Towering about 90 feet above sea level, the George Town Landfill represents approximately 40 acres of waste that has been accumulating since the 1970s. Fortunately, the days of relying exclusively on landfill disposal are numbered.
The Cayman Islands Government and the Decco Consortium, the preferred bidder to implement the country’s Integrated Solid Waste Management System, confirmed that remediation of the George Town Landfill is expected to begin this month.
Remediation of the landfill includes covering or capping the mound of waste, managing the landfill gas generated within the waste, controlling storm water run-off, and environmental monitoring of air, surface and groundwater quality. The first step in the technical closure of the site will be for tipping operations to move to a different location within the existing landfill footprint, freeing up the main mound to be capped.
Remediation works are expected to continue in stages, beginning with a one-acre site on the north slope of the waste mound. The waste will be covered with a layer of fill material similar to marl, then a layer of manmade, low-permeability material. This is then covered with more fill and, finally, with a layer of topsoil to support the growth of grasses and shrubs that will provide an attractive green surface that is resistant to erosion.
Remediation will also include landfill gas management: A network of collection wells and pipes connected to a gas blower will draw the gas from the waste mound. When the planned waste-to-energy plant is commissioned, the collected landfill gas will be piped to the facility for energy recovery through the waste combustion boiler.
Landfill gas collected while the waste-to-energy facility is under construction will be flared off to destroy odorous or noxious compounds as well as methane, which makes up approximately 50% of landfill gas and is a significant greenhouse gas.
The flare will be located beside the waste mound and stand approximately 10 to 15 feet tall. Landfill gas will be burned within the flare stack to avoid a visible flame and ensure complete combustion.
Throughout the process safety and efficiency will be ensured by monitoring the landfill cap for gas emissions, controlling the gas extraction process by balancing the well field and adjusting the blower to sustain control of the collection process.
Capping the waste mound will prevent potential vectors for disease – such as rats and flies – from accessing the decomposing waste and will eliminate odour emissions.
By reducing the amount of rainfall infiltration, capping the landfill will reduce the potential for leaching contaminants into the ground below the site.
Capping the landfill will enhance the effectiveness of the landfill gas collection system by preventing air from being drawn into the waste. By preventing air infiltration, thus cutting off oxygen from entering the waste, the possibility of combustion within the waste pile is practically eliminated.
While the vegetated landfill cap will improve the appearance of the site, options for future use are still under consideration and it will take several years for the site to stabilise sufficiently.
1. Methane is a potent greenhouse gas. It is 28 to 36 times more effective than carbon dioxide at trapping heat in the atmosphere over a 100-year period.
2. After carbon dioxide, methane is the most widespread greenhouse gas.
3. Landfills are the third-largest source of human-related methane emissions in the United States.
4. Since the Industrial Revolution, methane concentrations in the atmosphere have more than doubled.
5. About 60% of the methane in the atmosphere today comes from sources scientists think of as human-caused.
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This article appears in print in the March 2020 edition of Camana Bay Times.
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