COLUMNISTS

Science matters when discussing road salt

Justin Isherwood
Municipalities are adapting a salt brine mixture, an anti-icing technique used on roadways to prevents ice crystallization and the subsequent binding to the road surface.

The upside: according to the Highway Alliance, road salt reduces collisions 85%. The downside: the US road salt use is 24 million tons annually. The EPA estimates 5 billion in salt damage to vehicles and roadways.

Those 24 million tons critically impacts the northern tier. An abstract by Hintz, Fay and Relyea details the growing negatives of road salt on stream salinity, what has increased 3-fold in 45 years, in part because many northern Interstates are pledged to dry winter pavement.  Highway speeds during this same period have increased nearly 50%, 55 mph to something closer to 80, freight and car volumes similarly increased.

In a multi-year study, half the drinking water of rural a New York community exceeded EPA standard for sodium.

The River Keepers of the Hudson Valley recently suggested road salt is the next environmental timebomb, with decades of road salting now reaching urban and rural water supplies.

The Adirondack Watershed Institute estimates freshwater salt contamination exceeds toxicity thresholds for streams for several weeks each year, with chloride concentrations 100-200 times the natural background. 

Research at Mirror Lake of the Ausable region found salt contamination disrupted lake turnover vital to maintaining survivable oxygen levels.

WDNR and Salt Wise Wisconsin has initiated salt reduction programs for highway departments including the certification of highway professionals.

Municipalities are cautiously adapting brine, an anti-icing technique similar to aircraft wing de-icing that use preventative sprays of glycol. Brine on roadways prevents ice crystallization and the subsequent binding to the road surface. 

In practice de-icing with brine reduces salt use 75-80%. Where applied as routine before the snow event, brine spray leaves tell-tale stripes. The practice is particularly critical on bridges where salt reduces the engineered life of concrete reinforcement at a cost of millions to the infrastructure bill.

A 2015 Washington Post article falsely blamed brine as causing more vehicle damage because it is water based. Fact is, the science of salting within a distinct temperature gradient turns ice into water, that salt concentration is 4-5 times more than brine.

Justin Isherwood is a farmer near Plover, Wis.