To reduce hazardous road conditions caused by snow and ice, many counties, municipalities, homeowners, and others use deicers. Salt is the most common option to treat roads.
But how might road salt impact groundwater? Does it have impacts only in winter, or does it have lasting impacts year-round?
These are key questions that Rachel McQuiggan, a researcher at the Delaware Geological Survey, and colleagues wanted to answer. In their research, they monitored stormwater and groundwater at an infiltration basin.
“Most stormwater management practices are designed to protect surface waters,” McQuiggan said. “Infiltration basins, and even some types of green infrastructure, are designed with the idea that stormwater benefits from a natural ‘filtering’ of contaminants as it infiltrates through soil, and contaminants dilute as that recharge mixes with existing groundwater.”
She adds that these are used to prevent contaminants like salt from being discharged straight into surface water. But in states like Delaware, groundwater contributes up to 80 percent of the water in rivers and streams. This means that salt will eventually reach rivers and streams, just on a longer timescale.
The researchers monitored the infiltration basin from mid-May 2019 to mid-February 2022 to evaluate the impact road salt had on groundwater quality. One aspect of their findings showed that geological complexity, such as differences in subsurface soil properties, influenced how salty stormwater moved through groundwater.
The researchers explained it is important to consider things like placement, depth, and frequency of monitoring groundwater to get the full picture.
The team also found that groundwater is impacted by road salt throughout the year, not just during winter. This is because the salt is retained in the soil in the infiltration basin. Salt is made of sodium and chlorine atoms, and chloride more easily moves in water. However, sodium more easily latches onto soil particles.
During other parts of the year, stormwater that does not contain much salt enters the basin and flushes sodium from the soil into the water. The results of the study also suggest that a higher salt content can cause radium to enter the groundwater.
While there are other deicers available, they are not all as effective as road salt and each has its own pros and cons. Sand is a popular option to increase traction and minimally affect groundwater but could require extra maintenance like street sweeping, McQuiggan said.
Many cold areas depend on deicer to ensure the safety of drivers, bikers, and pedestrians. The researchers say their work provides direction on how to best monitor the impacts of deicer on groundwater so adjustments can be made if needed.
“Groundwater supplies almost half of all drinking water worldwide,” McQuiggan said. “In central and southern Delaware, groundwater is the only source of potable drinking water. Hopefully the results of this project will encourage best management practices for deicer use to protect groundwater resources.”
NGWA’s technical journal Groundwater has covered the topic multiple times through the years as well.
Among the papers on the subject are “Numerical Investigation of Road Salt Impact on an Urban Wellfield” by M.L. Bester, E.O. Frind, J.W. Molson, and D.L. Rudolph. It was published in the March-April 2006 issue and discusses the impact of road salt on a wellfield in a complex glacial moraine aquifer system.
Another paper, “Permeable Asphalt: A New Tool to Reduce Road Salt Contamination of Groundwater in Urban Areas” by Michael E. Dietz, Derek R. Angel, Gary A. Robbins, and Lukas A. McNaboe, was published in the March-April 2017 issue and details permeable asphalt as a potential tool to reduce road salt contamination in groundwater in urban areas.