Salt Vulnerability Analysis improves Canadian city's winter preparedness
At a glance
Like many municipalities forced to manage winter weather, our client, a city located in Ontario, Canada, administers a combination of snow plowing, rock salt, and pre-treated rock salt to keep its roads clear and its town moving. And, as a city that receives snowfall more than 67 days a year and average aggregates of about 640 mm (or more than 25 in) per year, our client stays busy during the winter months and required a Salt Vulnerability Analysis (SVA) to optimize and reduce salt usage and help protect its natural resources.
The challenge
Industry best practices for winter road maintenance primarily use salt, most commonly sodium chloride (NaCl), to melt snow and ice. Using salt to melt ice and snow is both practical and affordable.
However, the salt used on paved surfaces like roads, parking lots, and sidewalks contain chloride ions which persist and accumulate in the receiving landscape, thereby having the potential to affect the receptors in the natural environment detrimentally (i.e., drinking water sources, chloride-sensitive aquatic species, and wetlands).
With an expected population increase of approximately 25 percent through 2031, the City would add pressure for sodium chloride application during winter maintenance. To help better prepare for their winter maintenance program expansion without using greater amounts of salt and to help identify ways to reduce the current usage altogether, our client required an SVA to determine salt reduction strategies within their city limits.
Our response
Teams across GHD and GHD Digital helped our client determine the best management practices through a vulnerability analysis and reduction plan, which was completed across the city with an emphasis on critical infrastructure and key natural resources.
Our team conducted a risk-based assessment through a four-step approach:
- Identification: Our teams identified where salt loading occurred within the City’s jurisdictional area based on land-cover and land-use.
- Realization: We recognized where salt-vulnerable areas existed within the City and associated tolerance threshold concentrations for each receptor.
- Location: Leveraged the power of a geographic information system (GIS) and spatial analytics we identified and traced chloride migration pathways between chloride loading areas and vulnerable receptors.
- Mitigation: Finally, we determined chloride exposure mitigating activities for chloride loading areas that were found to have a substantial upstream impact on affected downstream vulnerable receptors.
The impact
Our results helped the City identify the lake watershed that was at a high to moderate risk of chloride contamination, with the largest source of chlorides coming from residential roads, with some contributions from other sources such as regional roads, parking lots and trails.
As part of the Salt Reduction Plan, we recommended that the City include within their winter maintenance operations alternative de-icing material (i.e., de-icing liquids) or salt application methods and equipment to optimize the amount of material needed to maintain safe road conditions. In addition, we recommended that the City consider exploring the potential for partial closures of low pedestrian and traffic volume parking lots and trails to eliminate the requirement for salt application in these areas.
As a result of this study, we were able to help the City identify locations of road salting impacts and prioritize areas that could benefit the most from salt reduction strategies, all while keeping roads, trails, and parking lots clear and safe for public use. This study also suggested the City should expand its chloride monitoring program to help gauge the effectiveness of the recommended management practices.