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Levenseat Ltd

Waste Management Specialists
Text Box: Levenseat Waste Management Site Landfill The landfill at Levenseat comprises a 2M m3 void which was formed by quarrying for sandstone. The landfill is engineered so that all water which lands on the waste as rainfall and thereby becomes contaminated is contained and collected for treatment. (The contaminated water is known as “leachate”.) Containment is achieved by lining the sides and base of the landfill with clay 1m thick and then covering this with heavy plastic. The clay is placed carefully in thin layers which are compacted and rolled out so that the clay forms a solid impenetrable mass. It is then subjected to a range of tests to confirm that it has reached the required impermeability. The plastic liner is black high density polyeurythene (“HDPE”) which is 2mm thick. The sheets of HDPE are welded together and the liner is tested using an electrical resistivity test - capable of finding one pinhole in several hectares of liner. Inside the liner there is a layer of disused car tyres which are used to form a drainage layer. This ensures that any water is allowed to flow freely to and along the base of the landfill. The base is profiled so that water drains to a single sump from where it can be pumped out. Once each section of the landfill is full of waste, the top of the waste is “capped” to prevent both rainwater getting in and gases getting out. In the first instance the cap used is clay which is engineered in the same way as for the base and sides of the landfill. As the waste within decomposes, it shrinks and the level of the surface drops. This can result in difficulties with draining water off the surface and so after about 5 or 6 years the clay cap is removed and more waste is added in order to raise the surface to a shallow dome shape which allows rainwater to be shed to the sides. Once it can be assumed that any further shrinkage will be minimal, the final cap is installed. The final cap comprises a layer of HDPE which is welded to the HDPE on the sides to form an enclosed bag. The cap is then covered with soils which are cultivated and sown with grass. The land can then be used for grazing. As waste decomposes it gives off gases the principal constituent of which is methane (CH4) which represents both a problem and an opportunity. It is a problem because methane is a greenhouse gas and if it were released into the atmosphere it would contribute to global warming. However it is an opportunity because it is a source of energy and can be burned to generate electricity. At Levenseat we therefore have a network of pipes and wells drilled into the waste which collect the methane and pipe it to a generation plant which at present is generating electricity at the rate of about 0.5MW- enough to meet the needs of about 1,100 homes.  Acceptance of waste in the landfill is a process which needs to be carefully managed. First of all it is important to ensure that only wastes which are legally permitted to be landfilled are accepted. Unacceptable wastes include ones which might give rise to hazardous conditions in the landfill (eg due to their chemical composition) or which might give rise to pollutants in the leachate which could not be removed by treatment. There are three checks to ensure that only acceptable wastes are landfilled: The waste producer and/or carrier must check and certify the nature of the waste The waste is inspected by the Site Controller when it is checked in at the weighbridge (this is of course limited to what the Site Controller can actually see) The waste is inspected when it is tipped onto the landfill. (In addition in some cases the waste producer is asked to obtain a chemical analysis of the waste before it can be accepted for landfilling.) Once waste has been deposited on the landfill it is spread out and then compacted in thin layers to ensure that air is excluded and that the waste takes up as little room as possible. This is done by a 55 tonne landfill compactor which has steel wheels with large “feet”. At the end of each day the waste is covered with a thin layer of soil or similar material. This ensures that litter doesn’t blow from the waste and that food particles are kept out of reach of scavenging birds. Text Box: Back Text Box: Back

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