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Towards Sustainable Landfill: Passive Fail-Safe Design and Engineering - WR0304

The time taken for landfills containing non-inert wastes (as defined by the Landfill Directive) to achieve completion and equilibrium is controlled by the landfills overall contaminant load, and by the measures taken to minimise releases. Landfill gas and leachate egress form the primary emission sources. The concentrations of contaminants within the emissions will fall away slowly with time. However, the flux or magnitude of the total emission will be controlled by the concentration and the rate of release of gas or leachate. The degree of harm caused will also be a function of the location of the emission in addition to its concentration and period of release. Leachate leaking through a thick unsaturated zone into a minor or non-aquifer will have a lower environmental impact than leachate flowing to a ditch that is discharging into a high quality surface water system.

The primary function of the engineering, careful siting and management of landfills aims to minimise and mitigate these emissions. However, predictions made by modelling point to very long periods of time before certain leachate contaminants are flushed from landfills. Sustainable landfill means minimising the time that landfills need active management (albeit that there may be a long term monitoring requirement). Recognising that landfill post closure management will become increasingly difficult with the long term degradation of engineering systems (liners, caps and leachate recovery systems), then it would be sensible to design landfills that have certain fail-safe features. These features might include natural wetland treatment systems that are purpose built to deal with the low level residual contaminant load that might seep from a landfill over a protracted period, but that would be highly amenable to such passive treatment. Alternately, is some instances, the correct selection of liner and capping systems could result in a landfill that is designed simply to increase its leakage rate as the cap begins to fail, thus negating the probability of leachate overtopping.

Landfill gas generation at very low levels may well continue long after it is economic or technically feasible to collect it. Passive treatment systems such as the utilisation of waste derived compost to actively encourage methane oxidation is specially constructed venting systems might provide a means of passive near zero maintenance emission control.

In order to develop the concepts of passive fail safe design further, some detailed modelling work is needed to fully understand issues like the speed of leachate recovery, the quality of leachate that might overflow the liner system, and physical and biochemical changes in the waste that might affect fluid flow (be it liquid or gaseous).

Further work within the project will examine the ability to select specific waste streams, or to treat the residual wastes, in such a way that the leaching of species that cause the need for such long term management are removed from the system. Lead is a element that has been identified in some waste types and can continue to leach from wastes for protracted periods. Removing the source of mobile lead or treating the waste in a way that reduces its solubility may create a solution.

Inevitably, the research needs to point operators and regulators towards a series of simple measures that can improve the reliability of passive landfill management. We believe that the ideas will need to be simple (either to install or implement) as fail-safe systems need to be simple (while at the same time robust).

The modelling in this research project will assist in the design of concepts that will further assist the industry and regulators to assess the ease of incorporation into existing and new landfill sites, and will contribute a step change in the move towards sustainable landfill and long-term environmental protection from the impacts of landfilling.

The overall aim of the research is to investigate the engineering and design features for landfills that will ensure that during post-closure, the period of active management is minimised and control systems will fail-safe to make any gas and leachate emissions acceptable.

Specific objectives of the research are:

1. to model leachate accumulation in a fully contained completed landfill and predict its likely composition at key times; to identify design options for the control of gas and leachate in post-closure landfills;

2. to consult all stakeholders on the practicality of conventional and innovative design options; and

3. to provide a specification for the acceptable wastes or treated wastes to be deposited in particular types of future landfills in order to improve sustainability.

Project Documents
• Final Report : Towards sustainable landfill: passive fail-safe design and engineering   (490k)
• Technical Report : Towards sustainable landfill: passive fail-safe design and engineering   (1579k)
Time-Scale and Cost
From: 2006

To: 2008

Cost: £71,000
Contractor / Funded Organisations
Golder Associates (UK) Limited
Environmental Protection              
Landfill Management              
Long-Term Monitoring              
Managing residual waste in landfill              
Residual Wastes Management              
Sustainable Development              
Waste Management              
Fields of Study
Waste Management