Breakdown: Road salts work, but why they also can harm the environment
MEMPHIS, Tenn. (WMC) - Winter is here! And with it, tons of salt on our roads.
Road salting is a necessity to keep people safe during snow or cold weather as they drive to work or take their kids to school. The amount of salt used for deicing roads and highways has increased over the years along with the year-round transportation of goods and services.
TDOT’s statewide 2021/2022 winter weather budget is $25.6 million and includes salt, salt brine, overtime for employees, and equipment maintenance. The department has nearly 200,000 tons of salt and more than 1.5 million gallons of salt brine ready for use with salt vendors to ready to refill salt bins as needed in all 95 Tennessee counties.
The many benefits that road salting provides, however are matched by some opportunities for improvement, according to the U.S. Environmental Protection Agency:
Though seemingly harmless to us, rock salt can have corrosive effects in large quantities that affects cars, trucks, bridges, and roads resulting in approximately $5 billion dollars in annual repairs in the U.S. alone.
In addition, road salt can contaminate drinking water, kill or endanger wildlife, increase soil erosion, and damage private and public property. Alternative methods are needed to mitigate these drawbacks.
High sodium levels in drinking water affect people with high blood pressure, and high chloride levels in surface waters are toxic to some fish, bugs, and amphibians. Furthermore, excess road salt accumulates on roadside areas killing roadside plants and harming wildlife that eat the salt crystals.
Salty roads also attract animals like deer and moose (who love licking up the salt), increasing the probability of accidents and roadkill.
The most common substance used for deicing roads and highways is Sodium Chloride (NaCl) or table salt known as rock salt when spread on the road because of its much larger granules.
Rock salt is very effective at melting snow and ice and is considered to be pretty cheap. But rock salt’s low cost does not include the potential damage to property, infrastructure, or the environment.
The environmental toll and long-term costs of rock salt have inspired some states to search for alternative management practices:
- Magnesium chloride (MgCl) is considered to be safer than NaCl but requires twice the amount to cover the same area, making it more expensive.
- Calcium chloride (CaCl) is safer for the environment but is three times more expensive than NaCl and so is typically reserved for use in vulnerable areas.
Innovative solutions that limit the amount of rock salt needed are also being explored, such as:
- Applying a brine solution (23.3% salt-water solution) to the roads before a forecasted snow event. Known as anti-icing, this practice prevents the formation of frost on pavement, and its implementation has been increasing across New England.
- Another alternative is the use a 50/50 salt and sand mixture. The sand doesn’t help to melt the snow or ice but increases traction, reducing the amount of road salt required.
- After the snow or ice melts, however, the remaining sand mixture gets washed away, filling catch basins or adjacent waterbodies with sediment, which then requires additional work hours and money to maintain and keep the basins clear.
- Occasionally, some sand gets washed away into adjacent water bodies: clouding the water and making it difficult for aquatic plants to photosynthesize.
- Other alternatives include adding biodegradable substances like beet juice, pickle juice, and molasses to the salt solution to enhance performance. These salt additives lower the freezing point of water, slowing down the formation of ice; they also aid in traction, and make the solution stickier so less salt gets splashed off the roads and wasted.
New technologies, such as porous pavement, are being engineered to reduce runoff from roads and have been found to reduce snow and ice cover.
- Porous or permeable pavement allows standing water to seep through, removing water from roads that would normally go through freeze-thaw periods, thus preventing ice formation on the roads. A recent study showed that the annual median snow/ice cover on porous pavement was three times lower than that of regular pavement, and that the low amounts of ice/snow accumulating on porous pavement led to a 77% reduction in annual salt used for maintenance.
- Another technology gaining traction is solar roads, made up of engineered solar panels that can be walked and driven upon. This technology has the potential of converting every single road into a source of renewable energy. In addition to the added energy source, this technology could also eliminate the need for road salt by melting ice or snow through heating water in pipes embedded in the road.
While no perfect solution exists to keep our roads clear in winter, the number of tools available to public works departments continues to increase, allowing for a tailored approach to clear roads in an environmentally conscious manner without risking driver safety.
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