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This week’s snowstorm coated roads and sidewalks with ice—and sent bags of rock salt and ice melt flying off store shelves. The products can make pavement safer, but decades of runoff are driving up salt levels in major Northern Virginia drinking-water sources.
Winter treatments typically include rock salt, or sodium chloride, and ice-melt blends containing sodium chloride, magnesium chloride and other salts.
Chloride concentrations in the Potomac River, which supplies drinking water to about 6.89 million people, have risen substantially in recent decades. Average winter concentrations have increased nearly tenfold, according to the Interstate Commission on the Potomac River Basin.
WSSC, the water utility serving Montgomery and Prince George’s counties in Maryland, reports that Potomac River salt levels have climbed 104 percent over the past 30 years. Runoff from roads, parking lots, sidewalks and other impervious surfaces is a major contributor.
Salt concentrations in the Potomac River and Occoquan Reservoir have also more than doubled on average over recent decades, the Northern Virginia Regional Commission reports. The Occoquan supplies drinking water to two million Northern Virginians.
A 2021 Wetland Studies and Solutions study identified deicing salt from roads, sidewalks and driveways as a major source of chloride around upper Accotink Creek, where measured concentrations spike during winter. Virginia Department of Environmental Quality officials said at the time that other Northern Virginia streams likely face similar conditions.
Safer Roads Come With Environmental Costs
Salt plays an important role in winter travel. The Northern Virginia Regional Commission reports that it can reduce vehicle crashes by 88 to 95 percent.
But salt does not biodegrade. It can wash into storm drains and eventually reach streams, rivers and oceans, while standard water-treatment technology generally cannot remove it. Elevated salt in drinking water may pose health concerns, particularly for people following low-sodium diets.
Salt is also corrosive, damaging plumbing, bridges and other highway infrastructure while accelerating rust on vehicles.
Wildlife can be put at risk when animals are drawn to salted roads. Birds may mistake salt crystals for seeds or grit. AAA reports roughly one million vehicle-animal crashes annually, resulting in 200 deaths and as much as $8 billion in costs.
Excess salt can degrade soil and harm plants and animals on land and in water. Salty runoff and spray from vehicles, spreaders and wind can also kill trees and shrubs.
How to Handle Ice With Less Salt
Fairfax Water recommends removing snow early and repeatedly, before it freezes into ice. Salt should be applied only after shoveling, not used to melt away accumulated snow.
Treat only the places needed for safe passage and spread salt evenly. Adding more does not produce more melting: A 12-ounce coffee mug holds enough salt for a 20-foot driveway or approximately 10 sidewalk squares.
Ordinary salt is ineffective below 15 degrees. At those temperatures, sand or native bird seed can provide traction instead.
Once the ice has melted, sweep up remaining salt and store it safely for reuse. Downspouts should also be directed toward ground areas rather than sidewalks and driveways, reducing runoff across pavement.
VDOT’s Winter Road Strategy
The Virginia Department of Transportation maintains 14,238 miles of roads in Northern Virginia and begins plowing after snowfall reaches two inches, Mount Vernon Supervisor Dan Storck wrote in a Jan. 3 constituent newsletter.
When hazardous weather is forecast, VDOT pre-treats some roads with brine, a saltwater mixture that helps prevent ice and frozen precipitation from bonding to pavement. That makes it easier for crews to restore passable conditions.
Crews prioritize interstate highways and limited-access routes first, followed by primary roads and major secondary roads. Low-volume secondary roads come afterward.