Winter road salt is making some Philly-area streams as salty as the ocean, enough to kill wildlife
Philadelphia has 2,500 miles of roads to consider when a storm approaches, and some big decisions to make: When and where to salt for public safety.
After Sunday’s ice storm, a water sensor in Tookany Creek in Jenkintown detected salt levels so high, it twice recorded peaks of more than 57,000 microsiemens per centimeter — a measurement of electrical conductivity that rises with salinity.
That meant the Tookany was even saltier than the ocean for brief periods at the creek sensor, near a major shopping area.
Freshwater streams, lakes, and rivers should measure close to zero, but no more than 1,500. Data curated by the Stroud Water Research Center in Avondale, Chester County, show there is currently enough salt in some streams to stress or kill certain species of fish, insects, amphibians, and mussels.
All that sodium chloride, the equivalent of many tons of table salt, flushing into local waterways can also impact wetlands, penetrate asphalt and concrete to promote potholes, and corrode metal pipes and other infrastructure.
“High salt levels negatively impact soil, plants, groundwater, and drinking water that wildlife and humans rely on,” said Julie Slavet, executive director at the Tookany/Tacony-Frankford Watershed Partnership, whose sensors captured the data. “This is why we advocate for transportation authorities and property owners to limit their use of salt on roads and sidewalks.”
Philadelphia has 2,500 miles of roads to consider when a storm approaches, and tough decisions to make: when and where to salt to keep the traveling public safe.
When up to 3 inches of snow is expected, 1,500 to 2,000 tons of salt could be dispersed, according to Steve Lorenz, chief highway engineer for the Streets Department.
The city currently has about 45,000 tons of salt available, and Lorenz is among those in his profession who increasingly urge caution about using it.
“We need to get away from the school of thought that more salt is better,” Lorenz said.
“This isn’t just a problem in the city,” Lorenz said. “It’s a problem across the country.”
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Road salt has become so pervasive that scientists like John Jackson at Stroud say they are seeing high levels of salt in freshwater streams months after winter is over. Jackson has examined data from testing monitors at First State National Historical Park at the Delaware and Pennsylvania border that, he says, “shocked me.”
High spikes like the Tookany’s decline as a stream flushes, Jackson said. Researchers tend to focus on levels right after winter storms, but he has been returning to the data as the weather warms.
“I started looking at the levels in summers and suddenly it just jumped out that this a problem year-round,” Jackson said. “It’s not just about winter storms.”
Salt levels in some local streams are 10 to 30 times higher than natural levels in summer, according to the Stroud center.
Use of road salt has more than doubled since the 1970s. It dissolves in water and enters streams quickly from roads and parking lots, before gliding into soil and groundwater.
Jackson said the salinized water percolates slowly into groundwater after winter storms, creating a steady flow into waterways months later.
“The stressors may actually be equal or greater in the summer, because the groundwater is contaminated,” Jackson said. “In other words, there’s road salt leaking out of these watersheds every day of the year. ... The toxicity of salt is much greater at warmer temperatures than it is at cooler temperatures.”
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The Philadelphia Water Department and other water companies that draw from rivers normally do not remove sodium, though they do test for it.
More development and more pavement mean more runoff into streams. Mall parking lots are thought to be a major source of salt contamination. Homeowners use salt, too.
Last winter, the Izaak Walton League, a national conservation nonprofit, worked with volunteers who documented salt levels in streams within the Philadelphia region. Overall, it found many were at levels toxic to aquatic life.
Alexis Campbell, a spokesperson for PennDot, says the agency is aware of issues surrounding salting. But at about $64 per ton, it “is one of the most cost effective and primary materials PennDot uses to help maintain safe, passable roads during winter storm conditions, especially considering that PennDot has over 94,000 snow lane miles to maintain — more than all the New England states combined.”
PennDot tracks how much salt is applied to each snow route and has standard rates of use depending on whether the forecast calls for light or heavy snow or freezing rain, Campbell said.
“PennDot has committed time and funds to a number of research projects related to de-icers and salt substitutes,” she said. “Materials such as manufacturing and agricultural by-products, manufactured de-icing composites, and treated rock salt have proven effective at lower temperatures, but cost significantly more than rock salt, require separate storage facilities and additional handling.”
Lorenz, the Philadelphia Streets Department chief engineer, said his crews use brine when possible to cut down on how much salt it uses. The city “brews” its own brine by adding salt to water in 15,000- to 20,000-gallon tanks days before a winter storm.
The brine, diluted rock salt, typically gets applied in higher areas of the city, such as in the Northeast and Northwest, and bridges, because they freeze sooner.
Lorenz started reducing rock salt as a preventive in 2013 because it was often wasted as it bounced off intended surfaces before storms even moved in. Brine, he said, sticks to the surface.
Other possible options, such as calcium or magnesium chloride, are too expensive and corrosive, Lorenz said.
Using less salt “amounts to a culture” change, Lorenz said, for workers used to applying copious amounts of salt.
“The old school said more salt is better,” Lorenz said. “But the downside is you’re not looking at the effect on the environment. Once it gets into streams and roadways, it stays there.”