4/13/2018 7:26:00 AM Impacts of road salt seen in surface water
Information session highlights what we can do
Beckie Gaskill/lakeland times
Hilary Dugan, assistant professor at the Center for Limnology and Integrative Biology at UW-Madison, gave a presentation last week at Nicolet College titled “Salting our Freshwater Lakes.”
Living in northern Wisconsin means cold winters and slippery roads. Slippery roads mean municipalities use road salt to make travel conditions better.
In the last few years, more and more attention has been given to understanding where that salt goes. It should come as no surprise that at least some of that road salt may wind up in our surface waters, especially those close to major roadways.
Several studies have been done regarding road salt and waterways in recent years. Last week, Hilary Dugan, assistant professor at the Center for Limnology and Integrative Biology at UW-Madison, gave a presentation at Nicolet College titled "Salting our Freshwater Lakes." The presentation was part of the Ced Vig series of Learning in Retirement.
Approximately 60 people attended the information session, which started with some of the basic information about the sodium and chloride that make up road salts as well as what chloride can do when it does find its way into our groundwater or drinking water.
Sodium chloride is used on roads for many reasons, Dugan said. The fact that it is very plentiful is a big part of the equation. Very few things use sodium or chloride, unlike an element like calcium, which is used for shell production in sea shells, for instance. It also dissolves very easily.
On the down side, if there is too much salt in the water, humans can taste it, she said, giving the example of Hoggie Doggie's in Woodruff. Further, however, it can also stress freshwater fish. Enough stress and the fish will die.
It also changes the physics of the water, she said, and can help to mobilize other contaminants such as mercury, nitrate and lead. Invasives, also, can do better with higher chloride levels, where native species need the freshwater environment to grow and thrive. If a lake becomes to salty, Dugan said, the lake may not "turn over" as it should seasonally. This means there will be less oxygen at the bottom, causing the ecosystem to change drastically, with plants dying off and fish unable to live there.
Dugan also explained there are different guidelines for how much chloride is acceptable in water. The EPA states it is a chronic affect at 230 mg/L and acute at 860 mg/L. Wisconsin's levels are higher at 395 mg/L and 757 mg/L. Conversely, Canada accepts much lower levels with their chronic threshold at 120 mg/L. She said the EPA chronic limit is the equivalent of one teaspoon of salt in a five-gallon bucket of water. The differences between these guidelines, she said, is due to the fact that different species may still be alive at certain concentrations, but they will be stressed.
She spoke about the ease with which water can be polluted by salt. Natural sources include salt springs and evaporation. As water evaporates, the salt is left behind, making concentrations of saline in the water higher. Human sources of salt include road salt, industrial brines, agriculture and water softeners. Private or commercial salt use, Dugan said, makes up for approximately half of all salt used. Because of that, it is difficult to know how much salt is being used. Salting of private parking lots and sidewalks also contributes to the overall salt load in the environment. The salt use data Dugan displayed, which was over 526,000 tons, was likely only about half of the salt being put down when private drives, parking lots and sidewalks were considered as well.
What to do
There are things we can do, however, to minimize the salt that leaches into our groundwater and surface water.
"Use less," Dugan said. "We can just use less. We can use salt in the right place, at the right time, in the right amount." In general, she said, we could use five to 10 times less salt than we are now. "It might mean a lifestyle change, but we can deal with it."
She spoke about not over-salting parking lots and other areas where, if people are simply a bit more careful, salt use could be drastically cut. Using brine on the roads, which has become more commonplace of late, is also a great slat saver, she said. This brine, which is put on before a snow storm, allows for just a fraction of the salt to be used versus traditional salting methods. The brine sticks to the road surface, meaning salt is not being thrown off the roadway by vehicles. Because salt will only work above 15 degrees, holding off on salting when it is very cold also reduces the chloride load going into the environment, lessening the amount that could wind up in our water.
Bruce Stefonek from the Oneida County Highway Department was also at the information session to talk with people about what the county does and why. He reiterated some of Dugan's best practices, stating the county does try to reduce its salt use when possible. While he does get people calling to complain at times when salt has not been put down when temperatures are below zero, for instance, he knows it will not work to melt snow and ice at those temperatures, and tries to explain that to callers.
"Temperature has a lot to do with it," he said. "If it's less than 10 degrees, we don't put it down. And it has to be rising. We're lucky right now, although it's snowing in April, but we're lucky that the sun is higher. It's going to start working faster."
Salt, he said, doesn't do anything until it starts creating moisture. Then it will melt the ice and hard pack faster. Cost, he said, is another factor. The cost associated with salting the roads is staggering.
"The brine solution that you're seeing in the roads," Stefonek said, "is actually a mixture of water mixed with salt. The perfect, optimum percentage is 23.3 percent. We get that as close as possible."
The brine, he said, is less corrosive than just straight salt. Other solutions, such as beet juice, he said, have unfavorable side effects. Rock salt consumption in Maine, he said was reduced 55 percent in the last few years by turning to using brine. He said he sees, in the future, using more and more brine and less salt. There is also the option to use more sand/salt now. This mix will be used strategically at intersections or in places where slower traffic might be in order to keep it from blowing off the road. Also, he hoped people would get the message to slow down during inclement weather.
"I wish they'd pass a law - for every inch of snow we get, the speed limit goes down five miles per hour," he said. "If people would just get the message to slow down - but that will never happen any time soon."
Much of the road conditions are dependent on when a storm happens, he said. A perfect storm, he said, would stop completely at 2 a.m., the plow drivers could come out at 3 a.m. and everything, including the hard pack, would be gone off the road by the time people were getting ready to go to work in the morning. That, however, is a rare occurrence, obviously, he said. Stefonek said the county would continue to look at best practices used in other places and to take those into consideration. While automation of the plow trucks putting down salt has come a long way from when he started, he said, he felt the use of more brine could help the environment even more and, in the end, urged people to simply slow down and not expect summer driving conditions on winter roads.
Beckie Gaskill may be reached via email at email@example.com.