Definition and Properties

Biogas is a gas produced by the biological breakdown of organic matter in the absence of oxygen. It is a combustible gas composed mainly of methane, carbon dioxide and varying amounts of water vapour and hydrogen sulphide. Biogas can be created naturally (as in marshes, for example) or by the disposal of residual organic materials (landfill).

Among gas generated, methane is of great concern for human health and safety as it is a colourless, odourless, and extremely flammable gas. It is explosive when its concentration in air varies from 50,000 parts per million (ppm) (5% volume/volume) to 150,000 ppm (15% volume/volume). Even when methane generation is low, there is a risk of explosive concentrations of the gas in place.

Surveys and Possible Mitigation Measures

The presence of biogas poses potential risks to human health and safety. In addition, the possibility of migration away from the disposal site may affect the population living in a much wider area than the site itself. Of course, the movement of gas through the soil is a complex phenomenon.

Thus, the methane in the biogas can migrate vertically toward the ground surface, but also migrate laterally. The gas tends to follow the pathways of least resistance until it can find a way to the surface. Cracked rock, permeable unconsolidated deposits, and the presence of underground structures such as excavations and water, power and sewer lines can all promote biogas migration.

For example, where the historical environmental assessment of the site suggests a former disposal site in the vicinity or at the study site, biogas surveys are recommended. The location of boreholes and the installation of observation wells are critical to the successful completion of the study. The subsequent surveys will help to recommend the most appropriate mitigation measures, such as the installation of membranes or an active or passive venting or collecting system. Various measures can be proposed to ensure health and safety.

It is possible to build on such a site, but several steps must be taken before obtaining a construction permit. Having several projects to its credit, the Groupe ABS Environment team can advise you on the realization of biogas surveys and to help you in the design of mitigation measures to be put in place for your construction projects. Don’t worry, the professionals of the Groupe ABS Environment team will be there to assist you.