Understanding the Impacts of Road Salt
Between 5 and 7 million tonnes of salt is applied every year in Canada for winter maintenance of roads and other paved surfaces, making it one of the most ubiquitous contaminants in urban environments. While the use of salt is essential to ensure public safety, there is a growing concern regarding the large quantities of salt (mainly chloride ions) being released into the environment.
Sodium chloride (NaCl) is the most common de-icer applied for winter maintenance, comprised of 40% sodium and 60% chloride. Liquid brines comprising NaCl, magnesium chloride (MgCl2), and calcium chloride (CaCl2) are also increasingly being used for anti-icing to help reduce the amount of rock salt used and lower overall operations costs.
However, this widespread use of salt has significant impacts on infrastructure, human health, and the environment. Some of the key issues include:
Impacts on Aquatic Ecosystems: Just as we depend on air with the right makeup of oxygen, freshwater species – like fish, frogs, mussels, salamanders, and zooplankton – need water with the right balance of chloride to survive. Increased chloride levels can disrupt their basic functions, such as regulating water content (osmoregulation) and breathing, leading to reductions in fecundity, size, shape, growth, and abundance.
Impacts on Vegetation: Salt in soil water generally makes it more difficult for plant roots to take up water, mimicking drought conditions. High concentrations of sodium and chloride can also be directly toxic to plants, causing leaves to die. Salt can also cause trace metals to be leached from the soil and into groundwater, further damaging the soil environment.
Impacts on Human Health: Ingestion of road salts has been associated with mammalian and avian behavioral and toxicological effects. Sodium from winter salts can also be dangerous for people on sodium-restricted diets, and chloride concentrations above 250 mg/L can give drinking water an unpleasant taste.
Impacts on Infrastructure: Chloride-based de-icers are highly corrosive and can cause significant damage to vehicles, steel bridges, railings, and other metal infrastructure. They can also cause deterioration of concrete structures by accelerating the corrosion of rebar.
Given these widespread impacts, the Government of Canada has designated chloride as a toxic substance under the Canadian Environmental Protection Act, 1999 (CEPA 1999). In response, the Code of Practice for the Environmental Management of Road Salts was established to help municipalities and other road authorities better manage road salt use and reduce adverse impacts while maintaining road safety.
Addressing Salt Impacts through Low Impact Development (LID)
As a stormwater management strategy, Low Impact Development (LID) seeks to mitigate the impacts of increased urban runoff and pollution by managing it as close to the source as possible. LID practices, such as bioretention cells, permeable pavements, and vegetated filter strips, can help address the challenges posed by road salt in several ways:
Reducing Salt Application Rates
Pavement Friction Testing: Research has shown that salting beyond the required amount does not translate into improved safety. Pavement friction testing can help property owners and winter maintenance professionals determine the optimal salt application rates to achieve safe conditions without excess use.
Contractual Clauses: Property owners can structure winter maintenance contracts to incentivize responsible salt use, including clauses that require contractors to monitor weather conditions, track application rates, and implement best management practices.
Delaying and Reducing Salt Discharges
Infiltration and Temporary Storage: LID practices can delay the release of salt to receiving waters by temporarily storing elevated chloride levels in soils and slowly releasing them over time. This can help reduce peak concentrations in discharges and push them into the spring when streams have greater dilution capacity.
Permeable Pavements: Permeable pavements can improve drainage and prevent melt water from ponding and refreezing, reducing the need for salt application.
Protecting Sensitive Environments
Bypass Systems: In drinking water protection areas, bypasses may be used to limit exposure to road salts during winter months, ensuring that heavily-laden stormwater will “bypass” the LID practice and flow to the downstream storm sewer system.
Salt-Tolerant Vegetation: Selecting salt-tolerant plant species for LID practices can help ensure the long-term survival and performance of the system, even in areas with high salt exposure.
Designing LID Practices to Manage Road Salt
When incorporating LID practices into areas with potential salt impacts, several design considerations should be made:
Bioretention Cells
Bioretention cells adjacent to parking areas should always have an underdrain to help manage salt impacts on the vegetation. Reducing salt use through good parking lot design and winter maintenance practices is also crucial.
Permeable Pavements
Permeable pavements can help improve drainage and reduce the need for salt application. Proper maintenance, such as vacuuming, is essential to prevent clogging and maintain infiltration capacity.
Vegetated Filter Strips
Resilient turf grasses, such as those in the ‘Salt Tolerant Mix’ recommended by the Ministry of Transportation, are particularly useful in the design of vegetated filter strips, dry ponds, and enhanced grass swales near salted areas.
Soil and Media Specifications
Careful selection of soil and filter media components is necessary to ensure the long-term viability of LID practices in areas with high salt exposure. Monitoring and testing for soluble salts concentration should be done during construction, assumption, and verification inspections.
Integrating LID and Salt Management Best Practices
By incorporating LID practices and following best management practices for salt application, property owners, businesses, and winter maintenance contractors can work together to create safe winter conditions while minimizing the environmental impacts of road salt.
Some key strategies include:
- Conducting a site assessment to identify problem areas and opportunities for improvement
- Developing a comprehensive winter maintenance policy and plan
- Utilizing specialized equipment and technologies (e.g., temperature sensors, weather forecasting tools) to optimize salt application
- Tracking winter conditions and maintenance activities to ensure adherence to the plan and provide evidence in the event of liability claims
- Structuring winter maintenance contracts to incentivize responsible salt use and implementation of best practices
- Exploring opportunities to close or reduce the use of certain parking areas during the winter months
- Incorporating design features in new developments or pavement upgrades to improve drainage and reduce the need for salt
By taking a proactive, collaborative approach to managing road salt and implementing LID practices, property owners, winter maintenance professionals, and municipal authorities can work together to protect our environment, infrastructure, and public health.
For more information on the latest research, case studies, and resources related to salt management and LID design, visit https://woodstoveheaters.com/.
Key Takeaways
- Road salt is a ubiquitous contaminant in urban environments, with significant impacts on aquatic ecosystems, vegetation, human health, and infrastructure.
- Low Impact Development (LID) practices can help address the challenges posed by road salt through reduced application rates, delayed and reduced discharges, and protection of sensitive environments.
- Careful design and integration of LID practices, such as bioretention cells, permeable pavements, and vegetated filter strips, can mitigate the impacts of road salt.
- Collaboration between property owners, winter maintenance professionals, and municipal authorities is essential to implement best management practices and create safe, sustainable winter conditions.
