Groundwater circulation wells for geothermal use and their impact on groundwater quality

Abstract Groundwater circulation wells provide an alternative source of geothermal energy to more commonly used shallow open two-well systems. Their efficiency and impacts on groundwater chemistry and microbiology have not previously been investigated. We have monitored newly installed and pre-existing systems over a two-year period. Monthly hydrochemical measurements and microbial qPCR analyses of circulated water showed no changes in the groundwater composition, at least as long as no oxygen entered. None of the systems showed any clogging or precipitation, even where the groundwater had a high ferrous iron concentration, which has previously been considered to be unsuitable for open geothermal systems.