Attenuation of Leachate in a Designed, Engineered and Instrumented Unsaturated Zone Beneath a Domestic Waste Landfill

Abstract

Abstract In recent years the effectiveness and reliability of “dilute and disperse” type landfills has been the subject of much debate. Much research has been reported which supports the view that intergranular unsaturated zones beneath sites can provide a high degree of aquifer protection, although detailed and continuing monitoring of such zones has been extremely rare. Aspinwall and Company are carrying out a major research project on behalf of the UK Department of the Environment at a landfill site in Southern England, which is operated by ARC South Eastern. The design of this landfill was produced by Aspinwall and Company, and is innovative in that it has incorporated an engineered, semi-permeable, attenuation blanket, using locally-available calcareous sands and silt, emplaced to a minimum height of 6 m above the water table. The site has a licence to deposit up to 1300 tonnes per day of domestic wastes derived from London. In early 1982 one portion of the quarry floor was selected for a programme of research, and over 100 instruments and sampling devices were installed before waste disposal began. A drilling programme during the summer of 1984 allowed further sampling, and the installation of more instruments within the wastes themselves, now about 2b to 30 m deep. This paper summarises and describes data obtained over the 3-year monitoring period to early 1985. The performance of the unsaturated zone is assessed, in terms of the attenuation of inorganic ions such as ammonia and chloride, and degradation of organic compounds such as fatty acids, which have occurred as leachate and gases have migrated from the wastes.