Ground gas investigations are typically undertaken as part of Phase II of these geo-environmental assessments, and are a planning condition for many proposed developments. Occasionally a stand-alone investigation may be required, where development sites or existing structures are potentially affected by ground gas.
Many consultants currently use CIRIA C665 as guidance for ground gas investigations, assessing the risk to buildings posed by hazardous ground gases. This guidance recommends a minimum of 3 months’ monitoring for a site with very low potential of source gas generation. Typically, investigations will include the installation of several gas monitoring wells which will undergo a regular monitoring schedule both to monitor the quantities of any gases – mainly methane (CH4) and carbon dioxide (CO2) – and to measure flow. Some wells will also need to be checked for low or falling atmospheric pressure, as this would indicate if the land was no longer producing gas and so potential remediation or building could begin.
Not only development sites may require gas monitoring. Existing structures can also be at risk from ground gas, and if the gas is from an off-site source then legislation within the Environmental Protection Act 1990 could determine that the land owner is responsible for undertaking any required remedial measures, including ground gas investigations.
The ATEX- and MCERTS-approved GA5000 from Geotech is a portable gas analyser used regularly in ground gas investigations. The GA5000 can measure up to 6 gases, including CH4, CO2 and hydrogen sulphide (H2S) as well as reading gas flow and monitoring atmospheric pressure, within one portable unit. With its easy to use interface and proven technology, providing accurate results, the GA5000 can be used on a wide range of different sites. The GA5000 is under continuous development, working with the feedback Geotech receives from clients. New features are made available for free download.