A rapid biogeochemical assessment protocol has been developed to assess the potential effects of returning heated groundwater to the Mullaloo aquifer in Perth, Western Australia. A multi-disciplinary study encompassed geochemical analysis of the aquifer sediment, and microbiological, organic contaminant and major ion surveys of the groundwater. Geochemical modelling indicates few, if any adverse implications of a proposed 10 degrees C temperature increase. A potential exists for chemical and biological clogging but this will be minimised by a closed loop design to avoid the introduction of atmospheric oxygen. Nevertheless, the need for regular monitoring of scheme performance and environmental impacts remains. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.