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Hazardous Ground Gas Risk Assessment (HGGRA) applies to both LFG and ground gas which can pose significant risks to both the environment and to human health. Risks from HGG are unique in comparison to other contaminants in the environment such as soil and water contamination, as gases can move in any direction, causes explosions and create an asphyxiating atmosphere.
LFG contains both methane, carbon dioxide and numerous trace gases or Volatile Organic Compounds (VOCs) that are generated by microbes from the anaerobic decomposition of organic compounds inside the landfill. In landfill situations these gases can migrate from the waste mass and into adjacent buildings and other sensitive receptors because of pressure changes in the atmosphere or by gaseous diffusion. This in turn can create explosive conditions, asphyxiating atmospheres and impact on vegetative growth.
Similarly, HGG risks are those that are typically a result of volatisation from a liquid phase contaminant such as a hydrocarbon leak from an underground storage tank. Gas phase compounds derived from solvents and hydrocarbons, can behave in a similar manner and have similar consequences to LFG but can pose a risk to longer term human health. The way in which these risks are assessed and managed does differ to LFG, but there are many similar principals for both sources of the gas.
Gas risk assessment is a specialised field that should only be undertaken by skilled and experienced practitioners. We see those in the general contaminated land industry undertaking HGG and LFG risk assessments, often with dire consequences. Both LFG and ground gases have unique attributes, and a risk profile which is usually higher than many other forms of contamination due to the extreme consequences of these risks. Therefore, skilled and experienced practitioners are essential in this field.