This is underlined by the Government's target of 60% of new housing development to be on Brownfield sites by 2008. All the parties involved are going to have to become more adept at dealing with Gas Migration.

The risks to development sites stem from the presence of ground gases that are generated from materials below the site or from adjacent landfills.

The figure below illustrates the principle source / pathway / receptor and why the virtual curtain system will be required. Gas is emitted from a source, in this instance a landfill but the source can be either manmade i.e. landfill or natural i.e. peat, coal measures, etc... The gas will follow a pathway of least resistance to atmosphere, generally pathways are naturally occurring permeable strata, the figure shows a gravel / sand lense. Any new development local to the pathway will be at risk, this is known as the receptor. The receptor can be a house, school, office block, warehouse, etc…

The Virtual Curtain System (VCS) is installed to intercept the pathway and provide a new preferential pathway (route of least resistance) to atmosphere. The gas emitting from the source will follow the natural pathway to the virtual curtain. The VCS intercepts the natural pathway, providing a new pathway of lesser resistance than the natural. The gas will follow the VCS pathway of lesser resistance due to the VCS barrier and the receptor will no longer be at risk.

It is vital that the migration of these gases is managed effectively, failure to do so carries the risk of prosecution and can render some sites uninsurable.

A further problem is the high cost of managing gas migration using conventional barriers such as gravel filled trenches and bentonite walls which require the excavation and disposal of large volumes of material that is often contaminated. Changing waste management legislation, such as the Landfill Tax Regulations 1996 and the Landfill Regulations 2002, as well as factors such as Aggregate Tax, has increased the difficulty and cost of using such methods.

The Virtual Curtain is an efficient and effective solution to lateral gas migration control offering lower costs and superior performance than conventional methods, delivering total assett protection and peace of mind.