Regenerative Design for Landfill Remediation

4 November 2024

Introduction

The disposal of waste is one of the major environmental issues facing society today.  In addition to this, rapid population growth, economic development and urbanisation have all resulted in the generation of various types of wastes.  Waste remediation practices vary widely around the world, reflecting differences in technological, economic, and regulatory contexts.  

For example, Singapore incinerates most of its waste but sends the incinerated ash and non-incinerable waste to create on an offshore artificial island.  Sweden recycles approximately 47% of its waste, incinerates another 52% for energy recovery, and landfills the residual balance, which is admittedly less than 1%.  China also incinerates most of its waste, despite the advent of waste sorting.  A few countries use anaerobic digesters, which are very expensive and generate biogas and fertilisers: however, this method is mostly effective for waste with a high organic content.  This is particularly relevant in developing regions, including Africa, the Middle East, parts of South America and Southeast Asia, as shown in Figure 1.

According to Jordan (2024) and Howell (2022), approximately five million tonnes of plastic waste are exported annually, with the majority (71%) originating from just ten high-income countries, including Germany, Japan, the United Kingdom, the Netherlands and the United States, making it someone else’s problem.  Unfortunately, this means that landfills will continue to be the most economical and straightforward means of disposing of waste globally.  However, realistically, as noted by Koerner (1997) and many others since, landfills serve more as a means of waste containment rather than treatment.  As our population grows, and the disposal of single-use packaging and products continues, landfills will likely be around for the foreseeable future.  

The generation and mismanagement of this waste poses many challenges, encompassing environmental problems such as clogging of drains (leading to flooding), physical pollution and ecosystem destruction, ocean contamination, and transmission of diseases.  These issues also extend to social hazards, including adverse impacts on human health and the depletion of valuable human resources.  Furthermore, there are economic losses, such as diminished property values, decreased tourism, and escalated clean-up costs, particularly when solid waste is poorly managed (Kaza et al., 2018).  Consequently, municipal organic waste is recognised as a critical sustainability challenge, a fact underscored by its inclusion in the United Nations Sustainable Development Goals (SDGs) (Soni et al., 2022).  

Environmental Legislation

In most countries, disposing of waste to landfill – despite being the least preferred and an unsustainable practice - is still a fulfilment of the minimum environmental legislation/requirements.  In South Africa, the landfilling method of waste disposal is still customary, and is regulated by the National Environmental Management Waste Act, 2008 (NEM: WA, No. 59 of 2008) to protect public health and the environment by ensuring the remediation of contaminated land.  The actual capping and closure of landfills must conform to the minimum requirements set by the Department of Environmental Affairs, known in South Africa as the Department of Forestry, Fisheries and the Environment (DFFE).  

The primary goal of any landfill rehabilitation design traditionally focuses on minimising environmental harm, with the end goal being to mitigate the adverse impacts of anthropogenic (human) activities.  

Where these impacts have been aggravated, efforts should aim to limit their significance to an acceptable level, being ever mindful that such efforts need to be strategic, focused, and sustainable, not to mention financially viable.  The rehabilitation and closure conditions in Environmental Authorisation (EA) Records of Decision (RoD) usually include conformity to minimum requirements for slope stability gradients, the prevention of water ingress into the waste body, free surface run-off to prevent ponding and/or waterlogging of the restoration layers, and the prevention of erosion in the final cover layer.  Minimal, if any details, are included regarding final rehabilitation of these slopes.  Furthermore, the opportunity to explore and design for the future social and ecological potential within these sites is seldom provided.

Holistic Design Approach

My training and work experience have taught me how to balance ecological function with aesthetic considerations to create visually appealing landscapes.  Inspired by Frederick Steiner (2010), who stated the following:

Any landscape holds the possibility to both improve and regenerate the natural benefits and services of ecosystems

I began to wonder whether it was possible to transform an anthropogenic site into an aesthetically pleasing novel ecosystem. The aesthetic characteristics could be employed to address the anthropogenic ecological or climate change crises, fostering resilience using regenerative techniques and thus creating a space that is both functional and attractive to the community.  As a result of urban sprawl, many landfills are uniquely situated to play a significant role in reinstating and potentially expanding the biodiversity in a particular area, ensuring sustainability and ecological gain.

Throughout my career, I have had the opportunity to work on several landfills in and around the Western Cape.  Regardless of status, each design only needed to address the EA conditions and accommodate for:

• The underlying capping system proposed for each site, and

• The future end-use of the site (usually inaccessible open green space).

I have added to this requirement list, incorporating issues that address a few of the Sustainable Development Goals for 2030, including the following aspects:

• Utilising the site-specific characteristics, location, and local climatic conditions.

