Thursday, May 23, 2013
Rock salt means safer roads, but it can also wreak havoc on the environment, leaving public works officials across the state trying to reduce salt use while preserving safe road surfaces.
Waterville Public Works Director Mark Turner said the department uses a ratio of 17 parts sand to one part salt on city roads. "We've found over the years that's the best mixture, " he said.
Photo by Jeff Pouland
Farmington Director of Public Works Denis Castonguay shows a small computer inside one of the town plow trucks. The equipment can be programed for the most efficient use of salt on winter roads, in terms of both economic and environmental impact.
Staff photo by David Leaming
Area towns were asked how much road salt they used last year and how many lane miles they used it on.
Farmington: 784 tons on 240 lane miles = 3.26 tons per lane mile
Waterville: 1,500 tons on 280 lane miles = 5.35 tons per lane mile*
Winslow: 1,000 tons on 172 lane miles = 5.8 tons per lane mile
Skowhegan: 1,150 tons on 192 lane miles = 5.99 tons per lane mile
Oakland: estimated 450 tons on 68 lane miles = 6.62 tons per lane mile
Augusta: 2,800 tons on 350 lane miles = 8 tons per lane mile **
Fairfield: 1,198 tons on 120 lane miles = 9.98 tons per lane mile
* Waterville Public Works Director Mark Turner said that the city also treats a significant amount of non-road pavement with its 1,500 tons, which he estimates at about 10 percent of the total lane miles. An adjusted figure based on that estimate is 4.87 tons per lane mile
** Augusta said there was a lot of ice last year, necessitating additional salt. Officials said the previous year, 2,200 tons were used, which was more typical. That year, the figure would have been 6.28 tons/lane mile.
Salt's advantages are obvious. It is cheap, natural, easy to apply and effective. Still, with concerns about the impact on the environment, human health, road infrastructure and vehicles, those who plow the roads are always seeking ways to use less salt.
A survey of area towns and cities shows dramatic differences in the amount of rock salt used on local roads, with Fairfield using more than three times the rock salt per mile than Farmington.
With roughly a billion pounds of rock salt spread on Maine's roads every year, the consequences for the environment, human health, public infrastructure and vehicles are significant.
"It doesn't disappear," said Sarah Flanagan, who published a study on ground water quality in New England for the U.S. Geological Survey earlier this year. "It has to go somewhere."
Salt can change the living conditions in the local watershed by increasing the salinity of lakes, streams and vernal pools, killing or weaken native species like white pines, salamanders, frogs and fish while encouraging more salt-tolerant invasive species, like phragmites, a hardy European reed.
Groundwater contaminated by rock salt is a human health hazard in the form of unwanted sodium.
And, as many vehicle owners are aware, salt's corrosive influence can shorten the life of a vehicle and lead to costly repairs. The total value of vehicle damage is not known, but the cost of corrosion on public roads and bridges is an estimated $16 billion to 19 billion per year.
During the past 10 years, as awareness has grown about the negative impact, technology and practices have emerged to minimize the amount of salt needed on the road.
A salty state
The state Department of Transportation treats 8,350 miles of road during about 30 storms per year. Depending on the storm conditions, anywhere from 20 to 800 pounds of salt can be used per two-lane mile per storm.
Roads in the Northeast get more road salt than in any other region in the country. Maine has 23,450 miles of public roads, more per person than any other state in New England, so the emerging issue of salting the state's environment is particularly important.
A 2010 University of Maine Study showed that 490,000 tons, or about one billion pounds, of rock salt was bought statewide in 2008 -- four times the total weight of the state's 1.3 million residents.
Nationwide, studies estimate that about 23 million tons of salt are applied to paved areas every year.
A study in New Hampshire found that private roads and parking lots accounted for about half of all road salt, while municipalities accounted for 30-35 percent. The state was responsible for the rest.
Some towns saltier than others
The amount of rock salt that communities throughout central Maine use on their roads varies widely.
Most used between five and seven tons per lane mile, but Augusta used eight tons and Fairfield 10. At the other end is Farmington, which used just 3.26 tons.
Farmington Public Works Director Denis Castonguay said the town has been making progress in leaps and bounds by participating in education programs offered by the state and the University of Maine.
"Our operators are just getting more and more aware," he said.
Last year, he said, the town used 784 tons, far less than the 2,000 used annually just six or seven years ago.
Castonguay couldn't point to a single factor to explain the improvement.
"It's the little things," he said. "We monitor the storms real close. We also monitor the road temperatures, and we start early."
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