Hydrogeological assessment of megawatt-scale low-carbon heat generation from a single mine water surface discharge

Mine water geothermal schemes (MWGS) typically involve two or more boreholes and require power to pump water from depth, incurring exploration, drilling, and operational costs. Gravity driven mine water surface discharges are a common feature of former coal mining areas. Where discharge flow rates are high enough, MWGS could be installed to provide low-cost, low-carbon heating. Situated in an urban environment, the Old Fordell mine water discharge is one of the largest in Scotland. With a total iron load of 130 tonnes/year, it also represents a significant environmental concern for the receiving watercourse. To determine potential heat output, a synthetic analysis was performed using legacy mine records and hydrogeological monitoring (chemistry, temperature, flow, water level measurements) data from the UK Mining Remediation Authority. Between 2007 and 2019, regional mine water levels rose from -120 m ordnance datum (OD) to +40 m OD before stabilizing. During this process, Old Fordell temperature rose by 2°C and chemical composition changed, indicating introduction of deeper-sourced water. Using a Δ T of 8°C for heat extraction, mean discharge temperature (12.6°C) and flow rate (98 L/s) values provide a heat output of 4.4 megawatts (MW), enough to heat c. 1,100 homes. The potential heat output is deemed sustainable as long as regional mine water levels remain stable, showing that such features can supply heat to local users and have dual benefit of offsetting costs associated with installation and operation of any future mine water treatment plants.