Road Salt that is routinely applied to Road surfaces in winter to make them less treacherous tends to linger in the environment, resulting in drinking water sources becoming contaminated. Now a new study which was recently published in the Journal of Environmental Quality, identifies geological and landscape characteristics associated with high salinity levels in water wells that supply a suburban area in Southeastern New York with drinking water.

According to Victoria Kelly, Environmental Monitoring Program Manager at the Cary Institute of Ecosystem Studies, and lead author of the study, every year millions of metric tons of road salt is applied to roads across the country. This salt can seep into the soil where it can accumulate and contaminate groundwater. The aim of this study was to gain a better understanding of why some wells are more at risk to contamination by road salt than others so that we can inform managers responsible for protecting water quality.

Kelly and her research team analyzed data from water samples collected from more than 950 private water wells supplying residents in the East Fishkill area of New York with drinking water. They found soduim levels in more than 50% of the wells was higher than the federal safety standard set by the EPA. They found that the distance of the well from the nearest road, as well as the amount of pavement nearby had a great influence on salinity levels of well water. Yet, the depth of the well and the type of road (back roads to interstate highways and everything in-between) had little influence, which was surprising.

The researchers used GIS technology to map sodium and chloride levels of wells and to identify landscape surface features found in the area surrounding each well. They looked at local variables such as depth of well, distance from roads, elevation of the well in relation to roads nearby, impervious surface, geology of the surface soils, and type of soil to identify links between well salinity and infrastructure development.

The study's finding echo similar studies that suggest impervious surfaces such as roads and pavements contribute to groundwater salinization and that it is ultimately a consequence of urban development. Chloride concentrations in wells located closer to roads was higher than those further away, but the type of road — whether a minor or major road — had no impact. The depth of the well had no significant impact on salt levels, and elevation in relation to roads nearby was only a factor when roads were located more than thirty meters from a nearby well.

The study identified several hotspots where groundwater salinization was particularly high. The authors suggest that steep inclines and sharp turns in some roads could be a contributing factor as these would require a heavier application of road salt. Similarly, narrow streets which only older salt trucks can pass through could result in less efficient salt application due to outdated application technology.

"Understanding the landscape features that lead to increased groundwater salinization can inform targeted salt application," explains Stuart Findlay, a freshwater ecologist at the Cary Institute of Ecosystem Studies and co-author of the study. "The time to act is now, as we know it can take decades or more for the salt currently in groundwater to flush out."

The study only identified a single cold spot, located in an area where housing density was low, which reinforced the link between urbanization, road salt application and groundwater salinization.

"In planning efforts to minimize road salt impacts, our findings tell us that smaller roads should not be overlooked and areas with a lot of pavement and porous, well-drained soils are most at risk of experiencing salinization", says Kelly. "Road salting is not one-size-fits-all undertaking. More targeted approaches will keep roads safe while reducing unintended consequences to drinking water supplies."

Journal Reference

Victoria R. Kelly, Mary Ann Cunningham, Neil Curri, Stuart E. Findlay, Sean M. Carroll. The Distribution of Road Salt in Private Drinking Water Wells in a Southeastern New York Suburban Township. Journal of Environment Quality, 2018; 0 (0): 0 DOI: 10.2134/jeq2017.03.0124