The feasibility of recovering heat energy from mine water contained within an abandoned coal mine in South Wales is assessed for a proposed district heating scheme. The study area is the village of Caerau, in the Upper Llynfi valley, Bridgend County Borough, South Wales, UK, comprising around 750 residential houses, a primary school and 17 commercial properties. This paper describes an archival geological and mining desk study focused on Caerau colliery, consideration of regional mine linkages, geographical information system (GIS) techniques used to create a 3D initial conceptual geological mine model of Caerau workings, permitting and licencing requirements, community engagement activities undertaken and the findings of a single exploratory borehole. The borehole intersected a void space in flooded mine workings around the horizon of the Six Foot seam at a depth of 224 m below ground level, as predicted by the conceptual mine model. The rest water level within the borehole lies at 92 m below ground level and the measured in situ temperature of the mine water at the base of the borehole was 20.3°C. An unexpectedly high and sustained geothermal gradient of c. 53°C km−1 was calculated from repeated measured temperature profiles.

Thematic collection: This article is part of the Keeping lessons alive in engineering geology collection available at https://www.lyellcollection.org/cc/keeping-lessons-alive-in-engineering-geology

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