‘Capping’ is defined as the sealing of a landfill to prevent the entry (ingress) of precipitation (rainfall, snow, etc.) and the escape (egress) of gas, odour and other fugitive emissions.
There are a number of geosynthetic products on the market that are suitable for use as an artificial sealing liner and these can be divided into two groups, namely polymeric geomembranes (polymeric geosynthetic barriers) and geosynthetic clay liners (clay geosynthetic barriers). Whilst the use of geosynthetic clay liners is increasing for the purpose of capping, geomembranes are more commonly used throughout the UK.
There are a number of polymeric geomembranes commercially available, the most common types used for capping are:
- high density polyethylene (HDPE);
- Linear Low Density Polyethylene (LLDPE);
- polpropylene (PP)
To guarantee an effective cover the landfill cap should incorporate a drainage layer above and a gas collection layer below the cap lining system.
A pozidrain will provide these functions with higher performance and lower cost than conventional crushed stone filters. This has been specially designed to be compatible with both HDPE and clay liners and to give the optimum performance over the whole life of the landfill capping and will enhance the performance of the GCL or HDPE liners by providing an additional barrier that prevents the majority of the water or gas reaching the liner.
Geocomposite drainage layers have a proven record in landfill capping.