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Photo: iStockphoto.com/hbak

The issue of groundwater and surface water contamination resulting from road deicing salt use is one of contaminant mitigation, not best management practices (BMPs). Nothing can be done to remove salt and its compounds once they get into water supplies, so the management focus is on reducing or eliminating salt in point and nonpoint sources before stormwater becomes a carrier of pollution to groundwater and surface waters. For years, the deleterious effects of road salt on infrastructure—concrete reinforcing steel and pavements, most notably—has been well known, but the adverse effects of salt on the natural environment have come to the fore more recently.

The most common type of road salt is sodium chloride. High sodium concentrations in drinking water—above 20 milligrams per liter (mg/l)—can contribute to hypertension. Chloride is considered harmful, because it damages wildlife food resources and shelter and can change the composition of the plant community in a wetland and allow invasive plant species to populate it. An estimated 10% of aquatic species exceed their critical tolerance values for chloride with prolonged exposure to concentrations above 220 mg/l, but many macroinvertebrates exhibit lower tolerances.

Besides sodium and chloride, road salts may have smaller amounts of calcium, potassium, and magnesium chlorides, and sodium ferrocyanide is added to chloride salts to prevent clumping during storage and application. In water, sodium ferrocyanide can be photolyzed to release approximately 25% cyanide ions. In 2003, the USEPA listed ferrocyanide as a toxic pollutant and hazardous substance under Section 307(a) of the Clean Water Act. EPA and validated states have also set chronic and acute limits on chloride.

It is estimated that annual salt deicer usage totals 15 million tons in the United States and about 4 million to 5 million tons in Canada. One might wonder why road salt is still used, given its ecological harm. That’s until one considers the case for road salt as a public safety tool and economic catalyst in northern climates. Salt dissolves in water from snow and ice to form brine, which lowers the freezing point of water, and thus breaks the bond between the pavement and snow or ice.

Chloride ions are relatively stable, meaning that they can move through the environment in solution without being lost or broken down through natural processes. As a result, almost all chloride ions that enter the environment reach surface water. “It’s essentially conservative—that’s the term people use,” notes Roger Bannerman, environmental specialist for the Wisconsin Department of Natural Resources (DNR). “Sometimes it can build up to the point where the lake will cease having its normal cycles. Lakes tend to turn over and the water becomes homogenous and the temperature becomes even, but the chloride will create a density gradient where it won’t turn over anymore. And of course, if the chloride concentration gets high enough, things living in it can’t tolerate that high level.”

Adds Phil Trowbridge, P.E., a coastal scientist with the New Hampshire Department of Environmental Services (DES): “We don’t have stormwater BMPs that can remove chloride. The only way to reduce the salt impact is to reduce the salt load.”

Photo: Roger Bannerman Salt dissolves in water from snow and ice to form brine, which lowers the freezing point of water, and thus breaks the bond between the pavement and snow or ice.

Organic substitutes for salt are not a panacea, Bannerman argues. “There are other calcium- and magnesium-based products coming out, but they still have chloride in them and they’re more expensive, unfortunately. I think one role EPA could play is to work on alternatives and fund research. Things like beet juice and other things are being tried. One thing we’re worried about is that any organic-based deicer might have high phosphorus content—that’s the last thing we can have.”

Since no “silver bullet” for solving the road salt problem currently exists, several long-term mitigation efforts have been undertaken in recent years. These efforts represent the latest approaches and philosophies being used to attack a very daunting problem.

Madison, WI
The Wisconsin capital has been in the forefront of the deicing salt issue for nearly 40 years, starting when the city’s Common Council directed the City Streets Division to reduce the amount of road salt used for winter maintenance in the Lake Wingra watershed starting in the winter of 1972–73, with the rest of the city following suit by 1977–78. Despite this early awareness, and notwithstanding the fact that chloride concentrations in Madison lakes are generally well below Wisconsin DNR and EPA toxicity standards for surface waters, the concentrations have nearly doubled in recent decades. In the winter of 2004–05, 48% more road salt was applied to Madison’s 750 street miles compared with 1972–1973, adjusting for the difference in street miles maintained.

One of the leaders of the sodium and chloride mitigation effort in Madison is Bannerman, who has been involved in the effort as a private citizen since the 1970s. According to Bannerman, despite the fact that in January 2000 the Wisconsin DNR established chronic and acute toxicity levels of 395 and 757 milligrams per liter, respectively, total maximum daily load (TMDL) standards for chloride are not used in Wisconsin. However, Madison has been in the forefront of investigating equipment modifications and new technologies that could prove to be effective components of mitigation strategies.

