride, NaCl) is the standard against which all other deicing materials and methods are compared. Road salt has contaminated some drinking-water wells and killed roadside vegetation. The public in the United States and Canada expects roads and streets to be kept safe for travel during the winter months. But stray from those statements, and watch the arguments begin.
Water contamination from road-salt use
During the 1940s, the "bare pavement" policy of winter road maintenance, promising "June travel in January," began to be adopted by highway departments, with road salt as the deicer of choice (Terry 1974, SI 1983). By winter 1965-66, more than two million tons of deicing salts were applied annually to roads in the U.S., mainly in the northeastern and north-central states; some roads received more than 20 tons of salt per season per lane-mile (Hanes et al. 1970). A dozen states reported water contamination and damage to plants.
The Commonwealth of Massachusetts created a commission to study those problems. The resulting report found that salt (chloride) contamination of public and private wells was becoming more common, paralleling the growing use of deicing salts (Terry 1974). Moreover, many contaminated areas were not near obvious point sources, such as uncovered salt piles.
A study in the Boston area found that if 20 tons of salt were applied per lane-mile per season, chloride levels in groundwater near major highways could exceed the 250 mg/l secondary (aesthetic) standard for chloride in drinking water (Huling and Hollocher 1972). High chloride levels give water a salty taste and increase corrosion of pipes, which can release lead and other metals into the water. The New Hampshire Highway Department replaced wells where chloride levels of 3,500 mg/l or higher caused corrosion of well casings and screens and made the water unpalatable (Hanes et al. 1970, Rail 1989). Similar high chloride levels in Michigan were also traced to salt stockpiling or spreading (Deutsch 1963). The U.S. Environmental Protection Agency (U.S. EPA 1990) noted, "Especially since the construction of the interstate highway system, water contamination due to wintertime road salting has become an increasing problem." For example, salty water in domestic wells near Muskegon was traced to deicing salt that ran off high-crowned roads into ditches cutting the same sandy, unconfined aquifer that served the wells.
SI (1991) admits that road salt has led to some groundwater contamination, but claims "improper stockpiling of salt is responsible for about 80 percent of environmental problems sometimes associated with salt use." In the Upper Peninsula, 21 of the 181 Act 307 Sites of Environmental Contamination known to exist in 1993 listed salt or brine as a pollutant. All but one were associated with highway commission facilities, where salt piles were the likely sources of pollution. Unless a site also has more serious contamination, such as from petroleum, it is of low cleanup priority.
Despite these known cases of road-salt contamination, MTU GEM staff were surprised by the extent to which the public and decision makers perceive road salt to be a major source of groundwater pollution. In our 1992 groundwater awareness survey of 170 county fair-goers, road salt was ranked as the most serious groundwater contaminant, ahead of the other choices: gasoline/oil, bacteria, pesticides, solvents, and nitrates. Similarly, the 105 respondents to our 1992 water resources needs assessment ranked road salt second only to gasoline/oil.
Road salt may seem to be a logical culprit, but it is often falsely accused. Pockets of naturally salty groundwater are found in the western U.P. and in oil-and-gas-producing areas of Michigan. Such saline layers of water formed during geologic periods when shallow seas covered the region or as groundwater flowed through salt deposits. "In fact, much of the nation's inland sources of fresh groundwater are in close proximity to natural bodies of saline groundwater" (Rail 1989).
In 1972, SI responded to concerns about environmental damage from road-salt storage and use by introducing the "Sensible Salting" program. Their brochure explaining the program maintains that "deicing salt is essential for winter road safety and mobility." Free seminars for road maintenance personnel and public officials emphasize using no more salt than is necessary for a given storm, storing salt and maintaining spreading equipment properly, and "setting the record straight about salt's true effect on our environment." Unfortunately, the environmental consequences and economic costs of salt use remain open to debate.
In addition to contaminating water supplies and damaging soil and vegetation, salt has been accused of causing road, bridge, and vehicle corrosion and harm to fish and wildlife. SI (1986, 1990) downplays these criticisms, emphasizing instead the cost-effectiveness of salting programs in terms of health and safety: ice-free roads reduce the number of accidents and injuries, allow shorter travel times for emergency vehicles, and save fuel by reducing slipping. Other economic benefits claimed are less absenteeism, reduced losses in production and shipping, and lower fuel costs for spreading salt instead of less efficient deicers. Using data from two studies in 1976, one by the U.S. EPA, the other by The Institute for Safety Analysis, SI (1986) calculated benefit/cost ratios for road salting of 6.3 to 1 and 18.1 to 1, respectively. SI (1990) described alternative deicers as less effective, more expensive, or environmentally questionable.
