SA Wilson, Environmental Protection Group and A Shuttleworth, SEL Environmental. This paper was first published in GE’s January 2002 edition.
The use of in-ground barriers, particularly vent trenches, is a common method used to protect development from landfill gas migration. A new system for installing passive venting barriers is described which overcomes many of the disadvantages associated with conventional trench systems. It uses highly efficient geocomposite vent nodes, which are driven into the ground and connected to a collection/ dilution duct, to allow safe venting to atmosphere. The system minimises spoil and contact by installers with contaminated soils and can be installed in restricted spaces.
There is little design guidance available for such barriers, because the performance depends on a complex relationship between several highly variable parameters. A simplified method is described which allows the relative performance of different vent node spacing and ventilation methods to be assessed. This should help to ensure that gas vented to atmosphere from the system is at acceptable concentrations.
A monitored trial of the system has been undertaken which demonstrates the barrier is effective in reducing migration of landfill gas and diluting methane and carbon dioxide concentrations at the vent outlets to less than 1%v/v.