health and science

Road salt has been a hot topic of discussion on LincolnTalk recently. How is it used to treat Lincoln’s roads? How much salt is in town water? Is it harmful for the environment?

Lincoln’s Department of Public Works, like that in most other U.S. cities and towns where it snows, have been spreading salt crystals on roads for decades. Road salt (sodium chloride, the same chemical as table salt) lowers the freezing point of water, so ice and snow containing dissolved salt will melt at colder temperatures, resulting in roads that are wet rather than slippery and thus improving safety for vehicles.

About four or five years ago, Lincoln began applying a thin coating of salt water (brine) on roads before an anticipated storm, which appears as thin white stripes. This prevents ice and snow from immediately adhering to the roadway and “breaks that bond,” DPW Superintendent Chris Bibbo said. Pre-treating roads with brine means that less road salt is needed during and after the storm.

In recent weeks, several residents have shared photos on LincolnTalk of what appeared to be heavy coatings of rock salt on some town roads. Around the same time, The New York Times and The Washington Post published stories about a study in the scientific journal Frontiers in the Ecology and Environment titled “Road salts, human safety, and the rising salinity of our fresh waters.” Road salt can damage plant life when it drains or plows push it to the side of the road, and too much sodium in drinking water over a period of years can be harmful to human health.

In the 1980s, there was enough concern over road salt that the amounts used in Lincoln were reduced, and signs appeared at the town line on some roads noting that “minimum salt is used in Lincoln” as a warning to drivers that the road they were on might suddenly get more slippery. But problems arising from under-salted roads caused the pendulum to swing back the other way.

“Some roads were just rutted ice in a particularly bad winter,” Water Commissioner Ruth Ann Hendrickson said. There have been at least two deaths in recent years after car accidents involving icy roads. George Elder died after his car skidded on Sandy Pond Road, according to the Boston Globe article published on March 4, 1984. There was  another accident on icy Moccasin Hill where the driver was badly hurt, “and it really triggered people to say we need to have more” salt, she added.

How much salt does the DPW use? That depends on the weather and road conditions. “We try and use the least amount of material possible during winter storm events while doing our best to provide a safe transportation network,” Bibbo said. “Most winter storm events provide different sets of challenges and therefore require different treatment options. For example, a fast-moving snowstorm typically requires a different strategy than a rain-to-freeze event. Storms that produce mostly snow typically require more of a plowing technique than treatment. The weather conditions that we had in mid- and late December were challenging, with rain and mist repeatedly freezing on the roads.”

On Christmas Day, there was light snow and rain while the temperature hovered around freezing, and police reported several car accidents that morning. On January 5, while Lincoln didn’t see particularly hazardous conditions, a flash freeze caused numerous accidents in central and western Massachusetts despite road treatments. “I’ll tell you that I can speak for all our snow and ice managers that I’d rather get a foot of snow,” state Highway Administrator Jonathan Gulliver was quoted as saying.

Another variable is the ratio of sand to salt used on a given day. The DPW has piles of both (though the salt is covered, as required by the DEP), and the department decides what mixture to use for each weather event, Bibbo said. A higher proportion of salt is needed for icy conditions, whereas snow calls for less salt but more sand to aid in traction.

Occasionally there’s an accidental release of a large amount of the salt/sand mixture in one spot, “but we obviously try to avoid that at all costs,” Bibbo said. The DPW is looking into purchasing calibration equipment to more precisely control the rate at which the material is released as trucks drive over roads. The rate is now manually controlled by DPW crews based on their experience and road conditions, he added.

Asked about the use of road salt in environmentally sensitive areas, Bibbo said, “We don’t do anything different on roads near wetlands.” Roads are treated differently only according to traffic volume and speed, so main roads like Route 117 and Route 136 will get more total sand and salt. “The more minor roads typically may not be treated at the same frequency as the major roads, but all roads typically get treated,” he said.

Sodium in town water

The Lincoln Water Department tests untreated water from Flint’s Pond and the well on Tower Road (which provides about 30% of town water) once a year. The most recent water quality report shows that sodium levels ranged from 14.1 to 54.5 milligrams per liter or parts per million (ppm) in 2020. Unlike with some other chemicals and bacteria, there are no regulatory limits on sodium in drinking water, but the state DEP’s Office of Research and Standards guideline (ORSG) is 20 ppm.

The U.S. Environmental Protection Agency also has nonenforceable guidelines for secondary maximum contaminant levels (SMCLs) for various contaminants; exceeding those levels can cause cosmetic or aesthetic effects in drinking water. The SMCL for sodium is 250 ppm.

Interestingly, Lincoln’s higher 54.5 ppm sodium concentration is in water from the well, not Flint’s Pond, which abuts a portion of Sandy Pond Road, according to Darin LaFalam, Water Department superintendent. This could be due to mineral deposits in the Tower Road groundwater, he said.

“Detected levels of sodium are well within recommended limits. Nonetheless, people restricted to sodium intake of 500 mg/day due to health issues such as high blood pressure, heart disease, or kidney failure should discuss with their doctors whether to drink Lincoln water,” the town’s 2020 report notes.

For healthy Americans, the Centers for Disease Control and Prevention recommends consuming no more than 2,300 mg per day of sodium. In comparison, a liter of water from the Lincoln well contained a maximum of 54.5 mg in 2020. More than 70% of dietary sodium comes from processed and restaurant food, with 14% from naturally occurring sources and 11% from salt added during cooking or at the table.

Water from the well and pond water is not tested at different times of year, so it’s impossible to know whether sodium levels vary by season (for example, whether there’s more in the winter from road runoff into the pond). It was not immediately clear whether sodium levels in Lincoln’s drinking water have been steady, rising, or falling over the years.

“We will put this on the next Water Commission agenda to discuss whether there’s anything useful we can do. We need to take our time to understand the whole area of salt in groundwater,” Hendrickson said.