How can we tell if shale gas exploitation will increase methane in groundwater?
The challenge
Evidence from the USA has shown high methane concentrations in some aquifers where shales are being commercially exploited for gas, raising the concern that hydraulic fracturing (fracking) is responsible. However, high-methane groundwater can also occur naturally, so the cause needs to be distinguished.
Baseline data on methane concentrations in groundwater before shale gas exploitation commences, is essential for the regulators such as the Environment Agency in assessing and dealing with any methane problems that may subsequently arise. The need for a UK baseline was recognised by BGS and supported in a recent report on shale gas extraction by the Royal Society and Royal Academy of Engineering.
The solution
Methane is a common trace component in UK groundwater, and may originate naturally from geological sources or, in some cases, from human activities such as coal mining or landfill operations. Scientific analysis of groundwater samples can be used to identify the different sources and potential origin of methane.
The British Geological Survey (BGS) started collecting information on methane in groundwaters for a number of major UK aquifers in the 1980s, and are now building on this previous work by measuring methane concentrations in groundwater in a wider range of aquifers before any shale gas development gets underway.
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. This work is continuing with sampling in Northern Ireland, Northumberland and Yorkshire, focusing on areas that have been identified as having potential shale gas resources.
The survey is being supported by the Environment Agency, Natural Resources Wales, water utilities and other private borehole owners, and initial survey findings have been released.
Resulting benefits
Understanding the current distribution of methane in UK groundwaters will provide regulators with a baseline against which any future environmental changes can be measured. This is particularly important because of the increasing interest in shale gas exploitation in the UK, and will help ensure that the scientific evidence is available to support aquifer management and environmental protection assessments.
Future directions
If elevated methane concentrations are found during the current survey, the source of methane will be investigated with a range of geochemical tools, including isotope analysis in collaboration with researchers at the University of Bristol.
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