Methane in UK groundwater

Methane (CH₄) is an important greenhouse gas and a common trace component of groundwater. BGS has been studying CH₄ in UK groundwaters since the 1980s to investigate:

• CH₄‘s contribution to total atmospheric emissions
• CH₄ baseline concentrations in UK groundwaters 
• What happens when CH₄ concentrations reach unsafe levels 

Groundwater methane contribution to total atmospheric emissions

Using baseline CH₄ concentrations for the main groundwater supply aquifers in the UK, we estimated that water-supply groundwater sources contribute only 0.05 per cent of total UK CH₄ emissions (up to 3.3 × 10^-4 teragrams a year) in 2005.

In terms of a global budget, the groundwater CH₄ input was estimated to be two orders of magnitude smaller.

• Find out more: The potential for methane emissions from groundwaters of the UK

Baseline concentrations in UK groundwaters

BGS undertook a national baseline CH₄ survey of groundwater across the UK. This work will enable future changes to be measured, which is of relevance to issues such as possible shale gas extraction. Understanding the ‘baseline’ concentrations of CH₄ in UK groundwater can also help us to assess future methane survey or incident data.

Measurements of potable water from the Cretaceous, Jurassic and Triassic carbonate and sandstone aquifers reveal CH₄ concentrations of up to 500 μg l^-1, but a mean value of less than 10 μg l^-1. Aquiclude and thermal waters from Carboniferous and Triassic rocks have concentrations in excess of 1500 μg l^-1.

• Find out more: The hydrogeochemistry of methane: evidence from English groundwaters

When does methane become explosive and create a potential safety hazard?

CH₄ becomes an explosive hazard at concentrations of 5 to 15 per cent by volume in air. Assuming complete outgassing from water, this requires a minimum dissolved methane concentration of 1600 μg l^-1.

This figure is considerably above the general CH₄ baseline, but concentrations of up to ten times higher have been found in tunnels drilled in organic-rich shales.

CH₄ is also produced by decaying organic matter, such as that in landfill sites. In 1986, methane leaking from a former landfill site caused an explosion in Loscoe, Derbyshire.

Contact

Please contact BGS Enquiries for further information.