Methods for sampling and analysing methane in groundwater: a review of current research and practice - summary
Published 17 December 2021
Applies to England
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1. Chief Scientist’s Group report summary
This project reviewed the factors that influence variability and uncertainty in measurements of concentrations of methane in groundwater. This information will help groundwater monitoring practitioners and the Environment Agency improve groundwater sampling for methane and increase confidence in groundwater monitoring.
1.1 Background
In recent years, significant efforts have been made to establish environmental baselines and to monitor groundwater quality around potential onshore oil and gas sites. Methane has been identified as a possible early indicator of leaks from oil and gas wells or through pathways (such as faults) in the sub-surface. Methane can also be released from landfill sites or during pollution incidents. Methane exists naturally in groundwater in certain environments and is a potent greenhouse gas contributing to climate change.
Reliable measurements of concentrations of methane in groundwater are needed to understand current levels and to monitor for any changes in the future. At present, uncertainty in measured methane concentrations can make it difficult to compare reported results.
1.2 Approach
The aim of this project was to understand the uncertainties in measurements of methane concentration in groundwater resulting from different field sampling and laboratory analysis techniques.
The project carried out a literature review of existing studies to understand where the greatest uncertainties could arise. The project team also sent out a technical questionnaire to groundwater practitioners in the UK, including laboratories, to identify common sampling and analysis approaches.
1.3 Findings
Field sampling accounts for greater uncertainties in the methane concentration data than laboratory analysis, but variability between different laboratories, even with ‘identical’ methods, can be high.
The greatest uncertainties are associated with sampling and analysis of higher methane concentrations, especially where gas-saturated conditions occur (about 20 mg l-1). At these concentrations, some of the dissolved gas can be released and can be difficult to collect.
To obtain representative methane values a sound understanding of groundwater conditions at a particular site is needed. This should be used to inform decisions about the choice of sampling device/pump, sampling depth, well purging and sample handling protocols. The lack of best practice guidance can lead to inappropriate sampling methods being selected.
The study found that in the UK there is limited commercial capability for dissolved methane analysis and currently no commercial laboratory that can carry out methane isotope analysis. This has implications for interpreting methane monitoring and permit requirements.
1.4 Conclusions
This review summarises current knowledge and practice for measuring methane concentrations in groundwater. There is a need for best practice guidance to improve both field and laboratory methods and to communicate these to the wider groundwater community.
1.5 Publication details
This summary relates to information from the following project:
- Report: SC190007
- Title: Methods for sampling and analysing methane in groundwater: A review of current research and practice
Project manager: Gary Edwards and Sian Loveless, Chief Scientist’s Group
Research contractor: British Geological Survey.
This project was commissioned by the Environment Agency’s Chief Scientist’s group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.
Enquiries: [email protected].
© Environment Agency