3D groundwater vulnerability

Fig 1: It is important that groundwater remains protected; there is a potential risk of groundwater being contaminated from leaks from oil and gas wells, through old infrastructure (mines and boreholes) and by transport through the rock mass from the source of the oil and gas. Schematic diagram, not to scale.

The British Geological Survey (BGS) and the Environment Agency (EA) have developed a method of assessing the vulnerability of groundwater from onshore oil and gas extraction activities in England. This new tool will improve our understanding of the risk to groundwater.

BGS conducted a study to develop an accessible and nationally consistent method for assessing the vulnerability of groundwater to potential contamination from any possible future activities deeper in the subsurface.

The method is based on well-established approaches already employed by the Environment Agency as part of the environmental regulation and permitting process. The UK oil and gas industry is one of the most regulated in the world and so risks to groundwater are already covered in UK law. This new vulnerability assessment will ensure that the UK continues to put safety first when investigating new energy sources.

The method uses the BGS' 3D geological model of England to show the locations of aquifers and rocks which could contain oil and gas. This allows identification of the key parts of the underground water system that might be affected by future hydrocarbon extraction. A tool developed to guide the assessment considers the following elements:

Classification of the groundwater, i.e. is it an aquifer, how is it used?
The type of hydrocarbon extraction processes, i.e. hydraulic fracturing?
The groundwater flow direction, i.e. is it towards or away from the hydrocarbon source?
The vulnerability of groundwater to underground sources of pollution derived from underground oil and gas activities. This includes factors such as the distance between the potential hydrocarbon source and the aquifer, the thickness of low permeability rocks and potential pathways for pollution i.e. via geological faults, boreholes and mines.

Based on these considerations, an overall risk group can be identified, as can the degree of certainty in this grouping.

The method was trialled on five case study sites across England addressing different extraction activities; conventional oil and gas in southeast England, coal bed methane in the East and West Midlands, shale gas in northwest England and shale gas and conventional oil and gas in northeast England.

Most aquifers were rated as being at low risk from contamination. There were occasional instances of medium to low risk ratings for important aquifers with a smaller separation from the oil and gas sources. Medium/high risk groups occur rarely, where important aquifers overlie shale gas and coal bed methane activities. There are no potential receptors in the high risk group in the case studies.

These initial findings are now being made available and we would welcome views on how to develop the methodology further.

Contact

Please contact BGS Enquiries or the Environment Agency National Customer Contact Centre (NCCC) Environment Agency National Customer Contact Centre (NCCC) for more information.