A 2006 report by the city’s Salt Use Subcommittee to the Commission on the Environment (COE) outlined several equipment modifications and technologies and made recommendations regarding their use. The city subsequently adopted several of the recommendations in a deicing salt-use ordinance, including:

• The use of Road Weather Information Systems (RWIS). Weather stations installed adjacent to highways and airport runways, working in conjunction with infrared pavement and air-temperature sensors installed on maintenance vehicles, have provided forecasters with real-time weather conditions for computer modeling since the mid-1980s. The models can allow public works officials to make more informed decisions of when and how much road salt to apply. The city has used weather/temperature monitoring data provided by a private weather contractor and the Wisconsin Department of Transportation, which has several weather stations located within the city limits, to determine storm severity for years. The salt-use ordinance mandates the continued use of advanced weather monitoring.
• Anti-icing, or applying pre-wetted salt well in advance of a storm to prevent a bond between snow and ice and pavement as a way to reduce the volume of salt required. A demonstration of anti-icing via the use of salt brine is being considered under the ordinance. Estimated cost: $5,000 to $10,000.
• Limiting the amount of salt in abrasives. Materials such as sand have been used to provide temporary traction. Typically, road salt is mixed with sand at 5% or 10% by volume to prevent the sand from freezing. The subcommittee pointed out that studies have shown that this amount of road salt does not provide snow-melting capacity, however, and small amounts of salt should be mixed with sand only to prevent the sand from freezing in stockpiles or spreader trucks. The subcommittee recommended striving to reduce the salt content of sand from 10% to 5%, continuing to work toward ways of more consistently mixing the sand/salt mixture, and continuing to test sand for salt content. Estimated savings: $500 per 100 tons of sand.
• Providing more training for city-employee and private-company snowplow drivers. Estimated cost: $500 per session, $3,000 for a training consultant. As of spring 2009, the city offered private-applicator training twice, and roughly 30 individuals showed up for each session.
• Proactively working with other county municipalities to systematically reduce the amount of salt used each year
• Considering on-board air- and pavement-temperature sensors installed in city supervisors’ vehicles. Estimated cost: $400 to $800 per vehicle
• Developing ordinances for regulating private commercial salt application, operating equipment, and annual compliance reporting requirements
• Measuring sodium and chloride levels in stormwater runoff, lakes, and groundwater and determining future levels of chlorides in city lakes and streams; considering working with the United States Geological Survey (USGS), to project the impact on the environment via computer modeling
• Considering development of an alert program for informing the public about expected winter driving conditions
• Mandating that the city of Madison annually update the COE regarding the implementation of salt-reduction recommendations and programs
• Requesting that the Dane County Lakes and Watersheds Commission survey other area governmental agencies, municipalities, and private salt applicators to determine their road salt policies; establish benchmarks for chloride content in lake water; and recommend policies to all governmental agencies, municipalities, and private salt applicators to achieve benchmarks by a commission-established date.

The COE contends that these measures, taken together, could reduce the amount of salt applied in the city by 20% to 30%. Accordingly, all applicators should be able to reduce their amounts applied by 20% to 30%.

Photo: Jim Lorman, Edgewood College Focusing on parking lots appears to be an area of huge untapped potential.

Another key step that the Madison City Council took toward reducing salt use was to prohibit its application to residential side streets starting in the mid-1970s. Some measures are taken to address public safety in these areas, such as applying sand at important intersections and on steep hills; the environmental impact is addressed by sending street cleaners out in early spring to pick up the sand. The city plows also get out as soon as possible after the snow starts falling. “Mechanical removal is still the best technique; the problem is, they can’t do all of the streets at once,” says Bannerman. “It’s not a perfect system, because they can’t possibly have enough plows to plow the streets simultaneously.” Bannerman says that, despite the fact that this move has drawn many complaints from residents through the years, the city has stood firm on the policy.

Shingle Creek, MN, Watershed
About a four-hour drive to the northwest of Madison, a chloride TMDL has been developed for the Shingle Creek watershed, located in the northwestern region of the Minneapolis metropolitan area covering 44.5 square miles and nine municipalities in east-central Hennepin County. In 1998, Shingle Creek was listed on the 303(d) list of impaired waters as exceeding state-mandated chloride standard for aquatic life, and the Minnesota Pollution Control Agency (MPCA) was required to develop a chloride TMDL for the watershed. In Minnesota, the chronic chloride standard for the protection of aquatic life for Class 2 water such as Shingle Creek is a four-day average of 230 mg/l, and the acute standard is 860 mg/l for a one-hour duration. Chronic contamination relates to long-term impacts on aquatic life such as interference with reproduction, while acute contamination can cause immediate effects, such as death.

