Salt: The urban watershed's double-edged sword - Metropolitan Planning Council

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Salt: The urban watershed's double-edged sword

Flickr user John Iwanski (CC)

Melty conditions like this are annoying; they also affect our water quality.

Our winter 2016 series on road salt looks at how these little crystals affect our region, from their impact on our waterways to their implications for government efficiency.

Just about everyone I talk to is ready for spring. It’s March in the Midwest. And while we’ve had a milder winter than in years past—maybe because of it—the sentiment is still palpable that we’re ready to see snow melt and enjoy longer days. But many of us don’t realize the significant environmental damage that will accompany our transition from winter to spring. It has to do with road salt and its impacts on our water.

Before explaining why road salt (mainly sodium chloride—it’s the chloride we're interested in here) is so harmful to ecosystems or even how it reaches our water resources, I believe the game-changing issue is this: Salt readily dissolves in water, but by doing so, breaks down into sodium and chloride ions. This releases chloride into water bodies, which then persists in the environment!

“Chloride is one of our biggest urban pollution problems today damaging our built and natural environments,” says Stephen McCracken, director of watershed protection for the Conservation Foundation. McCracken is blazing the path on combatting chloride with the DuPage River Salt Creek Workgroup.

Unlike many other pollutants, chloride is not easily broken down, metabolized, taken up or removed from the environment. Even in rain events, chloride concentrations prevail. While there are actually different sources of chloride pollution, most water bodies in the Chicago region are experiencing elevated levels of chloride (on the rise since the 1960s) primarily due to road salt runoff, according to a 2012 report issued by the Illinois State Water Survey. 

So here we are in winter, scattering road salt on highways and sidewalks as a public safety measure. As salt-laden snow begins to melt or the snowfall turns to rain, chloride is finding its way into ground and surface waters, such as rivers, streams and reservoirs—and staying there. The end result is impeded water quality which threatens our ecosystem services as well as our drinking water supply.

Salt is the urban watershed’s double-edged sword!

Flickr user John Iwanski (CC)

There are two sides to everything—even road salt.

As you may guess, ecosystems do not function as well as they should if too much chloride is present. Higher than normal levels of salinity in otherwise freshwater bodies create a toxic environment for fish and aquatic life, wildlife and surrounding plants. According to the U.S. Environmental Protection Agency, chloride at 230 milligrams per liter of water negatively affects aquatic organisms while 860 milligrams per liter of water kills many of them quickly. The amounts are surprisingly small; the latter is the equivalent of one tablespoon of salt dissolved in five gallons of water.

Even natural vegetation and green infrastructure like rain gardens along roadsides are in harm’s way, which I’ll explore more in the next post of this series. A report by the Cary Institute in New York shows that even relatively moderate levels of salt in water bodies can result in decreased reproduction in amphibians, plant browning and lower nutrient availability for plants and animals.

The take-away is that the increase in chloride concentrations in our water resources can be linked to our choices on the surface that are causing a tipping point in environmental damage. Because of this extensive and persistent harm to the environment, McCracken suggests that “Chloride is going to be one of the top urban water pollutants of concern over the next 50 years. It has an enormous environmental footprint, but it is also inherently very useful. We need to be clear about its costs and benefits and manage it accordingly.”

The Minnesota Pollution Control Agency looked into quantifying the environmental cost of chloride as part of its Chloride Management Plan project. One estimate modeled by Fortin Consulting equated chloride’s environmental impact on surface water and forests to adding $60 million to the price tag of an annual batch of 350,000 tons of salt. As a reminder, Chicago used 370,000 tons during the 2013-14 snow season.

For the City of Aurora, Water Production Division employees could taste the difference as higher chloride levels were detected in the Fox River, which provides 60 percent of the city’s drinking water supply. David Schumacher, the city’s superintendent of water production, explained that precisely after a snow storm like the system we just experienced this week, followed by a rapid thaw, chloride levels in raw surface water supplies can spike to higher levels than normal.

“We are fortunate that we can make adjustments if we experience high chloride in the Fox River. We can draw more drinking water supply from wells to maintain pleasant, drinkable water for our customers,” said Schumacher. “Other communities don’t have that luxury.”

Within our water supply management work, the Metropolitan Planning Council is collaborating with the City of Aurora and others in the Northwest Water Planning Alliance, chaired by Aurora Mayor Tom Weisner, on critical water resource management.

If your well runs dry, isn’t big enough or just doesn’t exist, there is no cost-effective treatment technology to physically remove the chloride from water resources. According to Schumacher, “Desalination, the process to remove chloride, is a very expensive proposition. Many local water treatment plants are not set up to remove salt from water.” So what do communities striving to protect drinking water from chloride do?

It seems that protecting our environment and palatable drinking water means putting less chloride in our waters in the first place. In 2015, the Illinois Pollution Control Board arrived at a similar conclusion and indicated what that chloride limit should be for the Chicago Area Waterway System for the first time.

The new chloride water quality standard takes effect in 2018, setting a limit of 500 milligrams per liter of water during winter months. The water quality of Chicago’s rivers is one of many aspects MPC is examining as part of Great Rivers Chicago, a 15-month effort to develop a long-term vision for Chicago’s rivers.

The Metropolitan Water Reclamation District of Greater Chicago knows a thing or two about water quality. The Ill. Environmental Protection Agency asked the reclamation district to lead the coordination required between the various municipalities, public works departments, water experts and treatment processes to work toward meeting the new water quality standard for chloride. Tony Quintanilla, assistant director in maintenance and operations at the district working with the Chicago Area Waterways Chloride Initiative Work Group, sums up what this new standard means:

“Chloride in our waters boils down to improving environmental degradation to enhance the macro invertebrates that are fundamental to the food chain. Treatment of chlorides already in the water is not a viable solution; we are focusing our efforts on source reduction in order to meet this new standard.”

Early signs of spring are in the forecast. Luckily, there are also signs of change in our attitude toward road salt. More efficient application can result in less polluted water, healthier ecosystems, protected drinking water in addition to more efficient government. Let’s keep shaking up our understanding of salt’s impacts in our region beyond the snowy day in February when it is first laid down to combat ice.

Curious about other aspects of road salt and Chicagoland? Read the whole series.


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