By: Imbrium Systems
It’s that time of year again - temperatures have dropped below freezing, and the wintery weather has blown in. Departments of Transportation, state, local and city road crews are being kept on their toes, applying roadway treatments and safe passage for all of us. It is estimated that the US spends approximately $2.3 billion annually to keep highways free of snow and ice, and roughly 20% of transportation department budgets goes toward winter road maintenance. Over 43% of the mined salt is applied for winter deicing efforts, when in comparison only 4% is applied to our food. In the US, over
19 million tons of road salt is annually spread over our highways, roads, parking lots and sidewalks to keep us safe.
As development and urban sprawl continues, our impervious surfaces continue to increase. Along with this is the need to keep these surfaces safely deiced. But, how do all those chlorides spread across the road, highway, parking lots and sidewalk impact us?
Currently, there are not many environmentally safe, effective and inexpensive alternatives to road salt. Sand and chip stone is likely the most environmentally friendly, however, these materials do not deice; they are applied to offer traction on top of ice. Once buried under new snowfall, more needs to be reapplied to be
effective. These materials are often ground down
by vehicle wear into smaller, finer particles over time. Once a thaw occurs, they are washed into our storm drains and waterways which is not desired. This can be prevented by stormwater treatment practices being implemented, both large and small scale, with land-based treatment or Oil-Grit-Separators (OGSs). Spring time clean- up is required, including street sweeping, and vactoring of catchbasins and OGS units to ensure the drainage system remains as designed.
Sodium chloride (salt), is only effective at temperatures above -18° C and, therefore, when colder temperatures get this cold, sodium chloride is not the salt type applied. Other chemical deicers are typically chloride-based salts of calcium, potassium, or magnesium, with some being effective at temperatures as low as -34° C. There are also non-chloride chemicals available including calcium magnesium acetate, potassium acetate, and urea. Newer liquid byproducts from the food or beverage industry, such as beer waste and beet juice, are mixed with rock salt and applied to roadways. The newer organic products come with other environmental issues. For example, as these byproducts like
beet juice or beer waste wash into our waters, they naturally breakdown, consuming oxygen from the water, the same way algal blooms do, which can have negative environmental impacts.
Bottom line, deicers are polluting our waters, while keeping our streets safe during winter travel. When snow and ice melts, all roadway treatments are washed into our catchbasins, eventually washing into our lakes, streams, wetlands and groundwater. Once present in water, there is no easy way to remove chlorides. No existing stormwater treatment system exists to capture and retain salts, or chlorides. Chlorides may be loosely retained in soils or in water, but will continue to flush through the system as more water enters, building up at the downstream end of the watershed, or within groundwater. Chloride from deicing salts also has the potential to increase the mobility of metals loosely attached to sediments, as does other deicing chemicals, calcium and magnesium. Additionally, research indicates the toxicity of available metals increases from the use of salts.
In high concentrations, chlorides can be harmful to our freshwater aquatic life. Chlorides also have negative and destructive impacts on our infrastructure, as they corrode metal and pit concrete, rust metal vehicle components, kill non-salt tolerant vegetation, and are harmful to soil, pets, and wildlife, as well as contaminate our groundwater and drinking water supplies. The Guidelines for Canadian Drinking Water Quality’s chloride threshold is 250 mg/L, which is based on taste and corrosion of distribution infrastructure. It only takes roughly 5 mg of salt in 20 liters of water to reach this concentration. The Canadian Water Quality Guideline for chloride for the protection of aquatic life has a long-term exposure limit of just 120 mg/L and a short-term exposure limit of 640 mg/L. To put this in perspective,
small urban watersheds with dense populations have measured chloride concentrations ranging from as low as 15 mg/L, to over 20,000 mg/L during the winter and spring melts, hence the issue at hand. Once chlorides are present in water, it is a permanent fresh water pollutant, and continues to accumulate
In 2001, an assessment report was conducted by Environment Canada leading to the addition of road salt on the Priority Substances List, and then a Code of Practice for the Environment Management of Road Salts in 2004. Since then, there have been many improvements, such as improved salt distribution management, storage management, use of new technology for more accurate material distribution on paved surfaces and application of wet brine pre-treatments prior to inclement weather approaching. Larger government agencies have begun using new weather measurement and real-time information, including imbedded road sensors combined with local weather stations, to better plan deicing operations and material use proactively. Smarter deicer application has also saved money on labor and products as well as reducing damage to infrastructure, vehicles, plants, water supplies and our environment. Each person contributes to the attitudes and practices leading to a growing volume of deicers applied each year. Shifting public attitude toward a more sustainable salt application is truly required to reduce usage.
So with doctors and dieticians alike telling many of us to reduce our salt intake, this winter, consider taking these same recommendations into account in your area of influence as it relates to impervious surfaces. Less is more when it comes to applying deicers.
In short, when it comes to maintenance of stormwater infrastructure…YES, WE HAFTA!
Part 1: Doo-Doo No-No
Part 2: Loving Your Car and the River Too!
Part 3: Taking Out the Trash
Part 4: AWW, DO I HAFTA?