During the next few years, Wenck Associates, an environmental engineering firm in Maple Plain, MN, developed a chloride TMDL report for the Shingle Creek Water Management Commission (SCWMC)—formed among the nine communities in 1982—and the MPCA.

For the purpose of TMDL standard development, a technical advisory committee was formed, consisting of the local communities, Hennepin County, the Minnesota Department of Transportation (Mn/DOT) and Department of Natural Resources, the Metropolitan Council, the USGS, and the MPCA. Committee meetings were open to interested organizations and the public and included work sessions to identify BMPs for addressing the chloride exceedances.

The report, which was approved by EPA in February 2007, indicated that road salt was making a significant impact on chloride levels in the watershed, notes Joe Bischoff, an aquatic ecologist and the TMDL development technical lead with Wenck Associates, which staffs the SCWMC. For 2002–03, reductions of at least 60% for all flow categories, and 72% for high flow periods, were needed to meet the TMDL standard. Further, the report concluded that 87% of the chloride load to Shingle Creek is related to application and storage of road salt by public entities. The remaining 13% was attributed to commercial, residential, and groundwater sources.

“The USGS has looked at groundwater concentrations around the Minneapolis area, and there are high chloride concentrations—and, in fact, in Shingle Creek we’re getting precariously close to that 230 mg/l at extreme baseload conditions in the middle of the summer,” says Bischoff. “So we’re seeing a lot of that salt coming back into the system in the summer, probably coming out of the wetlands or the groundwater.” He adds that a strong correlation exists between the median chloride concentration in winter and road salt application, and that the exceedances likely would not occur without the road-salt application.

The report points out that implementation will incorporate adaptive management principles, because it is difficult to predict the chloride reductions that will occur from implementing the TMDL strategies. The report also states that continued monitoring and “course corrections” to monitoring results will be used. Additionally, the standard implementation plan incorporates city salt management plans to be overseen by the cities; the plans are developed to allow comparisons among the cities’ activities. Stakeholder BMPs will be tracked by the MPCA as part of National Pollutant Discharge Elimination System (NPDES) Phase II Permit enforcement.

The report lists several recommendations for committee stakeholders, setting the general framework for enforcing the TMDL standard. Appendix H of the report provides key guidance for standard implementation based on the expertise of Mn/DOT: best available technologies (BATs), a term that originated with the Clean Water Act meaning those considered the best, although not necessarily most cost-effective, for pollution control.

The appendix provides BATs in five areas:

• Salt storage and handling. According to the appendix, the BAT is covering both the storage and loading areas, diverting surface water runoff away from loading and storage piles, and containing any runoff that does come in contact with the salt pile. The appendix notes that the majority of Mn/DOT salt storage facilities in the metro area have covered storage piles and loading areas.
• Operator training. Mn/DOT supervisors commonly provide salt truck drivers with recommended application rates based on an RWIS and other sources. Operators have the authority to alter these conditions in the field based on training, which consists of sessions for new operators and an annual refresher course using the Salt Solutions Program, a nationally recognized program created by Mn/DOT in 1998. The training covers pre-wetting, anti-icing, deicing, and sensible salt and sand usage and also includes computer-based training on the RWIS.
• Product application–equipment. The spreader that distributes the anti-icing or deicing product should be calibrated to significantly reduce the amount of misapplied product. Installing speed sensors or ground-oriented controls results in further reductions in the amount of misapplied product. All Mn/DOT trucks in the Minneapolis metro area are currently equipped with ground-oriented controls, which automatically regulate application rates as truck speeds fluctuate. Trucks purchased after 2004 are fitted with controllers that also record the amount of material applied, and 15% of those trucks are also outfitted with pre-wetting equipment, which can reduce salt waste by 20% to 30% and may provide faster melting action by activating the dry chemical with moisture.
• Product application–decision. Mn/DOT has a network of 90 sensors embedded in roadways around the state, and eight RWIS sites are located in the Minneapolis metro area. Information collected by Minnesota’s RWIS is available to other organizations via Mn/DOT’s Web site. The sensors can be used to identify weather approaching the metro area and help determine optimal application rates of salt and deicing and anti-icing products. An anti-icing agent such as a magnesium chloride solution or a sodium chloride solution is used to keep the bond between ice and the pavement from forming and is applied to areas that tend to freeze first, such as bridge decks and curves.
• Ongoing research. Limited road tests can help determine how new products or techniques can replace or reduce the amount of chloride used to keep roadways free of ice and snow. Mn/DOT conducts its own lab tests on deicing products—e.g., a salt brine-corn byproduct and magnesium acetate—prior to road testing.

