Road Salt: Still the Deicer of Choice
by Kristine Bradof
This article originally
appeared in the October-December 1994 issue of the Wellspring
Road salt is "cost effective, successful in de-icing highways, and an environmentally sound method to increase safe travel for the motoring public," according to a March 1994 Michigan Department of Transportation (MDOT) news release. A study, completed for MDOT by Public Sector Consultants (1993), compared road salt (sodium chloride) with a road salt/sand mixture and five other chemical deicers: calcium chloride, calcium magnesium acetate (CMA), Motech (CMS-B, a potassium chloride mixture), CG-90 Surface Saver (a corrosion-inhibiting salt), and Verglimit (a concrete road surface containing calcium chloride pellets).
The study, which included an extensive literature review of data on deicer performance and environmental effects, echoed earlier reports by concluding that the deicer of choice depends on the situation. Any adverse environmental impacts from deicers are localized. CMA was recommended for use on bridges to minimize corrosion and on roads in environmentally sensitive areas. Its cost is about $675 per ton versus $30 for road salt.
Public Sector Consultants used data from the Transportation Research Board, the U.S. Environmental Protection Agency, and MDOT to estimate direct and indirect costs associated with the use of each deicer per standard mile of roadway. In addition to purchase and storage of deicing materials, direct costs included personnel, equipment and maintenance, vehicle corrosion, bridge deck corrosion, roadway damage, environmental effects, and traveler safety. Indirect costs were associated with human health (sodium intake in sensitive individuals) and traveler productivity and time. The least expensive deicers in total cost per mile were the salt/sand mixture, CG-90 Surface Saver, and road salt, respectively. CMA cost about twice as much as road salt, and three times the salt/sand mixture. Calcium chloride, CMS-B, and Verglimit could not be compared directly with the others.
In order to address concerns about deicing salt runoff to the Great Lakes, the study developed a model to analyze the cumulative effect of chloride loading to each lake from road salt. Chloride levels have increased in the Great Lakes, but road salt is believed to account for 35 percent or less of the total. Other sources are industrial and municipal wastewater discharges, natural weathering of soil and rock, precipitation, and runoff from nonpoint sources other than road salt.
Under the modelís worst-case scenario, nine times the current annual usage of salt for all roads in Michigan would be dumped directly into each lake. Even then, "chloride concentrations in the Great Lakes will reach equilibrium (uniform distribution) at levels far below that toxic to aquatic organisms." Such levels, ranging from about 5 ppm for Lake Superior to about 80 ppm for Lake Erie, are also well below the chloride taste standard of 250 ppm for drinking water.
The news release concluded that "despite the study's findings, MDOT is committed to seeking new ways to reduce the use of de-icing chemicals while still providing safe roadways for the motoring public. Advances are being sought in the form of improved salt-spreading equipment, better operator training and a mapping of environmentally sensitive areas on MDOT's snow routes." For a copy of the study, contact Andy Zeigler, MDOT Environmental Section, P.O. Box 30050, Lansing, MI 48909 (517/373-3251).
Public Sector Consultants, 1993. The Use of Selected Deicing Materials on Michigan Roads: Environmental and Economic Impacts. Lansing, MI: Michigan Department of Transportation. December 1993. 135 pp.