Most brownfield development and environmental protection specifications require hydrocarbon resistant membranes; however, the majority of products claiming to be 'hydrocarbon resistant' may not be...
Many 'hydrocarbon resistant' membrane products are merely HDPE and Richard Menage, Technical Director of ITP Ltd, believes that the use of this material may not be adequate because, whilst HDPE passes the current tests for chemical resistance, permeability tests show that it is readily permeable to hydrocarbons and other environmental contaminants. ITP has therefore developed a new type of membrane, 'Puraflex', which overcomes the risks associated with HDPE, polypropylene and other homogenous monopolymer membranes.
To be an effective barrier, it is necessary for that barrier to not just maintain its physical integrity when exposed to chemicals, but to also perform as a barrier. Whilst chemical resistance tests provide a measure of resilience, the measure of barrier performance is the permeation rate. This is where HDPE fails as a hydrocarbon resistant barrier because polyethylene and other common homogeneous geosynthetic membrane materials are readily permeable to hydrocarbons, because they are hydrocarbons themselves.
Current industry standards for chemical resistance tests do not provide sufficient information in the selection of appropriate barrier material. Permeation data needs to be considered to determine whether the material is fit for purpose, particularly if hydrocarbons have been identified in the soil analysis. The accuracy of environmental risk assessments and modelling predictions should therefore take account of chemical permeability where a barrier is specified to provide protection from current or possible future contamination.
Puraflex® is a chemical resistant multilayer barrier membrane incorporating both polar and non-polar polymers. Typically, the installed cost is up to 20% more than HDPE, but this is heavily outweighed by substantially lower levels of risk, so ITP suggests that the term 'hydrocarbon resistant' should be replaced by 'an effective hydrocarbon barrier with appropriate permeation test data'.