Combining ground stability investigation with exploratory drilling for mine water geothermal energy development. Lessons from exploration and monitoring.

Mine water geothermal's potential for decarbonisation of heating and cooling in the UK has led to increased national interest and development of new projects. In this study, mine water geothermal exploration has been coupled with ground investigation techniques to assess ground stability alongside seasonal mine water hydrogeology and geochemistry. Drilling operations in late 2020 at Dollar Colliery, Clackmannanshire, Scotland, encountered mined coal seams with varying conditions (void, intact, waste, etc.), reflecting different techniques used throughout a protracted mining history. We found that time and resources spent grouting casing through worked mine seams (ensuring hydraulic separation) can be saved by accessing deeper seams where those above are unworked. Continued assessment of existing water discharges and completion of boreholes with slotted liners into mined coal seams and fractured roof strata allowed chemical and water level changes to be monitored across a 1-year period. Mine water heads and mine discharge flow rates vary seasonally and are elevated between late autumn and early spring. The mine water has a low dissolved solute content. Dissolved sulphate- 34 S isotope data suggest increased pyrite oxidation during lower water levels. These findings can inform future building decisions, whereby housing developments on site could use the mine water for heating. Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/topic/collections/early-career-research Supplementary material: https://doi.org/10.6084/m9.figshare.22188801