IMPACT OF WINTER DE-ICING CHEMICALS ON WATER QUALITY AND THE ENVIRONMENT: WHAT DO WE KNOW AND WHAT DOES THE FUTURE HOLD?

Because halite (NaCl), by far the most common road de-icing agent, is so soluble, it invariably ends up in our water resources. As a result, groundwater and surface waters in northern urban regions in the U.S., Canada, and Europe are seeing increases in chloride (Cl^-), sodium (Na), and TDS concentrations. These increasing trends date back to the 1960s, when widespread application of road salt began in earnest. The Chicago, IL, region is a prime example: almost all rivers and streams being monitored in the region have had significant increases in Cl^- and Na concentrations since at least the mid-1970s. Baseflow concentrations of Cl^- are > 100 mg/L in most streams in the region and some streams have peak concentrations in excess of 2,000 mg/L.

The amount of road salt applied during a winter that is retained within a particular watershed can vary widely, depending on hydrogeological conditions and stormwater management practices. Published estimates vary between 14 – 77% annually. This retained road salt provides a long-term source of elevated TDS to aquifers and stream baseflow.

The societal and financial costs of road salt runoff can be enormous but have been largely uncalculated. These costs include increased treatment for drinking water, ecological damage, and increased corrosiveness of water. These costs must be weighed against public safety and local economic considerations. The good news is that research is drawing attention to these problems and many agencies and entities responsible for road de-icing are adopting more environmentally friendly application practices.