Melting Away: The Environmental Impacts of Rock Salt and Possible Solutions

By Cassidy McMann

Since the 1940s, the use of rock salt, or sodium chloride (NaCl), combats snow and ice accumulation on roads during the winter. However, rock salt contaminates water resources, damages vegetation, and harms wildlife. Therefore, many state transportation agencies across the country now utilize alternatives and administer new practices to mitigate the environmental harms of rock salt. Yet, the use of more environmentally friendly methods is not widespread, and transportation agencies should look to the success of other states for guidance.

Transportation agencies often use various means and methods for de-icing roads. For example, the NYSDOT utilizes about six different chemicals and treatments to control ice and snow on its roads. These include rock salt, treated salt, calcium chloride, magnesium chloride, magnesium chloride with organic based performance enhancer (OBPE), and sand. However, rock salt is the most common and least expensive ice control chemical. Today, about 20 million tons of rock salt is used annually, which is equivalent to about 123 pounds for every American. Rock salt works by creating a saltwater brine on the ice, which lowers the ice’s melting point. The salt then breaks into separate sodium and chloride ions which ultimately make their way into waterways and ecosystems.

Once applied to roads, rock salt seeps into ground and surface waters such as streams, rivers, and lakes. High chloride levels in these waters negatively impact a large number of fish, bugs, and amphibians. According to a survey done by the U.S Geological Survey (USGS), 84% of urban streams had increased chloride levels, and 40% exceeded federal safety guidelines for aquatic life. The USGS concluded rock salt to be the source of the contamination. Moreover, high levels of chloride can hinder the growth and reproduction of aquatic species’ and organisms. Furthermore, increased chloride in freshwater ecosystems can negatively impact food sources and disrupt osmoregulation in amphibians.

Rock salt also harms vegetation alongside roadways. Salt, or salt-ladened water, is kicked up onto plants and trees by passing vehicles and covered by the overspray during salt application. Rock salt can cause discoloration or browning of needles on evergreen trees, bud damage, twig and stem dieback, reduced or distorted leaf or stem growth, and reduced plant vigor in contaminated plants and deciduous trees. Furthermore, rock salt negatively affects soil quality and health. Sodium ions in rock salt can displace important minerals like potassium and phosphorus when they become attached to soil particles. As a result, the soil becomes more dense and compacted leading to reduced drainage and aeration. Additionally, due to the increased presence of chlorine and sodium in the soil, plants will absorb these minerals instead of necessary nutrients resulting in deficiencies.

Above all, what may be the most concerning about rock salt is its persistence. Once salt is present in an ecosystem, in the soil, or in a waterway, biological processes will not remove it. According to Paul Gallay, the President of Riverkeeper, increasing sodium concentrations in many freshwater waterways and water bodies could have originated from salt applied decades ago. This salt is now percolating into surface waters today after reaching groundwater years ago. Salt can be transported out of a system through dilution by fresher water. However, this process is only successful when transport from the system is possible, such as through an isolated lake or aquifer.

While there is no perfect, singular solution to rock salt’s impacts, the implementation of new technologies and policies can reduce environmental damage while maintaining public safety. Changes in the maintenance and type of equipment used to de-ice roads offer many achievable options. For example, live edge blades on snowplows are more efficient at removing snow. Currently, the majority of snowplows currently have flat blades. However, most roads are built to have a small curve to prevent water from pooling on the lanes during rainfall. As a result, flat blades have a tendency to leave some ice behind on the road which leads to the need for more salt application. Unlike flat blades, live edge blades can adapt to curves in the road and efficiently remove more snow and ice.

Another change to implement is calibrating snowplows and trucks more frequently. Most agencies and municipalities only calibrate their trucks for salt flow at most once a year. Without proper calibration, trucks could be releasing more salt than intended. “Smart snowplows” are another new innovation that can aid in the reduction of salt use. These plows are outfitted with GPS technology that can gauge pavement temperature, the amount of residual salt from prior applications, and the presence of ice and amount of friction on the road. This sophisticated technology allows for operators to have unique control of the plow’s blades and application rates which results in less salt and chemical use.

Moreover, action can be taken through policy implementation at the state level. For example, in 2020 NY passed legislation establishing the Adirondack Road Salt Reduction Task Force. The Task Force is responsible for studying and assessing the impacts of road salt in Adirondack State Park and must complete a comprehensive review of rock salt application and best management practices. In 2023, the Task Force published its review, which identified instances of exceedances of regulatory contaminant levels and found current water quality standards are not protective enough for the Park’s resources. The review recommends implementing new environmental assessment and monitoring guidelines and providing training to snow and ice removal practitioners for best management practices.

Rock salt likely is not going away anytime soon. However, it is important to acknowledge and address the environmental impacts of rock salt, especially since climate change will likely intensify winter storms and make winter weather more erratic. Rock salt has lasting environmental affects and ultimately wreaks havoc on groundwater and surface waters. Therefore, transportation agencies should continue to implement new technologies that reduce the need for rock salt and states should encourage these changes through legislation and funding.