Road Salt, Winter Safety, and Stream Health – Dispatches from the Intern Desk

This series examines advanced stormwater programs and their technical underpinnings, providing insights for practitioners, policymakers, young professionals, and students across the Chesapeake Bay region.

by Jolette Lima

This winter, communities across Maryland prepare for snow and ice with a familiar solution: road salt. Spreading salt on roads, sidewalks and driveways helps prevent build up of ice and keeps daily life moving after heavy snowfalls. But road salt doesn’t just disappear when the ice melts. Instead, much of it moves through our neighborhoods and into nearby streams, where it can remain for years. As winter storms become more unpredictable and salt use continues year after year, understanding how the salt affects our waterways has become increasingly important. 

One researcher who has spent years studying this issue is Dr. Joel Moore, a professor at Towson University whose work focuses on how road salt impacts Maryland’s streams over the long term. 

Dr. Joel Moore is a Professor of Geosciences at Towson University and the Director of the Environmental Science and Studies Program. His research background is in geochemistry, with a particular focus on urban streams and groundwater systems. 

Since moving to the Baltimore region, Dr. Moore has been involved in long-term stream monitoring efforts and has collaborated with the Chesapeake Stormwater Network and researchers affiliated with the Baltimore Ecosystem Study. His work helps connect everyday winter practices, like salting roads, to changes in stream chemistry, aquatic life, and drinking water sources across Maryland. 

Road salt works by dissolving in water and making ice melt at lower temperatures. That same property, however, allows it to move quickly through the environment. 

After snowstorms, melting snow carries dissolved salt across roads, sidewalks, and parking lots. Then the runoff flows through storm drains and pipes directly into nearby streams, causing spikes in chloride concentrations during winter. Some salt may infiltrate into the ground instead of flowing straight into storm drains. From there, it enters groundwater, where it can remain for years or even decades before slowly emerging in streams. 

A key takeaway from Dr. Moore’s research is that some of the salt affecting streams today was applied many winters ago. Even if salt use were reduced immediately, chloride levels in many streams would take a long time to decline.  Dr. Moore’s research quantified chloride inputs from deicing salt to the Baltimore City region’s drinking water reservoirs over four decades, showing just how persistent these legacy salts can be. Their work used long-term monitoring and statistical modeling to show that decades of road salt application have steadily increased chloride inputs to major reservoir tributaries, affecting not just stream chemistry but also the quality of drinking water sources for large populations. Elevated chloride levels are linked to changes in water treatment dynamics, such as enhanced formation of disinfection byproducts and increased corrosivity, which can raise concerns for infrastructure and public health in addition to ecosystem stress. 

Long-term monitoring shows that chloride concentrations in Maryland streams are increasing over time, especially in urban areas. Highly developed watersheds with lots of pavement tend to experience the highest levels. 

In some urban streams, winter chloride concentrations already meet or exceed EPA criteria designed to protect aquatic life. But even in streams that fall below those thresholds, his aforementioned research suggests that lower concentrations can still harm sensitive aquatic insects and other organisms that form the foundation of stream ecosystems. 

Unlike many pollutants that fluctuate seasonally, chloride often remains elevated year-round. In urban streams, concentrations frequently stay high even in summer, meaning aquatic life is exposed continuously rather than just during winter storms. 

Stormwater management practices are designed to protect streams by reducing flooding and erosion. Instead of piping runoff directly into streams, modern systems like stormwater basins, infiltration practices, and green infrastructure allow water to soak into the ground. While these systems provide many benefits, Dr. Moore’s research revealed that they can move the salt runoff into groundwater more efficiently. Once there, chloride is stored and slowly released back into streams over time. 

This leads to higher summer chloride levels, longer-lasting contamination, and increased stress on aquatic organisms during the months when they are most active. The salt problem becomes a year-round challenge, instead of just a winter one. 

Since groundwater also supplies reservoirs and drinking water sources, in parts of Maryland, sodium levels in drinking water already exceed EPA recommendations for people on low-sodium diets, raising potential public health concerns. 

Salt also alters soil and groundwater chemistry which makes stream restoration projects more difficult and less effective. Elevated chloride can interfere with biological recovery even in streams where physical habitat has been improved. 

Over time, these chemical changes make it harder for streams to return to healthy, resilient conditions. 

One of the most surprising findings from Dr. Moore’s work is how long salt remains in groundwater, because it sometimes remains there for decades. In many cases, streams never fully return to fresh, low-salt conditions, creating chronic stress for aquatic life. 

One teaspoon of salt dissolved in a five-gallon bucket of water is enough to reach the EPA’s chloride threshold for aquatic life.

This simple fact shows just how little salt it takes to create environmental impacts and how easily over-application can occur. 

The overall goal isn’t to eliminate road salt entirely, but to use it more thoughtfully and efficiently. 

For residents, small changes make a big difference: 

• Use much less salt than you think you need (about one 12-oz coffee mug full covers about 10 sidewalk squares or a 20 foot driveway)
• Shovel first, salt second (you can even sweep and reuse unmelted salt!)
• Only salt areas that refreeze or remain icy 
• Pay attention to shaded areas, which stay cold and wet for longer, versus sunny areas (where salt will be more effective) 

For municipalities, solutions focus on smarter management: 

• Better calibration of spreaders and equipment 
• Increased use of brine and liquid salt methods as alternatives 
• Monitoring salt use under MS4 permit requirements 
• Long-term cost savings through reduced over-application 

Many of these approaches protect water quality while still maintaining winter safety. 

Ongoing research is now focused on determining whether recent changes in salt application practices are making a measurable difference. By establishing long-term baselines and tracking winter chloride spikes, scientists like Dr. Joel Moore hope to evaluate what strategies are truly effective. 

Winter safety and healthy streams don’t have to be in conflict with one another. Small changes in how we apply road salt, whether on a sidewalk, a parking lot, or a highway can significantly reduce harm to our waterways.