Mn/DOT has achieved a level of BAT in the areas of operator training, product application–decision, and ongoing research; and a level of Maximum Extent Practical—the level used by EPA in its NPDES MS4 Program—in the categories of salt storage piles and product application–equipment.

The SCWMC also agreed to take the lead on public education and private applicator education through the following actions:

• Coordinating an Annual Commercial Applicator Workshop to discuss salt usage, application techniques, storage issues, product type and alternatives, and other technologies. Estimated annual cost: $1,000.
• Educating private commercial, industrial, and residential applicators and homeowners on ways to reduce chloride-based deicer use via brochures, newsletters, Web content, and presentations. Estimated annual cost: $1,500.
• Incorporating permit requirements for reducing chloride use and inclusion of chloride reduction into the commission’s project review program. The commission will develop a template for private applicator salt-management plans. Estimated cost: $2,000.
• Educating city, county, and state officials on the TMDL and its implementation to allow a balance between public safety issues and environmental risks. Estimated annual cost: $1,000.
• Monitoring chloride and conductivity at two locations in the watershed. Estimated annual cost: $3,000.
• Educating the public on the environmental effects of road salt and ultimately gaining public acceptance in lowering driving speeds during icy conditions, as well as lowering public expectations for snow removal and deicing. Activities may include newsletter articles, brochures, Web content, and presentations. Estimated annual cost: $3,000.
• Producing an annual report on monitoring and activities that will provide the cities with necessary information for their annual NPDES reports. The report will track BMP scheduling, implementation, operations and maintenance, and environmental condition monitoring data. Estimated annual cost: $5,000.
• Monitoring implementation of policies and BMPs and including results in its annual report. Findings and public comments will be used to formulate the work plan, budget, capital improvement program, and specific measurable goals and objectives for the coming year, as well as to propose modifications or additions to the goals, policies, and strategies.
• Conducting increased followup monitoring at two stations in the watershed, to include grab samples of chloride and collection of conductivity at 15-minute intervals

According to Bischoff, one major variable in adhering to the TMDL standard is determining the amount of salt applied to private parking lots and then achieving a uniform reduction. A SCWMC analysis determined that these areas contribute about 12% of the total chloride load. Some evidence supporting the business case for reducing parking lot application rates does exist. The University of Minnesota facilities department, having completed an MPCA training course on winter parking lot and sidewalk maintenance, reduced the application of salt applied by 985 tons during the winter of 2006–07 for a savings of more than $65,000. The extra salt was replaced by employee training and equipment calibration at an investment of only $10,000.

Other variables, such as winter severity—which generates more snow water—can make progress more difficult to measure, Bischoff argues. “But if you can look at annual application rates by agency and see if we have reductions, that would be the most direct measure.”

Bischoff notes that the various stakeholders have different proportions of responsibility for helping to achieve the overall chloride reduction in the watershed. Mn/DOT, which faces the greatest public pressure for keeping expressways clear, has the greatest financial resources and has invested the most in research. The county uses the same methods and systems as Mn/DOT and manages many high-speed intersections where stopping is important. City roads have lower speed limits but are more heavily traveled, and city finances are more limited.

With so many variables involved, and given the long-term nature of the Shingle Creek TMDL standard initiative, Bischoff concludes that it will take at least 10 years to determine whether the various methods are working. But a comprehensive problem-mitigation framework is in place.

Policy-Porcupine Brook Watershed, Salem and Windham, NH
A TMDL standard was developed for the 10.18-square-mile watershed in southern New Hampshire in April 2008. The development process was characterized by a special emphasis on comprehensively measuring the contribution of chloride to the watershed by private parking lots and pavements.

New Hampshire is not a validated state, and EPA is the permitting authority for the nontidal Class B Policy-Porcupine Brook watershed. The chloride limits for Policy-Porcupine Brook are the same as for the Shingle Creek watershed: 860 mg/l for acute exposures over a one-hour period and 230 mg/l for chronic exposures over a four-day period.

