On Wednesday, June 5th 2019, EOS Eco-Energy, in partnership with Environment and Climate Change Canada, Green Communities Canada, the Freshwater Alliance, Our Living Waters and the Town of Sackville were at the Bill Johnstone Memorial Park in Sackville, NB to finish the first-ever depaving project in the Tantramar Region. Sackville Public Works tore up the asphalt pavement from a corner of the parking lot adjacent to the park on Monday, June 3rd, which was then covered in a permeable pavement layer by Dexter Construction on Wednesday, July 5th.
The 335 sq. ft parking area was covered in a porous asphalt layer. During heavy rains on Thursday, the asphalt allowed the rain water to enter the groundwater system naturally. Permeable asphalt and its base layers allow rainwater to pass through to the soil below, unlike traditional asphalt, which directs water to storm drains. The porous nature of the pavement also traps suspended solids and pollutants, keeping them from entering the soil. By covering parking lots and driveways in this type of asphalt, pollutants are filtered out before water reaches local water bodies and water pooling won’t occur.
Jamie Weatherbee, a Quality Control Manager at Dexter Construction, explained that the porous asphalt laid at the site is mixed differently than traditional asphalt. By adding a higher volume of large rocks, as opposed to sand, the permeable pavement has a higher percentage of air voids compared to traditional asphalt. These voids allow water to pass through it to the reservoir below. That reservoir is over a meter of ¾ inch clear stone subbase where water can be held before the ground absorbs it naturally.
“Another benefit to this type of pavement is its performance in the winter months. During periods of freezing, the kind of asphalt used in this project will still allow water to percolate to the ground below whereas soils would still be frozen and lead to an increase in storm water runoff,” explains Kelli-Nicole Croucher, EOS Watershed Coordinator.
This asphalt also prevents the formation of ice on the pavement surface, eliminating the possibility of black ice forming. This could lead to a reduction in the amount of road salt required. Researchers at the University of New Hampshire have observed that permeable asphalt only needs 0 to 25% of the salt routinely applied to normal asphalt.A 2014-2016 USGS study of permeablepavements in Wisconsin found that the deeper layers remained above freezing even when air temperatures dropped below freezing. While this temperature difference didn’t allow for the melting of snow and ice covering the sites, the higher temperatures below kept the voids open, promoting melted snow and ice to infiltrate the surface upon the rising of air temperatures.
“In terms of cost, comparing this project to large-scale implementation of permeable pavement, or even standard asphalt has its challenges. The permeable asphalt requires special processing and mixing equipment, raising costs,” Eric Arbeau, EOS Summer Intern, points out.
Also, because our project is a small-scale pilot, costs were higher (per tonne of material used) than a more substantial, full-scale repaving would be. Maintenance costs over the life of the pavement could be reduced though due to needing less road salt and repairing fewer pot holes. Due to the above factors, an accurate cost comparison is difficult to complete at this time.
More information about the depaving project can be found on the EOS Depaving webpage.
