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Water sampling key to harnessing coalmine geothermal energy

Using the UK’s abandoned coalmines as a source of geothermal energy for district heating schemes is a positive development for the nation’s Net Zero goals, though experts have warned that it will need to be allied to a stringent water sampling regime.

The warning, from QED Environmental Systems, follows the recently reported development that the Coal Authority, which is responsible for the UK’s disused coalmines, is looking to use Britain’s underground network of abandoned coal mines as a potential source of green energy. Since closure, many of the mines have flooded, with water temperatures within reaching as high as 40°C through natural geothermal processes.

It has been estimated that these flooded shafts are an annually-renewing supply of around 2.2 million GWh of heat. With roughly a quarter of the nation’s population situated over the mines, it has been suggested that the naturally-warm water within could be utilised as a heat source for the homes above.

However, extracting the mine water may invite the risk of contamination, as Mike White, territory manager for UK & Ireland at QED Environmental Systems, explained: “Britain’s abandoned mineshafts have enormous potential to be used as a major source of green heat as the water is naturally heated, making it ideal to be pumped to the surface and used as a heat source.”

“However, it has to remembered that this is likely to be contaminated water that must be treated with caution. There is a danger that the process of extraction could inadvertently introduce contaminants into the water table. This could potentially prove a major source of environmental contamination, making it critical that the chemical content of the water is assessed before it is brought to the surface.”

Traditional groundwater sampling techniques, such as hand bailing or high purge pumping, can often mobilise solids in the borehole’s sample area, making obtaining a representative sample difficult. High purge volumes can even lead to an underestimation of maximum contaminant levels due to dilution.

Mr Whitesays that commonly used sampling methods such as bailers may not be suitable. “Bailers risk disturbing contaminants in the water which can then cause water table contamination as it is brought to the surface. For water from coal mines to be accurately and safely sampled, low flow sampling methodologies would be far more accurate.”

Low flow sampling equipment, such as QED’s Well Wizard, enables the safe extraction of water using lower pumping levels that reduce turbidity, increase accuracy and reduce the risk of contamination.

Mr Whiteconcluded: “While harnessing the UK’s untapped geothermal energy may prove an effective method of transitioning away from fossil fuels, it should be executed with caution. The margin of error is small, and we simply cannot afford to rely on sampling methods that may invite any risk of inaccuracy or contamination. For this reason, opting for low-flow sampling techniques will be key to safely harnessing the potential of Britain’s abandoned mineshafts.”

1 March 2022

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