The environmental impacts and unsustainability of fossil fuel-based heating and cooling systems has encouraged a worldwide interest in developing sustainable sources of energy and complementary technologies for heating/cooling purposes. One of these technologies is ground source heat pump (GSHP) systems that use the ubiquitous low-enthalpy ground source heat found in the shallow subsurface and represents a sustainable way of heating and cooling homes and buildings. GSHPs can be used to extract or inject subsurface heat by installing boreholes that circulate an antifreeze-based carrier fluid which is cooled or heated through the subsurface. Although GSHPs have many advantages, they might develop subsurface thermal plumes, which can affect the efficiency and sustainability of the system and other subsurface infrastructures. In the present research, the effect of a multi-borehole vertical GSHP system designed to deliver annual heating and cooling to an office building located in three Canadian cities was examined. This was done using a three-dimensional model, developed in FEFLOW, that simulated a hypothetical GSHP system in all three cities. It was found that the city with the highest thermal load resulted in the biggest subsurface thermal plume showing a direct connection between building thermal load and thermal plumes. Cyclical simulations for 10 years showed that the plumes grew in both size and temperature disturbance after the 10-year operation. The developed model can be used to determine the thermal affected zone of a GSHP system to aid in planning of other subsurface infrastructures in that zone. (C) 2018 The Authors. Published by Elsevier Ltd.