Recent interest in use of the deep subsurface for energy and storage has highlighted a lack of knowledge about groundwater at depths greater than about 200 m – the maximum usual depth for groundwater abstraction in the UK. Questions are being asked about the quality and availability and therefore future resource potential of deep groundwater, and its role in linking the deep subsurface and shallow groundwater resources. However, a lack of data and understanding of fluid properties in the deep subsurface, often resulting from difficulties accessing, measuring and/or retrieving information from such depths, means that deep groundwater systems are still relatively poorly understood.
Here we describe initial results from a project bringing together information from a range of sources to produce a UK-wide resource that can be used to improve the knowledge and understanding of the deeper subsurface including groundwater processes and environmental response. The initial phase of work has focussed on collating Total Dissolved Solids (TDS) data in order to understand the distribution of water quality with depth, and in particular the base of freshwater aquifers. Analysis of this data indicates that freshwater may be present to a depth of about 500 m, with brackish water present to a depth of about 1 km. An understanding of basin history, geology, past and present hydrogeological systems and past climates are key to understanding this distribution. Results from preliminary work on collation and analysis of UK-wide groundwater chemistry (TDS/Specific Electrical Conductivity, major, minor and trace ions and environmental tracers such as stable isotopes and noble gases), deep groundwater pressure/head and hydrogeological property distributions (e.g. permeability/hydraulic conductivity, porosity, storativity, transmissivity) is providing insights into regional deep groundwater flow systems.