By Mike Ekberg, MCD water resources manager
The last couple of winters have had a strong grip on the region, making driving a challenge. Communities across the region use road salt to melt snow and ice and keep drivers safer, but at what cost?
Use of road salt in the northern U.S. has doubled the amount of chloride in rivers and streams in just two decades (1990-2011). “It’s estimated that more than 22 million tons of salt are scattered on the roads of the U.S. annually—about 137 pounds of salt for every American,” according to a Jan. 6, 2014 story at smithsonian.com.
A recent report showed that chloride levels in rivers and streams were highest in the winter, but chloride concentrations were rising even when road salt wasn’t being applied. This suggests that after salt applications, chloride was temporarily stored in shallow aquifers and then slowly released into rivers and streams throughout the year.
Runoff carrying road salt can have negative impacts on aquatic ecosystems but doesn’t present much of a threat in the Great Miami River. Data collected on the Great Miami River near Miamisburg shows that increased chloride concentrations from road salt applications don’t last long and the salt flushes through the river fairly quickly.
Perhaps, a greater threat is that dissolved road salt can penetrate into groundwater used as a source for drinking water. Salt reaching our aquifers (which stores groundwater) does not flush through as quickly as it does in rivers and streams. In extreme cases, improper storage or use of road salt can impact the quality of drinking water.
High chloride levels in drinking water forced the community of Camden to shut down a well in 2010. For years, chloride levels in the aquifer at Camden appeared to be relatively stable. But in 2009, chloride levels tripled, jumping from around 40 milligrams per liter to 120 milligrams per liter. That’s the same year that Camden residents began to complain about a salty taste in their water.
The cause was a large road salt storage facility located near the well field (drinking water source) that was not covered. When rain dissolved some of the salt, it was carried into the aquifer underlying the facility. Eventually, the levels of dissolved salt in the groundwater forced Camden to shut down the well so it was no longer used for drinking water. Camden was forced to seek an alternate source of drinking water.
The U.S. Environmental Protection Agency has set a secondary maximum contaminant level for chloride at 250 mg/L. Chloride in groundwater does not present a direct health risk. It does however present a taste issue when present in high enough concentrations.
After Camden’s experience, a work group, of which I was a member, developed statewide salt storage recommendations. Communities now have guidelines to follow for salt storage including:
- Guidelines for constructing salt storage facilities.
- Recommendations for covering salt stored outside.
- Managing storm water that flows off the storage site.
In addition to implementing guidelines for salt storage, communities can address potential impacts of road salt applications on groundwater through their source water protection programs.
The bottom line is we need to be aware of the most sensitive environments where road salt storage and applications have the greatest potential to get into aquifers. These areas can be mapped and monitored. If chloride levels begin to rise communities can reduce applications in the most sensitive areas near well fields.
Camden well field stories: