by Conrad deFiebre | September 17, 2009 • Road salt is degrading waterways in the northern United States, especially in urban areas such as the Twin Cities, according to a new report from the U.S. Geological Survey. The study found chloride concentrations in streams nearly 15 times greater in urban areas than in forests and levels considered hazardous to aquatic life 10 times more prevalent in cities than in farmland.
Five Twin Cities creeks — Battle, Bevens, Minnehaha, Nine Mile and Shingle — are rated as salt-impaired by the Minnesota Pollution Control Agency. This should come as no surprise in a state that applies more than 400,000 tons of salt and 2.3 million gallons of brine to keep roads and streets clear of winter snow and ice. More yet goes onto parking lots, sidewalks and other paved surfaces.
There aren’t good alternatives to common salt — sodium chloride — for keeping roadways free-flowing and safe in winter. It costs less and works better than substitute ice-melters such as calcium chloride and magnesium chloride, which also degrade streams. But while the economic and public safety advantages of road salt dictate its continued use for the foreseeable future, the environmental outlook may not be as bleak as it seems.
The Geological Survey found safe chloride levels in 98 percent of drinking water wells in the study. And only 15 of 100 streams studied in 19 states exceeded federal chloride standards for aquatic life, which comes in 82 times less salty than seawater. Finally, efforts to reduce the amounts of salt put on pavement without reducing its effectiveness are showing early positive results.
A Pollution Control Agency training program that has certified 355 salt applicators so far had participants calculating optimum spread levels at least 75 percent lower than their previous practice. The classes continue this fall, with a special effort to reach private applicators. There’s plenty of room for improvement in public pavement maintenance, too. A Twin Cities study in 2004, the last year covered by the Geological Survey, found that street crews in suburban Brooklyn Center and Brooklyn Park used nine times as much salt per lane mile than those in neighboring Crystal.