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Re-use of the UK's coal mine water heating, cooling and thermal storage resource is increasing in scale and the number of schemes. The upwards trajectory requires 3D planning, regulation and licensing to manage sustainable deployment. We review geological factors controlling thermal and flow processes in the anthropogenically-altered subsurface, critical for resource management with multiple users of the same space. Potential interactions of mine water geothermal schemes with the wider environment are also summarised, leading towards concepts of 3D mine water thermal blocks, protection zones, or management strategies integrating heating, cooling and storage demands. Factors such as the magnitude, extent and timescale of thermal processes to underpin management approaches are poorly quantified by data measured at-scale under varying pumping rates and thermal loads. We demonstrate early insights of how two infrastructures, the UK Geoenergy Observatory in Glasgow and the Coal Authority's Mine Water Heat Living Lab in Gateshead, can measure and monitor heat-flow processes in real world settings to provide an evidence base. For example, a thermal storage test at Glasgow showed rapid temperature changes in the rock and mine workings at the re-injection borehole and indicated an influence of lithologically-controlled transmissivity and thermal conductivity on temperature dissipation and recovery.

In July 2022, The UK Parliament’s Environmental Audit Commission (EAC) launched an inquiry on geothermal technologies as part of their Technological Innovations and Climate Change inquiry (https://committees.parliament.uk/work/6777/technological-innovations-and-climatechange- geothermal-technologies/publications/). The inquiry focussed on Enhanced Geothermal Systems and Mine Water Energy Systems. It investigated the potential scale of their deployment in the UK to provide heat and power; the role geothermal technologies could have in the UK’s Energy Strategy and what barriers there are to the deployment, economic impact, and environmental impact of these technologies. As part of the inquiry, the EAC issued a call for the submission of written evidence to provide answers to one or more of the following questions: 1. What role can geothermal technologies take in the transition to net zero in the UK? 2. What barriers (technological, regulatory, or otherwise) are there to deploying operational geothermal technologies in the UK? 3. What is the scale of the potential market for geothermal energy sources and which geographic or other geological types are most suitable for exploitation of this natural resource? 4. Are current government support schemes sufficient to grow geothermal energy deployment in the UK? 5. What environmental concerns are associated with geothermal technologies, and are they appropriately accounted for in regulations? 6. What risks are there to investors, operators, and consumers of geothermal energy? How can these be mitigated? 7. How does the density of mine water systems affect their efficiency? Could widespread uptake of geothermal systems in dense population centres lead to a reduction in their ability to provide heat? 8. What economic impact could the deployment of mine water geothermal systems have on the areas in which they are deployed? The written evidence received by the EAC for this inquiry is published on the UK Parliament website at http

Under the amended UK Climate Change Act, a reduction in the emission of greenhouse gases of at least 80% from 1990 levels is necessary to reach net-zero targets by 2050. The sixth carbon budget for the period 2033–2037 requires a reduction of at least 63% from 1990 levels. While the UK has made good progress in decarbonising electricity, the decarbonisation of heating and cooling remains a challenge. Buildings, for example, were the UK’s second largest source of emissions in 2021 (after surface transport), producing 20% of all UK emissions. Geothermal energy, the energy generated and stored in the form of heat in rocks, groundwater and soils, can provide a low-carbon source for heating, cooling and power generation. Deep geothermal resources, typically at depths of more than 500 m below the ground surface and temperatures between 50 and 200°C, are suitable for multiple uses, including direct use for space heating, cooling (using absorption chiller technology), horticulture, a variety of industrial processes or power generation. A ‘UK Deep Geothermal Energy White Paper’ was commissioned by the North East Local Enterprise Partnership (LEP) and funded by the Department for Energy Security and Net Zero (DESNZ) and the North East and Yorkshire Net Zero Hub in 2022. It aims to provide an evidence-based assessment and ‘case making’ document to help accelerate the development and deployment of deep geothermal energy projects in the UK. This report provides the underpinning evidence, background and data for the white paper. It describes stakeholder input which was collected through a range of engagement events, including a review of existing stakeholder evidence (including 31 submissions to a parliamentary inquiry on geothermal technology undertaken by the Environmental Audit Committee in 2022), a virtual stakeholder workshop (34 participants), an online stakeholder survey (59 respondents) and stakeholder interviews (7). Stakeholders that have participated in the engagement

