Q. Do I need to have my membrane/venting verified?
A. Yes ALL remedial works carried out on contaminated sites require a degree of verification and sufficient lines of evidence need to be provided to the regulator. Gas barriers are installed on contaminated land and therefore they require verification.


Q. Can I get the installation contractor or membrane supplier to provide a verification report of the installation?
A. The Environment Agency recommends that conflicts of interest in verification should be avoided (Environment Agency, 2010a) . "A contractor or gas membrane supplier certifying their own work or product is considered to be a conflict of interest and is not good practice. If verification is carried out by the same company (or related company) that carried out the installation then the process, the results and report should be audited by an independent consultant" (Ciria C 735).

It may be acceptable for the installation contractor to assist with integrity testing and CQA, however this needs to be agreed with the regulators and verification consultant prior to work starting and is normally taken into account when putting the validation plan together.

A membrane supplier cannot provide verification of a gas membrane installation. They can offer advice on whether a system has been installed in relation to their recommendations however this does not constitute validation of a protection system.


Q. Do I need to have all the plots/areas independently inspected?
A. It is not usually a requirement to have all plots/areas independently inspected. The frequency of independent inspections will depend on a number of factors. Guidance on this is available in CIRIA C735 by using a risk based methodology based on the complexity of the site, number of plots/buildings, gas regime on site and the competency of the installation contractor. The process of verification including integrity testing requirement and frequency of inspection visits should be set out in the validation plan set out at the design stage.


Q. What is a Specialist Installer?
A. A specialist installer is a contractor whose operatives hold the CSkills Awards L2 NVQ Diploma in sub-structure work occupations (construction) – installation of gas membranes or equivalent. An installer who has attended the Cskills upskilling course and is working towards the L2 NVQ Diploma may be classed as a semi- specialist, however evidence and previous experience should be taken into account when deciding on the degree of verification required. In all cases where the installer has not completed the diploma a more hands-on cautionary approach should be adopted by the verifier.


Q. Is an Approved Installer the same as a Specialist Installer?
A. An Approved Installer is a company that is approved by a membrane supplier as understanding their products and systems. The approved installer may have had some basic installation training from the supplier, but the training has not been carried out to any independently approved national level. Therefore an approved installer is not deemed as a specialist unless they also have Cskills Awards L2 NVQ Diploma in sub-structure work occupations (construction) – installation of gas membranes.


Q. What are the benefits of using a Specialist Installer?
A. From our experience we would always recommend the use of a specialist installer. The three main benefits are;

  1. Confidence that the installation will be carried out to recognised industry standards by a company that is affiliated to ‘The British Geomembrane Association’ (BGA)
  2. The install will usually be carried out more quickly, therefore providing a benefit in terms of programming of the works
  3. The install will be subjected to a reduced amount of independent validation in most cases


Q. Are GQA Environmental Specialist Installers?
A. No, GQA Environmental DO NOT install gas membranes. However, our inspection surveyors have completed the Cskills Upskilling Course on Gas Membrane Installations, as well as spending time with specialist installers gaining hands-on experience of installing gas membranes and venting systems on sites. All GQA Environmental surveyors have attended a specially tailored course provided by The Welding Institute (TWI) on carrying out the inspection of welds for various geomembranes. The course covers the destructive and non destructive testing of hot air, hot wedge and extrusion welds.