• Eliminating the nuisance conditions associated with landfills (e.g., odours, pests and vermin)

• Eliminating potential health hazards (e.g., windborne dust and litter)

• Providing vital visual screening of the waste body from nearby and overlooking areas.

• Restoring the natural functioning of the site concerning ecology, micro-climate, the continuation of green belts and/or biodiversity corridors, etc.

• Potentially creating accessible, attractive and usable public multifunctional spaces that contribute to social well-being and enhance the quality of life for local residents/local communities such as parks, community gardens, or recreational areas.

Case Study Comparison

As previously stated, there are environmental factors that need to be mitigated, and these are similar across all sites (e.g., nuisance conditions, health hazards, and visual impact).  However, to varying degrees, the age of the landfill, its activity status, the location, site characterisation, and orientation all provide site-specific considerations that play a major role in determining the most effective ecological rehabilitation approach for maximum sustainability from a whole-systems design perspective.  To illustrate my point, I have chosen two landfill site typologies; Atlantis Historical Landfill (closed) and Vissershok Landfill Site (operational).  I will discuss how regenerative design principles have been applied and why these should and do differ depending on the age of the landfill - whether historical (decommissioned and closed) or operational (active) – emphasising the integration of strategies that enhance environmental and social well-being.  

Atlantis Historical Landfill

It is critically important to acknowledge that each site is unique and should be treated as such.  My first example is Atlantis Historical Landfill, located within the Witzands Aquifer Nature Reserve, in a reasonably well-preserved area of endangered Cape Flats dune Strandveld and the critically endangered Atlantis sand fynbos (CoCT, 2008).  The reserve consists of the Atlantis dune field, an area of approximately 1750 hectares, comprising non-vegetated mobile dunes and rocky outcrops, which are hotspots for leisure activities (e.g., 4x4 tracks, bicycle trails, and sandboarding).  The landfill covers an area of approximately 9 hectares to the northeast of the dune fields and commenced operation in 1975 (Figure 2).  It mainly received general waste from the Atlantis residential and industrial areas until it was officially closed in 1988, although it is estimated that the landfill operated until 1997(CoCT, 2008).

No formal closure process (shaping or capping) was undertaken to officially close the site until 2014, when the consultant team was appointed.  Due to its location on the outskirts of Atlantis and within a nature reserve, with isolated remnant sand dunes supporting a variety of indigenous vegetation within the affected area, it was decided that the site would be inaccessible to the public for the 30-year observation period, due to the unknown character and content of the waste body. The Client, the City of Cape Town, was advised to remediate the landfill to blend into the broader natural environment, as the visual exposure would be almost insignificant.  

Obviously, this was not entirely possible, as the area does need to be fenced for public safety, but vegetatively it could blend into the broader natural environment.  To achieve this, my firm opted for a blanket planting scheme, consisting of approximately two plants per square metre (this equated to about 20 000 plants per hectare), in combination with hydroseeding for stabilisation. The reasons behind this included the lack of irrigation, and reliance on natural, seasonal rainfall, combined with a lack of maintenance after final project completion. Despite the contractor needing to excavate and relocate historic waste from areas surrounding the landfill due to historic uncontrolled dumping, the receiving environment was relatively homogenous, as the landfill is historic and therefore generates minimal to no methane gas emissions and no leachate.  

At the same time that the main contractor was appointed, in early 2016, to complete the shaping and capping of the waste pile at the site, the landscape subcontractor began seed collection and plant propagation from the sand dune pockets and the surrounding vegetation – a crucial factor for survival, as the existing species have adapted to the local microclimate. The plants were propagated and grown-on at a nursery located just over a kilometre from site, with a very similar microclimate.  Topsoil (or top material) had to be imported, but fortunately, a nearby construction site had stripped the topsoil from their site and was looking to dispose of it. As the site was literally across the road, it was a win-win situation, as the topsoil was similar in structure and physical composition to the existing dunes. Soil tests were still conducted for both the existing surrounding soil and the imported material to ensure compatibility, with minimal enhancement using organic nutrients and microbes.  

Plants were brought to a temporary holding nursery on site a few weeks prior to planting. Seeding and planting of the landfill and the previously uncontrolled dumping areas were done at the start of the winter rainfall season to ensure sufficient moisture in the soil. The site was then left to its own devices, with minimal input over the following 12-month maintenance period.  The only interventions were ensuring that alien vegetation was kept at bay and that a water bowser was available for use if summer temperatures continued unabated to the detriment of the establishing vegetation (Figure 3).

