January 15, 2008
Road Salt Takes a Toll; Mix Used to Treat Ice Often Pollutes Water, Kills Plants
Maine road crews spread more than 100 tons of road salt each winter. Thanks to a snowy December, they're already ahead of that pace this season.
All that sodium chloride allows motorists to travel safely, and at nearly their summertime speeds, but it has side effects that will continue to show up months and years down the road.Road salt kills trees and shrubs, changes the chemistry of ponds and lakes, and contaminates drinking water supplies. The long-term environmental effects are unknown, experts say.
All of it costs money. Portland regularly replaces trees that are killed by salt that soaks into their roots. The state spends about $250,000 a year providing clean drinking water to residents whose wells exceed limits for salt because of road treatments.
"Many people are not aware the road salt has an environmental downside," said Josh Katz, an environmental specialist for the Maine Department of Transportation. "There is sort of a trade-off of short- term benefits versus long-term costs. Some of the groundwater costs will be felt by future generations."
Katz handles 15 to 20 claims of tainted wells each year. He sometimes runs into clusters of salty wells. Twelve homes along a state highway in Gray, for example, had to be connected to public water three years ago at a cost of $300,000.
Homeowners often get used to the taste of salty water and discover the contamination only after water heaters and dishwashers corrode.
Road salt's effects on trees and plants are displayed each spring along the Maine Turnpike. The salt sprayed into the air by passing traffic attacks trees' leaves and needles, leaving a trail of brown pine trees months later.
In a city, the salt piles up on roadsides and sidewalks and gets flushed into soil and roots, where it prevents trees from getting water to branches and leaves.
Stephen Norton, a geological sciences professor at the University of Maine, and some of his students have published findings that road salt is changing the chemistry of lakes in Maine and other New England states.
"We have about 100 lakes that we've been monitoring for about 30 years" to see how fast they recover from acid rain, Norton said.
"It turns out now that over half of the candidate lakes that we've been studying have been contaminated by road salt and as a result are no longer useful," he said.
Salt can interact with other chemicals in waterways and in soils.
In Canada and New York, road salt has reached levels that threaten fish and other organisms, according to researchers.
Norton said he and his students did not document such effects in the lakes they studied. "I don't think we can really argue there's been tremendous biological impacts," he said.
Local and state officials say there is no practical alternative to using road salt.
It works, melting snow and ice, preventing accidents and keeping motorists more or less on schedule.
Alternatives are simply too expensive to replace salt, they say, and taxpayers have come to expect clear roads.
Road departments are trying to reduce the amounts they spread, however, because of environmental concerns, the cost, and, especially this winter, a fear of running out before the snow season ends.
"In the month of December, we've used more than any other December on record, probably," said Joe Colucci, supervisor of road maintenance in South Portland.
Crews in South Portland and elsewhere try to reduce their use of salt by using additives that are more expensive but make the salt more effective, especially at low temperatures.
Additives include calcium chloride and magnesium chloride, sometimes mixed with a sugar or syrup.
Additives, especially sticky ones, can make salt even more corrosive to vehicles and bridges, but they can be less harmful to the environment.
In Portland, for example, the city now uses calcium magnesium acetate on some sidewalks.
"We use it at City Hall and other places because it doesn't damage plants," said Jeff Tarling, the city's arborist.
The city also is testing granite barriers placed around tree wells along Congress Street.
The barriers seem to be keeping salt from washing into the tree wells and attacking the roots, according to Tarling.
Last fall, Tarling met with public works officials to discuss ways to keep salt away from trees and to simply use less when more is unnecessary.
The state Department of Transportation also is trying to use less salt, Katz said, although keeping it out of groundwater is trickier.
Experts are starting to look at groundwater in Maine to find out where all that salt is ending up and what happens to it, Katz said.
"We didn't really begin (salting roads) until the '60s," he said. "From a geologic perspective, we've just begun to do this, and we don't really know the consequences."
THE DE-ICERS that you put on sidewalks and driveways, like the stuff spread on roads, can kill plants and contaminate groundwater. Here are some tips to minimize the damage:
Avoid sodium chloride, basic rock salt, especially around trees and plants. Alternatives such as calcium magnesium acetate are more expensive but less harmful.
Use only as much de-icer as you really need. Shoveling is the cleanest alternative. Using sand for traction also is a safer option.
Watch for tree damage. Effects build over time, showing up first as brown edges on leaves. Applying gypsum can minimize salt damage to roots.