Former landfill site ground-gas risk assessment

Former landfill site ground-gas risk assessment

Project title: Fen Meadows Ground Gas Risk Assessment

Client: Large Scale Construction Company

Location: Fen Meadows, Nursling, Hampshire

Start date: March 2016

End date: April 2016


Services provided:

  • Purge & Recovery Tests
  • Continuous ground gas monitoring
  • Continuous groundwater sampling and monitoring
  • Surface emissions survey

Key benefits:

  • Saved time
  • Reduced costs


Ground-gas risk assessment of a former landfill site in Hampshire


Ground-Gas Solutions (GGS) was approached by a large scale construction company to undertake a ground-gas risk assessment for the fulfilment of health and safety requirements and due diligence for a housing development of over 100 homes.

The site currently consists of a one square kilometre of arable farmland used for animal grazing. However, from the early 1930s to the 1960s the site consisted of a gravel quarry, which was infilled with landfill waste in the late 1980s and early 1990s.The resulted in the infilled waste becoming a source of ground gases that subsequently requires monitoring.

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Image of the walkover survey results.

To start with, GGS identified appropriate boreholes in order to deploy continuous ground-gas and groundwater monitoring equipment. The subsequent data gathered through this process provided a more holistic representation of the gas regime at the site, and therefore the potential ground-gas drivers could be identified. Water samples were also taken to determine the extent of dissolution of these ground-gases in the groundwater.

The next step was to perform purge and recovery tests. This process is designed to measure the rate of gas recovery into a monitoring well following inert gas displacement. The gas recovery rate can then be used in conjunction with well volume to calculate a ground-gas flux, which can be used within detailed risk assessments and modelling. Finally, a surface emissions walkover survey was undertaken to identify elevations of methane at the surface.

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Example concentration duration graph.

Using the robust data collected during the project, GGS was able to provide detailed client reports on the development site’s ground-gas regime. Advice and recommendations for potential remediation strategies and mitigation measures were then made to ensure protect site users were protected.

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