Groundwater is by far the largest unfrozen freshwater resource on the planet. It plays a critical role as the bottom of the hydrologic cycle, redistributing water in the subsurface and supporting plants and surface water bodies. However, groundwater has historically been excluded or greatly simplified in global models. In recent years, there has been an international push to develop global scale groundwater modeling and analysis. This progress has provided some critical first steps. Still, much additional work will be needed to achieve a consistent global groundwater framework that interacts seamlessly with observational datasets and other earth system and global circulation models. Here we outline a vision for a global groundwater platform for groundwater monitoring and prediction and identify the key technological and data challenges that are currently limiting progress. Any global platform of this type must be interdisciplinary and cannot be achieved by the groundwater modeling community in isolation. Therefore, we also provide a high-level overview of the groundwater system, approaches to groundwater modeling and the current state of global groundwater representations, such that readers of all backgrounds can engage in this challenge.

This research report describes borehole geophysical and passive seismic surveys done at the Colchester Northern Gateway (CNG) geothermal district heat network and housing development in Essex, UK, between 10-13 February 2020. The first part of the report introduces the project context, the second part describes survey methods, and the third presents the ‘baseline survey’ results and stratigraphic interpretation. The final section summarises the key learnings, relevance of the findings to future geothermal district heating schemes in the Chalk and London Basin, and makes some recommendations for follow-up monitoring research. Five recently drilled production/injection boreholes at CNG were logged with Calliper, Temperature and Conductivity, Natural Gamma, Optical Televiewer (OPTV) tools. Some of the holes also had Resistivity and Impeller flow tools run but results were inconclusive. A site-wide Tromino H/V passive seismic survey was acquired to characterise the resonant frequency of the subsoils between the boreholes, to aid stratigraphic correlation, profile the concealed chalk ‘rockhead’ surface (i.e. depth of bedrock aquifer), and look for any evidence of the presence of faults/fracture zone, and characterise the thickness of karst and weathering profiles. The main geological formation boundaries were identified based on a combination of interpretation of Natural Gamma logs and correlation of sedimentary features observed in the OPTV images. The eroded top of the Newhaven Chalk is around 72 m below ground level (-24 m OD) in all five boreholes (BH1-5). The high-resolution OPTV images provide rich visual information on the fracture state of the upper ‘productive’ part of the chalk aquifer. A notable feature in BH4 is an 18 m long NW-SE orientated open vertical fracture that persists through the Newhaven Chalk but terminates at the top of the Seaford Chalk. The OPTV data also aids identification of key litho-stratigraphic marker horizons, such as tabular flint band

It is widely acknowledged that waterbodies are becoming increasingly affected by a wide range of drivers of change arising from human activity. To illustrate how this can be quantified a linked modelling approach was applied in the Thames river basin in southern UK. Changes to river flows, water temperature, river and reservoir quality were predicted under three contrasting future “storylines”; one an extension of present day rates of economic development, the others representing more extreme and less sustainable visions. Modelling revealed that lower baseflow conditions will arise under all storylines. For the less extreme storyline river water quality is likely to deteriorate but reservoir quality will improve slightly. The two more extreme futures could not be supported by current management strategies to meet water demand. To satisfy these scenarios, transfer of river water from outside the Thames river basin would be necessary. Consequently, some improvement over present day water quality in the river may be seen, and for most indicators conditions would be better than in the less extreme storyline. However, because phosphorus concentrations will rise, the invoked changes in water demand management would not be of a form suitable to prevent a marked deterioration in reservoir water quality.

The River Thames catchment is situated in the south-east of England. It covers approximately 16,000 km2 and is the most heavily populated river basin in the UK. It is also one of the driest and has experienced severe drought events in the recent past. With the onset of climate change and human exploitation of our environment, there are now serious concerns over the sustainability of water resources in this basin with 6 million m3 consumed every day for public water supply alone. Groundwater in the Thames basin is extremely important, providing 40% of water for public supply. The principal aquifer is the Chalk, a dual permeability limestone, which has been extensively studied to understand its hydraulic properties. The fractured Jurassic limestone in the upper catchment also forms an important aquifer, supporting baseflow downstream during periods of drought. These aquifers are unconnected other than through the River Thames and its tributaries, which provide two-thirds of London’s drinking water. Therefore, to manage these water resources sustainably and to make robust projections into the future, surface and groundwater processes must be considered in combination. This necessitates the simulation of the feedbacks and complex interactions between different parts of the water cycle, and the development of integrated environmental models. The Open Modelling Interface (OpenMI) standard provides a method through which environmental models of varying complexity and structure can be linked, allowing them to run simultaneously and exchange data at each timestep. This architecture has allowed us to represent the surface and subsurface flow processes within the Thames basin at an appropriate level of complexity based on our understanding of particular hydrological processes and features. We have developed a hydrological model in OpenMI which integrates a process-driven, gridded finite difference groundwater model of the Chalk with a more simplistic, semi-distributed conceptual

This report describes the use of the open-loop ground source heat pump web tool for the West Midlands and provides some technical information on the tool development and underlying data sets. Part 1 provides the background information to this study and outlines the purpose of this tool and the anticipated user groups. Part 2 explains how to use the tool. It provides detailed explanations of the different layers and their meaning within the context of GSHPs. It also explains how to use the results table and the visual summary of the results (Chernoff faces). Furthermore, this section outlines the limitations of the tool and lists the different aspects that are not considered by the tool. Where possible, it provides references and links to additional data sources that address the particular aspects which are not included in the tool. Part 3 provides more detailed information on how the individual data layers were derived. This information is not necessary to use the tool, but is included here for the interested few and for reference. In Part 4, links to data sets and additional resources are given that can help with a more detailed assessment of suitability and the planning of open-loop GSHP schemes. Please note that this tool provides only an initial assessment about whether an area may be suitable for an open-loop GSHP. You will need to undertake a detailed hydrogeological and environmental assessment of your location if you wish to install an open-loop GSHP.

Low order streams often show complex, nonlinear relationships between hydrologic conditions in the riparian zone, streamflow generation and the chemical signature of the stream water. Dynamic surface and subsurface flow paths create a mosaic of biogeochemical conditions that affect the transformation and export of solutes. These relationships are explored in a virtual modelling study of a riparian wetland that links an integrated surface–subsurface flow model with a stream tube approach for biogeochemical reactions along individual flow paths. It is shown that the interplay between water table depth and surface micro-topography in the riparian zone results in distinct shifts between surface and subsurface flow dominance and the development of specific surface flow connectivity. Distinct nonlinear relationships between water table depth and stream discharge that reproduce relationships observed in the field were found. Simulated hydrologic dynamics and the resulting flow paths result in biogeochemical patterns in the riparian zone that are congruent with patterns observed in the field.

This report presents a literature study that was carried out to collect data and information required for developing a strategy to assess the suitability and sustainability of UK aquifers for (open-loop) GSHP installations. Developing such a strategy requires a good hydrogeological understanding but also a good knowledge of what GSHP systems are currently in use, how they are used, what problems are associated with their use and how they are regulated. Once this is understood, a methodology can be devised that assesses the suitability of an aquifer/location for GSHP installations and considers its sustainable use. Considering the complexity of influencing factors and processes, this is likely to include the use of numerical models and/or data management tools, such as GIS. This report collects and summarizes the information available in the contemporary literature on open-loop ground source heat pump (GSHP) applications. Chapter 1 provides a brief introduction and background information on the subject. In Chapter 2, information on the general use of open-loop GSHP technology within the UK are gathered together with statistics on the number of installations and capacities. Chapter 3 gives specific examples of schemes that are currently in operation in the UK and worldwide. Where available, this includes system-specific data such as abstraction rates, thermal capacities and information on the system’s design. Chapter 4 summarizes available information and data on the costeffectiveness of GSHP installations while Chapter 5 discusses potential problems associated with the running of such schemes. Chapter 6 is concerned with the regulation of GSHP systems. It gives a brief outline of existing regulatory approaches as currently employed within different European countries as well as the US. Finally Chapter 7 examines existing modelling approaches that have been used to investigate how GSHP schemes impact on the source aquifer. The chapter also reviews GIS-based tools that

Understanding the processes controlling groundwater/surface-water interaction is essential for effective resource management and for protecting sensitive ecosystems. Through intensive monitoring of Chalk groundwater, shallow gravel groundwater and surface water in the River Lambourn, UK, using a combination of hydrochemical and hydrophysical techniques, a complex pattern of interactions has been elucidated. The river is broadly in hydraulic contact with the streambed sediments and adjacent gravels and sands, but these deposits are mainly hydraulically separate from the underlying Chalk at the site. The hydraulic relationship between the river and underlying alluvium is variable, involving components of groundwater flow both parallel and transverse to the river and with both effluent and influent behaviour seen. While the gravel aquifer is significant in controlling groundwater/surface-water interaction, its importance as a route for flow down the catchment is likely to be modest compared with river discharge. The hydrological complexity revealed in a geological setting typical of lowland UK Chalk streams has implications both for investigation methods and for management such as in the setting of environmental objectives in the European Water Framework Directive.

The importance of upland groundwater systems in providing a medium for nitrogen transformations and processes along flow paths is investigated within the Afon Gwy moorland catchment, Plynlimon, mid-Wales. Dissolved organic nitrogen (DON) was found to be the most abundant form of dissolved nitrogen (N) in most soils and groundwaters, accounting for between 47 and 72% of total dissolved nitrogen in shallow groundwater samples and up to 80% in deeper groundwaters. Groundwater DON may also be an important source of bio-available N in surface waters and marine systems fed by upland catchments. A conceptual model of N processes is proposed based on a detailed study along a transect of nested boreholes and soil suction samplers within the interfluve zone. Shallow groundwater N speciation reflects the soilwater N speciation implying a rapid transport mechanism and good connectivity between the soil and groundwater systems. Median nitrate concentrations were an order of magnitude lower within the soil zone (< 5–31 μg/L) than in the shallow groundwaters (86–746 μg/L). Given the rapid hydrostatic response of the groundwater level within the soil zone, the shallow groundwater system is both a source and sink for dissolved N. Results from dissolved N2O, N2/Ar ratios and dissolved N chemistry suggests that microbial N transformations (denitrification and nitrification) may play an important role in controlling the spatial variation in soil and groundwater N speciation. Reducing conditions within the groundwater and saturated soils of the wet-flush zones on the lower hillslopes, a result of relatively impermeable drift deposits, are also important in controlling N speciation and transformation processes.

This report describes the concentrations and distributions of uranium (U) in groundwater from aquifers in Great Britain and discusses the most likely sources and controls on U mobility. The report also reviews the ranges of U observed in groundwater worldwide in order to place the British data within a wider context. Groundwater-chemistry results are presented from 116 samples of raw groundwater taken from 101 operational boreholes and springs across England & Wales. The samples are from a selection of public and private water sources. Twelve of the sources were sampled twice, once in the spring of 2005 and once in autumn 2005 in order to provide some limited assessment of the temporal variation in U concentrations. The report also describes the results from 1556 analyses of groundwater U collated from the BGS groundwater-chemistry database and various published accounts. This provides a basis for assessing the implications to the water industry and regulators of U in groundwaters in England & Wales in the event that a new European drinking-water limit for the element is introduced in the coming years. The mobility of U in water is controlled by a number of factors, among the most important being pH, redox status and concentrations of coexisting dissolved ions. Uranium is a redox-sensitive heavy metal that occurs in water principally under oxic conditions in its hexavalent (U(VI)) form. It is usually complexed in solution, especially with carbonate ligands, but also less significantly with phosphate, fluoride or sulphate depending on their respective dissolved concentrations and ambient pH. Under anoxic conditions, U is reduced to its tetravalent U(IV) state and its concentration in water is usually low as a result of stabilisation of the sparingly soluble mineral, uraninite. Groundwaters often have higher concentrations of U than surface waters because of the large solid/solution ratios in aquifers and the greater influence of water-rock interactions. Uranium occur

This report describes the concentrations and distribution of uranium (U) in the groundwater of the Derbyshire Dome and discusses potential sources and controls on U mobility within the aquifer. The Derbyshire Dome is an anticlinal structure which consists of marine Carboniferous Limestone (Dinantian), flanked by shales and sandstones of the Millstone Grit (Namurian). The limestone is extensively mineralised in some parts, in particular in the east of the study area and different zones of mineralisation are distinguished, reflecting the west-east progression from calcite to barite to fluorite as the dominant gangue minerals. The hydrogeology of the study area is dominated by natural karstic features but even more by the ‘anthropogenic karst’ which has developed as a result of the extensive mining activities that have created a network of mine passages and drainage adits (“soughs”). Water movement through the aquifer is generally very rapid, but varies temporally as well as spatially. Thermal springs issue from a number of locations, some of which are known or believed to have bulk ages of up to several thousand years. Uranium is present in the bedrock as well as in the groundwater of the study area. The mineralogy and precise nature of U in the bedrock(s) is not known but a number of potential sources within the Dinantian and Namurian have been identified. These include organic matter fragments and hydrocarbon globules within the matrix of the Carboniferous Limestone, the organic-rich shales of the Namurian (Millstone Grit Series) and bedrock mineralization. A total of 26 groundwater samples were collected in July 2005 and analysed for a comprehensive suite of major, minor and trace elements, including U. Samples were collected from various sources including natural springs, decommissioned mines and soughs as well as from industrial and farm boreholes. The results show that aquifer lithology is the dominant control on the groundwater chemistry in the study area, henc

This report describes the results of a survey of groundwater nitrate concentrations in the Lower Nithsdale nitrate vulnerable zone (NVZ), southwest Scotland. The survey was carried out during September 2004. Rigorous field sampling techniques were used, and the samples analysed in the BGS laboratories at Wallingford. Shallow groundwater was targeted, where the effects of recent land use (within the past 10 years) would be reflected in the samples. Twenty-one sites were sampled comprising 5 springs and 16 boreholes; all the sites were rural – thirteen were located on dairy farms. None of the boreholes showed any signs of contamination from surface water. Most were located in huts with concrete plinths, others were under manhole covers in fenced areas. The springs were more vulnerable to surface water contamination. The median concentration of nitrate from the 21 samples was 33 mg NO3 L-1. Six samples had concentrations greater than 50 mg NO3 L-1, a further 3 sites had concentrations between 40 and 50 mg NO3 L-1. All sites with concentrations greater than 40 mg NO3 L-1 are located on dairy farms. There is broad agreement between nitrate concentrations measured in this survey and a previous survey in August 2002. This current survey indicates much higher nitrate concentrations than monitored by SEPA from their 12 monitoring sites in Nithsdale. This is due to the nature of the sampled sources. The SEPA monitoring network in the area comprises deep boreholes in the Permian bedrock; age dating has shown that much of the water sampled is pre-1950s. In contrast, much of the groundwater sampled during the current survey is young – recharged within the past decade. By making corrections for the dilution factor from the older water at the SEPA sites, it is possible to estimate nitrate concentrations in the recently recharged groundwater. These corrected concentrations are considerably higher, and consistent with those measured from the shallow groundwater sources in this curre