Vissershok Landfill Site

The second case study is Vissershok Landfill Site, which is located approximately 20km north of Cape Town on the outskirts of the northern suburbs, within the lowland sand thicket biome (Figure 4). Cape Flats dune Strandveld, Swartland shale renosterveld and Cape Flats sand fynbos are the dominant vegetation types.  The entire site is 117 hectares, and comprised of three distinct portions, namely: Vissershok South, the Triangle (a stockpile area) and Vissershok North (a future landfill area).  

Unlike, Atlantis, Vissershok South is still very much operational (active). Established in 1987, and licensed as a H:h landfill site, which can receive moderate to low hazard-rated wastes, the landfill was initially created to receive waste generated by the City of Cape Town and its suburbs, along with waste from the City’s contractors.  

Due to the rapid urban growth of Cape Town and increasing waste volumes, it has now become the main waste disposal site for the city, currently accepting around 3000 tonnes of waste daily.  The license dictates that the site cannot be used for public facilities as an end-use.  Thus, once capped, it will be vegetated to provide a fenced, green, open space that will be inaccessible to the public for a minimum of 30 years.

The landfill is situated on the middle slopes of a natural valley, while the broader visual environment is characterised by gently rolling low hills in the north and east, falling away toward the Atlantic Ocean in the west and towards the Cape Metropole in the south.  The general area has been heavily disturbed by agriculture and woody alien infestations to date, thus resulting in major losses of plant species.  Limited natural vegetation has survived within the greater site, except a ‘bulb island’, a relocated silcrete outcrop and those areas forming part of the Blaauwberg Conservation Area (BCA).  Large stands of trees, consisting predominantly of Eucalyptus spp. (gum trees), are dotted across the broader landscape.

Not only does Vissershok need to comply with strict environmental legislation concerning capping and closure, but it also requires an innovative landscape design that meets the operational and regulatory requirements while enhancing the overall quality of life in the area.  It was therefore proposed to commence with progressive capping, a system that involves closing off areas that have reached maximum filling capacity and commencing the installation of the final cap as well as the process of rehabilitation of these slopes.  This process began in 2012. The landscape design proposal had to acknowledge the sensitivity of the broader site and the uniqueness of the various areas within the site boundary, while blending the partial capping into its surroundings to reduce its negative visual intrusion.  The design also had to ‘future proof’ the site for when it could potentially be open to the public.

As Vissershok is an operational landfill, it presents unusual challenges in terms of logistics, due to the ongoing operation, but also results in an extremely variable and heterogeneous environment as well as comprising a sizable area of degraded land on the outskirts of a large urban area. Being an operational landfill, it is also distinctly unique in regard to the issues one has to contend with, and could include one or more of the following issues:

• Minimal available topsoil;

• Management of leachate from the working face - controlling potential run-off from the landfill with a cut-off drain, required to channel leachate from the active landfill areas (Figure 5);

• Soil wash-away and localised erosion; and

• Alien vegetation and weed establishment (Figure 6).

In addition to the core challenges, there are typically several other extenuating factors associated with progressive capping at an operational landfill like Vissershok.  These include:  

• Windblown litter: The implementation of wind suppression measures is recommended to stabilise the landfill’s slope and minimise contamination from windborne litter (Figure 7);

• ‘Edge effect’ contamination: Vegetation is often susceptible to odours from the working faces, so capping larger areas prevents dieback;

• Maintenance contract delays: When these delays occur, invasive alien vegetation and (agricultural) weeds can establish, outcompeting indigenous plants;

• Landfill cover failure: This causes breaches in the cover, leading to methane emissions and/or contamination of the top material by leachate overspill;

• Leachate pump failure: When pumps fail, or are stolen, leachate can back up on the working face, sometimes overflowing the cut-off drain.  This contaminates the capping layer, making it nearly impossible for any species, even grasses, to grow in these conditions.

To mitigate these issues, the design team continuously monitors environmental conditions and implements rehabilitation initiatives that enhance biodiversity.  Time is the biggest advantage on this site, as it will be a decade or more before the landfill is completely closed, allowing for long-term strategy development and refinement.  

Topsoil for the capping was sourced from Vissershok North, where material was stripped to construct new cells. Soil tests were conducted to determine both the physical and chemical properties, and our initial priority was to stabilise the slopes using a hydro seeding mix primarily composed of grass and pioneer species. We then planted clusters of vegetation, combining an equal mix of pioneer, intermediate, and climax species, as well as a few bulbs, to encourage sustainable growth. This method allowed the more permanent plants to establish without excessive competition.

