Through field and numerical studies, this paper describes the importance of thermal dispersivity in designing groundwater heat pump (GWHP) systems. A push pull test using heat as a tracer was performed to estimate the thermal dispersivity of the aquifer of this study at the Han River Environment Research Center in Korea. Measured data during the test were compared to the results of three-dimensional (3-D) groundwater flow and heat transport simulations. From the best fit between the measured data and the simulated results, thermal dispersivity was estimated to be 0.4 m. To evaluate the effects of the thermal properties on subsurface heat transport associated with GWHP systems, sensitivity analysis was also performed. The analysis confirmed that, despite small changes based on the estimated values, thermal dispersivity of the aquifer had a great influence on the subsurface temperature distribution as well as the extent of the thermal plume. Because groundwater pumping and injection can cause flow velocity around wells to be faster than natural groundwater velocity, thermal dispersion in this elevated velocity condition will have a considerable impact on the heat transport process with operation of the GWHP system. (C) 2015 Elsevier Ltd. All rights reserved.