This time of year, many treatment operations have to contend with a seasonal menace that pollutes waterways and threatens quality. In cold-weather regions, they grapple with road salt.
The substance, applied to roads to keep snow from accumulating, gets washed into water sources as the snow melts, carrying potentially harmful contaminants along with it.
“At the Madison Metropolitan Sewerage District (MMSD), we have a higher mass of chloride coming to our plant during winter melting periods,” said Kathy Lake, an environmental specialist with MMSD in Madison, WI. “We attribute this to road salt being carried into our sanitary-only sewer system with inflow and/or infiltration.”
Lake also said that road salt accumulates in Madison’s local drinking water, eventually reaching the wastewater treatment plant after it passes through homes and businesses. Inundation like this can pose potential hazards for consumers.
“The use of road salt can cause elevated sodium and chloride levels in sources of drinking water,” said Susan Miller, the public affairs manager for Fairfax Water in Virginia, which experiences some mild uptick in chloride and sodium levels in winter weather. “This can lead to taste and odor challenges for water suppliers and can be an issue for individuals restricted to a low-sodium diet.”
On top of health hazards, water utilities have another incentive to watch out for road salt inundation.
“The potential hazard for the water treatment industry is the increase in the likelihood of corrosion in service connection pipes and premise plumbing fixtures if a utility’s corrosion control strategy is limited to treat the changing chemistry of corrosion control with elevated chloride levels,” said Jodi Wallin, the public information officer for Saint Paul Regional Water Services in Minnesota. “This might place challenges on the utility to be able to comply with the Lead and Copper Rule.”
But, beyond the problems it poses for utilities and consumers, perhaps road salt’s greatest water threat is the one it brings to the source.
“Salt is increasing in our groundwater, drinking water, rivers, lakes, streams, and wetlands,” Lake said. “The chloride portion is toxic in the freshwater environment… Salt dissolves in water and is usually forgotten. It seems to go away, but it doesn’t go away. All the salt we use ends up somewhere. In our region, it’s now in our freshwater.”
There are some treatment options available to plants that find their influent contaminated by road salt, but they aren’t ideal.
“Salt cannot be easily removed from water,” said Lake. “Filtration techniques like reverse osmosis or desalination can remove the salt, but at extreme capital, operating, and environmental costs.”
Wallin added that ion exchange, microfiltration, and biosorption may also be employed, but echoed Lake’s finding that these technologies would be very costly to employ. Depending on the precise conditions, treatment operations may also create more problems than they solve by addressing road salt.
“If bromide is used as a chloride replacement for road salt usage, then it places challenges on the water treatment utility that utilizes ozonation technology to be able to comply with the Disinfection Byproduct Rule when bromate formation exceeds the U.S. EPA MCL,” said Wallin. “The ‘worst case scenario’ can be a Safe Drinking Water Act violation if it goes untreated.”
Not only is salt treatment costly and complicated, it does not even address the damage done to freshwater sources.
“While it could be possible to add treatment at a wastewater or drinking water plant, this would not be possible for other freshwater resources,” said Lake. “The technology needed to remove chloride would remove everything from the water needed for the water body to survive.”
So, with salt contamination persisting as a hazard and treatment options limited, many utilities turn to prevention measures to keep road salt out of water sources in the first place.
Firstly, monitoring efforts are key to helping utilities get a grip on the extent of their salt problems and pinpoint ways to curb it.
“Continuous monitoring of chloride can prepare the utility to act in advance when there is a rising trend of contamination,” said Wallin.
In addition to chloride levels, water’s conductivity can be an indicator of salt contamination.
“One of the best ways to track this is to employ online instrumentation to monitor levels of conductivity in the raw water entering the plant and the water as it leaves the plant,” Miller said.
When a road salt problem has been established, teaming with legislators can be the best way to advance prevention efforts.
“The water treatment utility should work with the state to address the salt-contamination issues and push for adopting comprehensive chloride or salt reduction legislation that should provide ongoing support of effective salt management in watersheds or receive funding to treat salt-contaminated water,” said Wallin.
With its combination of abundant freshwater sources and snowfall, Madison may have developed one of the country’s most involved public information efforts to reduce road salt contamination.
“We are focusing staff time and investing our resources in behavior change and incentive programs aimed at keeping salt out of water,” Lake said. “We have found many win-win solutions. Industries and homeowners have optimized their softening systems and saved money, time, and protected the environment. Winter maintenance professionals have gone through training programs and found significant reductions in salt use with minor investment in activities like calibrating their equipment… Homeowners are learning how to ‘shovel, scatter, switch’ and motorists are learning to ‘drive for conditions’ to further reduce use of deicing salt.”
No matter how you approach road salt, it’s clear that it doesn’t belong in our water.
Image credit: "Afdera" Isaac Sachs © 2015 used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by-nc/2.0/