My firm opted for three plant cluster types, each covering 150m2.  One large cluster contained 30 plants, while two smaller clusters contained 15 plants each. These ‘inner’ clusters overlapped by up to three meters and comprised an equal mix of five to eight species from the propagation list. Each individual cluster was planted at approximately two plants per square metre, with the total cluster types spaced about 8 to 12 metres apart, equating to roughly 8000 plants per hectare.  

The clusters included species indigenous to the Vissershok area, particularly from the lowland sand thicket biome. All three cluster types contained at least three to five duplicate species. This meant that a minimum of 30 species, encompassing a range of different plant types, were propagated locally. Successfully established vegetation from these clusters can be used in future for seeds and as propagation material to re-vegetate and rehabilitate further rehabilitation projects on and around the site (Figure 8).

Unlike Atlantis Historical Landfill, operational sites like Vissershok, are fluid environments, requiring the creation of a controlled ‘artificial’ environment to maximise rehabilitation success and minimise site variability. It is thus advisable to cap a larger area than initially proposed, as settlement of the underlying waste is inevitable. Stabilising the area with hydroseeding prevents not only prevents erosion, but manages surface water runoff, which is critical to mitigating the impact of landfill activities on the surrounding environment and downstream water resources. Long-term rehabilitation should only commence once stability (and the cap integrity) is ensured (Figure 9).

Sustainable and Regenerative Solutions

Despite both Vissershok and Atlantis landfills being located within the Cape West Coast Biosphere Reserve, the rehabilitation design proposals for each are distinct, shaped by the site-specific considerations and conditions that are crucial for effective ecological rehabilitation for maximum sustainability from a holistic design perspective. The key factors influencing design include:

• Orientation of the landfill: The slope orientation may determine the inclusion of full-sun species on north-facing slopes, while partial-sun and shade species might be better suited to shadier slopes.

• Predominant wind direction/s: In Cape Town, winds predominantly come from the southeast, so hardy, wind-tolerant species are essential.  Wind-breaks or other adaptive management techniques may also be necessary to mitigate the impact.  Operational landfills also benefit from the implementation of wind suppression measures, both to stabilize the slope of the landfill and minimise the windborne litter contamination.

• Final height of landfill form: This dictates whether a variation from the minimum acceptable slope gradient can be included, which in turn dictates the soil moisture gradient and influences stormwater run-off control.

• Climate and seasonal constraints: Water availability is a key issue, so working with the natural seasonal cycles is more effective.  Hydro seeding at the optimal time with either a summer or winter mix is vital for successful germination and to suppress invasive alien vegetation, as irrigation is financially impractical.  

• Topsoil availability and quality: Soil may need modification (e.g. through the addition of lime, phosphate, organic matter, enzymes, or microbes for bioremediation) to be suitable for the proposed vegetation.

• Alien vegetation control: This must be managed before, during, and after rehabilitation to suppress invasive species, using methods like stimulation followed by suppression.

• Vegetation biome: Indigenous vegetation of local genetic origin is preferable, as it is better adapted to the local microclimate and soil conditions, including odour resistance.  It further conserves rare or protected species, while creating or continuing a biodiversity corridor or green belt.    

• Visual exposure and integration: Blending the landfill into the broader natural environment is often necessary, as seen with the Atlantis Historical Landfill in the Witzands Aquifer Nature Reserve (Figure 10).

• End-use considerations: Whether the site will be accessible or inaccessible also influences design decisions.

Conclusion

Through my work, as illustrated through these two case studies, while it is crucial to comply with legislative requirements, it is equally essential to embrace a holistic design philosophy that prioritises the healing, restoration and revitalisation of these human-made landscapes.  This approach not only addresses environmental concerns but also transforms these sites into green spaces that contribute to ecological restoration, carbon sequestration, improved water management, and enhanced community engagement. In turn, this benefits social well-being by creating spaces that meet both ecological and human needs, fostering a sustainable legacy for future generations.  

Regenerative design is more than a response to the challenges of landfill closure; it is a proactive strategy for building a more harmonious relationship between people and the environment.  

By incorporating these strategies, landfill remediation can become a more economically and ecologically sustainable process, promoting long-term ecosystem health, reducing degradation, and enhancing resilience. Collaboration between government agencies, communities, and environmental organisations is essential for the successful implementation of these initiatives.

Our ability to stay creative, flexible and collaborative and adaptive in the face of changing environments is key to addressing the challenges we collectively face.  By preserving and regenerating life-supporting natural systems, we can make a positive impact on the environment and society.  My challenge to you, the reader, is to embrace the potential of landfill transformation, knowing that it is possible to create elegant solutions that not only reflect the biocultural uniqueness of each place but also re-imagine humanity’s impact on Ea

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