3D Groundwater Vulnerability Groundwater Programme Internal Report OR/18/12 BRITISH GEOLOGICAL SURVEY GROUNDWATER PROGRAMME OPEN REPORT OR/18/12 3D Groundwater Vulnerability S Loveless, M A Lewis, J P Bloomfield, R Terrington, M E Stuart, R S Ward Contributor/editor The National Grid and other Ordnance Survey data © Crown Ian Davey, Alwyn Hart (Environment Agency) Copyright and database rights 20178. Ordnance Survey Licence No. 100021290 EUL. Keywords Report; keywords. Bibliographical reference LOVELESS, S, LEWIS, M A, BLOOMFIELD, J P, TERRINGTON, R, STUART, M E AND WARD, R S. 20178. 3D Groundwater Vulnerability. British Geological Survey Internal Report, OR/18/12. 201pp. Copyright in materials derived from the British Geological Survey’s work is owned by United Kingdom Research and Innovation (UKRI) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. 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Since the late 1980s, groundwater protection in England has benefited from a series of national groundwater vulnerability maps. These are now routinely used to inform decisions around allowing and/or managing activities on, or just below, the land surface that are potentially polluting. The recent increased interest in onshore exploration and exploitation of the deeper subsurface and concerns about the risk to groundwater has highlighted the fact that the existing groundwater vulnerability assessment methodology focuses solely on risks from hazards that are above the groundwater that requires protection. Plans to exploit the deep sub-surface, in particular for shale gas using hydraulic fracturing, have attracted considerable public interest and concerns over the potential for these activities to cause pollution of groundwater. It is therefore essential that in considering any proposals for use of the deep sub-surface, tools and methods for assessing groundwater vulnerability and risk are fit for purpose. Hence, the aim of this project was to develop a new vulnerability method that could address the potential risks to groundwater from activities below, or at similar depths to, groundwater systems (aquifers) that are currently used or have the potential to be used in the future. These systems are those requiring protection under current EU and UK legislation. To this end we present a methodology along with five different hydrocarbon activity case study examples from across England. The report describes how information can be compiled, interpreted and presented in order to assess the vulnerability of groundwater and an indication of the risks associated with a hydrocarbon development activity at a site. The outputs are designed for use primarily by those needing to understand better the hydrogeological context of subsurface developments, the vulnerability of groundwater and the potential risks. It is also hoped that the hydrogeological data and methodology will aid decision making and provide impartial information to inform public debate. The report is not designed to set out in a formal way how information and modelling should be used to reach regulatory decisions. A wider set of site-specific information will be required for this and this is outside the scope of the research presented here. Acknowledgements The authors would like to acknowledge BGS staff who have made significant contributions to this report. The BGS’s National Geological Model (NGM) has been integral to developing this methodology and producing case study examples. This has entailed many years of BGS geologists’ work and in particular we acknowledge the input into the project from Jon Ford and Holger Kessler. Simon Kemp is thanked for providing information on the adsorption properties of different clays. The 3DGW Vulnerability project is a co-funded project between the British Geological Survey and the Environment Agency. The authors would like to thank the Environment Agency for their financial support for the project as well as contributing to the project vision. The project has also benefitted significantly from the contribution and involvement of the project Steering Group: Lynn Foord, Jan Hookey, Rudi Liu, Paul Doherty, Sarah Scott, Jenny Thomas and Sara Matthews. i OR/18/12 Contents Foreword ......................................................................................................................................... i Acknowledgements ......................................................................................................................... i Contents .......................................................................................................................................... ii Executive Summary ...................................................................................................................... 1 1 Introduction ............................................................................................................................ 3 2 Vulnerability screening methodology ................................................................................... 5 2.1 Approach ........................................................................................................................ 6 2.2 Development of a geological conceptual model ........................................................... 11 3 Receptors ............................................................................................................................... 14 3.1 Current EA practice related to the protection of groundwater in England ................... 15 3.2 Identifying 3D aquifer extent in England ..................................................................... 21 3.3 Water quality of deep groundwater systems in England .............................................. 21 3.4 Groundwater protection summary ................................................................................ 26 3.5 Potential receptor classification .................................................................................... 27 4 Intrinsic vulnerability .......................................................................................................... 28 4.1 Separation of the hydrocarbon source rock and potential receptor .............................. 28 4.2 Mudstones and clays in intervening zone ..................................................................... 32 4.3 Groundwater flow mechanism ...................................................................................... 34 4.4 Solution features ........................................................................................................... 36 4.5 Faults ............................................................................................................................ 37 4.6 Mines ...........................................................................................................................