Road Salt, Corrosivity and Lead
Every year in the fall, private contractors, road agents and state employees begin to prepare for winter. They go over their current routes, and make sure all of their trucks are tuned up and ready to handle the incoming storms. They also make their annual calls to their supplier and purchase all of the salt they’ll need. Over the course of the next five to six months salt will be spread over every road, parking lot, walkway and driveway in the state. While applying salt to these areas improves public safety, it has created an increasing problem right below our feet.
Salt lowers the freezing point of water. Once salt binds to the water molecules, the ice is turned into a mixture of water and salt, known as brine. This brine then seeps into the ground and makes its way into groundwater. Road salt is a compound of sodium and chloride. In high concentrations, the chloride in the brine can cause water to become corrosive because it lowers the water’s pH level. Our drinking water systems are reliant on thousands of miles of piping throughout the state. Once chloride enters distribution pipes, the risk for corrosion increases. Older water pipes may contain lead and copper. While public water systems are required to monitor drinking water for lead and copper levels and control pH, higher chloride levels leading to lower pH may present a risk for both private and public well users. (See a separate article in this issue on the TrACE program, which found that private well users in New Hampshire are more likely than PWS customers to have elevated lead levels in their drinking water.)
In 2011, DWGB worked with the United States Geological Survey (USGS) to analyze chloride and sodium trends in drinking water using historical water quality monitoring data from public water systems and private wells. The USGS report documented dramatic increases in groundwater levels of sodium and chloride between 1960 through 2011, particularly from 2000 to 2011. The report compiled groundwater quality data by town and notes, “Between 1995 and 2005, the number of towns with median concentrations of chloride greater than 20 mg/L almost doubled from 35 to 65, and the number of towns with concentrations of chloride greater than 40 mg/L more than tripled from 10 to 34.”
Although the use of road salt has been the number one contributor to chloride and sodium contamination in groundwater, water softeners are another growing source of salt contamination. There has been an increase in water softener installations across the state, despite the fact that most homeowners do not need it to make their water potable. Learn more about how to safely reduce the use of salt in your community here or contact Ted Diers at theodore.e.diers@des.nh.gov, Marilee Enus with the UNH T2 Program at (603) 862-1362 or the SnowPro Program at salt@des.nh.gov and call (603) 271-5329.