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Water Today Title August 19, 2018

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Update 2017/4/13
Chemicals

SODIUM FROM ROAD SALT EXTREMELY DIFFICULT TO REMOVE FROM FRESHWATER


By Cori Marshall


Canada's harsh winters require the use of harsh products to ensure safety on the roads, and sidewalks. Generally, road salt is what is used across the country, for de-icing purposes. We looked into the impacts of this widespread use of salt and whether regulations exist to manage its application.

Clark Gunter, a Senior Project Manager at WSP MMM Group, has been working in road salt management for over a decade and was the project manager who developed the Transport Association of Canada's (TAC) Salt Management Guide. Gunter said that for the most part road salts are just that, salt or "sodium chloride but municipalities do add an additive to keep [the salt] from clumping."

The additive in question is ferric ferrocyanide or Prussian blue, which is a dark blue pigment. It has medicinal applications as well, according to the Open Chemistry Database it is sometimes used as an antidote for certain kinds of heavy metal poisoning." Gunter added that it is used in small amounts, and tends to break down in the environment."

According to Gunter "there are other proprietary [salt] blends that coat the salt using calcium chloride, beet juice, or chemicals." The reason this is done is to "enhance the function" of the salt itself. An example of this is Ice Bite, which is a sugar beet based liquid de-icer which is 100% organic.

Salt levels in drinking water is not necessarily a human health concern, "unless you are on a sodium-restricted diet, you should talk to your doctor about drinking water with high sodium content" Gunter said. The salt content in drinking water is an aesthetic issue rather than health, according to Gunter after a certain level of sodium in the water "you begin to taste the salt." It tends to be more of a problem for plumbing fixtures.

Gunter added that "salt is unlike other pollutants, sodium chloride dissolves completely in water so it is very difficult to remove."

Gunter underlined that the spray that is caused by vehicles have a significant impact on the immediate surroundings. "Along highway 401 pine trees are dead, [and have turned] a rust colour," Gunter said. This can also affect soil and crops.

Once the salt drains from the roadways it causes other issues. Gunter added that salt in the freshwater system is cumulative. If it gets into the groundwater, "it can take a very long time for it to filter into the surface water" Gunter said. He highlighted the fact that "the salt that may be in your drinking water today, may be from salt that was laid down in the eighties and nineties."

We also spoke with Hilary Dugan, a Postdoctoral Fellow at the Centre for Limnology at the University of Wisconsin-Madison, and Research Lead on a study entitled Salting our Freshwater Lakes.

According to Dugan, the study found that lakes and rivers located near roadways "showed long-term increases in chloride, above what their natural background levels should be." The study "attributed road salt runoff as a primary driver in increasing these concentrations" Dugan said.

Dugan underlined that "just the presence of a single road near a lake increased its risk of having excess chloride" levels. Dugan added that in Wisconsin natural background levels of chloride in the water "is less than 5 mg/L." Natural levels of chloride depend on the geology of the region.

"As you start adding salt to the water you begin to stress species that are adapted [to freshwater conditions], and it leaves the environment more favourable for invasive species," Dugan said.

Canada has developed a code proposing a judicious use of road salts for the safety of drivers and pedestrians, while reducing impacts to the environment and infrastructure. The code includes a salt management plan, best management practices, and an outline for record-keeping and reporting."

The Code of Practice for the Environmental Management of Road Salts applies only to "organisations that use more than 500 tonnes of road salts per year", or to organisations that service territories with vulnerable areas. The code does not provide a framework for private users, and "does not apply to road salts used for domestic purposes, or for private or institutional uses."

Trevor Tenn Manager, Transportation Services with the City of Toronto said that the city "uses approximately 130,000 tonnes annually." Tenn added that the city "has a budget of $11 million" for the purchase of salts. Salt "is the most effective product," he says, when it comes to dealing with ice and snow.

Toronto does have a salt management plan, according to Tenn, that includes "spreading controls on salt trucks, sweeping up salt after loading, returning the unused salt to domes, and pre-wetting salt with brine." In some instances, Toronto streets are de-iced with brine alone.

The city of Vancouver said that this past winter was unusual and that they used "11,800 tonnes of salt and 477,000 litres of brine" on city roadways. The city did note damage to city infrastructure that included "circuit burn ups and short circuit problems from the saline stormwater runoff following salt application." There was also an increase of potholes and pop-outs.

The code's shortfall is that it does not deal with those who use less than 500 tonnes of salt a year. They are not bound to provide a management plan, implement best practices, or keep accurate records. Tenn added that Toronto does not monitor or regulate salt use by private users.

Parking lots and sidewalks account for approximately a third of road salt use, and financial impacts of its use can range in the billions of dollars. Road salt is corrosive and has a degrading effect on our infrastructure. Both Gunter and Dugan see more citizen awareness on the issue, and as people are more informed a change in practice will follow.





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