A photo of the pre-wetting system on a municipal snow plow.
Public Works expects all 18 of the City's snow plows to have the pre-wetting system installed by early March 2021. The project is expected to reduce road salt usage by 20-30 percent per year. (Photo provided by the City of Peterborough.)
About half of municipal snow plows equipped with new technology that uses salt more efficiently
Ayesha Barmania  - 
February 5, 2021

This winter season marks the first rollout of a new system for snow and ice control in Peterborough that aims to reduce salt usage by 1,500 to 2,000 tonnes per year (or 20 to 30 percent) when fully implemented. 

As of publication, eight of the City’s 18 snow plows have been equipped with pre-wetting capabilities, which means they mix the road salt with water to make a brine solution before it is applied to road surfaces. Public Works expects the full fleet to be equipped by early March.

Road plows without this new technology apply dry salt to road surfaces which, on average, uses approximately 7,500 tonnes of salt per year, according to Brian Jobbitt, manager of Public Works.

“When dry road salt is applied it needs to first attract moisture from either the road, snow or ice and then it begins its breakdown to a liquid brine that will melt snow/ice and most importantly break the bond between the snow/ice and the road surface,” he writes in an email to Peterborough Currents.

The pre-wetting system speeds up this process by creating the brine on the plow before it’s applied to the road surface.

Plows with the pre-wetting system spray dry salt with liquid while it’s still on the truck, Jobbitt explains. “When the material is applied [to the road] it tends to stick immediately to the road surface rather than the traditional dry salt bouncing across the road surface.”

By activating the salt as a brine before it hits the surface, the salt is used more efficiently to clear the roads. 

Pre-wetting systems have been implemented in many Canadian municipalities. The federal body Environment and Climate Change Canada (ECCC) reported that in 2019 65 percent of municipalities participating in the reporting process had implemented a pre-wetting or salt treatment system.

Using this system is one of the indicators that ECCC laid out for municipalities which signed on to the code of practice for the environmental management of road salts. Other elements to the code of practice include annually reviewing a salt management plan, salt storage best practices, and plans for mitigating environmental impacts on salt-vulnerable areas. The City of Peterborough is one of 189 Canadian municipalities reporting on their salt management practices to ECCC.

The City’s winter crews clear snow from the Rotary Greenway Trail on February 5, 2021. (Photo: Will Pearson)

A balancing act

Managing the use of road salt is a matter of balancing effective solutions for safe roads and reducing the amount of salt fed into the watershed, says Terri Cox, risk management official at the Otonabee Regional Conservation Authority (ORCA).

Cox points to several decades of research and policy making in Ontario on the negative impacts of road salt on local water systems. “Dissolved road salt can contribute to elevated salinity levels which can pose a threat to drinking water sources with long-lasting, adverse effects,” she writes.

Road salt has also been found to degrade the quality of soil and vegetation — impacting the survivability of native species, Cox says.

Reducing overall use of salt on municipal roads stands to mitigate these impacts, though not eliminate them entirely.

The shift to this new system has been many years in the making, stemming first from action on the E. coli outbreak in Walkerton, Ont. in 2000, which led to the provincial Clean Water Act, enacted in 2006. The act established a list of drinking water threat activities, which includes road salt use. 

The act created the Trent Conservation Coalition Source Protection Committee, which in 2015 published local policies for the Trent and Ganaraska watershed regions to manage activities that may be threats to sources of drinking water; for Peterborough that source is the Otonabee River.

The City of Peterborough took these policies and updated its salt management plan with the objective to improve efficiency and reduce unnecessary salt use.

Despite having that plan in place, Jobbitt points out that the City couldn’t move forward at first. He writes, ”The City was only able to take advantage when Public Works moved to the new facility on Webber Avenue as the old Townsend Street site did not have sufficient room for such a storage and dispensing system.”

“The City has installed two storage tanks and a pumping system here at the Operations Centre on Webber Avenue that will store and dispense liquid sodium chloride… Each road plow unit is currently being equipped with two onboard liquid storage tanks with a capacity of 1,200 liters for each unit and can be filled at the Operations Centre as part of the City’s winter control activities.”

The purchase and installation of the pre-wetting system is costing the City just over $250,000 and is expected to be completed this spring.

ORCA is also encouraging residents of Peterborough to reduce usage of salt at their homes and places of work. For information on best practices, visit their website.

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