This summary was written by Mark Southerland for the Howard County Environmental Sustainability Board.
We are all familiar with the use of road salt to melt ice and snow from paved roadways in the winter. There are a variety of deicer products, but the vast majority of what is used is common table salt—sodium chloride (Na-Cl). Road salt improves tire adherence to the pavement, greatly increasing vehicle safety, but has adverse effects on property and the environment beyond the road surface.
The types and extent of these adverse effects are becoming clearer through recent research. Most concerning is the discovery that high salt levels remain in streams throughout the summer, owing to salt contamination of shallow groundwater that feeds the streams. Chloride is inert and will remain in soils and groundwater indefinitely.
The significance of these effects has prompted the Maryland Department of the Environment (MDE) to develop draft water quality criteria for chloride in surface waters. Should these criteria become finalized, Howard County and other NPDES permit holders will face a serious challenge of meeting these water quality criteria and maintaining road safety.
Effects of Road Salt on Aquatic Life
Chloride in surface waters can be toxic to many forms of aquatic life, including fish, invertebrates, and amphibians. Elevated chloride levels pose a risk to species survival, growth, and/or reproduction. The range of effects varies with the mix of ions present, but can also include the release toxic metals from sediment. The EPA has established an acute (1-hour average) standard of 860 mg/l for chloride and a chronic (four-day average) standard of 230 mg/l. MDE draft criteria for both acute and chronic exposure are based on current research and range from 270 to 360 mg/l.
Other Effects of Road Salt
- Cost of Treatment for Drinking Water – The chloride concentrations in receiving waters at the WSSC Patuxent Water Filtration Plan has increased 3-fold since 1990. Costly additional treatment is required to address corrosion (such as leaching of lead in the distribution system that happened in Flint, MI), health, and taste concerns.
- Contamination of Wells – Sodium in drinking water is a health concern for individuals restricted to low-sodium diets due to hypertension (high blood pressure), as well as posing taste and odor issues. It can also corrode pipes and appliances. In Baltimore County, the number of claims for salt-contaminated drinking water wells has increased many-fold in recent years.
- Corrosion of Infrastructure – Chloride can penetrate and deteriorate concrete on bridges and other structures, as well as damage vehicle parts. The cost of corrosion damage and corrosion protection for highways and the automobile industry may cost billions of dollars a year.
- Soil, Vegetation, Wildlife, and Pet Impacts – Damaged terrestrial vegetation along roadsides is a visible impact of road salt, while the impact on emergent and submerged aquatic plants is less visible but equally common. Salt can also degrade soils and increase erosion. Both pets and wildlife are at risk for increased salt consumption, which can be fatal to birds.
- There are no easy solutions, but the State Highway Administration has reduced its application of salt by 1/3 over the last 5 years without degrading service through pretreatment with brine solution and other actions.
- All road salt operations should review and improve their storage and application practices so that they apply the right amount at the right time. Smart technologies for temperature prediction and precise routing and application should be pursued
- It is important to note that state highways apply only about 25% of the salt in Maryland, with 35% applied by local governments, and 40% by private property owners. New Hampshire has an innovative program to reduce over application by businesses concerned with “spill claims.” This GreenSnowPro programs provides insurance coverage for business that employee certified road salt applicators.
Take-a-way: Our actions always come back to haunt us … and cost us money. It is time to take a much harder look at the balancing act we are doing with short term public safety and long term water supply and quality impacts. Do we have to salt as much as we do?? What are the real costs of our current approach to snow and ice?
Mark Southerland has a doctorate in biology and lives and works in central Maryland. He can be reached at firstname.lastname@example.org.