The past few weeks of winter have been rough on commuters, schools and the elderly, but the longer-term impact could be on local waterways.
Millions of pounds of road salt used to make roadways safer has to go somewhere. With this week's thaw and rain, it will begin a migration that will eventually end in the Delaware River.
A growing number of studies in recent years have shown rising salinity in many American waterways. Scientists and environmentalists say changing the water chemistry not only poses a threat to aquatic life, but can also lead to scaling of old pipes. More importantly, they say, it could pose a potential health risk to humans who drink the water, specifically those who have high blood pressure, are at risk of stroke or have kidney issues made worse by salt intake.
In fact, 15 million people get their drinking water from the Delaware River, including 1.5 million Philadelphians.
A Rider University report concluded that sodium concentration in the Delaware River at Trenton was 4.5 times higher in 2014 than in 1945. The level of chloride was 7.6 times higher. At six different periods measured over those years, concentrations went above levels recommended by the Environmental Protection Agency and the American Heart Association for those on sodium restrictive diets. Five of those periods came after 2008.
Studies have also noted increased salinity in the Schuylkill, a major source of water into the Delaware.
Hongbing Sun, a Rider professor, began studying salinity in 2010 when he noticed that samples kept showing spikes each spring. He estimated concentrations have doubled over the past 20 years.
As snow and ice melt, road salts flow with the water down roads, running off into streams or flowing into storm drains before ending up in the Delaware. By fall, salt levels come down. But then the road salting cycle starts anew.
Gary Burlingame, director of the Philadelphia Water Department's lab, said sodium is a natural and critical part of what makes Philadelphia water unique, so there's no attempt to remove it. He said the sodium content will likely spike this weekend as road salts make their way into the river, but that they there's no real health concern for most people. He is aware, however, that salinity is creeping up.
"There's been a gradual, long-term increase in the sodium of our water due to urbanization of the watershed," Burlingame said.
The EPA does not enforce hard standards for sodium in drinking water. Instead, it has guidelines calling for sodium concentrations between 30 and 60 parts per million — a level too low to impart a salty taste. It also has a guidance of 20 parts per million for those with health issues impacted by sodium.
Tests by the Philadelphia Water Department show tap water contains, on average, anywhere between 24 and 45 parts per million, depending on where and when testing takes place. However, it can run as high as 76 parts per million at times.
Scientists say that as development continually adds to pavement and other impervious surfaces, especially around lakes and steams, the impact of road salt, the largest contributor to the problem, gets worse. But most acknowledge motorist safety is also paramount.
Last winter, a relatively mild one, PennDot spread more than 732,000 tons of salt. In 2015, the agency launched a study with Temple University to explore the impact of other deicing materials. PennDot spokesman Rich Kirkpatrick said a final report is expected later this year.
"All of the streams of the region around Philadelphia are really seeing the same thing," said Ryan Utz, assistant professor of water resources at Chatham University. He is co-author of a peer-reviewed paper published in the Proceedings of the National Academy of Sciences on what it calls
"the freshwater salinization syndrome."
The paper concluded that 66 percent of 232 sites monitored by the U.S. Geological Survey showed increased pH levels, with the highest increases in the Northeast. That "can have significant impacts on ecosystem services such as safe drinking water, contaminant retention, and biodiversity."
Another 2017 paper on the salting of freshwater lakes in the same publication found that 44 percent of lakes examined "have undergone long-term salinization."
"Aquatic species richness and abundance may decline, which could result in … altered water quality and ecosystem structure and function," the authors wrote.