Road Salt Contaminating Drinking Water, Urban Lakes
Last year, the Michigan Department of Transportation used more than 650,000 tons of salt on the state’s roads. That’s 130 pounds per person. Eventually, all of that salt washes into Michigan’s lakes and streams - which could be making the drinking water in Michigan’s urban areas unsafe.
For six years, Western Michigan University Geosciences Professor Carla Koretsky and her students have been studying Woods Lake in Kalamazoo. It’s a good test subject because of all the runoff that flows into it from nearby streets and lawns.
In 2003, the city of Kalamazoo put up a detention wall to keep out things like fertilizer and debris. So Koretsky’s team tests the water every year to see if the wall is working.
Instead of finding phosphorus or nitrogen, students have found high levels of sodium chloride - salt.
“So I right away assumed that they had made some kind of mistake, they hadn’t used the instrument correctly. It was a new instrument, maybe it wasn’t calibrated correctly or something like that. And so I kind of talked to them, looked at what they had been doing, looked the data, redid the sampling, redid the analysis. And sure enough those numbers were correct,” says Koretsky
Koretsky says unlike many pollutants, salt dissolves in water. So it doesn’t get caught by the detention wall. She says that’s a problem because it prevents the lake from “turning over.”
“So you never flush fresh oxygen down into the bottom of those anoxic waters,” she says.
Anoxic means little to no oxygen.
A Widespread Drinking Water Problem
This problem isn’t confined to one lake, however. Tons of road salt drains into urban rivers and streams every year. A 2013 report from the Michigan Department of Environmental Quality showed that streams near urban areas - like Detroit, Grand Rapids, and Saginaw - had significantly higher chloride levels.
What’s even more interesting is that Michigan has more salty lakes than the national average - even more than other upper Midwest states. That’s according to the Michigan National Lakes Assessment Project in 2007.
Koretsky says the United States has increased its use of road salt exponentially since the 1940s.
“So if you go back and you look at what the salt levels were 20 and 30 years ago, it’s not quite so high. It’s kind of creeping effect if you like. So I think that’s maybe one of the issues is that it’s a slow kind of process with salinizing these lakes,” she says.
So what does this all mean? Right now, Koretsky says, we don’t know - but it doesn’t look good. If too much salt gets into the groundwater, at best it could make a city’s water less appetizing.
At worst, it could corrode old water pipes - adding toxic heavy metals to drinking water wells. Professor Marc Edwards of Virginia Tech’s Environmental Engineering Department says salt is likely what caused Flint’s water to get contaminated with lead.
“Whether that salt is coming from a man-made source or it’s just naturally occurring, we’re not really sure. But there is nine times more chloride, which is the key ingredient in the corrosive water that was being used in Flint River than in Lake Huron water,” he says.
Edwards says there is a theory that once chloride levels in drinking water reach a certain point, you’ll see a dramatic increase in lead. He says his team is seeing this in cities they’re studying on the East Coast.
“Our old point of view was that, with time, the lead levels would invariably go lower and lower as the pipe got coatings on it and the lead leached from the plumbing. Instead what we’re discovering is that lead in water problems are increasing and salt in water is one of the reasons for that,” says Edwards.
Will this happen in your city? Edward says that depends on the chemistry of the drinking water and the age of the city’s pipes. But he says most urban centers are in trouble.
“The one thing that’s certain is higher chloride is bad. It eats up pipes - the iron pipes, it eats up the lead pipes, it eats up copper pipes. So this salt is having devastating economic impacts on our infrastructure. And I think if you factor in the billions and billions of dollars that are being lost from corrosion of just the water infrastructure alone, it would make people think twice - if they looked at it carefully - before they put so much salt on the roads.”
Unknown Ecological Effects
What about small urban lakes like Woods Lake? WMU’s Carla Koretsky says, right now, it doesn’t seem like the salt is having any effect on Woods Lake. Most of the fish and other aquatic life live closer to the lake’s surface. The salt sits at the bottom.
Koretsky says it could still affect microbes in the lake, but they’ll have to do more research to find out. More salt could also mean more methane in the lake - a greenhouse gas that contributes to climate change. Koretsky says they’re looking into that too.
Surprisingly, Koretsky says there hasn’t been much research into the effect of road salt in the United States. In many ways, her team is leading the way. They received a grant from the MDEQ to do further research on Woods Lake and similar lakes in the area.
“This is new territory in a way," she says.
Salt is certainly the most popular way to keep ice off of roads in big cities, but there are alternatives. Koretsky says, unfortunately, every de-icer has its downsides. Take sand, for example:
“In addition to the problem of turbidity and sediment in the lakes, when you drive over sand a lot of the fine particles go in the atmosphere. That can be a real problem with respiratory ailments. There are problems with respect to damage of the roads. So it’s more expensive in terms of having to kind of clear it at the end of the season and potentially also having the lifetime of road be less. So that’s very expensive as well. So sand is not a terrific alternative, although it is relatively inexpensive.”
Koretsky says other de-icers are less effective or more expensive than salt. Many of them still pollute lakes and streams in one way or another.
Some experts say Michigan should still use salt, just use less of it. The Michigan Department of Transportation is currently working on a project to reduce runoff from the state’s roads and use salt more efficiently. Hal Zweng manages MDOT’s stormwater program:
“We’ve done studies to try to determine the best speed for the trucks to operate when they spread salt on the road to try to minimize the amount that just bounces and scatters off the road. We pre-wet the salt which helps it stick to the road surface when it goes down rather than have it scatter as much. And we also accelerants, chemicals to the salt to help it start acting faster.”
But de-icing expert Mark Cornwell says the state could be doing more. Cornwell worked in the ice control business for about six years before starting Sustainable Salting Solutions, LLC. Now he helps municipalities around the country manage their road salt.
Cornwell says using more salt brine would reduce the amount of salt on the roads and save cities money. He says salt brine - salt dissolved in water - only uses about 120 pounds of salt per lane mile. That would save about 3,800 pounds of salt per year in Michigan.
“Solid salt doesn’t melt anything. It basically has to come in contact with water, pull heat off the pavement and start to create brine. So, in some instances that can be a challenge. And so by kind of going around that phase of the solid to liquid, you’re in to a more immediate effect,” says Cornwell.
Newer salt trucks would also help. Cornwell says MDOT has been forced to use old equipment that doesn’t place salt on the roads as precisely as newer models.