Overview of the Virtual Curtain

SEL Environmental Ltd     Tel: 01254 589987     Email: sales@selenvironmental.com


The Virtual Curtain System is a unique patented system which utilises a series of discreet vertically installed highly voided geosynthetic vent nodes, positioned at calculated centres to create a virtual curtain. The geosynthetic vents have an extremely high intrinsic permeability ‘k’ in excess of 1.75 x 10 –5 m2 (approximately 150 times greater than 20mm single sized gravel) and can accept inflows from both sides of the vertical vent nodes reducing the potential for gas build up. Each vent node has a zone of influence around it; the extent of this will be dependent on the local ground conditions. The vertical vent nodes connect to an upper horizontal gas collection and dilution duct which then connects to either a proprietary vent bollard or vent stack. The vents can be off-set from the virtual curtain providing flexibility for subsequent construction.

Forced Dilution Concept

The Forced Dilution Principle forms the basis of the Virtual Curtain system. Using passive ventilation techniques to create a zone of low pressure within the ground, the Virtual Curtain System attracts and dilutes ground borne gases to acceptable levels whilst providing a preferential pathway to atmosphere. The Virtual Curtain System is not a physical barrier and will not affect the groundwater characteristics of a site. Groundwater will continue to act in the same manner avoiding any potential issues with flooding, water abstraction and settlement or heave. With respect to gas, it acts as a pathway break and a conduit for safe and controlled venting to atmosphere. The virtual curtain is vented through purpose made vent stacks or vent bollards which exert a venturi effect in the ground. This encourage gas migration towards the virtual curtain and provides clean air for mixing and dilution and allows passive venting to atmosphere.

gas migration, forced dilution, part 2a, closed landfill
Design & Installation

The virtual curtain is specifically designed for each site. Gas types, concentrations and flows are used to calculate the size and spacing of vent nodes that are inserted into the ground using a no-dig method to minimize the amount of excavation which is usually no more than 650mm deep. The individual nodes are connected to a collector duct system which is wrapped in a geotextile. The duct system is located within a shallow trench which is backfilled on completion of the Virtual Curtain System with selected as-dug material. The design will confirm the capacity, number and spacing of the above ground venting infrastructure. The system is virtually maintenance free and has been widely accepted by regulators all over the UK.


The Virtual Curtain System is devised to mitigate ground gases such as:

  • Methane (CH4) 
  • Carbon dioxide (CO2) 
  • Carbon monoxide (CO) 
  • Diesel range organics (DRO) 
  • Petroleum range organics (PRO) 
  • Volatile organic hydrocarbons (VOCs)
Design Requirements

In order to develop a site specific designed solution for your project the following information would be required:

  • All site investigation data, including historical investigations to enable us to undertake a comprehensive review and desk study.
  • All gas monitoring and groundwater monitoring information including all historical monitoring information.
  • Detailed site survey, with a preference for .dwg format to enable us to draw our proposals using CAD.
  • All details of services, drainage or any other manmade structures that exist on or beneath the site.
  • Any other relevant information, anecdotal or otherwise that may affect or influence our proposals.
  • A copy of the part 2A determination document.


Virtual Curtain Technical Paper
Virtual Curtain Technical Paper.pdf Virtual Curtain Technical Paper.pdf
Size : 293.162 Kb
Type : pdf
Virtual Curtain Brochure
2017 Virtual Curtain Leaflet.pdf 2017 Virtual Curtain Leaflet.pdf
Size : 188.861 Kb
Type : pdf

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