LANDFALL SITE IN UK

Landfall Site in UK

Landfall Site in UK

Landfill Site

There is currently much debate on the desirability of landfilling particular wastes, the practicability of alternatives such as waste minimisation or pre-treatment, the extent of waste pre-treatment required, and of the most appropriate landfilling strategies for the final residues. This debate is likely to stimulate significant developments in landfilling methods during the next decade. Current and proposed landfill techniques are described in this information sheet.

For the controlled release strategy the most critical engineered component is the top cover, whose function is to control the rate of leakage by restricting the rate of leachate formation. In any given location, percolation through the top cover is a complex function of several factors, namely: slope the hydraulic conductivity of the barrier layer the hydraulic conductivity of the soils or materials placed above the barrier layer the spacing of drainage pipes within the soil layer Mineral barrier layers are typical for this application. They may also be used for total containment sites, where FMLs or even composite liners have also been used for the top cover. A review of mineral top cover performance (UK Department of the Environment, 1991) found that percolation ranged from zero up to ~200mm/a. To obtain very low percolation rates, protection of the barrier layer from desiccation was necessary, drainage pipes should be at a spacing of not greater than 20m, and the ratio of the hydraulic conductivity in the barrier layer to that in the soil or drainage layer above it should be no greater than 10-4.

2) Phasing and cellular infilling

Landfills are often filled in phases. This is usually done for purely logistic reasons. Because of the size of some landfills it is economical to prepare and fill portions of the site sequentially. In addition, active phases are sometimes further sub-divided into smaller cells which may typically vary from 0.5ha to 5ha in area. Often these cells may be engineered to be hydraulically isolated from each other. There are two main reasons for cellular infilling: To allow the segregation of different waste types within a single landfill. For example, one cell might receive MSW bottom ash, another inert wastes and another non-hazardous industrial wastes. In hazardous waste landfills different classes of hazardous waste may be allocated to dedicated cells. To minimise the active area and thus minimise leachate formation, by allowing clean rain water to be discharged from unfilled areas while individual cells are filled.

Where cellular infilling is carried out, the landfill is effectively sub-divided into separate leachate collection areas and each may need an abstraction sump and pumping system. This can increase the physical complexity of leachate removal arrangements and if the cells receive different waste types, each cell may produce leachate with different characteristics. This may in turn influence the design of leachate treatment and disposal facilities.

3) & 4) Waste emplacement methods and pre-treatment

Wastes are usually compacted at the time of deposit. This is done to gain maximum economic benefit from the void space and to minimise ...