Salt on the roads: Good for safety, bad for environment
By Sandy Bauers
Over the last 60 years - pretty much since regular use of sodium chloride on roads began - the annual average sodium concentration in the Delaware River has nearly tripled and chloride has increased fivefold, researchers have found. Because the department, like many others, can switch intakes and mix in water with lower salinity, the final product contains lower levels, said Chris Crockett, director of planning and research.
If current trends continue in the coming decades, however, experts say that aquatic life will suffer and water supplies could be threatened. Sodium is a concern for people with medical conditions such as hypertension. "This cannot go on indefinitely. It is not sustainable," said Jonathan Husch, chair of Rider University's department of geological, environmental and marine sciences, which has been researching salt issues locally. Unlike the pollutants that are typically removed by water-treatment plants, getting the salt out can require entirely different technologies such as reverse osmosis. Eventually, said Crockett, governments may need to decide on which end of the process to spend precious public funds: more environmentally friendly deicers for the roads or new treatments for the water. Both cost more. Officials - especially those in more northern areas - have been aware of the problems with salt for more than a decade. But it's only been in the last few years, with increased public focus on the environment, that significant innovations have emerged.
Highway crews in both Pennsylvania and New Jersey have been spraying ahead of time with a salty brine solution. The liquid - look for the stripes down the lanes before a storm - stays on a bare road better than salt, it delays the formation of ice and, when salt is spread later, it speeds melting.
In 1940, an estimated 149,000 tons of rock salt were sold in the United States for highway use. Now, we're up to about 18 million tons in a bad winter.
Meanwhile, study after study has found that from the Great Lakes to mountain streams, salinity in water bodies has been rising. In isolated cases, municipal water wells have had to be shut down because of contamination from road salt.
Wetlands have been affected. Salt-tolerant species have become more common along highways with high salt use. In 2009, a U.S. Geological Survey study found that 40 percent of streams in and around Northern U.S. cities underlain by certain kinds of aquifers had salt levels high enough to damage aquatic life.
Earlier this year, USGS researcher Steve Corsi and others collected water fleas and flathead minnows in streams around Milwaukee. They found that during winter deicing, water in more than half the streams sampled was toxic to the organisms or affected their growth and reproduction. Eventually, salt can change not only a stream's plants and aquatic organisms, but its entire ecosystem, said Philadelphia's Crockett. "You go from things that are not tolerant of a salty environment to things that can handle that kind of shock."
Spreaders have been reengineered and recalibrated to reduce overshoot and to keep the salt from bouncing onto the shoulder.
In some cases, workers can clean the same amount of snow with half the salt that they once used. Officials employ elaborate calculations to project nuances of temperature and precipitation as storms approach and intensify.
This year, PennDot is piloting a sophisticated storm-fighting computer system - with touch screens in the trucks - that helped Indiana reduce salt use by a third. Using radar, it forecasts road conditions and fine-tunes how much salt should be spread.
Manufacturers are coming out with new deicers, including one made from beet juice. Transportation officials in Maryland, New York, and Chicago are trying it. Marketed under brand names such as GeoMelt and IceBite, it is less corrosive for bridges and cars - another issue surrounding salt. Also unlike salt, it doesn't cause potholes.
This, like many other salt "alternatives," is really just an additive. It helps a brine solution stay put and enhances the melting effect.
But some have complained that the beet juice stains and stinks like rotting vegetables. It has unwanted environmental effects, too. Bacteria that break down the organic chemical consume oxygen - and low oxygen levels are another problem in many urban streams.
And a Madison, Wis., study found that substituting the beet product for the salt brine it used in 2008-09 would have cost more than 10 times as much.
So good old road salt is still the cheapest thing going and the primary deicer. Although anything that melts in water will lower its freezing temperature, no other broadscale substitutes have taken hold.