Science and strategies for the long-term management and remediation of landfills

Modern waste management is geared towards recycling and re-use. Inevitably, however, there will be some wastes that, having come to the end of their useful life, will require disposal to landfill. Many landfilled wastes are now treated prior to disposal, but the treatment does not necessarily remove all contaminants. In fact some pollutants can be concentrated into the final waste stream.Landfill sites are designed and operated to prevent contaminants contained in the wastes from polluting the surrounding environment (for example, water and air). However, the consequence of keeping the contaminants in the site is that the polluting potential of the site does not reduce and will last for a period measured in centuries rather than decades. This also means that the site will require looking after for a very long period (possibly hundreds of years), and it far from clear that the means to pay for this aftercare will last for that long into the future.The purpose of this research is to help develop techniques (simulations tools) that could be used to shorten the length of time that landfill sites pose a pollution risk. The research will be applicable to cleaning up the backlog of old landfill sites that exist across the UK. The research will also be of use in predicting the potential impact that new types of waste may have in landfills, in advance of any wholesale adoption of the technologies that produce them. This will make a positive and essential contribution to waste management policy and strategic decision making in the UK.The main way in which the pollution load of a landfill reduces is by the passage of water through the waste, accelerating breakdown mechanisms and flushing out contaminants. The introduction of air into landfills to encourage in situ 'composting' is also beneficial. It is important to understand the factors that control the movement of both water and air through landfills, and consequently there is a need to understand the relevant bulk properties of the wastes in landfills. We will develop a classification system that describes the essential characteristics of wastes, and undertake experimental work to quantify the bulk properties of wastes and link them to the description. From this it should be possible to improve predictions about how different waste types will behave in landfills. We will undertake tracer tests in both the laboratory and the field to develop an understanding of the bulk flow properties of wastes. However, very few tracers have previously been used successfully in wastes. Thus an early task will be to identify a range of tracers suitable for use in wastes, primarily by means of carefully controlled laboratory tests. Suitable tracers that we identify will be used in subsequent laboratory and field scale experiments. These experiments will be designed to investigate the process of contaminant flushing at a variety of scales. The results will be used to help develop a theoretical basis (modelling) that describes how efficiently contaminants will be removed from landfills in different situations. These models will be used to develop landfill management strategies by which the timescale of pollution can be reduced from centuries to decades or shorter.It is generally accepted that landfill gas generated within landfills as a result of ongoing degradation affects water movement and that water blocks gas flow. We will undertake laboratory experiments to provide visual evidence of the nature of the interference that gas and water have on each other. We will also develop models to explain and describe what we observe to help improve our understanding of the process.