The purpose of this study was to evaluate the potential enhancement of ground-source heat pipes by groundwater advection at two sites within an alluvial fan of Toyohira River, Sapporo. Two sites were selected: one in the fan toe, for negligible groundwater flow (Site 1), and the other in the apex for fast flows, the latter characterized by a specific discharge of 1.0 m/d from the losing river (Site 2). The evaporator section(s) of a single (double) heat pipe(s) was installed in a borehole at each site; the condenser section(s) on the ground was placed inside cooled brine at a set temperature, resulting in heat extraction under steady conditions. The single heat pipe experiments showed that the heat extraction rates ranged between 0.23 and 0.79 kW and were not clearly different at the two sites, considering some uncertainty. For double heat pipes, the heat extraction rates were unchanged at Site 1, but were about 146% higher at Site 2 compared to the single tests, due to groundwater advection. This study revealed that the number of ground-source heat pipes required could be reduced from three to two in areas near Site 2.