Former landfill site ground-gas risk assessment
Project title: Fen Meadows Ground Gas Risk Assessment
Client: Bloor Homes Southern
Location: Fen Meadows, Nursling, Hampshire
Start date: March 2016
End date: April 2016
- Purge & Recovery Tests
- Continuous ground gas monitoring
- Continuous groundwater sampling and monitoring
- Surface emissions survey
- Saved time
- Reduced costs
Ground-gas risk assessment of a former landfill site in Hampshire
Ground-Gas Solutions (GGS) was approached by Bloor Homes Southern 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.
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.
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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