Cook & Pink Road sites
Gatineau continues monitoring Aylmer’s closed dumps
Gatineau has received several bids to manage the former Cook Road and Pink Road dumps. Although both are closed, the city is looking for experts to deal with their upkeep.
The company must provide the city with technical advice on the treatment of ground- and underground-water at both sites. The task is to keep rain and surface water out of the dump and avoid contaminating ground water.
Roberto M. Narbaitz, University of Ottawa professor in Civil and Environmental Engineering, explained previously to the Bulletin that although most Aylmer residents are connected to the city water system, groundwater control at the dumps is crucial for environmental reasons.
“The idea is to prevent contaminated water percolating through the dump from reaching the groundwater,” he explained. “In the 1990’s (at the Cook dump), contaminants were reaching nearby water wells. The city installed several wells in a line to pump out this groundwater and treat it at a nearby facility.”
Rainwater cannot enter the landfill because the top is covered with an impermeable layer, but its sandy bottom is permeable. This could allow water running through the dump to pick up contaminants from the old waste.
The contract will require an operations report on the dumps’ existing collection and containment systems. Material inside the dumps produces gases which the city must control; the Cook Road site is filled with biodegradable materials.
“Landfills accepted all kinds of waste, including food and garden wastes which are biodegradable. The landfill’s bacteria decomposes the organic matter to produce CO2 and methane gas. This process lasts for a long time. It may take some landfills 50 years to become safe,” Narbaitz told the Bulletin.
“The danger comes from the migration of gases. Gas within the landfill is maybe 50% methane, 50% CO2. Methane, which is heavier than air, stays in the ground and migrates out from the landfill which itself is like a methane-producing machine. The methane tries to go up and out and so this pressure drives methane outside. Now, the danger is when you have 5% to 15% of methane in a building. Even if the methane is fairly diluted, it remains explosive. Thirty to 40 years ago, a few farmhouses exploded,” said Narbaitz.
As the engineering professor explained, methane, like natural gas, is flammable. This is why it must be controlled inside the landfills. To collect the methane so it doesn’t go off-site, Gatineau uses a gas collection system which captures Cook’s landfill gas and burns it by 'flaring'.
“The question is if it’s still worthwhile to keep this system going without worrying about public liability,” explained Narbaitz, who visited Cook dump several years ago. “The [city] has a nice system which has air-driven pumps so there’s no risk of explosion within the landfill itself. They’ve done a decent job.”
The city could also burn the gas to produce electricity, as do some larger dumps, but the cost of such an operation is high. “It’s probably not viable now, as the [defunct] dump has already produced a lot of its gas,” noted Narbaitz.