Monitoring of chloride levels in the watershed by the New Hampshire DES, EPA, and the New Hampshire Department of Transportation (NHDOT) determined that deicing of roadways and parking lots accounted for 89% of chloride import to the watershed and that parking lots were the single largest source at 50%. Salt pile runoff contributed 7%, and water softeners, food waste, and atmospheric deposition were minor contributors.

It was determined, during the monitoring period of July 1, 2006, to June 30, 2007, that total salt imports were 4,814 tons. To achieve a percent reduction goal (PRG) of 24.5%, imports would have to be reduced to less than 3,635 tons of salt per year. The report also identifies the various sources of import—each of which is to meet the PRG so that the total import reduction can be achieved:

• Two state roads (NHDOT)
• Municipal roads in cities of Salem and Windham
• Private roads in Salem and Windham
• Parking lots in Salem and Windham
• Salt piles in Salem
• Water softeners, food waste, and atmospheric deposition within the watershed

In 2006, NHDOT and DES established an interagency Salt Reduction Workgroup for the purpose of advising DES and NHDOT on TMDL studies in the I-93 corridor until the studies are completed, and then to advise and assist with the implementation of required salt-load reductions. The workgroup determined that:

• Ninety-six percent of the salt imports to the watershed were for deicing activities; so nearly all of the salt import reductions will need to come from reduced deicing loads.
• The allocation for salt pile runoff will be zero, because all salt and salt-sand piles should be covered.
• The existing loads from water softeners, food waste, and atmospheric deposition will be used as the allocation for these sources.

Trowbridge, who wrote the Policy-Porcupine Brook Watershed TMDL study report, reports that implementation of the TMDL standard will involve monitoring the watershed for chloride for at least 10 years. “If we find that we’re meeting the standards more rapidly, that would change the implementation, or, conversely, if we’re not making any progress, we might have to change the plan,” he says.

The study involved detailed inventorying of the amount of deicing salt applied to private parking lots and pavements. “One thing I’d say that’s a little bit unique about our work is the evaluation of loads from parking lots and private entities,” says Trowbridge. “We contracted with Plymouth State University, and they did a very good job of estimating it. The main concern of the owner is slip, trip, and fall liability, and there really is no permit in place for that parking place, so it really is a much harder thing to get a hold of than highway maintenance.”

The university used GIS to verify the location of parking lots in the watersheds. Contractors and property owners were surveyed on salt use, and a large collection of data was averaged to determine the average loading rate for parking lots.

“There’s certainly a lot more [salt on parking lots] than we expected,” continues Trowbridge. “It’s about the same as on a roadway; the difference is that you don’t see it because you’re not normally walking on a roadway. Furthermore, the salt is crushed pretty quickly by tires. In a parking lot, people are amazed by seeing large chunks of salt.”

Ontario, Canada
An effort to legislate reductions in deicing salt in Canada is being led by environmental groups such as the Toronto-based RiverSides Stewardship Alliance and Ecojustice (formerly known as the Sierra Legal Defence Fund). These groups contend that deicing salt should be listed as a Schedule 1 toxic substance per the 1999 Canadian Environmental Protection Act (CEPA). The basis for such a listing is a 2001 CEPA Priority Substances List Assessment Report for Road Salts indicating that road salt is toxic to the ecosystem, according to the groups. Canada’s Ministers of the Environment and Health have also recommended that road salts be added to the list of toxic substances under CEPA, which would form a regulatory basis for corrective action. However, to date, road salts have not been officially listed, and the issue is in regulatory limbo amid lobbying by special-interest groups.

The CEPA priority substances list report does include considerations for further action, including:

• Storage of salts and abrasives to reduce losses through weathering, reduce losses during transfers, and minimize releases of stormwater and equipment washwater
• Reduction of the overall use of chloride salts in areas of high salt use and high road density via the use of alternative products or of appropriate practices of technology
• Release of salty snowmelt waters into surface waters with minimal environmental sensitivity or into storm sewers, or dilution before release
• Reductions in the addition rate of ferrocyanide to road salt

The government’s Environment Canada agency also has a Code of Practice that recommends the voluntary development of salt management plans to implement BMPs by road authorities using more than 500 metric tons of road salts annually, or applying salt in environmentally vulnerable areas. These BMPs focus on three areas: storage, application, and snow disposal. Application recommendations include the use of calibrated spreaders, RWIS, infrared thermometers and road surface friction sensors, pre-wetting, and anti-icing techniques.

