Leachate Attenuation in the Unsaturated Zone Beneath Landfills: Instrumentation and Monitoring of a Site in Southern England

Unlike a number of other countries, where legislation requires that all landfills are lined with impermeable materials, in the United Kingdom great reliance is placed upon the attenuation of contaminants which occurs as leachate seeps through intergranular unsaturated zones beneath sites. Much research has been reported which supports this view, although in recent years the effectiveness and reliability of these processes has been the subject of much debate.

This paper describes, and presents results from, a major research investigation which has been funded by the United Kingdom Department of the Environment at a site in Southern England where the landfill design has incorporated an engineered, semi-permeable attenuation blanket, using locally available calcareous sands and silt, which have been emplaced to a minimum depth of 6 m above the water table.

Installation of over 100 sampling and monitoring instruments within this unsaturated zone before waste disposal began in June 1982 has made it possible to obtain water samples from the saturated and unsaturated zones, gas samples from the unsaturated zone, and to measure soil water pressure, electrical conductivity, and temperature in situ, at 3 monthly intervals since this date, to allow movement and attenuation of decomposition products of solid wastes to be monitored.