Baseline methane survey of UK groundwaters

Map of existing UK groundwater methane data and areas where new baseline sampling is being focussed

Methane (CH4) is an important greenhouse gas and a common trace component of groundwater.

The British Geological Survey (BGS) has been studying methane in UK groundwaters since the 1980s, to investigate sources of methane in the subsurface, the hydrogeochemical controls on its fate and behaviour and potential for methane emissions from groundwaters.

Initial results (June 2013) from the new survey and summary of existing data.

How does methane get into groundwater?

Methane in groundwater is derived from two main sources:

  • biogenic methane, which is bacterially produced, and is often associated with shallow anaerobic groundwater environments, such as peat bogs, wetlands, lake sediments and landfills, although it is detectable in nearly all groundwater.
  • thermogenic methane, which is formed during thermal decomposition of organic matter at depth under high pressures, and is often associated with coal, oil and gas fields.

In the UK most methane in groundwater is likely to be biogenic in origin, although thermogenic contributions may be locally important where gases have migrated from depth or there is slow release from previously deeply buried, low permeability, organic-rich rocks.

Dissolved gas and stable isotope analysis of groundwater samples can be used to identify the different sources and potential origin of methane.

Why is a national baseline methane survey important?

Understanding the current distribution of methane in UK groundwaters will provide a baseline against which any future changes can be measured. This has become particularly important with increasing interest in shale gas in the UK.

Evidence from the USA has shown very high methane concentrations in some aquifers in some areas where shales are being commercially exploited for gas. However, there is considerable uncertainty and argument over the source(s) of methane and how it has entered the aquifers.

Crucially, there are no consistent baseline data on methane concentrations in groundwater in the USA collected before shale gas exploitation began, which makes it very difficult to assess and deal with the observed problems of methane in groundwater.

The need for a baseline in the UK was recognised in the recent report on shale gas extraction published by the Royal Society and Royal Academy of Engineering 7.9 MB pdf.

In the UK, BGS scientists are building on our previous work and measuring methane concentrations in groundwater in a range of aquifers before any shale gas development gets underway. This will provide a baseline against which any future environmental changes can be assessed, and will enable informed management decisions to be taken.

The methane baseline is therefore defined for this project as the current background range of methane concentrations in UK groundwaters before any significant exploitation of unconventional hydrocarbons, such as shale gas, takes place.

The measured methane may not necessarily originate naturally from geological sources — in some cases it may have been produced or released because of human activities such as coal mining or landfill operations.

UK baseline survey

The BGS already has some information on methane in groundwaters for a number of UK aquifers, collected since the 1980s. The current survey began in 2012, with initial sampling campaigns in aquifers in Lancashire and Cheshire; south Wales; and Hampshire, E and W Sussex and Kent.

The work will continue with sampling in Northern Ireland, Northumberland and Yorkshire. These areas have been selected as they have been identified as areas underlain by potential shale gas resources (DECC, 2010 3.5 MB pdf).

Fieldwork and sampling

Measuring unstable parameters with field meters while sampling groundwater.

Collecting groundwater samples for methane analysis is straightforward providing certain precautions are undertaken.

To get an accurate concentration measurement, groundwater has to be sampled before it comes into contact with air so that no gas can escape. This means collecting a sample directly from a pumped borehole, by attaching a hose with an airtight connection at the top of the borehole before the pumped water enters a storage tank or is treated in any way.

Special containers are used to preserve the sample until it reaches the laboratory. In addition to sampling for dissolved methane, a number of chemical parameters are measured in the field (e.g. groundwater temperature, dissolved oxygen, and redox potential) and samples are collected for laboratory analysis of a broader range of chemical parameters.

Other web pages provide further information on the UK BGS baseline groundwater chemistry programme.


Sampling dissolved gases (including methane) in groundwater: the metal sample container is attached to plastic sampling tubes through which water flows, to ensure an air-tight connection.
MSamples collected for lab analysis of dissolved gases (including methane), dissolved organic carbon and ionic content

Partners

To find suitable boreholes, BGS greatly appreciates the support provided by the Environment Agency, Natural Resources Wales, water utilities and other private borehole owners such as farms and golf courses.

Results and references

Initial results (June 2013) from the new survey and summary of existing data.

Results from previous BGS methane surveys have been published in papers and reports that are available from the BGS website. Some of the references are shown below.

Gooddy, D, and Darling, W G.  2005.  The potential for methane emissions from groundwaters of the UK.  Science of the Total Environment, 339. 117–126. http://dx.doi.org/10.1016/j.scitotenv.2004.07.019

Darling, W G, and Gooddy, D C.  2006.  The hydrogeochemistry of methane: evidence from English groundwaters.  Chemical Geology, 229 (4). 293–312. http://dx.doi.org/10.1016/j.chemgeo.2005.11.003

Ó Dochartaigh, B E, Smedley, P L, MacDonald, A M, Darling, W G, and Homoncik, S.  2011.  Baseline Scotland: groundwater chemistry of the Carboniferous sedimentary aquifers of the Midland Valley.  British Geological Survey Open Report OR/11/021. 91pp.

Contact

Contact Dr George Darling for further information