As landfill space in South Africa reaches capacity, the controlled, planned and systematic filling of landfill cells requires progressive closure and rehabilitation, says infrastructure delivery company Aecom, adding that it can provide this specialised service.
Landfills may need to be closed for various reasons, including unacceptable environmental impacts such as groundwater pollution, and/or unmanageable air pollution such as dust or odours.
Geological issues include dolomitic ground conditions which can result in water ingress and sinkhole formation. In many cases, improving landfill management and operations is a necessary first step but, if this proves unsuccessful, closure becomes necessary.
Landfills are usually designed with a specific life span determined by the volume of waste that can be handled. Once filled to capacity, landfills must be closed and decommissioned as stipulated in the waste management licence. However, effective landfill remediation poses a challenge for both public and private entities.
Navigating the regulatory process, coordinating the different phases of the project, and establishing a long-term plan for post-closure reuse are only the beginning. Landfill site problems are often bigger than the eyesore created by the huge pile of waste. At some point, landfill sites will have to be closed.
“While this may seem like the end of the story, it is only the beginning of the next chapter in the life of the landfill,” notes Aecom remediation services practice lead Nicolas Vanhecke.
The process of landfill closure and remediation is legislated by the National Environmental Management Waste Act, the Water Act and the Waste Management Series, as promulgated by the Department of Water and Sanitation.
While it might seem that the closure process only starts once the landfill has reached the end of its useful life, there are factors that may need to be attended to while the site is still operational.
The slopes of the waste body must be resolved to ensure they lie at a safe angle. This should be maintained throughout the operational phase, after which capping is carried out by means of an engineered liner.
Further, all stormwater run-off must be diverted away from the waste body to separate the clean and dirty water circuits, and to prevent leachate soaking into the waste body, which can result in subsequent groundwater pollution and odours.
The site must also be fully secured and access controlled to prevent trespassers; for example, there could be an issue with people remining the waste body for recyclables, which presents a fire risk, and could allow rainwater to permeate the waste body.
“In the past, little to no consideration was given to the potential environmental impacts of landfills on human health and the larger environment, which is why today’s landfills are licensed and with very specific engineering design,” highlights Aecom environmental scientist Soleil Jones.
The remediation process depends on factors such as the type and classification of the waste, and the size of the landfill. Generally, the remediation process consists of waste reprofiling; capping, usually with topsoil such as clay or with a geotextile; revegetating, usually with indigenous grass; and, finally, closure.
Once properly remediated, the landfill site could be used for anything from parkland to recreational infrastructure or even grassland, depending on the preference of the landfill owner, the surrounding community, and the regulatory authorities.
If the site is smaller, site reclamation can be conducted through an excavation-transfer-treatment process. A key element in site reclamation is the transformation of anaerobic to aerobic conditions in the landfilled waste. Depending on the waste accumulated in the landfill, a methane gas plant can be installed to recuperate methane for energy purposes.
Following closure and remediation, the landfill site is subject to a post-closure monitoring period, which is recommended for up to 30 years. This is to monitor the integrity of the capping, and the impact on the quality of the groundwater in and around the waste body.
There may also be a need for ongoing pumping and treatment of the leachate that gathers in the leachate collection system.