An alphabet soup of alternative deicers
Even as road salt began to be implicated for environmental damage in the 1960s and 1970s, its use increased to 10 million tons annually in the U.S. and 3 million in Canada (SI 1983). By the 1990s, a variety of alternative deicers CMA, CG-90, NaFo, Freezgard + PCI, Ice Stop CI, Quiksalt + PCI, and urea—were shown to be effective in studies by the Washington Department of Transportation, the Federal Highway Administration, or the City of Ottawa, Ontario (Nevada Milepost 1993, Better Roads 1989, 1991).
Still, in a 1990 survey, 87 percent of highway engineers reported using salt for deicing (Better Roads 1991). More than half also used calcium chloride, and one-fifth used calcium magnesium acetate (CMA). Cinders, sand, urea, and corrosion-inhibited salts were used by some highway departments. Effectiveness and cost were the main reasons for choosing a deicer. Less than 20 percent of respondents ranked environmental concerns as top priorities. Costs of the major alternative deicers (calcium chloride, CMA, and corrosion-inhibited salt) ranged from $110 to $1,200 a ton, compared to $25 for rock salt.
General recommendations from state transportation departments and the Transportation Research Board of the National Research Council were summarized in Nevada Milepost (1993): "Use less salt, and use alternative deicers (including CMA) for corrosion-prone bridges and environmentally sensitive areas." However, even CMA, which biodegrades readily, may reduce oxygen levels in streams or ponds receiving runoff from roads, according to its developer, Chevron (Wyatt and Fritzche 1989).
Clearly, there are no simple answers, and the deicing debate is far from over. Even promoters of alternative deicers acknowledge that "salt will continue to be the workhorse for snow and ice control" (Wyatt and Fritzsche 1989). But they urge evaluation of the full cost of each winter road maintenance method—including damage to highways, vehicles, and the environment—not just the initial cost.
Thanks to Celeste Nguyen and Terry McNinch of the MTU Transportation Technology Transfer Center for providing photocopies of articles. Watch Wellspring for an update after the Michigan Department of Transportation releases a new study by Public Sector Consultants.
Better Roads 1989. Ottawa tests salt alternatives. March 1989: 43-45.
_____ 1991. What you need to know about deicers. January 1991: 26-27.
Deutsch, M., 1963. Groundwater contamination and legal controls in Michigan. U.S. Geological Survey Water-Supply Paper 1691. 79 pp.
Hanes, R.E., L.W. Zelasny, and R.E. Blaser, 1970. Effects of deicing salts on water quality and biota: Literature review and recommended research. National Cooperative Highway Research Program Report 91. Highway Research Board, National Research Council. 70 pp.
Huling, E.E., and T.C. Hollocher, 1972. Groundwater contamination by road salt: Steady-state concentrations in east central Massachusetts. Science 176: 288-290.
Nevada Milepost 1993. Everything you always wanted to know about chemical deicers. Winter 1993: 10-11.
Rail, C.D., 1989. Groundwater Contamination: Sources, Control, and Preventive Measures. Lancaster, PA: Technomic. 139 pp.
Salt Institute, 1983. Deicing Salt Facts (A Quick Reference). Alexandria, VA: Salt Institute. 4 pp.
_____ 1986. Benefits and Costs of
Road Salting. A Summary of the TISA Report. Alexandria, VA: Salt
Institute. 12 pp.
_____ 1991. The Snowfighter's Handbook. Alexandria, VA: Salt Institute. 18 pp.
Terry, R.C., Jr., 1974. Road Salt, Drinking Water, and Safety: Improving Public Policy and Practice. Cambridge, MA: Ballinger. 161 pp.
U.S. Environmental Protection Agency, 1990. Handbook. Ground Water. Volume 1: Ground Water and Contamination. U.S. EPA Office of Research and Development. Center for Environmental Research Information, Cincinnati, OH. EPA/655/6-90/016a. 144 pp.
Wyatt, J. and C. Fritzsche 1989. The snow battle: salt vs. chemicals. American City and County, April 1989: 30-36.