The Link Between Road Salt & Drinking Water Contamination:
Road salt is a well-documented contaminant of drinking water sources in both Ontario and across Canada. Each year, rising temperatures during the winter to spring transition leads to snow and ice melt, and eventually rainfall. The road salt accumulated in snowbanks and along the margins of roads and walkways can then percolate through the soil and enter groundwater supplies, or even run-off into nearby surface water reservoirs. As weather regimes shift during advancing climate change, mid-winter thaws are also becoming increasingly common, leading to an increased opportunity for road salt contamination.
One of the greatest concerns about road salt contamination of drinking water is the impact on human health. Although sodium is an essential nutrient, significant research has been conducted on the negative effects of high-sodium intake. Indeed, in the province of Ontario, levels of sodium in raw water sources of 20 mg/L or higher must be reported to Public Health Ontario, even though the taste of water is not expected to be altered until concentrations reach 200 mg/L or higher. Unfortunately, reducing the sodium levels in private well water can be a costly endeavour, and therefore not always accessible to the average well-owner.
Importantly, road salt can also lead to heightened risk of water contamination by other sources through the corrosion of drinking water infrastructure, including residential wells. The chloride in road salt can accelerate the process of “galvanic corrosion”, leading to the thinning and eventual deterioration of well casings and pipe walls. Holes in well structures provide a clear and direct pathway for other contaminants (including pathogens and synthetic chemicals) to enter drinking water supplies.
Mitigation Tactics:
…But how do we protect our drinking water sources while also protecting against accidents on icy roads? Rock salt remains one of the most commonly used de-icing agents of road surfaces in Ontario. However, its ability to melt ice is temperature-dependent; at temperatures below -15 degrees Celsius, the effectiveness of this de-icer is substantially reduced. A common compromise involves the application of a mixture of salt and sand (a popular friction aid) to road surfaces; this practice not only lowers the total volume of salt that is introduced to the environment but also protects against vehicular accidents in colder weather by increasing friction at the road level, even in the presence of persistent ice.
For the individual property owner, the risks of road salt contamination can be mitigated not only by applying a mixture of salt and sand (or another friction aid) but also by understanding just how much salt is needed in order to melt the ice of a given surface area. On average, only a single tablespoon of salt is required to thaw 1 square metre of icy ground – therefore, less than 2 cups of salt are needed to melt the entirety of the average-sized, single-car driveway in Ontario.
A proactive snow and ice management strategy can further empower individuals and households to reduce their road salt application. This can include:
- Identifying the high traffic zones of your property (i.e. areas where you or others will be walking/driving) and limiting salt application to these areas.
- Shovelling or sweeping up loose salt prior to thaw events to reduce the risk of ground or surface water contamination.
- Shovelling snow in piles away from storm/sewer drains, or uphill of bodies of open water.
- Properly storing road salt and other de-icers.
Road salt should be stored in a covered, sealed container and placed over top a waterproof or impermeable pad/surface. These containers should be placed out of the way of large equipment or vehicles (e.g. snow ploughs) to avoid damage that could result in a spill.
Tips for Private Well Owners:
For households relying on private wells, additional steps are recommended to protect the quality of your drinking water. A wide buffer should be left around all wells, where no salt is applied or stored, in order to limit the potential for salt damage and contamination. Similarly, shovelled snow should not be piled and stored directly near or uphill of a well.
The Cataraqui Source Protection Authority, in line with provincial government, strongly advises that well owners test the quality of their water following heavy storm events and major periods of thaw to stay apprised of the condition of their well water quality. Well water can be assessed for sodium levels (and other parameters) through an accredited laboratory. Unfortunately, unlike tests for bacterial indicators of contamination (such as E. coli and total coliform count), tests for sodium levels are undertaken at the cost of the well owner. Some households might choose to delay testing until visible signs of corrosion of household pipes and plumbing are evident, signalling a high sodium content in their well-water, but testing for sodium in advance of this could prolong the lifespan of this infrastructure.
Resources:
The following is a list of helpful resources for more information about road salt and drinking water protection: