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Many UK towns were eep mining in the UK has coal deposits, coal is now regarded as a left a legacy of flooded former “dirty” because of the associated CO2 built on coal. mines. within these and other pollutant emissions, and is mines can provide a source of being phased out of our mix. UK Charlotte Adams, D heat energy. Durham government demonstrated its University is researching the potential of commitment to reducing coal use by Alison Monaghan this and the British Geological joining 27 other national governments that Survey (BGS), commissioned by the have signed up to the “powering past coal and Jon Gluyas Natural Environment Research Council alliance” and there are now days when (NERC), are constructing and operating a coal is not being burned to produce highlight the vast research site in Glasgow to further in the UK. potential to repurpose understanding of mine energy systems. The UK has made good progress in decarbonising its electricity supplies over our abandoned When coal was king the past decade, with around half of UK Over the past century, vast quantities of electricity demand supplied from low- mining infrastructure coal were mined from the UK subsurface carbon sources (DBEIS, 2018). However, as it fuelled our industrial and economic electricity provision is only part of the as a low-carbon heat growth. The 15 billion tonnes mined are story and half of the UK’s total energy equivalent to a 5-cm-deep layer of coal demand is used to produce heat, most of source spread over the entire UK surface. which is consumed by the domestic sector. Despite the wealth generated by the UK’s Heat is predominantly produced from

10 | MAY 2019 | WWW.GEOLSOC.ORG.UK/GEOSCIENTIST WWW.GEOLSOC.ORG.UK/GEOSCIENTIST | MAY 2019 | 11 Fig 1: Schematic Diagram of a mine water system (Drawn by Charlotte Adams)

Energy Centre or Heat User

Heat Pump

Warm Water Cooled Water Pumped Returned to Mine from Mine Water Level ç√ Mine Shaft

Coal Seams

ç√

Flooded Abandoned Mine

burning . In the meantime, the but heat pumps can boost temperatures to Mine-water heat systems are generally UK has been a net importer of natural gas provide hot water and space heating. Heat operated open-loop, which offers better for over a decade and is reliant on other pumps require an energy input, but than standard closed- nations to meet any shortfalls in demand. because each kW of input loop ground-source heat systems. Finally, could be expected to deliver a heat output mine-water systems offer economies of Developing a legacy of 3-4 kW, heat is provided in an energy- scale, meaning that clusters of hundreds of Our abandoned mining infrastructure efficient way. properties could be served from a single now lies largely derelict and many have Mine water is accessed by drilling mine and a few boreholes. To deliver this forgotten its existence. Yet, people in boreholes into flooded workings through vision requires changes to planning and former mining towns and villages remain which water is abstracted, heat is removed building control policies that support the strongly connected to their mining and the temperature boosted with a heat future development of low-temperature heritage, even though its decline brought pump, before the water is returned to the energy systems. hardship and, in some areas, subsurface (Fig. 1). Using mine water as at Durham environmental pollution. an energy source compared with University is undertaking national, Our mining legacy and the associated individual closed-loop, ground-source regional and local assessments of mine infrastructure could be repurposed and heat pumps offers some advantages for energy potential for a range of has potential as a future energy source. domestic properties. Decreased garden applications, under the auspices of The mine shafts and galleries that are now size of newer housing stock leads to BritGeothermal, which is a national flooded contain copious volumes of water reduced space for horizontal ground research partnership for deep geothermal at 12-20℃. Clearly you would not want to arrays, meaning that boreholes would be energy. This includes assessing take a bath in water of this temperature, required, which are more capital intensive. domestic residences, industrial

10 | MAY 2019 | WWW.GEOLSOC.ORG.UK/GEOSCIENTIST WWW.GEOLSOC.ORG.UK/GEOSCIENTIST | MAY 2019 | 11 Fig 2: Stoop-and- room (Scottish terminology for pillar-and-room) mine workings subsequently exposed by opencast coal workings at Blindwells, Scotland. Photo number P001520 BGS©UKRI. The image illustrates the connected void space (‘rooms’) that could be targeted for mine water geothermal projects

developments and municipal ochre precipitation is key for mine- that involves driving tunnels to the buildings for mine energy systems. water treatment, in a heat-exchange farthest extent of the mine, then For these assessments, we need to system this can cause severe clogging removing coal from the seam laterally understand the nature of the and fouling of system components. whilst retreating from the workings. subsurface infrastructure and Ochre precipitation is normally Many areas formerly mined by the appreciate how can avoided by keeping systems under room-and-pillar method were latterly evolve, both during mine positive pressure, limiting dissolution reworked using longwall extraction. abandonment and following periods of oxygen. As longwall mining proceeds the of abstraction. Research shows that To assess the potential of this overburden above the seam subsides following long periods of resource, it is necessary to obtain from producing “goaf” (collapsed waste). abandonment, water within mines the UK Coal Authority the Consequently, an area mined by can become highly stratified, with abandonment plans for seams within room-and-pillar methods can be better-quality water generally lying the collieries worked, and then use assumed to have around 50% of the above poorer-quality water (Nuttall & these to calculate the worked areas original void space remaining and, for Younger, J. Contam. Hydrol. 2004). and seam thickness. The large-scale longwall mining, around 20% of the Pumping and abstracting water from extraction of coal from the subsurface original void space remains (Younger mines induces turbulence and mixing leaves voids that remain long after & Adams, Tech. Report 1999). These within the mine. This means that the mine abandonment. Yet, these voids voids, in effect, have created an eventual quality might be poorer than will not remain exactly as they were anthropogenically-enhanced expected and it is important to take at abandonment. Shafts were often in which heat can be extracted from samples of the entire water column if filled with rubble from the or reinjected into the large water possible. Water quality may change demolished topside colliery volumes existing within the mine with pumping rate and is linked to infrastructure before being capped, workings. the areas of workings being drawn rendering many of no value for future The potential for the flooded from. Quality may improve once a few water pumping. The floor of galleries abandoned collieries of the UK to shaft volumes have been pumped. may heave and roof material may provide a source of heating, cooling Many mine contain iron, collapse, leading to tunnels with and is huge. The UK which is a remnant of the interaction partial blockages along their length. Coal Authority estimates that between the oxygenated mine-water The amount of remnant void space abandoned flooded mines contain and pyrite within the coal depends upon the method of deep around 2.2 million GWh of heat, (particularly high-sulphur ) and mining employed. Early ‘room-and- with an even greater potential for is the nemesis of mine-water pillar’ mining involves working a heat storage. Furthermore, because management. As long as air is grid, leaving pillars of coal intact for coal spawned the development of excluded from a mine-water heat roof support and mining the areas many of our towns and cities, mine pump system, iron remains in between (Fig. 2). Room-and-pillar energy resource aligns well with solution, but introducing air even mining was later replaced by centres of heat demand. The Coal when there are low concentrations of longwall mining (first developed in Authority estimates that around one iron present (1mg/l) leads to the Shropshire in the 17th Century), a quarter of UK housing stock overlies deposition of ochre. Though iron more efficient means of removing coal areas of abandoned mine workings.

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There are a few examples of mine to flow adequate quantities of water for relatively cheap gas supplies provide energy projects that serve smaller and energy extraction. There is only one some answers. Complexities associated individual developments in the UK. operational deep geothermal heat scheme with retrofit of heat exchangers and heat Bridgend Council in Wales is working to in the UK, at Southampton. It was pumps, economic risks linked to deliver a larger system developed in response to a national audit difficulties in securing long-term that will initially supply heat to around of the UK’s geothermal in the contracts for heat supply and system 150 homes. At Heerlen in the 1980s, prompted by the oil crisis. maintenance, as well as concerns over Netherlands, abandoned mines are used Although abandoned mines are water quality and may effectively to deliver space heating and shallower and the temperature of water present barriers to widespread cooling to around 200,000 m2 of mixed within them is cooler, copious quantities development. use new and retrofit buildings via a of water flow through these systems, thus BritGeothermal is lobbying for 7-km-long heat network (Verhoeven et reducing development risk. The UK is changes to national planning policy, al., Energy Procedia 2014). In addition to sitting above an extensive but yet-to-be licensing and regulation of subsurface delivering low-carbon energy to Heerlen, commissioned heat network. Mine energy use to ensure that mine energy potential the money spent on heat by their has a much higher technology readiness is considered when planning new customers is retained within the region level than other low-carbon replacements developments. This group is also rather than going to a major, national for natural gas, such as hydrogen. investigating the mine energy supplier, thereby promoting Heat-pump technology is proven, we of a number of former coalfields and it is economic regeneration to a formerly have a long experience of drilling in hoped that the new Glasgow Geothermal deprived mining region. mining areas and have evidence of Energy Research Field Site (BGS, 2018), success, as demonstrated by projects in as well as a variety of industrial and Hostages to fortune the UK and beyond. Why then is this type council supported projects in north-east The UK geothermal industry has of heat not used more widely? A whole England, will significantly reduce struggled to develop, not from lack of new approach to the licensing of heat, - subsurface, geoscientific uncertainties potential but because of the upfront [risk-averse attitudes] to “untested and risks, raise awareness and stimulate capital cost and risks involved with technologies” (Banks, GSL SP 2004) and the market for this low-carbon energy drilling boreholes that are not guaranteed the fact the UK has had ready access to source.

Fig 3: Cross-section of the geology in the Cuningar Loop area with the planned borehole target depths shown, UK Geoenergy Observatory in Glasgow. Note that the thick black lines represent areas recorded on abandonment plans as mine workings. TVD=true vertical depth relative to Ordnance Datum, top X-axis is in metres

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UK Geoenergy Observatories glacial and post-glacial Quaternary Glasgow site aims The BGS is constructing and operating the superficial deposits, overlain by a The Glasgow Geothermal Energy Research UK Geoenergy Observatories on behalf of variable thickness of made Field Site aims to provide access to NERC. This is an ambitious £31 million (anthropogenic) ground. The infrastructure and a wide range of openly investment that will develop and operate Quaternary deposits vary in thickness accessible data to answer key research two subsurface research observatories. up to 30 m. The upper surface of questions on low-carbon, mine energy Funded by the UK Government bedrock was incised, with thicker systems, to enable sustainable, responsible Department for Business, Energy and accumulations of superficial deposits and more widespread use of this resource. Industrial Strategy (DBEIS), the infilling a broadly NW-SE trending This facility will develop understanding of observatories will facilitate improved channel following the modern-day factors critical to successful development understanding of subsurface change River Clyde. There is widespread made, of mine energy systems, such as the beneath our feet. filled and landscaped ground relating longevity and sustainability of the resource The Glasgow Geoenergy Observatory, to a variety of prior industrial , and the hydrogeochemistry of the mine currently being constructed, will focus on in some places this is 10 to 15 m thick. water through time. Development of the shallow, low-temperature mine energy These deposits rest on approximately field site will also explore the risks opportunities using the flooded 300 m of bedrock strata of the Scottish associated with drilling into the roadways, abandoned mine workings below the east Upper, Middle and Lower Coal pillars and goaf at different depths within end of the city. The other UK Geoenergy Measures formation—cyclical abandoned mines. It will also explore the Observatory, in the Ince Marshes area of sedimentary rocks of sandstone, potential for subsurface connections to north Cheshire, will focus on improved siltstone, mudstone and coal. Recorded exist between near-surface and mine understanding of the subsurface coal mine workings in the area were waters, and the consequences of this for environment across a 12 km2 area, down to active from 1810 to 1934, with total environmental protection. 1,200 m below ground. This knowledge extraction and stoop-and-room workings The infrastructure to be installed will can be applied to a range of energy shown on abandonment plans. It is include an array of 12 boreholes at technologies. expected that total extraction areas various depths equipped to provide a collapsed within a few years of mining continuous time-series of geological, Site geology to form goaf and that the mines will be hydrogeological and thermal datasets The Glasgow Geothermal Energy flooded. As the cross-section in figure 3 (Fig. 3). Samples, tests and measurements Research Field Site is located on the shows, there are multiple levels of mine will be taken from the boreholes, such as western side of the Central Coalfield of workings in the area where the Glasgow temperature and aquifer properties, the Midland Valley of Scotland, within research site will be situated. water chemistry and microorganisms

Fig 4: Map of the UK Geoenergy Observatories: Glasgow borehole locations. Contains Ordnance Survey Taking a sample of borehole water during drilling of the seismic data © Crown copyright and database rights. All rights reserved [2019] Ordnance Survey monitoring borehole at Dalmarnock, Glasgow in November 2018. [100021290 EUL] Photo number P987023 BGS©UKRI

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(geomicrobiology). Environmental help characterise and monitor the In 2019, the continuous data from the monitoring of near-surface chemistry, environmental baseline by targeting the boreholes will be available and freely soil gases, seismicity, surface and upper bedrock and the superficial accessible to the public, government, will also be undertaken deposits. A range of sensors such as regulators, academia, and industry via prior to development, to provide a site resistivity and temperature cables and an online portal. Rock and fluid sample baseline before any geothermal research data loggers will be material will also be available for takes place. Existing, commercially installed. Regular water samples will research and there will be limited early developed mine energy systems focus on also be taken for geochemical analysis. access to the observatory, including heat production and there is limited In addition, there is one seismic training opportunities for students to subsurface and environmental monitoring borehole of around 200 m observe borehole drilling and sampling. monitoring data. In contrast, the Glasgow drill length at Dalmarnock (Fig. 4), research site offers huge potential for which has recently delivered a borehole Future energy source researchers to access large, integrated core. A new core-scanning facility at The high-resolution datasets from datasets on the mine-water system. It will BGS Keyworth will be used to give a Glasgow’s subsurface will provide a also provide opportunities for researchers high-resolution geophysical, step change in understanding of to undertake their own experiments, with mineralogical, geochemical and optical/ low-temperature heat resources, the common aim of reducing uncertainty X-ray downcore record (see BGS 2018 balanced with their impacts on people on mine energy systems and for more detail). and the subsurface to surface environmental impacts for schemes across environment. Clearly the potential to the UK and beyond. Timescale develop our mining heritage as a future Drilling of the first phase of boreholes energy source is huge. The message The infrastructure started in November 2018, with that our abandoned mining Planning approval and permits for the construction and testing expected to infrastructure, which was so hard won, characterisation and monitoring phase take a year or so. Subsequent to that could provide a source of low-carbon have been granted, with the majority of and permissions for the installation of energy for the future is a powerful one. the boreholes located at the Cuningar the heat pumps and above-ground Loop, Rutherglen (Fig. 4). Planned drill infrastructure that will allow Charlotte Adams is Assistant Professor at lengths are between 10 and 90 m. Six geothermal research, the research site Durham University; Alison Monaghan is science mine-water boreholes target the will be open to the whole of the UK lead for the Glasgow Geoenergy Observatory at Glasgow Upper and Glasgow Main coal science community to undertake the BGS; Jon Gluyas holds the Ørsted/Ikon Chair in Geoenergy and CCS at Durham University workings (Figs 3, 4). Five boreholes will research, for a 15-year lifespan.

Drilling of the Glasgow Geoenergy Observatory seismic monitoring borehole at Dalmarnock in November 2018. Photo number P987021 BGS©UKRI ▼

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