Research and analysis

3D groundwater vulnerability - summary

Published 22 October 2019

1. Chief Scientist’s Group research summary

Oil and gas exploration and production has the potential to release pollutants deep below the ground surface which could then move upwards into groundwater. Most important groundwater resources are found near to the surface, but deeper rocks can also contain water and may be the source of springs in some areas. Although water at such depths is usually of poorer quality, potential resources like this may also need protection.

The Environment Agency has studied the vulnerability of groundwater to pollution from activities at the ground surface for many years and has published maps to help assess risks. This new and innovative work carried out with the British Geological Survey uses the same principles to examine pollution sources deep below the ground surface and to assess subsurface groundwater vulnerability.

1.1 Why was this project needed?

Detailed numerical models have been developed for research purposes but a simpler methodology is needed for initial assessments. Such an assessment should:

• present information in a way that is easy for non-technical audiences to understand
• produce illustrations to help show the scale of risk and the geological protection that exists for groundwater in a particular area of interest

Assessments should also be scientifically sound and help experts to identify where further data are required for more detailed appraisal.

1.2 What did the project involve?

The project examined how subsurface activities for unconventional and conventional oil and gas exploration, coalbed methane and underground coal gasification might have an impact on groundwater.

To do this, a screening methodology was developed using a scoring system to assess groundwater vulnerability in 3 dimensions. The scores can be combined to indicate risks to groundwater at different depths and cross-sections can be produced to help in communicating outputs to various audiences.

The assessment takes account of the importance of the groundwater. For example, if it is of good quality it may be used as a drinking water resource and help support river flow and wetlands. In other cases, it could potentially be used in the future as a drinking water resource or for other beneficial purposes (after treatment if necessary). Water quality declines with depth and, although information on this decline is generally sparse, this is also considered in the methodology.

The methodology looks at the risks associated with the type of hydrocarbon extraction process (for example, hydraulic fracturing). The distance separating the oil or gas source rock and the aquifer can protect groundwater, as can the presence of low permeability rock layers. The project also considered whether groundwater flows towards or away from the oil or gas source rock, and potential pathways for pollution such as geological faults, boreholes and mines.

Using these factors, the methodology ranks the risk of groundwater pollution as low, medium–low, medium–high or high, and estimates how certain the ranking is.

The methodology was trialled at 5 case study sites across England for different extraction activities:

• conventional oil and gas in south-east England
• conventional oil and gas in north-east England
• coalbed methane in the East and West Midlands
• shale gas in north-west England
• shale gas in north-east England

1.3 What were the findings?

Most of the aquifers studied were found to be at low risk of contamination, with some at medium–low and medium–high risk. None were found to be at high risk.

1.4 What is the next step?

The methodology is now available to both Environment Agency staff and external users to help in the preliminary assessment of risks to groundwater from subsurface oil and gas activities. It is intended that experience in the methodology’s use will help in developing it in the future. Note that while the new methodology can be used as part of the initial assessment of proposals, it should not take the place of a detailed site-specific assessment.

1.5 Publishing details

This summary relates to information from project SC150023 reported in detail in the following output:

Report:

SC150023

Title:

3D groundwater vulnerability

October 2019

Project manager:

Ian Davey, Research, Analysis and Evaluation

Research contractor:

British Geological Survey Environmental Science Centre, Keyworth, Nottingham NG12 5GG

This project was funded by the Environment Agency’s Research, Analysis and Evaluation 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