Engineering a controlled landfill

Over the years, as Maltese society generated more income and consumption patterns altered, consumers began to be driven by fashion, seeking products that were easier to handle and aesthetically more pleasing.

Industry too identified ways of cutting costs and ensuring competitiveness. Products became cheap and expensive to repair, easier to mass produce and the materials more hazardous to dispose of.

Society prospered, the tourist industry boomed but the generation and management of waste was an unforeseen consequence. More consumption, more waste and the vicious circle goes on. We are now faced with a pressing problem, one that threatens our well-being if not properly addressed.

There is an urgent need for a sustainable waste management system, a quantum leap in culture and society facilities. Waste minimisation and prevention successfully safeguards the health of society, sustains industrial activity and protects the environment.

We need to understand the true value of waste and the cost of its disposal. Facilities, distinctively diverse from those presently available, are needed for the reuse, recovery and recycling of material.

However, though there is much talk about recycling, unfortunately technology is not sophisticated enough to be able to recycle every bit of waste. A small fraction still needs to be disposed of safely. The new facility that must be developed is the controlled landfill.

We tend to cringe when the word `landfill` crops up. We think of that awful place where rotting rubbish is being dumped and where no one has any idea what is going in. Litter blowing around, rats, smells, occasional fires and pollution: this is the image that comes to mind. But a modern, controlled landfill goes well beyond this. Dumping waste without complying with the existing environmental and health criteria is simply unacceptable.

The proposed development

A controlled landfill facility is a large void sectioned in zones and developed to a profile that contains about 40 per cent surcharge of material. The site may be developed in a quarry or on natural ground. In both instances the phasing of operation varies but the technology remains unchanged.

Such a site will accommodate mainly the disposal of non-hazar-dous and non-inert waste material.

Leaking gases, unbearable smells, rats, disruption, noise and other pollution-related problems - these are major concerns when we talk about dumps especially for those living in the vicinity. A modern landfill facility tackles these problems and is constructed, maintained and managed to eliminate all the nuisances commonly associated with dumps.

The facility will include

¤ a reception area for inspecting and analysing, weighing and recording vehicles and waste arriving at and leaving the facility;

¤ systems for surface and ground water management and leakage detection;

¤ systems for managing leachate;

¤ systems for landfill gas management; and

¤ systems for environmental monitoring and control.

A landfill facility is zoned and each zone is sub-divided into cells, each of which is developed in three phases: preparation, operation and restoration.

Each zone will last for about one year and the area of operation will not be larger than 2,500 square metres, more or less the size of half a football pitch.

The cells are developed in such a way that the proposed site is not disturbed entirely from the outset but developed progressively as landfilling proceeds. Site restoration starts as early as is technically possible allowing the site to blend in with the surrounding landscape.

Before developing the site, water quality and gas monitoring boreholes are sunk up and down the hydraulic gradient of the landfill area. Access routes, a weighbridge, a wheel-washing system and security fencing are put in place and the site is landscaped to help minimise the impact of landfill operations on neighbouring areas.

Site preparation

Before a landfill is constructed the authorities responsible need to specify exactly what type of waste, how much and how it should be operated on a daily basis.

The site will be cleared of vegetation and any old structures while topsoil and subsoil will be stockpiled. The area for filling will be shaped to promote falls for internal drainage and ensure stability of the final fill.

Some excavation material that is either brought in from ongoing works elsewhere or that is generated on site will be used to form peripheral covers to help screen the landfill from view. Additional material will be used to prepare the formation levels to receive the base protection layers while some materials will have to be stored for the construction of the cells as well as to provide for cover as needed.

Tackling potential impacts

Rotting waste generates two potential environmental and health risks, that is leachate and landfill gas. For this reason, a leachate collection and detection system is incorporated within the lining system of the site.

Landfill gas, consisting of carbon dioxide and methane, is contained, collected and treated. For this reason, a landfill gas management system must be incorporated within the site to contain, and extract and treat the gas.

Wells are constructed progressively by drilling within the waste as restoration proceeds. The gas will either be utilised as a fuel for the generation of electricity or flared depending on the volumes of gas produced. The effectiveness of such protective measures must be verified using an environmental monitoring system.

Operation

Every vehicle arriving at the site will be inspected visually to check on the identity, status and condition of the vehicle and the wasteload being carried. Any vehicle or load considered to be in a dangerous condition will be immediately placed in a quarantine area provided for this purpose and notified to the appropriate authorities.

Waste is also randomly off-loaded in a specialised area and analysed for leachate and emission levels as directed by international regulation.

All waste inputs to the site will be weighed and the origin, nature, and type and weight recorded. Only waste that complies with the conditions of the waste management licence will be permitted to enter the landfill facility. Any unpermitted waste will be quarantined until disposed of appropriately elsewhere.

The load is discharged at the tipping face and levelled and compacted using a steel wheeled compactor. The tipping face is covered with soil when the facility is not in operation to eliminate the potential for smouldering, littering, vermin and similar nuisances. As the tipping continues, the refuse is compacted and covered and regular checks are made and any problems dealt with.

Using this filling methodology it is virtually possible to track down any problematic material that would have been tipped over the 20-year life span of the facility. If such material is found to pose a threat to the environment or human health then this may be extracted and treated appropriately.

Restoration and aftercare

The site will be restored in a way that conforms to the surrounding landscape. It is expected that the site will settle over time to about 25 to 40 per cent of the finished landform.

The cover to the site will include a 2.5 metre layer of gravel, clay, crushed rock, subsoil and topsoil. The active gas extraction infrastructure will be maintained and the site developed for agriculture or for similar purposes.

Monitoring of the site will be on- going and any necessary maintenance will be carried out for up to 40 years after completion.

We can no longer talk of - or even consider - the use of uncontrolled dumps. A well-run modern landfill that is environmentally sound, totally safe and as unobtrusive as possible to the local community is urgently required.

It is obvious that people do not welcome the presence of a landfill but as long as we continue to produce waste, it has to go somewhere - but not just anywhere.

Developing a facility like this requires a lot of effort, care, planning and expense to ensure the best possible results have been achieved.

Dr Ciantar, B. Eng. (Hons), M.Sc. (Brunel), Ph.D., is on the staff of the Works Division.