The Effect of Geothermal Heat Pumps on Subsurface Flow and Contaminant Transport

Geothermal or ground source heat pumps (GSHPs) are among the growing renewable energy technologies used for heating and cooling of buildings. However, little work has been done to investigate their geo-environmental effects within the subsurface. This research uses FEFLOW software, to simulate heat and mass transport for a vertical closed-loop GSHP system. Steady and transient flow and heat transport results for a multiple borehole system are presented which indicate long-term effects on ground temperature. Moreover, the impact of heat exchanged with the subsurface on contaminant transport and biodegradation processes is studied to evaluate the possibility of utilizing this heat as a remediation strategy. The results reveal that temperature changes caused by GSHP operation can significantly enhance biodegradation of hydrocarbon contaminants. For instance, elevated subsurface temperature resulted in 96% reduction in benzene concentration, from 0.306 to 0.011 mg.L-1, after one year of GSHP operation for an office building in Toronto.