In Ontario, these groups are disputing Regulation 339, which exempts from the provincial Environmental Protection Act the use of deleterious substances for winter road maintenance. This exemption prevents the Ontario Ministry of the Environment (MOE) from issuing certificates of approval with conditions for road salt storage, application, and snow disposal, or from issuing pollution prevention and abatement orders relating to excessive road salt application. The groups asked the environmental commissioner of Ontario, a government watchdog in regard to environmental law appointed by the legislative assembly, for a regulatory review of Regulation 399. The MOE deemed the request unreasonable, and the commissioner informed the MOE that its position is mistaken. This issue, too, is in regulatory limbo.

In the report conclusion, RiverSides and Ecojustice recommend that Ontario’s 2006 Clean Water Act include a requirement that all drinking water source-protection plans address the issue of road salts. The conclusion includes five other recommendations:

• The Environmental Protection Act’s Regulation 339 be immediately revoked
• The Ontario MOE immediately implement a phased-in mandatory road salt management regime requiring all road authorities to seek a certificate of approval under the Environmental Protection Act for storage and application of road salt and for snow disposal in Ontario
• The Ontario government institute an educational and regulatory program to reduce the incidence of accidents on winter roads, including mandatory reductions in speed limits during winter conditions and mandatory requirements for snow tires under the Highway Traffic Act
• The government of Canada immediately list road salts on Schedule 1 under the Canadian Environmental Protection Act of 1999
• The federal government pursue changes to the Great Lakes Water Quality Agreement that would require proper management of road salts use throughout the Great Lakes Basin Ecosystem. The groups point out that high near-shore chloride levels resulting from land impacts, combined with the presence of invasive aquatic species, is fundamentally altering the lakes’ ecosystem.

Kevin Mercer, former executive director of RiverSides and current president of Hampton Group Consulting Inc. in Toronto, argues that the CEPA Code of Practice recommendations could make a big difference. He points out that road patrol yards that contain salt storage facilities often are significant point sources of chloride. “We no longer see large uncovered piles of salt in transit,” says Mercer. Also, “the road authorities have done a great deal of work on their code of practice to educate their drivers to put in computerized spreaders on their trucks and use pre-wetting and [RWIS].”

Another major source of salt import is private parking lots, he adds. These used to be considered a contributor of perhaps 10% of the total chloride load to Ontario’s watersheds, but RiverSides’ research indicates that the contribution could be as high as 25% to 30%.

Conclusion
Addressing excessive chloride levels in natural water supplies resulting from deicing salt runoff is a complex, daunting challenge, and no easy solutions currently exist. Judging from these cases, though, several practices are effective means of mitigating the problem. Using advances in equipment to facilitate the adherence to TMDLs is a strategy that shows promise. Tactically, focusing on parking lots appears to be an area of huge untapped potential.

In the longer term, eliminating rather than mitigating excessive chloride levels will require some as-yet-unforeseen fundamental change. Perhaps a viable organic salt substitute will be discovered through research. But the most necessary and crucial development would be a fundamental change in public attitudes toward the use of deicing salt—that is, viewing its environmental impact as more important than the vehicular safety benefits its use provides. Such a philosophical shift would be drastic, because it challenges the assumption of the automobile’s role in daily life, which may ultimately occur for reasons of energy scarcity anyway. With little or no deicing salt applied to pavement, winter storms may sharply curtail driving out of necessity, and business would just have to adapt to a new reality.

“We always think in terms of catastrophic damage, but road salt creates a chronic damage and it’s that chronic, low-level loss of ecosystem health that we tend to ignore at our peril,” says Mercer. “I appreciate what road authorities do because I drive, but, on the other hand, we are going to have to move toward a world where salt is not used anywhere nearly as frequently as we use it now. What we’ve got is a social marketing issue—people expect that the only road that’s safe is the one that’s blacktopped. We assume that road authorities are arbiters of risk; they are really people who help get things from point A to point B and keep roads passable. Some people think we must drive risk to zero—that’s rubbish.”

“I’d like to think that in the next 10 to 15 years we’ll come up with more serious alternatives,” adds Bannerman. “We keep tweaking how much we put down and use more anti-icing and keep tweaking what we know, but I’d hate to see that become the long-term solution. I think the long-term solution is going to have to be that we stop using [deicing salt]. I’m always optimistic that research can be done to find an alternative that hopefully is highly effective.”